SnO2-NiO heterojunction based self-powered UV photodetectors

Thin film p-n heterojunction diodes using NiO and SnO2 are fabricated, and the performances are studied. NiO was deposited using rf magnetron sputtering and SnO2 using the electron beam evaporation technique. The diodes are fabricated in the configuration, FTO/SnO2/NiO/Au, with two different device areas; smaller with 0.35 mm circular diameter and larger with 2 x 2 mm square. The smaller device has a reverse leakage current of 20 mu A at - 2 V, turn-on voltage of 1.2 V, and diode rectification ratio of 160, which are much higher than the reported SnO2/NiObased diodes. On the other hand, the larger area device exhibits a smaller rectification ratio of 4. UV photoelectron spectroscopy (UPS) analysis was carried out, and the work function of NiO was calculated as 5.31 eV. The deduced staggered band alignment of SnO2/NiO favors the effective separation of photogenerated charge carriers when illuminated with UV light. Subsequently, the diodes were tested for UV photodetection. Remarkably, the FTO/SnO2/NiO/Au diodes display self-powered UV photodiode characteristics using 365 nm light. Photoresponsivity of 3.3 mA/W, ON/OFF ratio of 4.16 x 104, and detectivity of 7.4 x 1010 Jones are obtained for the larger area device. At low incident light intensity, the larger area device exhibited a response time of 89 ms.