Recombination dynamics for photogenerated carriers in germanium-doped ZnSe epilayers grown by molecular beam epitaxy

Abstract

Germanium-doped ZnSe epilayers have been grown on (001)-oriented semi-insulating GaAs substrates by molecular beam epitaxy. The photoluminescence (PL) spectra exhibit strong near-band edge emission similar to those from undoped, chlorine-doped and gallium-doped samples, though some differences exist. The prominent PL peak at 2.795 eV (10 K) is attributed to the germanium-bound exciton recombination and is accompanied by free exciton (2.802 eV), Ia-type exciton (2.785 eV) and Iv-type exciton (2.775 eV) emission peaks. Following an increase in temperature, the intensity of all the IGe, Ia, and Iv emission peaks decreases gradually, indicating the presence of nonradiative recombination mechanisms with thermal activation energies of 40, 70, and 50 meV respectively. However, for the Iv peak, there is one additional nonradiative recombination mechanism in accordance with the thermally activated transfer of excitons from the Iv-type centers to Ia-type centers. This nonradiative recombination mechanism with activation energy of 9 meV is responsible for the decrease of the Iv peak intensity when the sample temperature is changed from 15 to 100 K. Following an increase in temperature, the Iv peak, Ia peak, and germanium-related peak disappear gradually and successively. Finally, the PL spectrum is dominated by free exciton emission at temperatures exceeding 210 K.