Self-powered, wide spectral UV response out-of-plane photodetector based on ZnO/porous silicon heterostructure

Abstract

Abstract The photoresponse of the ZnO/porous silicon (p-Si) heterojunction is studied in an out-of-plane contact configuration. p-Si substrate is fabricated by anodic etching followed by the electrochemical deposition of ZnO NR film, forming ZnO/p-Si heterojunction.
XRD study is done to understand the effect of the substrate on ZnO film growth in terms of strain and crystal size. UV-Vis absorbance spectrum shows a broad absorption for wavelengths from 230 to 380 nm. The PL emission shows two narrow and prominent electron transition peaks at 263 and 383 nm and a peak of ~ 550 nm corresponding to defects. The 263 nm wavelength responsivity of the photodetector from UV-Vis and PL data suggests the presence of a defective SiOx as an intermediate layer between ZnO and p-Si. 
The photodetector is measured for its spectral selectivity and responsivity for both 266 and 370 nm. Under self-powered conditions, the device shows a low dark current of a few nA and enhancement of ~100 nA and ~1.37 µA for both wavelengths. A responsivity of 527 mA/W and 14.8 mA/W and detectivity of 2.5E10 and 2.9E9 Jones at 1 V bias under 266 and 370 nm UV illumination are observed. The fast rise/decay time of 67/65 ms and 29/18 ms is observed for the self-powered condition of the device under both wavelengths respectively.
The photoresponse of the modified ZnO/SiOx/p-Si heterojunction for both wavelengths is analyzed for the electron transfer mechanism using the heterojunction band bending model. The short circuit current and open circuit voltage of the photodetector is estimated to be 293 nA, 56.33 mV, and 13.63 µA, 124.8 mV for 266 and 370 nm, respectively. It is concluded that the 266 nm responsivity comes from the defects in the SiOx intermediate layer, and the photocurrent generated in the device is due to tunneling across the junction.