Direct and indirect electron-hole plasmas in gallium selenide

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Abstract
A detailed study of the electron-hole plasma in the indirect semiconductor GaSe is presented. The simultaneous presence of direct and indirect e-h plasmas in highly excited GaSe is expected as a consequence of the almost degenerate direct and indirect gaps. Simultaneous plasmas have been clearly observed in spontaneous emission measurements. Only the amplification channel associated with the indirect e-h plasma is observed in the stimulated emission and optical gain spectra at low temperature. Both e-h plasmas give rise to light amplification above 70 K with different optical gain coefficients. The mechanisms involved in the competition between the two amplification channels and their dependences on sample temperature and pumping intensity are discussed. An experimental determination of the photogenerated e-h pairs densities, obtained by using a particular calibration technique of the experimental setup, allowed us to carry out the theoretical line-shape analysis of emission and gain bands, without uncertainties of the values of the physical parameters involved in the calculations.