Bandgap Fluctuations, Hot Carriers, and Band-to-Acceptor Recombination in Cu2ZnSn(S,Se)(4) Microcrystals

Temperature and laser power dependencies of the band-to-acceptor recombination in Cu2ZnSn(SxSe1-x)(4) (x = 0.7) microcrystals, which exhibit large bandgap energy fluctuations, are studied. The average depth of these fluctuations is approximately 79 meV. The shape of the corresponding wide photoluminescence (PL) band is analyzed using a modified localized-state ensemble model. The temperature dependence of this PL band is demonstrated to be influenced by the redistribution of holes between potential wells in the valence band with varying depths. The shape of this band at different temperatures is well fitted when an effective carrier temperature is introduced. This temperature is found to be approximately 300 K higher than the lattice temperature in the samples, and it is mainly caused by the very short minority carrier lifetime. According to the laser power-dependent PL studies, there is a consistent reduction in the effective carrier temperature as the laser power increases. This phenomenon is explained by the dominance of nonradiative Shockley-Read-Hall recombination at lower temperatures.