Enhanced radiative absorption of thin, heavily beryllium-doped GaAs films

Beryllium-doped GaAs layers have been grown by molecular beam epitaxy with doping concentrations up to 1.2 × 1020 cm−3. Upon initiation of doping, an unintentional substrate temperature rise is observed pyrometrically that is caused by various radiant sources used in the growth process. The heating effect is correlated with the doping concentration and dependent upon machine configuration and geometry. Electrical and secondary ion mass spectrometry measurements indicate that the temperature rise can cause significant beryllium diffusion. Since most of the temperature rise occurs during the first 1000A of growth, degradation of thin device layers is possible. Transmission and reflection measurements on the beryllium-doped samples indicate strong sub-bandgap absorption that correlates with the doping concentration. The absorption is due to intervalence band transitions as well as free carrier absorption.