Activation of Cr1+ (3d5) Level in GaAs:Cr Induced by Hydrostatic Pressure
The absorption spectrum of n-type GaAs:Cr, in which the Cr2+ EPR signal remains stable under illumination, was measured under hydrostatic pressure up to 10 kbar at liquid nitrogen temperature. The intracentre Cr2+ transition (5T2→5E) disappears with increasing pressure; simultaneously, a rapid rise in resistivity is observed. These results can be explained by the existence of the Cr1+ level in the conduction band. Under hydrostatic pressure, this level lowers relative to the conduction band minimum and its population increases, i.e. conduction electrons are trapped by Cr2+ centres. Above 9 kbar the saturation of the observed effects appears, indicating that at this pressure the Cr1+ level is below the conduction band. This observation locates the Cr1+ level no higher than 100 meV above the conduction band minimum at 77 K, i.e. about 1.6 eV above the valence band maximum.
KeywordsConduction Band Hydrostatic Pressure Liquid Nitrogen Temperature Chromium Concentration Valence Band Maximum
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