Effect of pressure on the structural properties and electronic band structure of GaSe

Abstract

The structural properties of GaSe have been investigated up to 38 GPa by monochromatic X-ray diffraction. The onset of the phase transition from the ε -GaSe to a disordered NaCl-type structural motif is observed near 21 GPa. Using the experimentally determined lattice parameters of the layered ε -phase as input, constrained ab-initio total energy calculations were performed in order to optimize the internal structural parameters at different pressures. The results obtained for the nearest-neighbor Ga -Se distance agree with those derived from recent EXAFS measurements. In addition, information is obtained on the changes of Ga -Ga and Se -Se bond lengths which were not accessible to a direct experimental determination yet. Based on the optimized structural parameters, we report calculations of band gap changes of ε -GaSe under pressure. The optical response and electronic band structure of the metallic high-pressure phase of GaSe are discussed briefly.

Layered Indium Selenide under High Pressure: A Review

“…The combined analysis of XRD and XAS results in DAC for other III-VI layered compounds (GaS, GaSe. GaTe) [32][33][34][35][36] showed that this behavior can result in an unexpected effect: the thickness of the layer can actually increase under pressure, as shown in Figure 3b [37]. This behavior is very relevant to the discussion of the reliability of deformation potential models that were proposed to give quantitative account of the extremely non-linear pressure dependence of the bandgap in III-VI semiconductors, as we will discuss in Section 3.…”

“…These authors reported complex behavior including (i) a nonlinear pressure dependence of the direct bangap, exhibiting a low-pressure interval with negative pressure coefficient and then increasing with pressure after a minimum, as shown in Figure 5b; (ii) a large negative pressure coefficient for the indirect gap of GaS; and (iii) a progressive widening and disappearing of the exciton peak, as shown in Figure 5a. Concerning ε-GaSe, Panfilov et al [50] suggested that nonlinear behavior was the result of a phase transition to a different polytype occurring at 0.6 GPa, a hypothesis that was not supported by later XRD experiments [32,34]. badgap of 2 eV at RT [46].…”

“…In contrast, both the hole concentration and mobility increase monotonously under pressure in p-type ε-GaSe and do not exhibit any dramatic changes (Figure 21). Ab-initio band structure calculations [32,94] do not show any trace of a toroidal maximum or any other dramatic modification of the VBM (occurring at the Γ point) in ε-GaSe, at 7 GPa [94], or at 16 GPa [32]. The different pressure behavior of the VBM in ε-GaSe with respect to γ-InSe has been attributed to differences in the band mixing and dipole matrix elements between the highest energy valence bands imposed by symmetry elements of the P6m2 group (to which ε-GaSe belongs) [94].…”

Nanoindentation of GaSe thin films

“…While unloading, pressure release will lead to further transformation into amorphous Si or a mixture of bcc Si and rhombohedral Si phases depending on the unloading rate [ 19 , 24 ]. On the other hand, the pressure-induced structural phase transition in GaSe has been investigated by diamond anvil cell experiments previously [ 25 ]. The magnitude of pressure required to induce phase transitions is significantly higher than the apparent room-temperature hardness of the GaSe thin film measured in this study.…”

Theoretical studies of defect states in GaSe and GaTe

“…[45][46][47][48] However, band structures of -and -GaSe are almost identical. Here we briefly review some of the general features of the band structure obtained with the full potential method (Fig.…”