Indirect Energy Gap in GaSe and GaS

Abstract

Optical absorption measurements on thick monocrystalline samples of GaSel-& show that in these mixed crystals the lowest energy gap is indirect in the complete range 0 5 x 5 1. These results are contrary to earlier reports which indicate that GaSe is a direct gap semiconductor. I n the case of Gas the absorption spectra allow a tentative identification of the phonons involved in the indirect transition.Optische Absorptionsmessungen an dicken, einkristallinen Proben von GaSel -%SX zeigen, On the basis of their optical absorption the semiconducting compounds Gas and GaSe have been reported to have an indirect and a direct energy gap, respectively [I, 21. Furthermore, the work of Basov et al.[3] appears t o indicate that stimulated emission is possible from GaSe crystals under electron bombardment, and there has been speculation on the occurrence of such emission in electroluminescence [4]. Stimulated emission would of course most readily be reconciled with the presence in GaSe of a direct gap.We now present evidence that as in Gas the smallest energy gap in GaSe is indirect and lies about 53 meV below the direct gap. The earlier failure to recognize the indirect gap is due to the crystal habit of the then available transport-reacted single crystals of GaSe. With very few exceptions these crystals had the form of thin flakes (thickness to 10-1 mm) whose faces were perpendicular to the c-axis, and most experiments were carried out with light incident normal to the flake faces so that c-axis. In this geometry the indirect tran-2 sition is very weak because in the absence

Low-temperature photoluminescence study of GaS0.5Se0.5 layered crystals

“…Both peaks show varying degrees of red shift with increasing temperature. The full temperature dependence of the band gap of GaS 0.5 Se 0.5 has been reported in [1][2][3]5], and the temperature coefficient of the band gap was shown to be negative. As the peak energy due to a donor-acceptor pair transition should decrease with the band-gap energy, the observed red shift of the two bands is in agreement with the hypothesis of a recombination over donor-acceptor pairs.…”

“…The exact nature of the crystalline structure present in a semiconductor may be important in determining the electrical and optical properties of the crystal. It has already been established that different crystal modifications in GaSe lead to slightly different band gaps [5].…”

Temperature-dependent Raman scattering spectra of ε-GaSe layered crystal

“…Crystals suitable for measurements were obtained by easy cleavage perpendicular to optical c-axis. As grown GaSe is an p-type semiconductor having an indirect band gap with energies of 2.065 and 2.075 eV at 77 and 4.2 K, respectively [17].…”

Synthesis and Characterization of Pb@GaS Core–Shell Fullerene-Like Nanoparticles and Nanotubes

“…The GaS crystalline structure consists of double layers of gallium and sulfur with strong intralayer metal-metal bonds (S-Ga-Ga-S sheets) that are stacked along the c-axis via weak van der Waals forces. This combination gives rise to strongly anisotropic optical, electrical and mechanical properties, and makes GaS -which is a wide-bandgap semiconductor 6 -a promising candidate for assorted optoelectronic devices and sensors, e.g., nearblue light-emitting diodes 7 and¯eld-emission-based devices. 8,9 In addition, nanomaterials from layered metal sul¯des in general, and GaS in particular, can intercalate foreign atoms, yielding electrochemical properties that render them suitable for rechargeable secondary batteries.…”