Low-dark-current metal-semiconductor-metal ultraviolet photodetector fabricated on homoepitaxial GaN

A low-dark-current (~5~pA at 20~V bias) metal-semiconductor-metal ultraviolet photodetector fabricated on a GaN homoepitaxial layer grown by metal organic chemical vapour deposition is reported. The dislocation density of the homoepitaxial layer characterised by the cathodoluminescence mapping technique is of the order of mid-10⁶ cm^-2. The photodetector exhibits a sharp band-edge cutoff with a peak responsivity of 0.27 A/W at 362 nm under 5 V bias, corresponding to a quantum efficiency of 92.4 . Overall photo-responsivity increases as a function of applied bias, indicating that an internal gain mechanism still exists.