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

The influence of post-annealing on the spatial redistribution of silicon do pants in delta-doped GaAs (100) was studied by high resolution electron ene rgy-loss spectroscopy (HREELS). Samples with different delta-layer depths ( 100, 200 and 300 Angstrom) were investigated. As follows from the model cal culations, plasmons of the two-dimensional electron gas in the delta layer couple to phonons, giving rise to the plasmaron modes omega(-) and omega(+) . The lower-energy plasmaron omega(-) causes an appreciable broadening of t he quasi-elastic peak in HREEL spectra, compared with that of undoped GaAs( 100). However, the post-annealing affects the energy-loss spectra of the sa mples differently. For the samples with the delta-doping plane at a depth o f 200 or 300 Angstrom, the quasi-elastic peak broadening still persists eve n after annealing at up to 580 degrees C. In contrast, after annealing of t he sample with the delta-doping plane at a depth of 100 Angstrom, the broad ening 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 eff ect manifests the full free-electron compensation in this sample, contrary to the samples with the deeper position of the delta layer beneath the surf ace. The free-electron compensation is explained by the trapping of free el ectrons by acceptor defects, which are effectively produced at the surface during annealing, and also by defects formed within the delta-doped layer. The irregular variation of the areal free-electron density in the delta lay ers during annealing to successively higher temperatures is interpreted as a result of a complex redistribution of the silicon dopants. (C) 1999 Elsev ier Science B.V. All rights reserved.