Pv Of Gan-based Msm Structure Uv Detector Research

GaN-based meta1-semiconductor-metal (MSM) structure has been one of the focuses of interest in recent years for UV Photodetector because of its plane structure, fabrication simplicity, and the easiness of integration. According to the existing theory, the dark I-V characteristics and the I-V characteristics under illumination are simulated using ATLAS software. The major topic focuses on the detector electrode asymmetric structure, barrier layer and the photocurrent gain.First, Simulations demonstrates that the application of asymmetric workfunction electrodes can effectively suppress dark current for optical applications and the photocurrent characteristics of the device isn't sacrificed. A new metric NPDR was introduced by normalizing detector on-to-off current ratio to input optical power, At 20V bias, the highest NPDR of 10⁵μW^-1 was obtained for Au-GaN-Ni PD. Similarly, simulations demonstrates the application of asymmetric area electrodes in MSM-PDs can effectively suppress dark current. At 20V bias, considerabie I_dark drop (3×) is obtained for MSMs with identical total electrode area and spacing. With the degree of asymmetry in the electrode increased, the dark current can be reduced more. Because electrode spacing isn't, photocurrent characteristics of affected small.Then, the MSM-PDs with an additional thin p-GaN cap layer is investigated. The simulation results showed the dark current is 1.122×10^-13A for MSM-PDs with p-GaN concentration 1.0×10¹⁷cm^-3,thickness 100nm,while the dark current is 7.721×10^-12A for the conmmon device The efects of thickness and carrier concentration of p-GaN layer on the dark current of the photodetector were also studied. It is suggested that the dark current of the new structure device could be better reduced by employing p-GaN with higher carrier concentration as the cap layer.At last, the photocurrent gain under illumination is investgated. A model of I-V characteristics under illumination in GaN-based metal-semiconductor -metal photodetectors has been built, using steady-state continuity equations and including the effect of surface states. This model can explain the current under illumination and the responsivity change sharply with the biased voltage. The responsivity equation can be proposed from our model and be used to explain the photocurrent gain.