High-Performance Solar-Blind p-NiO/n-ZnO/p-Si Ultraviolet Heterojunction Bipolar Phototransistors With High Optical Gain

Ultraviolet (UV) photodetectors (PDs) have attracted significant attention for civil and military applications. Zinc oxide (ZnO) and nickel oxide (NiO) have been widely applied in UV-PDs due to their wide bandgap (3.2–3.8 eV), transparency, excellent optical and electrical properties, and good chemical stability. However, UV signals are generally weak; hence, UV-PDs with high optical gain are essential. In this work, high-performance solar-blind p-NiO/n-ZnO/p-Si heterojunction bipolar phototransistors (HBPTs) were fabricated. The fabricated HBPTs exhibited a high responsivity of $9.4\times 10^{{3}}$ A/W at a wavelength of 280 nm with ${V}_{\text {CE}}$ = −7 V, a high optical gain of $3.96\times 10^{{4}}$ , and a large detectivity of $3\times 10^{{13}}$ Jones. In addition, the UV/visible rejection ratio was as high as 880. These behaviors indicate that the prepared HBPTs are good solar-blind PDs and suitable for the detection of weak UV signals. However, for ${V}_{\text {CE}}$ value below −7 V, ( $\vert {V}_{\text {CE}}\vert >$ 7 V), the optical gain decreased due to the punchthrough effect. Furthermore, band diagrams showed that the photogenerated electrons were blocked by the potential barrier at the NiO/ZnO interface (base–emitter junction) due to a large conduction-band discontinuity ( $\Delta {E}_{C}{)}$ of 2.7 eV, which resulted in a large optical gain in the prepared HBPTs.