A comparison of photoconduction effects in (Al, Ga)As and GaAs/(Al, Ga)As heterostructures

The authors have studied the temperature, exposure time and wavelength dependence of the photo-conduction processes in thick Si-doped Al0.33Ga0.67As layers, and also in 2DEG samples with the same (Al, Ga)As composition, with and without a GaAs capping layer. They have deduced the spectral dependence of the photo-ionisation cross section for the Si-related DX centre in the (Al, Ga)As, and used this to model the expected persistent photo-conduction (PPC) behaviour of the 2DEG samples. Although good agreement has been obtained for a restricted range of experimental conditions, significant differences have also been found between the predicted and observed PPC effects, and also between the behaviour of capped and uncapped 2DEG samples. Other inconsistencies have been found, in the decay rate of the PPC on warming the sample and in the number of carriers that can ultimately transfer to the 2DEG channel, which suggest that the ionisation and capture processes for the DX centres in a 2DEG structure are modified from those in bulk (Al, Ga)As.