Photoluminescence of electron-hole plasma in semi-insulating undoped GaAs

The dependence of the photoluminescence spectrum of electron-hole plasma in semi-insulating undoped GaAs on the concentration of the background carbon impurity NC(3×1015 cm−3≤NC≤4×1016 cm−3) is studied at 77 K. It is established that the density of the electron-hole plasma, which is equal to ne−h≈1.1×1016 cm−3 in crystals with the lowest impurity concentration at an excitation intensity of 6×1022 photons/(cm2 s), decreases considerably as the value of NC increases in the range mentioned above. A decrease in the density of the electron-hole plasma with increasing NC is attributed to the effect of fluctuations in the carbon concentration NC, which give rise to a nonuniform distribution of interacting charge carriers and to localization of holes in the tails of the density of states of the valence band.