Temperature dependence of the Hall-effect electron concentration in n-Al0.28Ga0.72 As/GaAs heterostructures

A precise model for calculation of the spatial distribution of electrons in n-(Al,Ga)As/GaAs heterostructures is described. The model has been used to investigate the spatial distribution of electrons in a n-Al0.28Ga0.72 As/GaAs structure as a function of temperature. The results were compared with Hall-effect experiments on heterostructures as well as thick Al0.28Ga0.72 As films grown by molecular-beam epitaxy (MBE). For both types of samples it was found that it was necessary to use either a conduction-band density of states which is much higher than expected from literature data or to use a temperature-dependent activation energy. The slight increase in concentration of the two-dimensional electron gas observed for lower temperatures could be attributed to a sharpening of the transition region between high- and low-ionization degrees in the depletion layer close to the interface. It thus indicates that the Hall factor changes very little as expected for a degenerate electron system.