Luminescence Investigation of Direct and Indirect Excitons Bound to Deep-Neutral Acceptors in e-GaSe

We report on our investigations of excitonic luminescence spectra of Bridgmann grown GaSe crystals from the liquid N2 temperature up to 300 K and at weak laser excitation intensity. We measured the spontaneous luminescence due to direct and indirect excitonic recombinations. Moreover, a detailed analysis of the intensity of the lines composing the emission spectrum versus the temperature and the excitation intensity permits to detect and assign two lines of the excitonic luminescence as due to the recombination of direct as well as indirect excitons bound to localized centres in the forbidden energy gap. On the basis of recent theories on bound exciton-impurity complexes we found that both direct and indirect excitons are bound to neutral and deep acceptor centres. From the measured dissociation energy of these bound excitons we could estimate the ionization energy of the acceptor levels, which were already identified independently in GaSe by electrical transport measurements.