Reduced temperature dependence of refractive index in TlInGaAs addition of Tl

Optical properties of TlInGaAs quaternary alloy were studied by spectroscopic ellipsometry (SE), reflectance, and transmittance. Spectroscopic ellipsometry and reflectance measurements suggest that TlInGaAs is a semiconductor system having a temperature-stable refractive index. The square of the absorption spectra, α², measured by transmittance, also determined the temperature-stable E₀ edge. It was found that the temperature coefficients of both refractive index and E₀ edge of TlInGaAs are much smaller than those for InGaAs. These results facilitate the fabrication of the temperature-stable-wavelength optoelectronic devices using this alloy system.