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Engineering

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Published: February 27th, 2013

DOI:

10.3791/50297

1Department of Energy and NEMAS - Center for NanoEngineered Materials and Surfaces, Politecnico di Milano, 2Center for Nano Science and Technology, Instituto Italiano di Tecnologia

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (>80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

Pulsed Laser Deposition (PLD) employs laser ablation of a solid target which results in the formation of a plasma of ablated species which can be deposited on a substrate to grow a film (see Figure 1) 1. Interaction with a background atmosphere (inert or reactive) can be used to induce homogeneous cluster nucleation in the gas phase (see Figure 2) 2,3. Our strategy for material synthesis by PLD is based on the tuning of material properties in a bottom-up approach by carefully controlling the plasma dynamics generated in the PLD process. Cluster size, kinetic energy and composition can be varied by a prope....

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1. Substrate Preparation

  1. Cut 1 cm x 1 cm silicon substrates from a Si wafer, Silicon is good for SEM characterization (plane view and cross section).
  2. Cut 1 cm x 1 cm glass (soda-lime, 1 mm thick), glass is optimal for optical and electrical characterization.
  3. If contacts are needed on glass substrates, Au contacts can be evaporated in vacuum by using a mask. Deposit 10 nm of Cr as an interlayer to improve adhesion of Au, deposit 50 nm of Au.
  4. Cut 1 cm x 1 cm pol.......

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The deposition of AZO by PLD in oxygen atmosphere produces compact transparent conducting films at low background gas pressure (i.e. 2 Pa) and mesoporous forest-like structures constituted by hierarchically assembled clusters at high pressures (i.e. 160 Pa). The material is constituted by nanocrystalline domains whose size is maximum (30 nm) at 2 Pa 22.

Due to collisions between the ablated species and the background gas, the shape and length of the plasma p.......

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The plasma plume shape is closely related to the ablation process, especially in the presence of a gas; monitoring the plasma plume by visual inspection is important to control the deposition. When depositing a metal oxide by ablating an oxide target, oxygen is needed to support oxygen losses during the ablation process. At lower oxygen background gas pressure, the deposited material may have oxygen vacancies. This effect is reduced by increasing the gas pressure. To separate stoichiometry from morphology gas mixt.......

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Name Company Catalog Number Comments
Name of Reagent/Material Company Catalog Number
Pulsed Laser Continuum-Quantronix Powerlite 8010
Power meter Coherent FieldMaxII-TO
Ion Gun Mantis Dep RFMax60
Mass flow controller Mks 2179 °
Quartz Crystal Microbalance Infcon XTC/2
Background gas Rivoira-Praxair 5.0 oxygen
Target Kurt Lesker (made on request)
Isopropanol Sigma Aldrich 190764-2L
Source meter Keithley K2400
Magnet Kit Ecopia 0.55T-Kit
Spectrophotometer PerkinElmer Lambda 1050

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