Optical Study of Indium Phosphate Related Semiconductor Alloys

In this thesis, spectroscopic ellipsometry is used to study the effects of disorder, self-ordering, strain, and dopants on electronic band structure of In _{rm x}Ga_ {rm 1-x}P grown on GaAs, In _{rm x}Ga_ {rm 1-x}P grown on GaP substrate with composition-graded InGaP buffer layer and lattice matched (Al_{rm x}Ga _{rm 1-x}) _{0.5}In_{0.5 }P grown on GaAs semiconductor alloys with assistance from measurements of Raman spectroscopy and transmission electron microscopy. Our studies of In_{rm x}Ga_{rm 1-x} P/(GaAs, graded GaP) and (Al_{ rm x}Ga_{rm 1-x})_ {0.5}In _{0.5}P/GaAs heteroepitexial layers principally demonstrate the efficacy of using spectroscopic ellipsometry to probe the modulations of critical points, the high symmetry points of electronic band structure, which are caused by long (or short) range ordering, misfit strain, defects, or dopants. For example, in the case of ordered and doped In_{0.5} Ga_{0.5}P/GaAs materials, the amplitudes and peak positions of the signal of the E_1 critical point decrease as CuPt-type ordering increases whereas the linewidths and phases strongly correlate with dopant concentrations. In contrast, the same properties of E_2 critical points decrease as CuPt-type ordering increases. We attribute this ordering dependent correlation of critical point parameters to the formation of a spontaneous (111) InP/GaP superlattice. We also studied the effect of misfit strain on the E_1 critical point parameters of 1 μm thick In _{rm x}Ga_ {rm 1-x}P/GaAs (0.4 <= x <= 0.6) as a function of In composition. We observed near cancellation of In composition dependence of the E_1 peak position by the effect of misfit strain, and also found that the linewidth of the E_1 peak broadens rapidly in those compositions under tensile stress even below the critical thickness, where elastic energy originating from misfit strain relaxes generating defects, e.g. microcracks. Finally, the investigation of the critical points of the E _1 and E_2 gaps of (Al_{rm x}Ga _{rm 1-x})_{0.5} In_{0.5}P/GaAs leads to the conclusion that the electronic charge distributions of Ga-P and Al-P bonds may be similar because their critical point parameters linearly interpolate between those of the endpoint ternaries, Ga_{0.5} In_{0.5}P and Al _{0.5}In_ {0.5}P. There is at present no agreement for In _{rm x}Ga_ {rm 1-x}P alloys on the value of the crossover composition, x_{rm c}, of the direct and indirect gaps and whether the L_{rm 1c} must be included among Gamma_{rm 1c}, and X_{rm 1c }. The quasi-direct transitions of E _{rm L1} and E_ {rm X3} observed by ellipsometry favor the two conduction band model. We also discuss the origin of the quasi-direct transitions. In addition, the mode behavior of optic phonons in the In_ {rm x}Ga_{rm 1-x}P alloys is controversial. Using Raman spectroscopy, we studied the LO phonon-plasmon interaction of the doped In_{0.5}Ga _{0.5}P/GaAs alloys and found that one mode behavior is a more appropriate description than two mode behavior.