Luminescence from a multicomponent electron-hole plasma in Ga(As,P)

The luminescence of high-purity direct-gap GaAs 0.55 P 0.45 islands-their composition is close to that at the Gamma -X crossover-has been investigated under intense band-edge resonant dye laser excitation at T=2 K. At this mole fraction the difference between the direct (E g Gamma ) and the indirect energy band gap (E g x ) amounts to only about 15 meV. This material peculiarity opens the possibility to examine the properties of a multicomponent electron-hole plasma (EHP) consisting of photoexcited holes, Gamma electrons and X electrons. For plasma densities n e.h ranging between 5*10 16 and 6*10 17 cm -3 the EHP contains only holes and Gamma electrons, and the observed lowering of the fundamental band gap agrees well with the universal scaling rule, as known for a neutral two-component electron-hole plasma. At higher densities, where the chemical potential of the Gamma electrons becomes higher than the conduction band X minimum, the EHP spectral analysis indicates occupation of the X valleys. The authors discuss how the population of these valleys influences the direct-gap luminescence. The experimental EHP spectra are compared with line-shape calculations in the random phase approximation (RPA).