Optical property comparison of GaAsBi and TlGaAs measured by variable angle spectroscopic ellipsometry

III-V semiconductors have broad uses in optoelectronics due to their direct band gaps and high carrier motilities. GaAs(1-x)Bix and TlxGa(1-x) As ternary alloys are of interest for light emitting, light absorbing and other applications (e. g. communication lasers, photovoltaics, and high speed transistors) in the infrared spectrum due to their decreased bandgap relative to GaAs. While GaAs has been extensively studied, the optical properties of GaAsBi and TlGaAs are less documented and show significant variation with Bi and Tl content respectively. This study characterized the optical properties of GaAsBi and TlGaAs films of varying Bi and Tl composition using variable angle spectroscopic ellipsometry (VASE) in a range of temperatures from 25 degrees C - 300 degrees C. GaAsBi films were grown between 3.3% and 6.5% bismuth. TlGaAs films were grown between 1.7% and 2.7% thallium. Modeling using a superposition of Gaussian oscillators fit to the dielectric functions of sample layers was used to separate film optical properties from the pseudooptical properties of the sample. The analysis in this study directly compares the inclusion of the two largest III-V constituent atoms, Bi and Tl. Comparison of the refractive index and absorption coefficient of samples was done over a spectral range of 0.5 eV to 5 eV (250 nm to 2500 nm). This region displays the absorption edge corresponding to the bandgap of the material, which is then correlated to the incorporation of Bi and Tl in the samples. This characterization allows for better modeling of these alloys for both a fundamental understanding of their properties and for their inclusion in future devices.