Interdiffusion of Al and Ga in (Al,Ga)As/GaAs superlattices

Abstract

We have employed photoluminescence spectroscopy to determine the temperature and composition dependence of the interdiffusion of Al and Ga in (Al,Ga)As/GaAs superlattices. The position of the band to band luminescence in the superlattices was measured both before and after thermal anneal. The diffusion equation was solved with a fixed value of D, to establish the potential profile of the superlattice structure after anneal. A solution of the Schrödinger equation where the electron or hole wave function was expanded in a Fourier series was employed to determine the position of the superlattice band edges both before and after anneal and hence infer the expected luminescence peak positions. The value of D which yielded a calculated shift in agreement with the measured shift in the luminescence was taken to be the actual value of the interdiffusion coefficient. For structures consisting of GaAs wells and AlxGa1−xAs barriers with x=1.0 and 0.3 the interdiffusion process is characterized by an activation energy of 6.0 eV with a value of 4×10−19 cm2/s at 850 °C. For x=0.7 the interdiffusion is characterized by an activation energy of 4.0 eV with a value of 7×10−18 cm2/s at 850 °C.