N-ZnO/p-GaN heterojunction ultraviolet (UV) photo detectors with high responsivity and fast response time grown by chemical vapor deposition technique

Abstract

High quality c-axis oriented n-type ZnO epitaxial films are grown on p-type c-GaN/sapphire templates using a chemical vapor deposition technique where metallic zinc is used as the Zn source. n-ZnO/p-GaN heterojunctions were thus formed and show rectifying behaviour with a turn-on voltage of ∼2.4 V and a very low leakage current of 1 × 10−11 A. Study of the spectral distribution of the photo response properties of these heterostructures shows a maximum at a wavelength of 366 nm with a peak responsivity of ∼0.4 mA/W at zero bias condition. The peak responsivity increases further with the applied forward bias and reaches ∼191 mA/W at 1 V. The spectral profile shows a sharp reduction in responsivity for wavelengths larger than ≈400 nm, making these devices suitable for application in solar blind UV detection. These devices are also found to show a fast response with a rise/decay time of only a few milliseconds. The study also reveals that the photo-responsivity of these devices depends crucially on the microcrystalline quality of the ZnO layers.