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

Thermoreflectance spectroscopy was used to precisely determine the direct o ptical gap E-g(Gamma), as a function of composition and temperature of a se ries of AlxGa1-xSb layers (0.0 less than or equal to x less than or equal t o 0.5) epitaxially grown on GaSb. The experimental line shapes were fitted with a critical-point functional form including excitonic effects, to deriv e the direct gap and broadening parameter values. The relation between E-g( Gamma) and x shows a x-dependent bowing, which was compared with previous r esults and theoretical models, leading to the conclusion that E-g(Gamma) (x ) curves in AlxGa1-xSb alloys have a cubic polynomial form. [S0163-1829(99) 10303-5].