Abstract

The conduction band of the layer semiconductor Gallium Selenide has an indirect minimum at the M point of the Brillouin zone which is very closed (25 meV) to the higher direct conduction edge. The coexistance of these two minima largely influences the features of the photoluminescence spectra in the range from 580 to 800 nm. At low temperatures the emission spectra show intrinsic lines due to free -as well bound- direct and indirect excitonic recombinations and extrinsic bands at lower energy /1/. We measured spontaneous luminescence of GaSe Bridgmann grown crystls at He and N₂ temperatures, exiting selectively (with a dye laser) a wide region of wavelengths on the excitonic absorption structures. In the same energy range we also recorded the excitation spectra of the prominent features appearing in the luminescence spectrum. Flourescence line narrowing effect on the direct free excitonic emission is observed even up to 80 K where localization of excitons, due to random microscopic lattice disorder, is not espected to occur /2/. This anomalous behaviour is interpreted in terms of macroscopic strains in our crystals, probably due to stacking faults which easily form in growing semiconductor layered compound.

© 1984 Optical Society of America