Characterization of Novel Semiconductor Alloys for Band Gap Engineering

The novel semiconductor alloys, In1-xAlxN, GaN1-xAsx, and ZnSe1-xOx, are promising materials for low-cost and high-efficiency solar cells and efficient solid-state lighting. The band gap of all of the alloys can be controlled through the visible electromagnetic energy spectrum by varying x. In-rich InAlN tends to be degenerately n-type due to the high electron affinity of InN and the conduction band and light hole band are non-parabolic due to the narrow band gap and the interaction of the conduction band and valence bands. The absorption spectra can be blue shifted due to the Burstein-Moss Shift. GaNAs and ZnSeO are highly mismatched alloys, where the alloying involves elements that are very dissimilar in terms of electronegativity and size. The band anticrossing model, which treats the interaction of a localized defect level with the extended states of the conduction and valence bands, quantitatively describes the properties of highly mismatched alloys. The band gap bowing parameter, which quantifies the band gap dependence on composition, of InAlN is determined while accounting for the effects of degenerate electron concentrations and non-parabolic bands on the absorption spectra. The composition is independently determined by two complimentary methods. The band gap and temperature dependence of the band gap of ZnSe1-xOx are determined by optical spectroscopy and can be understood in terms of the band anticrossing model. The exciton kinetics is quantified through time-resolved photoluminescence and is found to cause a low temperature enhancement of the photoluminescence. The band gaps of GaNAs are determined for the full composition range for both crystalline and amorphous phases. The composition dependence of the band gap can be quantified by the band anticrossing model across the full composition range through a linear interpolation of the conduction band and valence band anticrossing models