Examining the effects of changing film composition and temperature on the optical properties of GaAsBi epitaxial films

GaAs_1-xBi_x semiconductor alloys are being considered for a range of new infrared optoelectronic applications. This is because small changes in Bi content can produce large decreases in film bandgap, opening up new lattice parameter and bandgap combinations for devices. However, the optical properties of GaAsBi as a function of changing Bi content have not been thoroughly documented and seldom tested at temperatures relevant for infrared detectors or thermophotovoltaics. In this work we study the optical properties of GaAsBi films of varying Bi composition grown by solid source molecular beam epitaxy (MBE). Optical properties are measured by variable angle spectroscopic ellipsometry over a wavelength range from 300 nm to 32 μm and at temperatures ranging from 77K to 600K. The optical properties of the system are modeled so that the GaAsBi optical constants can be separated from those of the underlying substrate. Characterization of GaAsBi optical properties over a range of Bi compositions and temperatures will provide the necessary data for design of future devices and a better fundamental understanding of the material system.