Optical characterization of compound semiconductors using photoconductivity and photoreflectance

Custom photoreflectance modulation spectroscopy and photoconductivity spectroscopy set-ups were constructed and used to characterize semiconductor materials. The ternary Cd1--xZnxTe compound was studied to achieve fine control over its composition to provide lattice-matched substrates for the growth of Hg1--xCdxTe which is used in infrared detectors. Photoreflectance spectroscopy, capable of accurate estimations of energy levels in semiconductors, was applied to determine composition in CdZnTe standards via band gap energy determinations. The excitonic contributions at room temperature were shown to be in agreement with literature data. The lack of lattice matched substrates for the growth of GaN is still providing material with considerable defect densities despite substantial efforts in material research to date. Photoconductivity spectroscopy was used to characterize various epitaxially grown GaN samples via studying defects and imperfections present in the material. Distinct photoconductance features were observed near the GaN band edge, being attributed to sub-band imperfection levels.