Low-Dark-Current Photodiodes Comprising Highly (100)-Oriented Hexagonal Selenium With Crystallinity-Enhanced Tellurium Nucleation Layers

The fabrication of low-dark-current heterojunction photodiodes based on p-type highly (100)-oriented crystalline selenium (c-Se)/n-type gallium oxide (Ga
₂
O
₃
) was demonstrated by enhancing the crystallinity of the tellurium (T
_e
) nucleation layer. The preferential (100) crystal orientation of c-Se is significantly improved by using high-quality T
_e
nucleation layers that are thermally evaporated at a relatively high Te-source temperature (T
_Te
) without substrate heating. The fabricated device exhibits an extremely low-dark current under 100 pA/cm
²
(at room temperature) and a high external quantum efficiency of over 85% at a wavelength of 550 nm at a reverse bias of 15 V. These results demonstrate the potential of c-Se-based photodiodes to provide highly sensitive imaging devices.