GaN-Based Ultraviolet Phototransistor With Two Parallel Polarization-Doped Junctions and an Al_0.20Ga_0.80N Insertion Layer to Achieve Low Dark Current and High Detectivity

In this report, a polarization-doped n-p-i-p-n GaN/AlxGa $_{{1}-{x}}\text{N}$ /GaN ultraviolet phototransistor with an Al0.20Ga0.80N insertion layer is proposed. The AlxGa $_{{1}-{x}}\text{N}$ layer with graded AlN composition is utilized as a p-type layer. The Al0.20Ga0.80N insertion layer is embedded into the unintentionally doped GaN (i-GaN) absorption layer, which can increase the conduction band barrier height and reduce the electron leakage from the substrate for the device. As a result, the dark current lower than $3.40\times 10^{-{11}}$ A/cm2 can be obtained. When the device is illuminated with ultraviolet light, the forward biased junction facilitates the photo-generated carrier transport. As a result, a photo-to-dark-current ratio (PDCR) larger than 104 at the applied bias of 5 V is realized. The carriers are transported in the region far apart from the device surface, and this gives rise a response with the rise time of 27 ms and decay time of 44 ms, respectively.