N-ZnO/p-Si heterojunction nanodiodes based sensor for monitoring UV radiation

Abstract

ZnO nanowire array on p-type Si (100) substrate based PN-heterojunction photodiode type UV radiation detector was fabricated using rf-magnetron sputtering. The detector exhibited visible blindness below the band gap of the material (3.2 eV) and ultra-fast response for ultraviolet radiation with a peak responsivity at around 380 nm. The temporal photocurrent response of the detector was measured to be 0.1 s which is much better than a commercially available UV-detector. The design, construction and working of the detector are discussed here in detail. The origin of selective and fast response has also been discussed with support of existing theoretical models. Accordingly, electron hole pairs created by the UV radiation at the p-type Si and n-type ZnO nanowire junctions and separated by junction barrier get immediately recombined to enhance the photoconductivity due to applied electric field. The barrier potential and the junction capacitor could be tuned and depend on the size of the nanowires and the band bending on surfaces of nanowires due to heterojunction. The steady state response of the detector studied by keeping it in a reverse biased condition and exposing to UV radiation shows very high stability of the device (around 4% decrease in the photocurrent in over five weeks for −3 V biasing and ∼50 μW/cm2 UV power). Other potential applications for this UV detector are in the field of medicine and in spectroscopy where UV sources are being used. It could also be used to take protective measures for eye damages and skin cancer by monitoring UV radiation levels.