ANNEALING EFFECT ON THE ELECTRICAL-PROPERTIES OF HEAVILY C-DOPED P+GAAS

The carrier concentration in heavily carbon-doped p+-GaAs epilayers (about 1.3 X 10(20) cm-3) is decreased together with the mobility by annealing at temperatures of 700-degrees-C or higher but not at temperatures of 600-degrees-C or lower. In comparatively lightly C-doped p+ epilayers (about 3.5 X 10(19) cm-3), the carrier concentration is not decreased by annealing at temperatures from 500 to 850-degrees-C. The deep photoluminescence peak at a wavelength of around 1080 nm accompanied by a hump at around 1420 nm are found only in heavily C-doped epilayers; the wavelength of this peak is very close to that of the Ga vacancy - the C donor center. The photoluminescence intensity is increased by the annealing at 850-degrees-C but not at 600-degrees-C. The thermal behaviors of the deep photoluminescence levels can well explain those of carrier concentration and mobility if we consider the photoluminescence levels to be the index for the compensation centers.