Spectroscopic Study of Ga-Doped Ge under Uniaxial Pressure

Abstract

To identify the optical transitions responsible for the excitation of long-wavelength stimulated emission in uniaxially compressed Ga-doped Ge, the optical absorption and photoconductivity spectra of the material were investigated at a wide range of pressures in directions [111] and [001]. The dependence of the valence band splitting between the light-and heavy-hole subbands in Ge as a function of the applied pressure was found. As determined from this dependence, the deformation potential constants for the valence band appeared to be less than the presently accepted values. It is shown that, as pressure increases, some of the excited states of the Ga impurity levels reach the light-hole band, enter it, and remain close to its edge (the resonant states). It is possible that a population inversion of these resonant states gives rise to the excitation of stimulated emission at a photon energy of about 10 meV. No specific features confirming the existence of resonant impurity states near the edge of the heavy-hole band were found in the spectra.