The nature of energy bands of AIIIBVI layered crystals near the absorption edge

Abstract

Transmission and photoluminescence spectra are investigated of GaSe1−xTex and Ga1−xInxSe crystals in the temperature range 4.2 to 100 K. It is shown that low temperature radiative recombination in these crystal is mainly due to direct bound exciton decay. In the temperature range 10 K < T < 77 K radiative recombination has an impurity character, and at T = 77 K direct free exciton radiative recombination takes place. The examination of direct exciton zone behaviour when substituting the anions Te, S for Se in GaSe (Se → Te, S) and cations (Ga → In) allows to conclude, that the anions make the major contribution to the formation of electronic states at the direct absorption edge of GaSe and its analogs. It is shown that the bottom of the conduction band at the edge of Brillouin zone of the investigated crystals is formed with considerable participation of cations.

Excitons in gallium sulphide

“…5). Absorption and luminescence spectra of Gas are mainly polarized with E 11 C , however, the polarization degree for Gas is weaker than that for GaSe [7,8]. The latter circumstance may mean that the distance between mixed levels in the Gas valence band is smaller than that in GaSe.…”

Photoluminescence spectra of nitrogen implanted GaSe crystals

“…In undoped and Ge doped GaSe crystals, the direct free excitons (n=1) were shown to be dominant in the photoconductivity spectra [12,13]. Analysis of the temperature dependences of the peak intensity, energy position and FWHM of the A band observed in the PL spectra of undoped and N-implanted crystals, and consideration of the band structure of GaSe show that this band is related to the direct free excitons (DFE) [14][15][16][17][18]. Similar behavior of DFE peak intensity in the PL spectrum was also observed in phosphorous doped GaSe and in annealed GaSe crystals [10,11].…”

“…4. The activation energies of the B band are calculated as [10,11,[14][15][16][17]. The activation energy for 10 14 ions/cm 2 N-implanted GaSe crystal is very close to the energy difference between the A and B bands (hu A -hu B E27 meV, Fig.…”

“…The activation energy DE is related to the binding energy as DhuEE A -E B ¼ E b . The ionization energy of the centers to whom excitons are bound can be calculated from E i ¼ DE/0.115 eV [14][15][16][17]. Hence, the ionization energies of these centers are calculated to be E i =234 and 52 meV for the 10 14 ions/ cm 2 N-implanted and 10 16 ions/cm 2 N-implanted GaSe crystals, respectively.…”

“…2. As seen, the PL spectra of undoped and N-implanted GaSe crystals consist of characteristic intrinsic and extrinsic regions [10,11,[14][15][16][17]. The intrinsic region of the PL spectra contain a main peak denoted as A, and two peaks at low temperatures denoted as B and B 1 while the extrinsic region contain a broad band labeled as C, which is also observed at low temperatures.…”