Enhancing ultraviolet-to-visible rejection ratio by inserting an intrinsic NiO layer in p-NiO/n-Si heterojunction photodiodes

Abstract

Conventionally, p-NiO/n-Si (p-n) heterojunction photodiodes (HPDs) exhibit a larger visible response than the ultraviolet response due to the thick Si substrate; hence, it is used as a broadband photodetector with a poor ultraviolet (UV)-to-visible rejection ratio. Herein, an intrinsic NiO (i-NiO) layer is inserted between the p-NiO and the n-Si substrate to fabricate p-NiO/i-NiO/n-Si (p-i-n) HPDs, significantly suppressing leakage current and visible response. Compared with the conventional p-n HPDs, the insertion of the i-NiO layer significantly reduces leakage current by approximately 241 times and enhances the rectification ratio from 13.8 to 3228 for the p-n and p-i-n HPDs. The insertion of an i-NiO layer not only increases the UV-response but also suppresses the visible response. These issues enhance the UV-to-visible rejection ratio from 72.2 in p-n HPDs to 915.3 in p-i-n HPDs. The p-NiO reveals a poorer crystalline structure than the i-NiO film because the Ag dopants accumulate at the grain boundary and inhibit crystalline growth. The Ag diffusion in the Si substrate causes defect states within the Si bandgap, whereas it is retarded by the i-NiO layer in the p-i-n HPDs. The poor crystallinity in the p-NiO and defect states within the Si bandgap contributes to a high leakage current and visible response in p-n HPDs. The p-i-n HPDs demonstrate a higher UV-response due to absorption by the i-NiO layer. Because visible light cannot be absorbed by the i-NiO layer, visible response is suppressed in p-i-n HPDs.

A novel NiO-based p-i-n ultraviolet photodiode

“…Although there are several NiO-based p-n and p-i-n junctions photodetector studies in the literature, these are not in homojunction structure due to the challenge of making n-type doped NiO. Studies in the literature have been mainly focused on the heterostructures that comprised of a p-type NiO and n-type of other semiconductors such as ZnO [16][17][18][19][20] TiO2 [21,22] and Ga2O3 [23,24] for UV applications, and n-type Si [25,26] for UV-visible applications. While these kinds of NiO-based, highly sensitive, heterojunctions are utilized as a photodetector, to create NiO-based emitters the fabrication of homojunction p-n and p-i-n diodes are critical.…”

Solution-Processed NiO/Si Heterojunctions for Efficient Self-Powered UV–Vis-NIR Broadband Photodetection

“…In recent years, Si-based heterojunction PDs combining with various wide bandgap semiconductors such as ZnO, 13,14 SnO 2 , 15,16 and NiO 17,18 involving careful design of device structures and interfacial engineering have been explored to realize efficient and broadband photodetection. Notably, the rapid progress of power conversion efficiency of lead halide perovskite solar cells recently has witnessed that efforts have been devoted to the scalable and controlled synthesis of the above-mentioned wide bandgap oxides.…”

“…In typical Si homo p-n/p-i-n structured devices, however, the carriers generated in the neutral region exhibit no response owing to recombination, which simultaneously lowers the overall performance and narrows the spectral range of photodetection due to the self-filtering effects. , Notably, such limitations may be avoided in Si-based heterojunction PDs consisting of the Si and a wide bandgap semiconductor, where the latter one induces a built-in electric field at the heterojunction interface without absorbing the incident light. In recent years, Si-based heterojunction PDs combining with various wide bandgap semiconductors such as ZnO, , SnO 2 , , and NiO , involving careful design of device structures and interfacial engineering have been explored to realize efficient and broadband photodetection. Notably, the rapid progress of power conversion efficiency of lead halide perovskite solar cells recently has witnessed that efforts have been devoted to the scalable and controlled synthesis of the above-mentioned wide bandgap oxides. , Typically, the controlled growth of uniform and large-area NiO nanocrystal thin films with a thickness as small as sub-100 nm by a simple low-temperature solution growth method has been reported. − Meanwhile, the as-prepared NiO nanocrystal thin films have further been shown to be highly transparent over the UV–vis-NIR spectral range , and intrinsic p-type conductivity because of the facile formation of native Ni vacancies (V Ni ). , Theoretically, the PDs have working principles similar to those of the solar cells, where the efficient generation and extraction of photoexcited carriers within the active layer are mainly concerned.…”