Deep Level and Near-Band-Edge Recombination in Semiconducting Antiperovskite Hg₃Se₂I₂ Single Crystals

The wide-bandgap, semiconducting ternary compound Hg₃Se₂I₂ has shown promise as room-temperature hard-radiation detector. Since this compound was first reported, there has been significant improvement in crystal growth using a chemical vapor transport method with a polyethylene growth agent. To study the effects of this additional precursor on crystal quality, the nature of radiative and nonradiative defects using photoluminescence (PL) and photocurrent (PC) studies of Hg₃Se₂I₂ single crystals are investigated. In contrast to earlier studies, excitation intensity-dependence of PL emission shows that the near-band-edge (NBE) emission bands are all excitonic in nature. The PL intensity decreases with increasing temperature, with the higher energy peaks quenching by 40 K and the deeper levels quenched after 110 K. The PC spectra show a complex structure at room temperature related to NBE transitions in the band structure, while at low temperature only the direct gap transition is observed due to phonons freezing out. The PC spectra at low temperature also indicate several midgap levels that are attributed to native defects within the bulk crystal. These results indicate that the high quality of Hg₃Se₂I₂ single crystals is maintained when the transport agent is used during growth, although there are still a variety of defects present.