Study of generation-recombination processes of non- equilibrium charge carriers in single crystalline thin GaSe(Cu) films

The generation-recombination processes of non-equilibrium charge carriers in undoped and Cu-doped (in the range 0.1-0.5 at.%.) single crystalline GaSe films with thickness d in the range 1.5-225 pm are investigated. Cu doping of GaSe crystals up to 0.5 at.% leads to an increase of electrical conductivity by over 4 orders of magnitude, as well to enhancement of impurity luminescence band (PL) and extension of photoconductivity spectral range. By studying PL and photonductivity spectra, for different excitation (photon) energies in temperature range (78-420) K, energies of localized states due to both Cu and accidental impurities are determined. By analysing temperature dependence of electrical conductivity and photoconductivity for undoped and Cu-doped films, the activation energy of acceptor levels in doped films was determined as 0.058 and 0.025 eV. Increasing Cu doping from 0.1 to 0.5 at.%. results in decreasing energy of acceptor levels up to -0.02 eV. By analysing the impurity absorption and photoconduction at 78 K the energy of acceptor levels was determined as 12-15 meV greater than previously evaluated, depending on Cu concentration. For films with d<5 μm, the surface states concentration increased for Cu doping over 0.3 at.%.