BANDGAP SHRINKAGE OF DEGENERATE P-TYPE GAAS BY PHOTOLUMINESCENCE SPECTROSCOPY

Photoluminescence characteristics of heavily carbon-, beryllium- and zinc-doped GaAs were studied in this investigation. The band-to-acceptor (e,A) transition was identified via various doping concentrations from 10(17) to 10(20) cm(-3) and the temperature from 20 to 300 K. As a result the (e,A) peak was found to be a dominant peak at 20 K instead of the band-to-band (B,B) peak at p> 1 x 10(19) cm(-3). The (e,A) peak was also observed at 300 K and enhanced with the increasing carrier concentration at p> 2.8 x 10(18) cm(-3). Bandgap shrinkage of these samples was qualitatively obtained. When p> 1 x 10(19) cm(-3), the impurity band merges with the valence band and the binding energy of the acceptor is equal to zero. Consequently, the bandgap can be taken as the energy between the conduction-band minimum and the top of the impurity band.