Development and optimisation of supercritical fluid deposition of semiconductor films

Abstract

This thesis is concerned with the deposition, and characterisation, of semiconductor thin films and microstructures deposited from a supercritical fluid. Thin films of CdS, GaP, InP, InAs, and Ge were deposited using supercritical CO₂ and CO₂-solvent mixtures. Ge was deposited into macropores etched into crystalline silicon substrates. A variety of reactors were designed in order to achieve the successful deposition of the materials. The surface morphology and crystallinity of the films were characterised by scanning electron microscopy and X-ray diffraction. The chemical composition of the films was analysed by energy or wavelength dispersive X-ray spectroscopy, secondary ion mass spectroscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The optoelectronic quality of the CdS and InP films was analysed by photoluminescence spectroscopy and mapping. The CdS films deposited were confirmed to be of hexagonal phase by X-ray diffraction and exhibited band edge luminescence. The InP and InAs films were determined to be of cubic structure and the InP films were found to exhibit weak band edge luminescence. The fabrication of macroporous silicon templates by photoelectrochemical etching is also discussed. Pores with diameters of between 60 nm and 2 µm were fabricated, having aspect ratios of up to 100:1. Ge was successfully deposited into macropores etched into these crystalline silicon templates with near conformal coverage.

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