First-principles analysis of the photocurrent in a monolayer α-selenium p–n junction optoelectronic device

Two-dimensional monoelemental materials have emerged as promising candidates for use in the development of next-generation optoelectronic devices. In this work, we investigate the photovoltaic effect of monolayer (ML) α-selenium p-n junctions by using <i>ab initio</i> quantum transport simulations. Our research results indicate that the photocurrent of the ML α-selenium p-n junction optoelectronic device exhibits anisotropy. The maximum photoresponsivity (178.49 <i>a</i>₀² per photon) in the armchair (ARM) direction is one-half that (341.72 <i>a</i>₀² per photon) in the zigzag (ZZ) direction. When stress is applied, the most significant modulation of photoresponsivity occurs in the ZZ direction, reaching a value of 613.21 <i>a</i>₀² per photon. When a gate voltage is applied, the most significant modulation of photoresponsivity occurs in the ARM direction, reaching a value of -684.88 <i>a</i>₀² per photon. When a thermal difference is applied, the most significant modulation of photoresponsivity occurs in the ARM direction, reaching a value of 412.14 <i>a</i>₀² per photon. Thus, ML α-selenium in the ZZ direction can be used for photodetection and photosensing, while ML α-selenium in the ARM direction can be used for photosensing. Both strain engineering and temperature differences cause a blueshift in the photocurrent as a function of energy. Our work paves the way for research into low-dimensional monoelemental-material optoelectronic devices.