Semi-insulating GaAs materials, undoped or doped with concentration of chromium varying from 6×1015 to 4×1017 cm−3, have been studied using both Hall effect measurements and optical absorption measurements. It is definitively concluded that compensation comes from the presence of the deep donor EL2 in undoped materials, and from both this deep donor and the deep acceptor related to chromium in Cr-doped materials. Sets of curves are given which allow the determination of ND-NA, the concentration of shallow donors and acceptors, knowing the Hall mobility and the Cr concentration in a given sample. Such curves can be a working tool for assessing any piece of semi-insulating GaAs in a routine way.
Transient-capacitance-spectroscopy experiments yielded electron-emission-rate and electron capture crosssection versus temperature data for the main electron trap in vapor-phase epitaxial Ga&, ln"As layers with 0 & x & 0.21. The ionization energy Ec-ET was obtained from these. Theoretical calculations using the pseudopotential method were performed for substitutional oxygen donor in GaInAs, and the calculated energy levels were compared with the experimental ones. The electron-capture cross sections, as well as optical photoionization data are also discussed from the theoretical point of view. It is argued that most of the experimental evidence is not consistent with the idea that the observed electron trap is simple (substitutional) donor oxygen.
Quantitative Mn, Si, Cr, and Fe profiles have been obtained by secondary ion mass spectrometry on Cr-doped semi-insulating GaAs subjected to unencapsulated anneals at 750 °C in a hydrogen ambient. The chemical concentration of Mn induced by annealing is greater than can be realized by diffusion from the bulk (Mn = 3×1013 cm−3), and relates directly to both the free-hole concentration measured in the conducting surface layer and the 5 K photoluminescence (PL) intensity of the zero-phonon emission at 1.409 eV. Post anneal profiles of the elements Si and Cr, which are present in the bulk prior to annealing, indicate that Si remains uniformly distributed while Cr suffers out-diffusion in conjunction with surface accumulation. The distribution of Fe which peaks at 5×1015 atoms cm−3 may, like Mn, arise from incorporation from the annealing ambient.
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