Name: plasma-assisted molecular beam epitaxy of n-polar inaln-barrier high-electron-mobility transistors
Uploaded: 2016-11-24T13:00:00.000+00:00
Duration: 10 min 31 s
Description: Watch this Scientific Journal Video about Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors at JoVE.com

The authors thank Mr. Neil Green for assistance with sample preparation. This work was supported by the Office of Naval Research under funding from Dr. P. Maki. MTH was supported by a National Research Council Postdoctoral Fellowship.

1. Effusion Cell Ramp and Flux Calibration
<ol>
	<li>Confirm liquid N2 is flowing to the cryo-panels and that the growth chamber has reached base pressure.</li>
	<li>Ramp up the effusion cells to their beam flux measurement (BFM) temperature at a ramp rate of 1 &#176;C/sec for Ga and In cells, and 10 &#176;C/min for Al. Wait 1 hr for cells to thermally stabilize.</li>
	<li>Open the shutter of each cell for 30-60 sec, and then close the shutter for 1-2 min. Repeat three times for each cell. Discard the first beam flux ion gauge measurement and average the second two. Adjust the cell temperature to achieve the desired flux according to previous flux/temperature calibrations.</li>
</ol>
2. Substrate Preparation and Loading
<ol>
	<li>Ex situ substrate cleaning
	<ol>
		<li>Load epi-ready N-polar GaN substrates directly, without any ex situ cleaning. If the wafer has been exposed to air for more than a few hours, rinse under acetone (30 sec), isopropanol (30 sec) and de-ionized (DI) water (60 sec). Rinsing is preferred to immersion when possible as it tends to leave less particles on the wafer surface. 
		NOTE: For Ga-polar GaN substrates a more rigorous surface clean is recommended.23</li>
	</ol>
	</li>
	<li>Load wafer
	<ol>
		<li>Close the load-lock isolation gate valve, and vent with N2.</li>
		<li>Load the wafer on the holder and return the cassette to the load lock. Turn on the load lock roughing pump and open the roughing pump valve and manifold valve.</li>
		<li>When the manifold pressure has dropped below 0.1 Torr, close the manifold and roughing pump valves. Turn off the roughing pump and open the load-lock turbo-pump isolation valve.</li>
		<li>Allow the load lock to pump down for 30-60 min. Ideally, use a load lock pressure of 10-6-10-7 Torr before transferring to the preparation chamber.</li>
		<li>Open the load lock into the preparation chamber, and transfer the wafer to the trolley using wobble stick. Then use the trolley to transfer the wafer to the outgassing station in the preparation chamber. Move the trolley manually along a rail using a rotary feedthrough on the preparation chamber.</li>
	</ol>
	</li>
	<li>Outgas wafer
	<ol>
		<li>Ramp the outgassing station heater temperature to 700 &#176;C over 10 min.</li>
		<li>After 30 min, ramp the temperature back down to 100 &#176;C. When the temperature is &#8804; 250 &#176;C, transfer the wafer back to the trolley using the wobble stick at the outgassing station.</li>
	</ol>
	</li>
	<li>Load wafer into the growth chamber
	<ol>
		<li>Lower the substrate manipulator to the load position, open the preparation/growth chamber gate valve and transfer the wafer holder to the manipulator.</li>
		<li>Raise the manipulator to growth position, near the substrate heater.</li>
		<li>Remove the trolley and close the gate valve.</li>
		<li>Open the N2 bottle valve, regulator valve and isolation needle valve. Set the mass flow controller (MFC) to 1.5 sccm (or as needed to get a chamber pressure of 3-4 x 10-5 Torr). The optimal pressure for plasma ignition is strongly system dependent. Note that the N2 must be ultra-high purity (preferably better than 6N) and an additional filter is used in line to further reduce impurities.</li>
		<li>With the N* and main shutters closed, turn on the plasma RF power supply and auto-matching network controller. Increase the RF power until the plasma ignites.</li>
		<li>Set the RF power and N2 flow to the desired process conditions, in this case 350 W and 2.0 sccm. The N* flux resulting from given plasma conditions is system dependent, but here, these conditions yield a GaN growth rate of 5.0 nm/min, or a N* flux of 1.8 nm-2sec-1. Monitor the plasma stability with a spectrometer attached to the rear window of the plasma chamber.</li>
	</ol>
	</li>
	<li>In situ surface preparation: Ga deposition and desorption
	<ol>
		<li>Ramp up the substrate heater to 10 &#176;C above the desired GaN growth temperature with a ramp rate of &#8804;1 &#176;C/sec. In this case, use an estimated wafer temperature of 730 &#176;C.</li>
		<li>Turn on the RHEED system to watch for degradation of the wafer surface and monitor Ga coverage. Manually turn on the substrate rotation. Set up the triggered RHEED acquisition software to collect a RHEED pattern once per substrate rotation to provide a static image while the substrate is rotating during growth.</li>
		<li>Open the substrate shutter and Ga shutter for 1 min. Ensure the RHEED intensity decreases then reaches a plateau as Ga accumulates. Ga flux should be similar to that used for GaN growth. Here, the Ga flux is approximately, 3.7 nm-2sec-1.</li>
		<li>Close the shutter for 2 min and ensure the RHEED intensity increases and reaches a plateau before the end of the 2 min, indicating Ga desorption.</li>
		<li>Repeat Steps 2.5.2-2.5.4 three times,24 and then ramp the substrate to the GaN growth temperature.</li>
	</ol>
	</li>
</ol>
3. HEMT Growth
<ol>
	<li>Buffer growth
	<ol>
		<li>Initiate growth by opening the N* shutter for a 1 min nitridation.</li>
		<li>Grow a thin 1-3 nm N-rich AlN nucleation layer by opening the Al shutter. This AlN layer can help prevent threading dislocation generation,25 however, the AlN layer complicates X-ray diffraction (XRD) measurements and is not recommended for XRD-based calibration samples. Use the same Al flux as for the InAlN layer, or about 0.36 nm-2sec-1, giving a growth rate of approximately 1 nm/min.</li>
		<li>Close the Al and N* shutter and immediately open the Ga shutter for 10 sec to allow Ga to saturate the surface, the RHEED intensity should decrease rapidly. Open the N* shutter (with the Ga shutter still open) and grow 5 min of GaN. Use Be or C doping, especially for freestanding GaN substrates, to prevent electrical leakage currents in the buffer.</li>
		<li>Close the Ga and N* shutters for a 1 min growth interruption. Monitor the RHEED intensity. If the RHEED intensity immediately increases, then the Ga flux is not high enough. If the RHEED intensity increases after &#62;30 sec or does not reach a plateau within 1 min then the Ga flux is too high. See Figure 3.</li>
		<li>Increase the substrate temperature by a few degrees (or reduce the Ga effusion cell temperature) to compensate for high Ga flux seen in 3.1.4. If the Ga flux was too low, decrease the substrate temperature (or increase the Ga effusion cell temperature) to compensate.
		<ol>
			<li>Repeat Steps 3.1.3-3.1.5 until there is a 15-30 sec delay before the RHEED intensity increases and the RHEED intensity reaches a plateau before 1 min.</li>
		</ol>
		</li>
		<li>Continue repeating Steps 3.1.4-3.1.5 until the desired GaN thickness is reached. Determine thickness by multiplying the total growth time by the calibrated growth rate. For Ga-rich growth, determine the growth rate by the N* flux, which can in turn be calculated using XRD to measure the thickness for a known growth time in a separately grown calibration sample.</li>
	</ol>
	</li>
	<li>InAlN barrier growth
	<ol>
		<li>Wait an additional 1 min after the final GaN growth step to ensure all Ga has evaporated.</li>
		<li>Quickly ramp down to the InAlN growth temperature to approximately 630 &#176;C. Allow the substrate temperature to stabilize for about 2 min.</li>
		<li>Open the In, Al, and N* shutters. The RHEED intensity should decrease and reach a plateau within the first 3 min. Continued decrease of RHEED intensity may indicate accumulation of In, which is detrimental to InAlN growth. The RHEED pattern should remain streaky, indicating a smooth surface. The In and Al fluxes are about 0.31 and 0.36 nm-2sec-1, giving a group-III limited growth rate of 1.25 nm/min.</li>
		<li>Close the In, Al, and N* shutters after the desired barrier thickness has been reached. For N-rich growth, determine the growth rate by the total group-III flux. Measure the growth rate using XRD on a separately grown InAlN calibration sample. For a 15 nm InAlN barrier using the conditions given here, open the shutters for 12 min 30 sec.</li>
	</ol>
	</li>
	<li>Interlayer and channel growth
	<ol>
		<li>First open the Ga shutter for 5 sec, then open the N* shutter and grow the GaN interlayer. The substrate temperature should still be at the InAlN growth temperature.</li>
		<li>Open the Al shutter without closing the Ga or N* shutters to grow the AlN interlayer. The Al flux for the interlayer should be the same or slightly higher than the N* flux, ideally using a different Al effusion cell then that used for the InAlN barrier layer, to avoid having to change the cell temperature. See step 3.2.4.</li>
		<li>Close the N* and Al shutters but leave the Ga shutter open. Ramp the substrate temperature to the GaN channel temperature.</li>
		<li>After 30 sec close the Ga shutter. Wait 30 sec (or as soon as the RHEED intensity starts to increase) and re-open the Ga shutter. Continue to cycle the Ga shutter until the substrate has reached the GaN channel growth temperature. This will protect the surface while preventing excessive Ga accumulation.</li>
		<li>Open the Ga shutter for 5 sec, then open the N* shutter and grow the GaN channel.</li>
		<li>Close the Ga, N* and main shutters. Ramp the substrate temperature down to 200 &#176;C, turn off the N* plasma and shut off the N2 gas flow.</li>
		<li>Ramp the cells down to their standby temperatures if finished for the day.</li>
		<li>Wait for the substrate temperature to decrease below 250 &#176;C and the chamber pressure to drop below 8 x 10-7 Torr, then open the growth chamber gate valve and transfer the wafer holder back to the trolley.</li>
		<li>Follow the reverse of Step 2.2 to transfer the wafer back to the load lock, vent with N2 and remove the wafer. Make sure the growth chamber gate valve is closed before opening the load lock, and that the load lock turbo pump gate valve is closed before venting.</li>
		<li>Follow Steps 2.2.3-2.2.5 to return the cassette and load lock to high vacuum.</li>
	</ol>
	</li>
</ol>
4. Characterization
<ol>
	<li>Characterize the material quality using optical microscopy to check for pits, cracks or Ga-droplets that may have formed during the channel growth, XRD to check the interfacial and structure quality, and AFM to check the surface morphology.20,21</li>
	<li>If Ga-droplets are present, immerse the wafer in concentrated HF acid for 5-10 min to remove the droplets without damaging the chemically sensitive N-polar surface.</li>
	<li>Measure sheet resistance using Lehighton contactless resistance measurements.</li>
	<li>Process the sample to allow electrical characterization, including Hall and CTLM measurements and dc and RF transistor characterization.9,26</li>
</ol>

<ol>
	<li>Hughes, W. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+beam+epitaxy+growth+and+properties+of+GaN+films+on+GaN/SiC+substrates.">Molecular beam epitaxy growth and properties of GaN films on GaN/SiC substrates.</a> J. Vac. Sci. Technol., B. 13 (4), 1571-1577 (1995).</li><li>McSkimming, B. M., Wu, F., Huault, T., Chaix, C., Speck, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasma+assisted+molecular+beam+epitaxy+of+GaN+with+growth+rates+2.6+&#181;m/hr.">Plasma assisted molecular beam epitaxy of GaN with growth rates 2.6 &#181;m/hr.</a> J. Cryst. Growth. 386, 168-174 (2014).</li><li>Grandjean, N., Massies, J., Leroux, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nitridation+of+sapphire.+Effect+on+the+optical+properties+of+GaN+epitaxial+overlayers.">Nitridation of sapphire. Effect on the optical properties of GaN epitaxial overlayers.</a> Appl. Phys. Lett. 69 (14), 2071-2073 (1996).</li><li>Corrion, A. L., Wu, F., Speck, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+regimes+during+homoepitaxial+growth+of+GaN+by+ammonia+molecular+beam+epitaxy.">Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy.</a> J. Appl. Phys. 112 (5), 054903 (2012).</li><li>Mazumder, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atom+probe+analysis+of+AlN+interlayers+in+AlGaN/AlN/GaN+heterostructures.">Atom probe analysis of AlN interlayers in AlGaN/AlN/GaN heterostructures.</a> Appl. Phys. Lett. 102 (11), 111603 (2013).</li><li>Feezell, D. F., Speck, J. S., DenBaars, S. P., Nakamura, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Semipolar+(2021)+InGaN/GaN+Light-Emitting+Diodes+for+High-Efficiency+Solid+State+Lighting.">Semipolar (2021) InGaN/GaN Light-Emitting Diodes for High-Efficiency Solid State Lighting.</a> J. Disp. Technol. 9 (4), (2013).</li><li>Hardy, M. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=True+Green+Semipolar+InGaN-Based+Laser+Diodes+Beyond+Critical+Thickness+Limits+Using+Limited+Area+Epitaxy.">True Green Semipolar InGaN-Based Laser Diodes Beyond Critical Thickness Limits Using Limited Area Epitaxy.</a> J. Appl. Phys. 114 (18), 183101 (2013).</li><li>Wong, M. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=N-polar+GaN+epitaxy+and+high+electron+mobility+transistors.">N-polar GaN epitaxy and high electron mobility transistors.</a> Semicond. Sci. Technol. 28 (7), 074009 (2013).</li><li>Hardy, M. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Charge+control+in+N-polar+InAlN+high-electron-mobility+transistors+grown+by+plasma-assisted+molecular+beam+epitaxy.">Charge control in N-polar InAlN high-electron-mobility transistors grown by plasma-assisted molecular beam epitaxy.</a> J. Vac. Sci. Technol., B. 33 (6), 061207 (2015).</li><li>Piquette, E. C., Bridger, P. M., Beach, R. A., McGill, T. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Buffer+Layer+and+III/V+Ratio+on+the+Surface+Morphology+of+GaN+Grown+by+MBE.">Effect of Buffer Layer and III/V Ratio on the Surface Morphology of GaN Grown by MBE.</a> Symposium G '-' GaN and Related Alloys. , (1998).</li><li>Tarsa, E. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Homoepitaxial+growth+of+GaN+under+Ga-stable+and+N-stable+conditions+by+plasma-assisted+molecular+beam+epitaxy.">Homoepitaxial growth of GaN under Ga-stable and N-stable conditions by plasma-assisted molecular beam epitaxy.</a> J. Appl. Phys. 82 (11), 5472-5479 (1997).</li><li>Kuzmik, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Power+electronics+on+InAlN/(In)GaN:+Prospect+for+a+record+performance.">Power electronics on InAlN/(In)GaN: Prospect for a record performance.</a> IEEE Electron Device Lett. 22 (11), 510-512 (2001).</li><li>Fern&#225;ndez-Garrido, S., Ga&#269;evi&#263;, &. #. 3. 8. 1. ;., Calleja, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comprehensive+diagram+to+grow+InAlN+alloys+by+plasma-assisted+molecular+beam+epitaxy.">A comprehensive diagram to grow InAlN alloys by plasma-assisted molecular beam epitaxy.</a> Appl. Phys. Lett. 93 (19), 191907 (2008).</li><li>Katzer, D. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+beam+epitaxy+of+InAlN&#8725;GaN+heterostructures+for+high+electron+mobility+transistors.">Molecular beam epitaxy of InAlN&#8725;GaN heterostructures for high electron mobility transistors.</a> J. Vac. Sci. Technol., B. 23 (3), 1204-1208 (2005).</li><li>Kaun, S. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=GaN-based+high-electron-mobility+transistor+structures+with+homogeneous+lattice-matched+InAlN+barriers+grown+by+plasma-assisted+molecular+beam+epitaxy.">GaN-based high-electron-mobility transistor structures with homogeneous lattice-matched InAlN barriers grown by plasma-assisted molecular beam epitaxy.</a> Semicond. Sci. Technol. 29 (4), 045011 (2014).</li><li>Hoke, W. E., Torabi, A., Mosca, J. J., Kennedy, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermodynamic+analysis+of+cation+incorporation+during+molecular+beam+epitaxy+of+nitride+films+using+metal-rich+growth+conditions.">Thermodynamic analysis of cation incorporation during molecular beam epitaxy of nitride films using metal-rich growth conditions.</a> J. Vac. Sci. Technol., B. 25 (3), 978-982 (2007).</li><li>Koblm&#252;ller, G., Reurings, F., Tuomisto, F., Speck, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+Ga/N+ratio+on+morphology,+vacancies,+and+electrical+transport+in+GaN+grown+by+molecular+beam+epitaxy+at+high+temperature.">Influence of Ga/N ratio on morphology, vacancies, and electrical transport in GaN grown by molecular beam epitaxy at high temperature.</a> Appl. Phys. Lett. 97 (19), 191915 (2010).</li><li>Zhou, L., Smith, D. J., McCartney, M. R., Katzer, D. S., Storm, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+vertical+honeycomb+structure+in+InAlN&#8725;GaN+heterostructures+due+to+lateral+phase+separation.">Observation of vertical honeycomb structure in InAlN&#8725;GaN heterostructures due to lateral phase separation.</a> Appl. Phys. Lett. 90 (8), 081917 (2007).</li><li>Ahmadi, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elimination+of+columnar+microstructure+in+N-face+InAlN,+lattice-matched+to+GaN,+grown+by+plasma-assisted+molecular+beam+epitaxy+in+the+N-rich+regime.">Elimination of columnar microstructure in N-face InAlN, lattice-matched to GaN, grown by plasma-assisted molecular beam epitaxy in the N-rich regime.</a> Appl. Phys. Lett. 104 (7), 072107 (2014).</li><li>Hardy, M. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphological+and+microstructural+stability+of+N-polar+InAlN+thin+films+grown+on+free-standing+GaN+substrates+by+molecular+beam+epitaxy.">Morphological and microstructural stability of N-polar InAlN thin films grown on free-standing GaN substrates by molecular beam epitaxy.</a> J. Vac. Sci. Technol., A. 34 (2), 021512 (2016).</li><li>Hardy, M. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Indium+incorporation+dynamics+in+N-polar+InAlN+thin+films+grown+by+plasma-assisted+molecular+beam+epitaxy+on+freestanding+GaN+substrates.">Indium incorporation dynamics in N-polar InAlN thin films grown by plasma-assisted molecular beam epitaxy on freestanding GaN substrates.</a> J. Cryst. Growth. 245, (2015).</li><li>Leszczynski, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Indium+incorporation+into+InGaN+and+InAlN+layers+grown+by+metalorganic+vapor+phase+epitaxy.">Indium incorporation into InGaN and InAlN layers grown by metalorganic vapor phase epitaxy.</a> J. Cryst. Growth. 318 (1), 496-499 (2011).</li><li>Storm, D. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrathin-barrier+AlN/GaN+heterostructures+grown+by+rf+plasma-assisted+molecular+beam+epitaxy+on+freestanding+GaN+substrates.">Ultrathin-barrier AlN/GaN heterostructures grown by rf plasma-assisted molecular beam epitaxy on freestanding GaN substrates.</a> J. Cryst. Growth. 380, 14-17 (2013).</li><li>Storm, D. F., Katzer, D. S., Meyer, D. J., Binari, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oxygen+incorporation+in+homoepitaxial+N-polar+GaN+grown+by+radio+frequency-plasma+assisted+molecular+beam+epitaxy:+Mitigation+and+modeling.">Oxygen incorporation in homoepitaxial N-polar GaN grown by radio frequency-plasma assisted molecular beam epitaxy: Mitigation and modeling.</a> J. Appl. Phys. 112 (1), 013507 (2012).</li><li>Storm, D. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+interfacial+oxygen+on+the+microstructure+of+MBE-grown+homoepitaxial+N-polar.">Effect of interfacial oxygen on the microstructure of MBE-grown homoepitaxial N-polar.</a> J. Cryst. Growth. 409, 14 (2014).</li><li>Meyer, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Electron+Velocity+Submicrometer+AlN/GaN+MOS-HEMTs+on+Freestanding+GaN+Substrates.">High Electron Velocity Submicrometer AlN/GaN MOS-HEMTs on Freestanding GaN Substrates.</a> IEEE Electron Device Lett. 34, 199 (2013).</li><li>Moseley, M., Billingsley, D., Henderson, W., Trybus, E., Doolittle, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+atomic+behavior+and+surface+kinetics+of+GaN.">Transient atomic behavior and surface kinetics of GaN.</a> J. Appl. Phys. 106 (1), 014905 (2009).</li><li>Koblm&#252;ller, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ga+Adlayer+Governed+Surface+Defect+Evolution+of+(0001)GaN+Films+Grown+by+Plasma-Assisted+Molecular+Beam+Epitaxy.">Ga Adlayer Governed Surface Defect Evolution of (0001)GaN Films Grown by Plasma-Assisted Molecular Beam Epitaxy.</a> Jpn. J. Appl. Phys. 44 (28), L906-L908 (2005).</li><li>Poblenz, C., Waltereit, P., Speck, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Uniformity+and+control+of+surface+morphology+during+growth+of+GaN+by+molecular+beam+epitaxy.">Uniformity and control of surface morphology during growth of GaN by molecular beam epitaxy.</a> J. Vac. Sci. Technol., B. 23 (4), 1379-1385 (2005).</li></ol>

The authors have nothing to disclose.

Growth of a high quality GaN buffer layer is critical to achieving high electron mobility in any III-nitride HEMT. In the case of an N-polar InAlN HEMT, the buffer layer growth is complicated by the requirement that all Ga be removed from the surface prior to InAlN growth. There are a variety of techniques to accomplish this in addition to the procedure described here, such as metal-modulated epitaxy,27 using growth conditions at the edge of the intermediate Ga coverage and Ga droplet accumulation regime,...

Molecular beam epitaxy (MBE) is a versatile epitaxial thin film growth technique that employs an ultra-high vacuum environment with base pressures as low as 10-11 Torr to ensure low impurity incorporation in the grown film. The composition and growth rate of the epitaxially grown layers are determined by controlling the temperature of each effusion cell, and thus the evaporated flux of the various source materials. In the case of III-nitride epitaxy, the group III-elements (In, Al, Ga) are typically provided by effusion cells while the active nitrogen (N*) flux is provided by either an N2 plasma1,2 (RF plasma-assisted MBE: PAMBE or RFMBE) or ammonia (NH3-MBE).3,4 MBE growth is characterized by lower growth temperatures and sharper interfacial abruptness than other epitaxial growth techniques, such as metalorganic chemical vapor deposition.5 A schematic is shown in Figure 1.
<img alt="Figure 1" src="/files/ftp_upload/54775/54775fig1.jpg" /> 
Figure 1: MBE system schematic. Schematic showing the load lock, transfer system, outgassing station and growth chamber. <a href="http://cloudflare.jove.com/files/ftp_upload/54775/54775fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
III-nitrides can be grown on substrates having a variety of crystal orientations. The most commonly used orientation is the Ga-polar c-plane, which allows the formation of a two-dimensional electron gas without doping by utilizing the difference in polarization between the barrier layer, typically AlGaN, and GaN channel. Various non-polar and semi-polar orientations of GaN have received significant attention for optoelectronics due to reduced polarization effects in the quantum wells,6,7 which also makes these orientations less desirable for HEMT applications. N-polar oriented devices are attractive for next-generation high-frequency HEMT operation due to several intrinsic advantages over conventional Ga-polar devices.8 The barrier layer in N-polar devices is grown beneath the GaN channel as shown in Figure 2, resulting in a natural back barrier that aids electrostatic control of the channel and reduces short channel effects, while allowing easier current access to the GaN channel and reducing contact resistance. The barrier can also be controlled separately from the channel, so that as the channel thickness is scaled down for high-frequency devices the barrier design can be modified to compensate for channel charge lost to Fermi level pinning effects.
<img alt="Figure 2" src="/files/ftp_upload/54775/54775fig2.jpg" /> 
Figure 2: Epitaxial layer schematic. Layer structure of (a) an N-polar HEMT and (b) a Ga-polar HEMT for comparison. <a href="http://cloudflare.jove.com/files/ftp_upload/54775/54775fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
HEMTs used in high-speed, high-power amplifiers are normally grown on SiC substrates to take advantage of the high thermal conductivity of SiC. Low threading dislocation density freestanding GaN substrates can be employed to improve the electron mobility,9 thus improving the high-frequency performance. Following the growth of an AlN nucleation layer, a thick GaN buffer is grown to spatially separate the impurities at the regrowth interface from the HEMT channel and improve electrical isolation. Unlike other III-V materials, GaN grown by PAMBE typically needs growth conditions with a group-III/V ratio greater than 1, i.e., metal-rich conditions,10,11 in order to achieve a smooth surface morphology. InxAl1-xN is an alternative barrier material for III-nitride HEMTs, and has received significant attention recently because it can be grown lattice matched to GaN for x &#8776; 0.18 and can generate over twice the channel charge relative to AlGaN barriers due its high spontaneous polarization.12-15 Unlike AlGaN barriers, Ga will incorporate preferentially to In in InAlN layers,16 thus care must be taken to ensure the surface is free of excess Ga after the Ga-rich GaN buffer layer growth and prior to InAlN growth.
Control of Ga on the surface can be accomplished by suppling a Ga flux slightly less than the flux required for Ga-droplet formation. However, this growth window is small, and insufficient Ga surface coverage will cause the surface morphology to degrade into plateau/trench morphology while excess Ga flux will result in Ga accumulation and macroscopic droplet formation.17 Reflection high-energy electron diffraction (RHEED) intensity can be used to monitor Ga accumulation and desorption. Ga surface coverage is indicated by a reduction in RHEED intensity, and any lag between closing the Ga (and N*) shutters and the initial increase in RHEED intensity indicates accumulation of Ga, as shown in Figure 3.
<img alt="Figure 3" src="/files/ftp_upload/54775/54775fig3.jpg" /> 
Figure 3: Monitoring Ga coverage with RHEED intensity. RHEED intensity signal measured from RHEED pattern acquired under rotation using triggered acquisition. Insufficient Ga flux is indicated by an immediate increase in intensity after closing the shutters (not shown). Saturated/ideal Ga coverage is indicated by a delay between shutter closure and abrupt RHEED brightening and excess Ga coverage in seen as both a delay in initial RHEED brightening as well as a more gradual intensity increase resulting in full intensity recovery taking longer than 60 s. <a href="http://cloudflare.jove.com/files/ftp_upload/54775/54775fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Achieving high quality InAlN by PAMBE is complicated by the presence of lateral composition fluctuations, resulting in a &#34;honeycomb&#34; microstructure consisting of Al-rich domains surrounded by In-rich boundaries.18 Elimination of this microstructure is achieved by using a substrate temperature about 50 &#176;C above the onset of In desorption,15,19,20 or approximately 630 &#176;C for N-polar InAlN. In this high temperature growth regime, the InxAl1-xN composition is a strong function of substrate temperature, with higher temperatures resulting in lower In incorporation. The In flux can be increased to compensate for In lost to evaporation, although in practice the maximum In flux is limited by a reduction in incorporation efficiency with increasing In flux.21 In addition to reducing the substrate temperature or increasing the In flux, increasing the growth rate can also increase the In composition due to the &#34;In burying effect&#34;, where incoming Al atoms trap In and prevent it from evaporating.21,22 Higher growth rates can be achieved by increasing the In and Al flux proportionally. To keep the growth conditions N-rich, the N* would need to be increased as well, which can be achieved by increasing the RF plasma power, increasing the N2 flow rate, improving the plasma chamber design, or increasing the aperture plate hole density.
Additional epitaxial layers in InAlN-based HEMTs include GaN and AlN interlayers (ILs) and a GaN channel. An AlN IL inserted between the barrier and channel can increase mobility &#181; as well as channel sheet charge density ns. The increase in mobility is attributed to reducing electron wave function overlap with the InAlN barrier and subsequent alloy scattering.9 To ensure high-quality growth of the AlN IL, an excess of Ga flux is supplied during growth to act as a surfactant. A GaN IL can be used between the AlN IL and barrier to further improve the mobility while reducing channel charge. The GaN channel can be grown at the same temperature as the InAlN barrier, allowing continuous growth from the barrier though the ILs and channel. Improved mobility has been obtained by interrupting growth after the AlN IL and increasing the growth temperature before growing the GaN channel. In this case a protective Ga surface coverage has to be maintained during the interrupt to prevent mobility degradation.
The following protocol applies specifically to InAlN-barrier HEMTs grown on N-polar GaN substrates. It can be directly extended to growth on C-polar 4H- or 6H-SiC substrates by including a 50 nm thick N-rich AlN layer.

<table><tbody><tr><td>Freestanding N-polar GaN wafer</td><td>Kyma</td><td></td><td>10 mm x 10 mm</td></tr><tr><td>C-polar SiC wafer</td><td>Cree</td><td>W4TRE0R-L600</td><td>3 inch diameter</td></tr><tr><td>Microelectronics grade acetone</td><td>Fischer Scientific</td><td>A18-4</td><td></td></tr><tr><td>Microelectronics grade isoproponal</td><td>J.T. Baker</td><td>9079-05/JT9079-5</td><td></td></tr><tr><td>Al source material (6N5 pure)</td><td>UMC</td><td>ALR62060I</td><td></td></tr><tr><td>Ga source material (7N pure)</td><td>UMC</td><td>GA701</td><td></td></tr><tr><td>In source material (7N pure)</td><td>UMC</td><td>IN750</td><td></td></tr><tr><td>ULSI N&lt;sub&gt;2&lt;/sub&gt; source gas (6N pure)</td><td>Matheson Tri-gas</td><td>G2659906D</td><td></td></tr><tr><td>PRO-75 MBE system</td><td>OmicronScientia</td><td></td><td></td></tr></tbody></table>

plasma-assisted molecular beam epitaxy of n-polar inaln-barrier high-electron-mobility transistors

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt interfaces required for high-quality high-electron-mobility transistors (HEMTs). A procedure is presented for the growth of N-polar InAlN HEMTs, including wafer preparation and growth of buffer layers, the InAlN barrier layer, AlN and GaN interlayers and the GaN channel. Critical issues at each step of the process are identified, such as avoiding Ga accumulation in the GaN buffer, the role of temperature on InAlN compositional homogeneity, and the use of Ga flux during the AlN interlayer and the interrupt prior to GaN channel growth. Compositionally homogeneous N-polar InAlN thin films are demonstrated with surface root-mean-squared roughness as low as 0.19 nm and InAlN-based HEMT structures are reported having mobility as high as 1,750 cm2/V&#8729;sec for devices with a sheet charge density of 1.7 x 1013 cm-2.

X-ray diffraction (XRD) scans of InAlN thin films shown grown on N-polar GaN substrates in Figure 4(a) are single peaked both for 50 and 200-nm-thick films. The XRD scan of the 50 nm thick InAlN film exhibits Pendell&#246;sung fringes up to 15th order, indicating very high interfacial quality. The asymmetric reciprocal space map in Figure 4(b) shows that the 200 nm thick InAlN layer has the same q&#8214;, and thus the same in-plane l...

Watch this Scientific Journal Video about Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors at JoVE.com

Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors

Molecular beam epitaxy is used to grow N-polar InAlN-barrier high-electron-mobility transistors (HEMTs). Control of the wafer preparation, layer growth conditions and epitaxial structure results in smooth, compositionally homogeneous InAlN layers and HEMTs with mobility as high as 1,750 cm2/V&#8729;sec.

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt ...

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8.5K Views.  Naval Research Laboratory. Molecular beam epitaxy is used to grow N-polar InAlN-barrier high-electron-mobility transistors (HEMTs). Control of the wafer preparation, layer growth conditions and epitaxial structure results in smooth, compositionally homogeneous InAlN layers and HEMTs with mobility as high as 1,750 cm2/V∙sec.

Video: Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy and dynamics1-4. Fundamental studies of photoionization processes of biomolecules provide information about the electronic structure of these systems. Furthermore determinations of ionization energies and other properties of biomolecules in the gas phase are not trivial, and these experiments provide a platform to generate these data. We have developed a thermal vaporization technique coupled with supersonic molecular beams that provides a gentle way to transport these species into the gas phase. Judicious combination of source gas and temperature allows for formation of dimers and higher clusters of the DNA bases. The focus of this particular work is on the effects of non-covalent interactions, i.e., hydrogen bonding, stacking, and electrostatic interactions, on the ionization energies and proton transfer of individual biomolecules, their complexes and upon micro-hydration by water1, 5-9.
We have performed experimental and theoretical characterization of the photoionization dynamics of gas-phase uracil and 1,3-dimethyluracil dimers using molecular beams coupled with synchrotron radiation at the Chemical Dynamics Beamline10 located at the Advanced Light Source and the experimental details are visualized here. This allowed us to observe the proton transfer in 1,3-dimethyluracil dimers, a system with pi stacking geometry and with no hydrogen bonds1. Molecular beams provide a very convenient and efficient way to isolate the sample of interest from environmental perturbations which in return allows accurate comparison with electronic structure calculations11, 12. By tuning the photon energy from the synchrotron, a photoionization efficiency (PIE) curve can be plotted which informs us about the cationic electronic states. These values can then be compared to theoretical models and calculations and in turn, explain in detail the electronic structure and dynamics of the investigated species 1, 3.

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

A molecular beam coupled to tunable vacuum ultraviolet photoionization mass spectrometer at a synchrotron provides a convenient tool to explore the electronic structure of isolated gas phase molecules and clusters. Proton transfer mechanisms in DNA base dimers were elucidated with this technique.

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy ...

Nanofabrication of Gate-defined GaAs/AlGaAs Lateral Quantum Dots

A quantum computer is a computer composed of quantum bits (qubits) that takes advantage of quantum effects, such as superposition of states and entanglement, to solve certain problems exponentially faster than with the best known algorithms on a classical computer. Gate-defined lateral quantum dots on GaAs/AlGaAs are one of many avenues explored for the implementation of a qubit. When properly fabricated, such a device is able to trap a small number of electrons in a certain region of space. The spin states of these electrons can then be used to implement the logical 0 and 1 of the quantum bit. Given the nanometer scale of these quantum dots, cleanroom facilities offering specialized equipment- such as scanning electron microscopes and e-beam evaporators- are required for their fabrication. Great care must be taken throughout the fabrication process to maintain cleanliness of the sample surface and to avoid damaging the fragile gates of the structure. This paper presents the detailed fabrication protocol of gate-defined lateral quantum dots from the wafer to a working device. Characterization methods and representative results are also briefly discussed. Although this paper concentrates on double quantum dots, the fabrication process remains the same for single or triple dots or even arrays of quantum dots. Moreover, the protocol can be adapted to fabricate lateral quantum dots on other substrates, such as Si/SiGe.

This paper presents a detailed fabrication protocol for gate-defined semiconductor lateral quantum dots on gallium arsenide heterostructures. These nanoscale devices are used to trap few electrons for use as quantum bits in quantum information processing or for other mesoscopic experiments such as coherent conductance measurements.

A quantum computer is a computer composed of quantum bits (qubits) that takes advantage of quantum effects, such as superposition of states and ...

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization.

The fabrication process and experimental characterization techniques relevant to single-electron pumps based on silicon metal-oxide-semiconductor quantum dots are discussed.

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

Attainment of high-quality Schottky contacts is imperative for achieving efficient gate modulation in heterostructure field effect transistors (HFETs). We present the fabrication methodology and characteristics of Schottky diodes on Zn-polar BeMgZnO/ZnO heterostructures with high-density two dimensional electron gas (2DEG), grown by plasma-assisted molecular beam epitaxy on GaN templates.

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device ...

Plasma-Assisted Molecular Beam Epitaxy Growth of Mg3N2 and Zn3N2 Thin Films

This article describes a procedure for growing Mg3N2 and Zn3N2 films by plasma-assisted molecular beam epitaxy (MBE). The films are grown on 100 oriented MgO substrates with N2 gas as the nitrogen source. The method for preparing the substrates and the MBE growth process are described. The orientation and crystalline order of the substrate and film surface are monitored by the reflection high energy electron diffraction (RHEED) before and during growth. The specular reflectivity of the sample surface is measured during growth with an Ar-ion laser with a wavelength of 488 nm. By fitting the time dependence of the reflectivity to a mathematical model, the refractive index, optical extinction coefficient, and growth rate of the film are determined. The metal fluxes are measured independently as a function of the effusion cell temperatures using a quartz crystal monitor. Typical growth rates are 0.028 nm/s at growth temperatures of 150 &#176;C and 330 &#176;C for Mg3N2 and Zn3N2 films, respectively.

Plasma-Assisted Molecular Beam Epitaxy Growth of Mg3N2 and Zn3N2 Thin Films

This article describes the growth of epitaxial films of Mg3N2 and Zn3N2 on MgO substrates by plasma-assisted molecular beam epitaxy with N2 gas as the nitrogen source and optical growth monitoring.

This article describes a procedure for growing Mg3N2 and Zn3N2 films by plasma-assisted molecular beam epitaxy (MBE). The films are grown on 100 oriented ...

Graphene-Assisted Quasi-van der Waals Epitaxy of AlN Film on Nano-Patterned Sapphire Substrate for Ultraviolet Light Emitting Diodes

This protocol demonstrates a method for graphene-assisted quick growth and coalescence of AlN on nano-pattened sapphire substrate (NPSS). Graphene layers are directly grown on NPSS using catalyst-free atmospheric-pressure chemical vapor deposition (APCVD). By applying nitrogen reactive ion etching (RIE) plasma treatment, defects are introduced into the graphene film to enhance chemical reactivity. During metal-organic chemical vapor deposition (MOCVD) growth of AlN, this N-plasma treated graphene buffer enables AlN quick growth, and coalescence on NPSS is confirmed by cross-sectional scanning electron microscopy (SEM). The high quality of AlN on graphene-NPSS is then evaluated by X-ray rocking curves (XRCs) with narrow (0002) and (10-12) full width at half-maximum (FWHM) as 267.2 arcsec and 503.4 arcsec, respectively. Compared to bare NPSS, AlN growth on graphene-NPSS shows significant reduction of residual stress from 0.87 GPa to 0.25 Gpa, based on Raman measurements. Followed by AlGaN multiple quantum wells (MQWS) growth on graphene-NPSS, AlGaN-based deep ultraviolet light-emitting-diodes (DUV LEDs) are fabricated. The fabricated DUV-LEDs also demonstrate obvious, enhanced luminescence performance. This work provides a new solution for the growth of high quality AlN and fabrication of high performance DUV-LEDs using a shorter process and less costs.

A protocol for graphene-assisted growth of high-quality AlN films on nano-patterned sapphire substrate is presented.

This protocol demonstrates a method for graphene-assisted quick growth and coalescence of AlN on nano-pattened sapphire substrate (NPSS). Graphene layers ...

The Effect of Anodization Parameters on the Aluminum Oxide Dielectric Layer of Thin-Film Transistors

Aluminum-oxide (Al2O3) is a low cost, easily processable and high dielectric constant insulating material that is particularly appropriate for use as the dielectric layer of thin-film transistors (TFTs). Growth of aluminum-oxide layers from anodization of metallic aluminum films is greatly advantageous when compared to sophisticated processes such as atomic layer deposition (ALD) or deposition methods that demand relatively high temperatures (above 300 &#176;C) such as aqueous combustion or spray-pyrolysis. However, the electrical properties of the transistors are highly dependent on the presence of defects and localized states at the semiconductor/dielectric interface, which are strongly affected by the manufacturing parameters of the anodized dielectric layer. To determine how several fabrication parameters influence the device performance without performing all possible combination of factors, we used a reduced factorial analysis based on a Plackett-Burman design of experiments (DOE). The choice of this DOE permits the use of only 12 experimental runs of combinations of factors (instead of all 256 possibilities) to obtain the optimized device performance. The ranking of the factors by the effect on device responses such as the TFT mobility is possible by applying analysis of variance (ANOVA) to the obtained results.

Anodization parameters for growth of the aluminum-oxide dielectric layer of zinc-oxide thin-film transistors (TFTs) are varied to determine the effects on the electrical parameter responses. Analysis of variance (ANOVA) is applied to a Plackett-Burman design of experiments (DOE) to determine the manufacturing conditions that result in optimized device performance.

Aluminum-oxide (Al2O3) is a low cost, easily processable and high dielectric constant insulating material that is particularly appropriate for use as the ...

Chemistry

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different materials show variability in resistive switching properties due to the intrinsic nature of the material used, leading to discrepancies in the field because of underlying operation mechanisms. This highlights a need for a reliable technique to understand mechanisms using nanostructural observations. This protocol explains a detailed process and methodology of in&#160;situ nanostructural analysis as a result of electrical biasing using transmission electron microscopy (TEM). It provides visual and reliable evidence of underlying nanostructural changes in real time memory operations. Also included is the methodology of fabrication and electrical characterizations for asymmetric crossbar structures incorporating amorphous vanadium oxide. The protocol explained here for vanadium oxide films can be easily extended to any other materials in a metal-dielectric-metal sandwiched structure. Resistive switching crossbars are predicted to serve the programmable logic and neuromorphic circuits for next-generation memory devices, given the understanding of the operation mechanisms. This protocol reveals the switching mechanism in a reliable, timely, and cost-effective way in any type of resistive switching materials, and thereby predicts the device&#39;s applicability.

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Presented here is a protocol for analyzing nanostructural changes during in&#160;situ biasing with transmission electron microscopy (TEM) for a stacked metal-insulator-metal structure. It has significant applications in resistive switching crossbars for the next generation of programmable logic circuits and neuromimicking hardware, to reveal their underlying operation mechanisms and practical applicability.

Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors

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