Role of the Metal–Semiconductor Interface in Halide Perovskite Devices for Radiation Photon Counting
2020
Shrestha, Shreetu | Tsai, Hsinhan | Yoho, Michael | Ghosh, Dibyajyoti | Liu, Fangze | Lei, Yusheng | Tisdale, Jeremy | Baldwin, Jon | Xu, Sheng | Neukirch, Amanda J. | Tretiak, Sergei | Vo, Duc | Nie, Wanyi
Halide perovskites are promising optoelectronic semiconductors. For applications in solid-state detectors that operate in low photon flux counting mode, blocking interfaces are essential to minimize the dark current noise. Here, we investigate the interface between methylammonium lead tri-iodide (MAPbI₃) single crystals and commonly used high and low work function metals to achieve photon counting capabilities in a solid-state detector. Using scanning photocurrent microscopy, we observe a large Schottky barrier at the MAPbI₃/Pb interface, which efficiently blocks dark current. Moreover, the shape of the photocurrent profile indicates that the MAPbI₃ single-crystal surface has a deep fermi level close to that of Au. Rationalized by first-principle calculations, we attribute this observation to the defects due to excess iodine on the surface underpinning emergence of deep band-edge states. The photocurrent decay profile yields a charge carrier diffusion length of 10–25 μm. Using this knowledge, we demonstrate a single-crystal MAPbI₃ detector that can count single γ-ray photons by producing sharp electrical pulses with a fast rise time of <2 μs. Our study indicates that the interface plays a crucial role in solid-state detectors operating in photon counting mode.
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