Thermoreflectance study of the direct optical gap in epitaxial AlxGa1-xSb (x<=0.5)

Thermoreflectance spectroscopy was used to precisely determine the direct optical gap EgΓ, as a function of composition and temperature of a series of AlxGa1-xSb layers (0.0<~x<~0.5) epitaxially grown on GaSb. The experimental line shapes were fitted with a critical-point functional form including excitonic effects, to derive the direct gap and broadening parameter values. The relation between EgΓ and x shows a x-dependent bowing, which was compared with previous results and theoretical models, leading to the conclusion that EgΓ(x) curves in AlxGa1-xSb alloys have a cubic polynomial form.