X–Γ indirect intersubband transitions in type II GaAs/AlAs superlattices

Intersubband transitions indirect in both real and momentum spaces were observed in GaAs/AlAs type II short period superlattices. Significant absorption of normal incident radiation, with ‘‘forbidden’’ polarization was measured, in addition to absorption in the ‘‘allowed’’ configuration. The transition energy shows a strong temperature dependence. This absorption is attributed to X–Γ transition. Both doped and undoped samples were investigated. Normal incidence absorption is stronger for the doped superlattices. Simulations using a two band model show good agreement to experimental data.