The electric‐field effect on the exciton photoconductivity and Urbach tail in GaSe crystals

Abstract

The direct free exciton (n = 1) photoconductivity in GaSe crystals has been investigated as a function of applied electric field. The changes observed in the exciton photoconductivity have been analyzed using the Franz–Keldysh, exciton electroabsorption, and Frenkel thermoelectric‐field effects. The intensity of exciton photoconductivity peak was found to increase exponentially with the applied field. The exciton peaks broaden as the magnitude of applied field is increased and shift to lower energies with the square root of applied field. The Urbach energy determined from the long‐wavelength part of the exciton photoconductivity in GaSe crystals varies with the applied electric field. The Frenkel thermoelectric‐field effect has been found to be dominant for the changes observed in the exciton photoconductivity as a result of the applied field. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pool–Frenkel thermoelectric modulation of exciton photoluminescence in GaSe crystals

“…As seen from the analyses, these peaks shift to longer wavelengths with the square root of applied field consistent with the Pool-Frenkel thermoelectric field effect. In a previous study, we have shown that the exciton photoconductivity varied with applied field according to the Pool-Frenkel thermoelectric field effect [13]. In that study, the contribution of excitons to the increase in photoconductivity was explained by the thermoelectric field ionization of excitons to free charge carriers.…”

“…Excitonic effects are important in the optic absorption, electrophotoluminescence and photoconductivity of GaSe crystals, which are members of layered A III B VI crystal family, and these effects have been investigated widely [1,[13][14][15][16][17][18][19]. Unlike other crystals, exciton states continue to exist at room temperature and above in GaSe crystals [13].…”

“…Unlike other crystals, exciton states continue to exist at room temperature and above in GaSe crystals [13]. Exciton electroabsorption and exciton photoconductivity in GaSe crystals have been investigated and it has been seen that exciton states broadened and ionized to free charge carriers in the presence of external electric field [1,[13][14][15][16][17][18][19].…”