Resolving the trap levels of Se and Se1−xTex via deep-level transient spectroscopy

Benefiting from the facile fabrication and tunable optoelectronic properties, Se and ${\mathrm{Se}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ are promising candidates for optoelectronic applications, e.g., thin film solar cells and short-wavelength infrared detectors. However, the trap features of selenium based semiconductors are complicated mainly due to the low crystallinity induced dispersive nature. In particular, the underlying charge transport properties of ${\mathrm{Se}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ have not been systematically investigated, which is crucial for device optimization in real applications. In this work, we first introduce deep-level transient spectroscopy to characterize Se and Se-based semiconductors, and we also compare it with reverse-bias deep-level transient spectroscopy. It was found that the latter technique can result in much higher transient capacitance signal and better energy resolution. Based on the full analysis of the transient capacitance, we found the introduction of Te into Se can easily form two additional deep trap states around 0.55 eV and 0.75 eV, respectively, and it also explains why the device performance of ${\mathrm{Se}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ are still suffering from the large dark current and recombination losses.