Carrier dynamics in highly excited TlInS2: evidence of 2D electron–hole charge separation at parallel layers

Abstract

We report a comprehensive study of the time-resolved photoluminescence (PL), carrier recombination, and carrier diffusion under diverse laser pulse excitation in TlInS₂. The 2D-layered crystals were grown by the Bridgman method without or with the presence of a small amount of erbium in the melt. The investigation exposes large differences in two crystal types, although, a linear nonradiative lifetime and carrier diffusivity attain close values under high excitation with no contribution of the Auger recombination and the absence of the band gap narrowing effect. Moreover, at high pulse power, we detect imprinted transient grating fringes which are attributed to a new crystal phase formed by 2D electron–hole charge separation on local layers. The versatile model of the spontaneously polarized 2D-crystal has been developed to explain the observed features and ergodicity of charge dynamic processes. The model embraces the planar stacking fault (PSF) which edge provides a distortion and act as sink of strong recombination. The reduced occurrence of the PSFs in the erbium doped TlInS₂ is the main attribute which determines the enhancement of PL by a factor of 50 and improves carrier diffusion along 2D-layers. The simulation permits evaluation of the PSF sizes of about 0.7 μm. The presented results allow improving 2D-crystal growth technology for novel sensor devices with separated excess charges.