Post-annealing-induced free-carrier compensation in shallow-buried δ layers of GaAs(100)

Abstract

The influence of post-annealing on the spatial redistribution of silicon dopants in δ-doped GaAs(100) was studied by high-resolution electron energy-loss spectroscopy (HREELS). Samples with different δ-layer depths (100, 200 and 300 Å) were investigated. As follows from the model calculations, plasmons of the two-dimensional electron gas in the δ layer couple to phonons, giving rise to the plasmaron modes ω − and ω +. The lower-energy plasmaron ω − causes an appreciable broadening of the quasi-elastic peak in HREEL spectra, compared with that of undoped GaAs(100). However, the post-annealing affects the energy-loss spectra of the samples differently. For the samples with the δ-doping plane at a depth of 200 or 300 Å, the quasi-elastic peak broadening still persists even after annealing at up to 580°C. In contrast, after annealing of the sample with the δ-doping plane at a depth of 100 Å, the broadening of the quasi-elastic peak is no longer indicated and the energy-loss spectrum appears to be very similar to that of the undoped sample. This effect manifests the full free-electron compensation in this sample, contrary to the samples with the deeper position of the δ layer beneath the surface. The free-electron compensation is explained by the trapping of free electrons by acceptor defects, which are effectively produced at the surface during annealing, and also by defects formed within the δ-doped layer. The irregular variation of the areal free-electron density in the δ layers during annealing to successively higher temperatures is interpreted as a result of a complex redistribution of the silicon dopants.