Radiative Decay from Free and Bound Excitons in GaSe

Abstract

Spontaneous excitonic luminescence in GaSe is investigated from 80 to 300 K and a t weak laser excitation intensity. Radiative recombinations of direct and indirect free excitons are clearly observed. The analysis of the emission lines as a function of the temperature, of the excitation intensity, and of laser energy permits to attribute two lines of the intrinsic luminecsence to the recombination of direct and indirect excitons bound to defect centres localized in the energy gap. On the basis of recent theories on exciton-impurity complexes, it is found that in the crystals the excitonic binding centres are deep neutral acceptors. From the dissociation energy of the bound excitons the ionization energy of the acceptor levels is estimated. Moreover, the measurements seem to indicate that thermal equilibrium between direct and indirect excitonic states is lacking below about 100 K.Die Spontane Exzitonenlumineszenz in GaSe wird zwischen 80 und 300 K und mit schwacher Laseranregungsintensitat untersucht. Strahlende Rekombination von direkten und indirekten freien Exzitonen wird deutlich beobachtet. Die Analyse der Emissionslinien in AbhLngigkeit von der Temperatur, der Anregungsintensitat und der Laserenergie erlaubt, zwei Linien der intrinsischen Lumineszenz der Rekombination von direkten und indirekten Exzitonen zuzuordnen, die an in der Energielucke lokalisierten Defektzentren gebunden sind. Auf der Grundlage neuerer Theorien zu Exziton-Storstellenkomplexen wird gefunden, dal3 in den untersuchten Kristallen die Exzitonenbindungszentren tiefe neutrale Akzeptoren sind. Aus der Dissoziationsenergie gebundener Exzitonen l&Bt sich die Ionisierungsenergie der Akzeptorniveaus berechnen. Dariiberhinaus scheinen die MeBergebnisse zu zeigen, dal3 unterhalb etwa 100 K kein thermisches Gleichgewicht mehr besteht zwischen direkten und indirekten Exzitonenzustiinden.

Optical Properties of GaSe Crystals Containing Mn Impurity Atoms. I. Exciton‐Phonon Interaction

“…When the temperature is high enough for the electrons in ICB to acquire the energy E , =: E,, -EICB, then the scattering couples the states k = ki and k = 0 and electrons from IC'B populate the FE state. Recent studies of photoluminescence spectra of GaSe crystals [24] confirm the model [23] and it was shown that energy redistribution between emission from direct and indirect bands with increasing temperature 2 80 K was observed.…”

Investigation of the Light Absorption Mechanisms near Exciton Resonance in Layered Crystals

“…From eqs (15). and(16) it is seen that inequality (14) contains the half-width G,4bam HH2 $ f exc aG 2 X 17…”

Deterministic Localization of Strain-Induced Single-Photon Emitters in Multilayer GaSe

“…The ratio of the strain localized GaSe PL to the band edge emission X E g is significantly enhanced by two orders of magnitude on the pillars. At a much lower laser power density of 44 nW/μm 2 , PL spectra measured at T = 3.5 K on the pillars exhibited a few strong and well-separated features without the broad background or additional defect-related bands that are often observed in WSe 2 and hBN. , For example, in Figure c, the PL spectrum collected from GaSe on a pillar shows a single peak X S at ∼1.90 eV (∼652 nm), about ∼0.15 eV below the well-studied GaSe band edge emission X E g at 2.05 eV. − Note that the emission energies of GaSe SPEs measured here are consistent with previous study on GaSe SPEs associated with strain developed on GaSe film on randomly distributed selenium clusters …”