Defects forming the optical absorption edge in TlGaSe2 layered crystal

•Optical transmittance spectra of TlGaSe2 in regime of memory effect was studied.•Modification of the Urbach's tail of TlGaSe2 was found.•Native defects forming the band edge of TlGaSe2 were identified.

In this work, we present the results of optical experiments designed to investigate the changes in optical absorption spectra of TlGaSe2 ferroelectric-semiconductor with incommensurate (INC) phase in experimental conditions where crystal is kept several hours within the INC-phase (the regime of so called “memory” effect). The fundamental absorption of TlGaSe2, experimentally investigated by optical transmission measurements performed in the temperature range 15–300 K. An extraordinary modification of the optical absorption edge in the range of Urbach's tail is discovered as a result of the annealing within the INC-phase. The role of native defects forming the band edge in the observed phenomena in TlGaSe2 is discussed.