This work was supported by the Department of Energy under the FPACE program (DE-EE0005398), the Ohio State University Institute for Materials Research, and the Ohio Office of Technology Investments&#8217; Third Frontier Program.

This protocol was written with an assumption that the reader will have a working understanding of standard SEM operation. Depending upon the manufacturer, model, and even software version, every SEM can have significantly different hardware and/or software interfaces. The same can be said with respect to the internal configuration of the instrument; the operator must be cautious and observant when following this protocol, as even relatively small changes in sample size/geometry, sample orientation (tilt, rotation), and working distance, can present a risk for making contact with the pole&#8211;piece, especially if not at eucentric height. The instructions provided here are for the instrument used to perform this work, a FEI Sirion SEM equipped with a field emission gun and a standard, pole-piece mounted, annular Si backscatter detector. Therefore, it is imperative that the reader understand how to perform the equivalent actions on their own specific equipment.
1. Sample Preparation
<ol>
	<li>Cleave sample, GaP/Si for this study, into a suitable size depending on the size of the SEM sample mount that is to be used. Note: The sample can be as small as 5 mm x 5 mm or as large as a full wafer (4 inches long), depending on the internal geometry of the SEM used and the available chamber space.The sample surface should be very clean and free of contamination that could disturb the channeling (e.g., crystalline or amorphous native oxides).</li>
	<li>Place the sample onto the SEM sample mount. Note: The mounting method may change depending on the type of SEM stub used, typically either a clip style or via some adhesive (e.g., carbon tape, silver paint). The method of placement must ensure that the sample will not move and that it is electrically grounded to prevent sample charging.</li>
</ol>
2. Load Sample
<ol>
	<li>Vent the SEM by clicking the &#8216;Vent&#8217; button in the software interface and insert the sample after reaching atmospheric pressure.</li>
	<li>Before closing the SEM door, ensure that the sample is at an appropriate height so as to not strike the BSE detector upon moving into the SEM.</li>
	<li>Pump down the SEM by clicking the &#8216;Pump&#8217; button in the software interface. Wait until system indicates that the pressure is low enough to start the measurements.</li>
</ol>
3. Set Appropriate Working Conditions
<ol>
	<li>Turn on the electron beam via the control button in the &#8216;Beam&#8217; control area and set the accelerating voltage via the &#8216;Beam&#8217; drop-down menu in the software interface. For the work presented here, 25 kV was used.</li>
	<li>Set the beam current to an appropriate value via &#8216;Beam&#8217; drop-down menu. This is determined within the system used here by way of the spot size setting, which was set to 5 (approximately 2.4 nA). Note: High beam current is typically necessary because the ECCI signal is generally weak and larger current allows for a more distinguishable image.</li>
	<li>Using the secondary electron detector, adjust the image focus and stigmation via the software interface. Note: This is performed here by right-clicking and dragging the mouse on the software interface; vertical for focus, horizontal for stigmation. Also, it is usually helpful to find a small particle or surface feature on the sample to provide a clear subject for focus/stigmation adjustment.</li>
	<li>Move the sample into the vertical working distance by incrementally changing the Z position of the stage and adjusting the focus and stigmation as needed. The Z position is changed through the &#8216;Z&#8217; drop-down menu in the &#8216;Stage&#8217; control area of the software interface. For the work described here, a working distance of 5 mm placed the same at eucentric height and provided for a strong ECCI signal.</li>
</ol>
4. Visualize Sample ECP
<ol>
	<li>Switch into BSE mode through the &#8216;Detectors&#8217; drop-down menu in the software interface.</li>
	<li>Decrease magnification to its lowest setting (27x), which is done here via the computer keyboard minus (-) key, to visualize the ECP.</li>
	<li>Adjust the scan rate, done here via the &#8216;Scan&#8217; drop-down menu, to provide an image with sufficient signal-to-noise (e.g., slow scan rather than TV mode). Note: Averaging or integrating the image may be necessary to obtain a clearer, more discernable image.</li>
	<li>Adjust the image contrast and brightness, accomplished here via the &#8216;Contrast&#8217; and &#8216;Brightness&#8217; sliders, to help enhance the visibility of the ECP, being careful not to oversaturate.</li>
	<li>Adjust the sample rotation and tilt, using the &#8216;R&#8217; and &#8216;T&#8217; entries in the &#8216;Stage&#8217; control area in the software interface, to help make features of the channeling pattern more apparent. Sample rotation will result in a rotation of the ECP (as shown in Figure 2) and tilting will result in a translation of the ECP (as shown in Figure 3).</li>
</ol>
5. Image Defects/Features
<ol>
	<li>Adjust sample tilt and rotation, as described in step 4.5, to set the desired diffraction condition. Accomplish this by translating and/or rotating the ECP to align the target Kikuchi band edge (i.e., inflection point between the bright Kikuchi band and its associated dark Kikuchi line) with the SEM optic axis. While maximum channeling actually occurs at the Kikuchi line, aligning in the method described here provides visualization contrast for defects with both dark and bright contrast levels (see Figures 4 and 5).</li>
	<li>Once the desired diffraction condition is achieved, increase magnification, done here via the keyboard plus (+) key.</li>
	<li>Refocus image and adjust for stigmation, as described in step 3.2. Note: Here, the focus and stigmation is best adjusted with respect to the specific defect/feature being imaged.</li>
	<li>Because small deviations from the edge of the band can make large differences in the appearance of the target defect or feature, optimize the diffraction condition by making small (no more than adjustments to the sample tilt orthogonally to the Kikuchi band/line of interest, while watching a specific feature for maximum contrast. Note that moving toward the inside of the Kikuchi band will typically reduce the relative contrast of &#8220;bright&#8221; features, while moving toward the outside of the band (toward the Kikuchi line) will typically reduce the relative contrast of &#8220;dark&#8221; features.</li>
	<li>Once the desired contrast is obtained, decrease the magnification to verify that the same band is still on or very near the optic axis; too much tilt can change the diffraction condition altogether.</li>
</ol>

<ol>
	<li>Zaefferer, S., Elhami, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theory+and+application+of+electron+channelling+contrast+imaging+under+controlled+diffraction+conditions.">Theory and application of electron channelling contrast imaging under controlled diffraction conditions.</a> Acta Mater. 75, 20-50 (2014).</li><li>Crimp, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A.+Scanning+electron+microscopy+imaging+of+dislocations+in+bulk+materials,+using+electron+channeling+contrast.">A. Scanning electron microscopy imaging of dislocations in bulk materials, using electron channeling contrast.</a> Microsc. Res. Tech. 69 (5), 374-381 (2006).</li><li>Joy, D. C., Newbury, D. E., Davidson, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+channeling+patterns+in+the+scanning+electron+microscope.">Electron channeling patterns in the scanning electron microscope.</a> J. Appl. Phys. 53 (8), R81-R122 (1982).</li><li>Williams, D. B., Carter, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Transmission Electron Microscopy: A Textbook for Materials Science. , (2009).</li><li>Picard, Y. N., 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=Future+Prospects+for+Defect+and+Strain+Analysis+in+the+SEM+via+Electron+Channeling.">Future Prospects for Defect and Strain Analysis in the SEM via Electron Channeling.</a> Micros. Today. 20 (2), 12-16 (2012).</li><li>Naresh-Kumar, 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=Rapid+Nondestructive+Analysis+of+Threading+Dislocations+in+Wurtzite+Materials+Using+the+Scanning+Electron+Microscope.">Rapid Nondestructive Analysis of Threading Dislocations in Wurtzite Materials Using the Scanning Electron Microscope.</a> Phys. Rev. Lett. 108 (13), 135503 (2012).</li><li>Naresh-Kumar, 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=Electron+channeling+contrast+imaging+studies+of+nonpolar+nitrides+using+a+scanning+electron+microscope.">Electron channeling contrast imaging studies of nonpolar nitrides using a scanning electron microscope.</a> Appl. Phys. Lett. 102 (14), 142103 (2013).</li><li>Kamaladasa, R. 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=Identifying+threading+dislocations+in+GaN+films+and+substrates+by+electron+channelling.">Identifying threading dislocations in GaN films and substrates by electron channelling.</a> J. Microsc. 244 (3), 311-319 (2011).</li><li>Picard, Y. N., 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=Nondestructive+analysis+of+threading+dislocations+in+GaN+by+electron+channeling+contrast+imaging.">Nondestructive analysis of threading dislocations in GaN by electron channeling contrast imaging.</a> Appl. Phys. Lett. 91 (9), 094106 (2007).</li><li>Picard, Y. N., 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=Electron+channeling+contrast+imaging+of+atomic+steps+and+threading+dislocations+in+4H-SiC.">Electron channeling contrast imaging of atomic steps and threading dislocations in 4H-SiC.</a> Appl. Phys. Lett. 90 (23), 234101 (2007).</li><li>Picard, Y., 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=Epitaxial+SiC+Growth+Morphology+and+Extended+Defects+Investigated+by+Electron+Backscatter+Diffraction+and+Electron+Channeling+Contrast+Imaging.">Epitaxial SiC Growth Morphology and Extended Defects Investigated by Electron Backscatter Diffraction and Electron Channeling Contrast Imaging.</a> J. Electron. Mater. 37 (5), 691-698 (2008).</li><li>Wilkinson, A. J. <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+strain+distributions+in+partially+relaxed+In0.2Ga0.8As+on+GaAs+using+electron+channelling+contrast+imaging.">Observation of strain distributions in partially relaxed In0.2Ga0.8As on GaAs using electron channelling contrast imaging.</a> Philos. Mag. Lett. 73 (6), 337-344 (1996).</li><li>Wilkinson, A. J., Anstis, G. R., Czernuszka, J. T., Long, N. J., Hirsch, P. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+Channeling+Contrast+Imaging+of+Interfacial+Defects+in+Strained+Silicon-Germanium+Layers+on+Silicon.">Electron Channeling Contrast Imaging of Interfacial Defects in Strained Silicon-Germanium Layers on Silicon.</a> Philos. Mag. A. 68 (1), 59-80 (1993).</li><li>Carnevale, S. D., 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=Rapid+misfit+dislocation+characterization+in+heteroepitaxial+III-V/Si+thin+films+by+electron+channeling+contrast+imaging.">Rapid misfit dislocation characterization in heteroepitaxial III-V/Si thin films by electron channeling contrast imaging.</a> Appl. Phys. Lett. 104 (23), 232111 (2014).</li><li>Kvam, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interactions+of+dislocations+and+antiphase+(inversion)+domain+boundaries+in+III&#8211;V/IV+heteroepitaxy.">Interactions of dislocations and antiphase (inversion) domain boundaries in III&#8211;V/IV heteroepitaxy.</a> J. Electron. Mater. 23 (10), 1021-1026 (1994).</li><li>Grassman, T. 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=Control+and+elimination+of+nucleation-related+defects+in+GaP/Si(001)+heteroepitaxy.">Control and elimination of nucleation-related defects in GaP/Si(001) heteroepitaxy.</a> Appl. Phys. Lett. 94 (23), 232106 (2009).</li><li>Grassman, T. 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=Nucleation-related+defect-free+GaP/Si(100)+heteroepitaxy+via+metal-organic+chemical+vapor+deposition.">Nucleation-related defect-free GaP/Si(100) heteroepitaxy via metal-organic chemical vapor deposition.</a> Appl. Phys. Lett. 102 (14), 142102 (2013).</li><li>Volz, K., 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=GaP-nucleation+on+exact+Si(001)+substrates+for+III/V+device+integration.">GaP-nucleation on exact Si(001) substrates for III/V device integration.</a> J. Cryst. Growth. 315 (1), 37-47 (2011).</li><li>Beyer, A., 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=GaP+heteroepitaxy+on+Si(001):+Correlation+of+Si-surface+structure,+GaP+growth+conditions,+and+Si-III/V+interface+structure.">GaP heteroepitaxy on Si(001): Correlation of Si-surface structure, GaP growth conditions, and Si-III/V interface structure.</a> J. Appl. Phys. 111 (8), 083534 (2012).</li><li>Touloukian, Y. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Thermal Expansion: Nonmetallic Solids. , (1977).</li><li>Yamaguchi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dislocation+density+reduction+in+heteroepitaxial+III-V+compound+films+on+Si+substrates+for+optical+devices.">Dislocation density reduction in heteroepitaxial III-V compound films on Si substrates for optical devices.</a> J. Mater. Res. 6 (2), 376-384 (1991).</li><li>Nemanich Ware, R. J., Gray, J. L., Hull, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+a+nonorthogonal+pattern+of+misfit+dislocation+arrays+in+SiGe+epitaxy+on+high-index+Si+substrates.">Analysis of a nonorthogonal pattern of misfit dislocation arrays in SiGe epitaxy on high-index Si substrates.</a> J. Appl. Phys. 95 (1), 115-122 (2004).</li><li>Ghandhi Ayers, S. K., Schowalter, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystallographic+tilting+of+heteroepitaxial+layers.">Crystallographic tilting of heteroepitaxial layers.</a> J. Cryst. Growth. 113 (3-4), 430-440 (1991).</li><li>Yamane, T., Kawai, Y., Furukawa, H., Okada, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+of+low+defect+density+GaP+layers+on+Si+substrates+within+the+critical+thickness+by+optimized+shutter+sequence+and+post-growth+annealing.">Growth of low defect density GaP layers on Si substrates within the critical thickness by optimized shutter sequence and post-growth annealing.</a> J. Cryst. Growth. 312 (15), 2179-2184 (2010).</li><li>Jimbo Soga, T., Umeno, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dislocation+Generation+Mechanisms+For+GaP+On+Si+Grown+By+Metalorganic+Chemical-Vapor-Deposition.">Dislocation Generation Mechanisms For GaP On Si Grown By Metalorganic Chemical-Vapor-Deposition.</a> Appl. Phys. Lett. 63 (18), 2543-2545 (1993).</li><li>Weidner, A., Martin, S., Klemm, V., Martin, U., Biermann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stacking+faults+in+high-alloyed+metastable+austenitic+cast+steel+observed+by+electron+channelling+contrast+imaging.">Stacking faults in high-alloyed metastable austenitic cast steel observed by electron channelling contrast imaging.</a> Scripta Mater. 64 (6), 513-516 (2011).</li></ol>

The authors have nothing to disclose.

An accelerating voltage of 25 kV was used for this study. The accelerating voltage will determine the electron beam penetration depth; with higher accelerating voltage, there will be BSE signal coming from greater depths in the sample. The high accelerating voltage was chosen for this system because it allows for visibility of dislocations that are far from the surface of the sample, buried at the interface. Other types of defects/features may be more or less visible at different accelerating voltages depending on the ty...

Detailed characterization of crystalline defects and microstructure is a vitally important aspect of semiconductor materials and device research since such defects can have a significant, detrimental impact on device performance. Currently, transmission electron microscopy (TEM) is the most widely accepted and used technique for detailed characterization of extended defects &#8211; dislocations, stacking faults, twins, antiphase domains, etc. &#8211; because it enables the direct imaging of a wide variety of defects with ample spatial resolution. Unfortunately, TEM is a fundamentally low-throughput approach due to lengthy sample preparation times, which can lead to significant delays and bottlenecks in research and development cycles. Additionally, the integrity of the sample, such as in terms of the as-grown strain state, can be altered during sample preparation, leaving the opportunity for adulterated results.
Electron channeling contrast imaging (ECCI) is a complementary, and in some cases a potentially superior, technique to TEM as it provides an alternative, high-throughput approach for imaging the same extended defects. In the case of epitaxial materials, samples need little to no preparation, making ECCI much more time efficient. Additionally advantageous is the fact that ECCI requires only a field-emission scanning electron microscope (SEM) equipped with a standard annular pole-piece mounted backscatter electron (BSE) detector; forescatter geometry can also be used, but requires slightly more specialized equipment and is not discussed here. The ECCI signal is composed of electrons that have been inelastically scattered out of the in-going channeled beam (electron wave-front), and through multiple additional inelastic scattering events, are able escape the sample back through the surface.1 Similar to two-beam TEM, it is possible to perform ECCI at specific diffraction conditions in the SEM by orienting the sample so that the incident electron beam satisfies a crystallographic Bragg condition (i.e., channeling), as determined using low-magnification electron channeling patterns (ECPs);1,2 see Figure 1 for an example. Simply, ECPs provide an orientation-space representation of incident electron beam diffraction/channeling.3 Dark lines resulting from low backscatter signal indicate beam-sample orientations where Bragg conditions are met (i.e., Kikuchi lines), which yields strong channeling, whereas the bright regions indicate high backscatter, non-diffractive conditions. As opposed to Kikuchi patterns produced via electron backscatter diffraction (EBSD) or TEM, which are formed via outgoing electron diffraction, ECPs are a result of incident electron diffraction/channeling.
In practice, controlled diffraction conditions for ECCI are achieved by adjusting the sample orientation, via tilt and/or rotation under low magnification, such that the ECP feature representing the well-defined Bragg condition of interest &#8211; for example, a [400] or [220] Kikuchi band/line &#8211; is coincident with the optic axis of the SEM. Transitioning to high magnification then, because of the resultant restriction of the angular range of the incident electron beam, effectively selects for a BSE signal that ideally corresponds only to scattering from the chosen diffraction condition. In this manner it is possible to observe defects that provide diffraction contrast, such as dislocations. Just as in TEM, the imaging contrast presented by such defects is determined by the standard invisibility criteria, g &#183; (b x u) = 0 and g &#183; b = 0, where g represents the diffraction vector, b the Burgers vector, and u the line direction.4 This phenomenon occurs because only diffracted electrons from planes distorted by the defect will contain information about said defect.
To date, ECCI has predominantly been used to image features and defects near or at the sample surface for such functional materials as GaSb,5 SrTiO3,5 GaN,6-9 and SiC.10,11 This limitation is the result of the surface-sensitive nature of the ECCI signal itself, wherein the BSE that make up the signal come from a depth range of about 10 &#8211; 100 nm. The most significant contribution to this depth resolution limit is that of broadening and damping of the in-going electron wave front (channeled electrons), as a function of depth into the crystal, due to the loss of electrons to scattering events, which reduces the maximum potential BSE signal.1 Nonetheless, some degree of depth resolution has been reported in previous work on Si1-xGex/Si and InxGa1-xAs/GaAs heterostructures,12,13 as well as more recently (and herein) by the authors on GaP/Si heterostructures,14 where ECCI was used to image misfit dislocations buried at the lattice-mismatched heteroepitaxial interface at depths of up to 100 nm (with higher depths likely possible).
For the work detailed here, ECCI is used to study GaP epitaxially grown on Si(001), a complex materials integration system with application toward such areas as photovoltaics and optoelectronics. GaP/Si is of particular interest as a potential pathway for the integration of metamorphic (lattice-mismatched) III-V semiconductors onto cost-effective Si substrates. For many years efforts in this direction have been plagued by the uncontrolled generation of large numbers of heterovalent nucleation related defects, including antiphase domains, stacking faults, and microtwins. Such defects are detrimental to device performance, especially photovoltaics, due to the fact that they can be electrically active, acting as carrier recombination centers, and can also hinder interfacial dislocation glide, leading to higher dislocation densities.15 However, recent efforts by the authors and others have led to the successful development of epitaxial processes that can produce GaP-on-Si films free of these nucleation related defects,16-19 thereby paving the way for continued progress.
Nonetheless, because of the small, but non-negligible, lattice mismatch between GaP and Si (0.37% at RT), the generation of misfit dislocations is unavoidable, and indeed necessary to produce fully relaxed epilayers. GaP, with its FCC-based zinc blende structure, tends to yield 60&#176; type dislocations (mixed edge and screw) on the slip system, which are glissile and can relieve large amounts of strain through long net glide lengths. Additional complexity is also introduced by the mismatch in GaP and Si thermal expansion coefficients, which results in an increasing lattice mismatch with increasing temperature (i.e., &#8805; 0.5% misfit at typical growth temperatures).20 Because the threading dislocation segments that make up the remainder of the misfit dislocation loop (along with the interfacial misfit and the crystal surface) are well known for their associated non-radiative carrier recombination properties, and thus degraded device performance,21 it is important to fully understand their nature and evolution such that their numbers can be minimized. Detailed characterization of the interfacial misfit dislocations can thus provide a substantial amount of information about the dislocation dynamics of the system.
Here, we describe the protocol for using an SEM to perform ECCI and provide examples of its capabilities and strengths. An important distinction here is the use of ECCI to perform microstructural characterization of the sort typically performed via TEM, whereas ECCI provides the equivalent data but in a significantly shorter time frame due to the significantly reduced sample preparation needs; in the case for epitaxial samples with relatively smooth surfaces, there is effectively no sample preparation required at all. The use of ECCI for general characterization of defects and misfit dislocations is described, with some examples of observed crystalline defects provided. The impact of invisibility criteria on the observed imaging contrast of an array of interfacial misfit dislocations is then described. This is followed by a demonstration of how ECCI can be used to perform important modes of characterization &#8211; in this case a study to determine the GaP-on-Si critical thickness for dislocation nucleation &#8211; providing TEM-like data, but from the convenience of an SEM and in significantly reduced time frame.

<table><tbody><tr><td>Sirion Field Emission SEM</td><td>FEI/Phillips</td><td>516113</td><td>Field emission SEM with beam voltage range of 200 V - 30 kV, equipped with a backscattered electron detector</td></tr><tr><td>Sample of Interest</td><td>Internally produced</td><td></td><td>Synthesized/grown in-house via MOCVD</td></tr><tr><td>PELCO SEMClip</td><td>Ted Pella, Inc.</td><td>16119-10</td><td>Reusable, non-adhesive SEM sample stub (adhesive attachment will also work)</td></tr></tbody></table>

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 GaP/Si samples for this study were grown by metal-organic chemical vapor deposition (MOCVD) in an Aixtron 3&#215;2 close-coupled showerhead reactor following the authors&#8217; previously reported heteroepitaxial process.17 All growths were performed on 4 inch Si(001) substrates with intentional misorientation (offcut) of 6&#176; toward [110]. All ECCI imaging was performed on as-grown samples with no further sample preparation whatsoever (aside from cleaving to yield approximately 1 cm x 1cm pieces for lo...

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Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

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 ...

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11.0K Views.  The Ohio State University. 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.

Video: Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

Characterization of Anisotropic Leaky Mode Modulators for Holovideo

Holovideo displays are based on light-bending spatial light modulators. One such spatial light modulator is the anisotropic leaky mode modulator. This modulator is particularly well suited for holographic video experimentation as it is relatively simple and inexpensive to fabricate1-3. Some additional advantages of leaky mode devices include: large aggregate bandwidth, polarization separation of signal light from noise, large angular deflection and frequency control of color1. In order to realize these advantages, it is necessary to be able to adequately characterize these devices as their operation is strongly dependent on waveguide and transducer parameters4. To characterize the modulators, the authors use a commercial prism coupler as well as a custom characterization apparatus to identify guided modes, calculate waveguide thickness and finally to map the device's frequency input and angular output of leaky mode modulators. This work gives a detailed description of the measurement and characterization of leaky mode modulators suitable for full-color holographic video.

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic video.

Holovideo displays are based on light-bending spatial light modulators.  One such spatial light modulator is the anisotropic leaky mode modulator.  This ...

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.

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 ...

In Situ Characterization of Boehmite Particles in Water Using Liquid SEM

In situ imaging and elemental analysis of boehmite (AlOOH) particles in water is realized using the System for Analysis at the Liquid Vacuum Interface (SALVI) and Scanning Electron Microscopy (SEM). This paper describes the method and key steps in integrating the vacuum compatible SAVLI to SEM and obtaining secondary electron (SE) images of particles in liquid in high vacuum. Energy dispersive x-ray spectroscopy (EDX) is used to obtain elemental analysis of particles in liquid and control samples including deionized (DI) water only and an empty channel as well. Synthesized boehmite (AlOOH) particles suspended in liquid are used as a model in the liquid SEM illustration. The results demonstrate that the particles can be imaged in the SE mode with good resolution (i.e., 400 nm). The AlOOH EDX spectrum shows significant signal from the aluminum (Al) when compared with the DI water and the empty channel control. In situ liquid SEM is a powerful technique to study particles in liquid with many exciting applications. This procedure aims to provide technical know-how in order to conduct liquid SEM imaging and EDX analysis using SALVI and to reduce potential pitfalls when using this approach.

In Situ Characterization of Boehmite Particles in Water Using Liquid SEM

We present a procedure for real-time imaging and elemental composition analysis of boehmite particles in deionized water by in situ liquid Scanning Electron Microscopy.

In situ imaging and elemental analysis of boehmite (AlOOH) particles in water is realized using the System for Analysis at the Liquid Vacuum Interface ...

Chemistry

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Reduction of threading dislocation density (TDD) in epitaxial germanium (Ge) on silicon (Si) has been one of the most important challenges for the realization of monolithically integrated photonics circuits. The present paper describes methods of theoretical calculation and experimental verification of a novel model for the reduction of TDD. The method of theoretical calculation describes the bending of threading dislocations (TDs) based on the interaction of TDs and non-planar growth surfaces of selective epitaxial growth (SEG) in terms of dislocation image force. The calculation reveals that the presence of voids on SiO2 masks help to reduce TDD. Experimental verification is described by germanium (Ge) SEG, using an ultra-high vacuum chemical vapor deposition method and TD observations of the grown Ge via etching and cross-sectional transmission electron microscope (TEM). It is strongly suggested that the TDD reduction would be due to the presence of semicylindrical voids over the SiO2 SEG masks and growth temperature. For experimental verification, epitaxial Ge layers with semicylindrical voids are formed as the result of SEG of Ge layers and their coalescence. The experimentally obtained TDDs reproduce the calculated TDDs based on the theoretical model. Cross-sectional TEM observations reveal that both the termination and generation of TDs occur at semicylindrical voids. Plan-view TEM observations reveal a unique behavior of TDs in Ge with semicylindrical voids (i.e., TDs are bent to be parallel to the SEG masks and the Si substrate).

Theoretical calculation and experimental verification are proposed for a reduction of threading dislocation (TD) density in germanium epitaxial layers with semicylindrical voids on silicon. Calculations based on the interaction of TDs and surface via image force, TD measurements, and transmission electron microscope observations of TDs are presented.

Reduction of threading dislocation density (TDD) in epitaxial germanium (Ge) on silicon (Si) has been one of the most important challenges for the ...

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 ...

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.

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different ...

3D Depth Profile Reconstruction of Segregated Impurities Using Secondary Ion Mass Spectrometry

The presented protocol combines excellent detection limits (1 ppm to 1 ppb) using secondary ion mass spectrometry (SIMS) with reasonable spatial resolution (~1 &#181;m). Furthermore, it describes how to obtain realistic three-dimensional (3D) distributions of segregated impurities/dopants in solid state materials. Direct 3D depth profile reconstruction is often difficult to achieve due to SIMS-related measurement artifacts. Presented here is a method to identify and solve this challenge. Three major issues are discussed, including the i) nonuniformity of the detector being compensated by flat-field correction; ii) vacuum background contribution (parasitic oxygen counts from residual gases present in the analysis chamber) being estimated and subtracted; and iii)&#160;performance of all steps within a stable timespan of the primary ion source. Wet chemical etching is used to reveal the position and types of dislocation in a material, then the SIMS result is superimposed on images obtained via scanning electron microscopy (SEM). Thus, the position of agglomerated impurities can be related to the position of certain defects. The method is fast and does not require sophisticated sample preparation stage; however, it requires a high-quality, stable ion source, and the entire measurement must be performed quickly to avoid deterioration of the primary beam parameters.

The presented method describes how to identify and solve measurement artifacts related to secondary ion mass spectrometry as well as obtain realistic 3D distributions of impurities/dopants in solid state materials.

The presented protocol combines excellent detection limits (1 ppm to 1 ppb) using secondary ion mass spectrometry (SIMS) with reasonable spatial ...

Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar energy and fuel generation, and electrochemical energy storage. Nanoscale characterization of such interfaces has recently been achieved using cryogenic electron microscopy, thereby providing a new path to advancing our fundamental understanding of interface processes.
This contribution provides a practical guide to mapping the structure and chemistry of solid-liquid interfaces in materials and devices using an integrated cryogenic electron microscopy approach. In this approach, we pair cryogenic sample preparation which allows stabilization of solid-liquid interfaces with cryogenic focused ion beam (cryo-FIB) milling to create cross-sections through these complex buried structures. Cryogenic scanning electron microscopy (cryo-SEM) techniques performed in a dual-beam FIB/SEM enable direct imaging as well as chemical mapping at the nanoscale. We discuss practical challenges, strategies to overcome them, as well as protocols for obtaining optimal results. While we focus in our discussion on interfaces in energy storage devices, the methods outlined are broadly applicable to a range of fields where solid-liquid interface play a key role.

Cryogenic Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) techniques can provide key insights into the chemistry and morphology of intact solid-liquid interfaces. Methods for preparing high quality Energy Dispersive X-ray (EDX) spectroscopic maps of such interfaces are detailed, with a focus on energy storage devices.

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar ...

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

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