Study On AlGaN-Based MSM Solar-Blind Ultraviolet Photodetector With Integrated Photonic Crystal Filter

Ultraviolet detection technology is widely used in missile early warning,ultraviolet communication,flame detection,medical examination,water pollution detection and other military and civil fields.It is one of the key technologies in China.To realize the detection of weak UV signal,the detector must have high sensitivity,high gain and strong ability to inhibit out-of-band signal.Al Ga N material has become the preferred material for preparing UV detector because of its wide direct band gap,high electron saturation drift velocity and good thermal conductivity.This paper focuses on the Al Ga N based MSM UV detector,designs the device structure through simulation and fabricates the devices.In order to improve the detection performance of the device,we innovatively introduced Si O2/ Si3N4 one-dimensional photonic crystal,and focused on testing the photoelectric characteristics of the device.The main research results are as follows:(1)According to the simulation results,the device structure of Al Ga N based MSM UV detector is designed.The thickness,composition and doping concentration of each layer of Al Ga N heterojunction are determined.Alx Ga1-x N(0.52> x >0.42)gradient layer is applied to reduce lattice mismatch and internal dislocations to improve the device performance.(2)One dimensional photonic crystal structure is designed,which is composed of14 groups of Si O2 and Si3N4.The Al Ga N based MSM UV detector was fabricated and Si O2/Si3N4 photonic crystal was applied on the back of the device.We also accurately characterize the Schottky contact characteristics of the device,and test the characteristics of the photonic crystal.The results show that the central wavelength of the photonic crystal is 320 nm.The photonic crystal also has high reflectivity in long wavelength ultraviolet region which means its great optical filtering characteristics.(3)The results of I-V curves show that the dark current of the device is in the order of p A at 20 V bias,and the light / dark current ratio of the device is more than 103 at10 V bias.The results of spectral response curve show that detector exhibits obvious solar-blind response peak at 285 nm and high solar-blind/ UV rejection ratio.The light absorption outside solar-blind ultraviolet caused by impurity and defect energy levels is significantly suppressed by the 1-D PC.The high reflection outside solar-blind ultraviolet makes the device have a narrow solar blind optical window(281nm~292nm),which is conducive to the high-precision detection of solar-blind ultraviolet.In addition,we also explore the effect of interdigital electrode spacing on the photoelectric characteristics of the device.The results show that the photocurrent and spectral responsivity of the device increase with the decrease of interdigital electrode spacing.