Performance enhancement of a hydrothermally grown ZnO-based ultraviolet photodetector using substrate transfer and pyramid-like surface texture

A comparative study of the performance of lateral- and vertical-structured UV photodetectors (PDs) based on a hydrothermally grown (HTG) n-ZnO/sputtered p-CuO heterojunction (HJ) is presented. After substrate transfer (ST) conducted using a sonicating bath process, the vertical-structured UV PD showed a fast response and a 310-fold improvement in light responsivity compared with that of the lateral-structured UV PD under UV illumination (365 nm at 3 mW cm^-2) at a reverse bias of -1 V. This improvement is attributed to the much shorter conduction path and lake of a seed layer for the vertical structure. With further surface chemical etching of the HTG n-ZnO layer after ST, a pyramid-like surface texture formed and a significantly enhanced UV light response (as high as 943-fold higher) was obtained. The increase in photo-responsivity is due to the removal of the high defect density initial ZnO growth layer and reduced light reflection.