On exciton absorption, band structure, and phase transformation of GaSe under pressure

Abstract

The spectra of the absorption coefficient (a) of GaSe a t the photon energy range 1.94 t o 2.64 eV and a t pressures between 1 bar and 12 kbar are investigated a t 295 O K . Data a t 1 t o 4360 bar confirm that the edge exciton of GaSe is the direct allowed one. The pressure coefficient of the band gap (dE,/dP = -6.2 x eV bar-I), one of the Rydberg exciton constant (dR/dP = -0.6 x eV bar-*), and one of the exciton effective massIt is supposed that two interband exciton transitions a t 2.001 and 3.25 eV give the contribution into the a spectrum above 2.1 eV. The assignment of these transitions is discussed in connection with the band structure calculation of Schluter. At 5280 bar a discontinuous jump of the absorption edge shape is observed for GaSe, with a change of t h e sign and a value for dE,/dP of +2.0 x 10-6 eV bar-' within the range of 5280 t o 11780 bar. This effect is interpreted as the transformation of one GaSe polytype into another, i.e. as a possible phase transformation close to t h a t of second kind. B HHTepBane 3~e p r~f i @oToHa OT i,94 no 2,64 eV y1 DaBneHHR OT 1 6ap no 12 kbar npH 295 O K accnenoBaHx cnempbI K O~@ @~U M~H T~ n o r n o q e~n~~ a ceneHana r a n n m GaSe. JJaHHbIe B ~n a n a a o~e OT 1 AO 4360 bar nonTsepmaamT, TO ~K C H T O H Ha KpaIo IIOrJIOIIJeHHFI GaSe RBJIReTCR IIpFIMbIM pa3peUIeHHbIM 3IECHTOHOM. npH6JIPiweHHO OIrpe~eneHbI K03@@Pi4HeHTbI HaBneHHR IUllpllHbI a a n p e q e~~o a 30HbI (dEg/dP = ---6,2 x eV -bar-I), ~C

Infrared and UV-visible spectra of layer semiconductors Gas, GaSe and GaTe

“…-As is well known, gallium sulphide, selenide and telluride are semiconducting layer structure compounds built up from weakly interacting two-dimensional layers. A lot of theoretical and experimental information [1][2][3][4][5][6][7][8][9][10][11][12][13] is available on these III-VI semiconductors. Recent thermoreflectance [14,15], electroreflectance [16][17][18] and wavelength modulation [19] together with normal reflectivity [20] and absorption [21] measurements have been carried Qut, making an interpretation of the main optical behaviour of these compounds possible.…”

Layered Indium Selenide under High Pressure: A Review

“…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].…”