Study On AlGaN-based UV Detector Based On The Regulation Of Polarization Electric Field

With the stable physical and chemical characteristics,and the adjustable band gap changing from 3.4-6.2 eV which covering a range of 200-365 nm,Al GaN-based materials are suitable for the high sensitivity ultraviolet detector.In addition,as solidstate devices,AlGaN based UV detectors not only can work in complex and harsh environment,but also have low energy consumption,small volume,easy integration and without filtering system.Therefore,AlGaN based UV detectors have important application prospect in the field of aviation,civilian and defense.In order to adjust the response band and improve the quantum efficiency,the hetero-structure is introduced in the AlGaN-based UV detector.The electric field of polarization is caused by the discontinuity of polarization constants at hetero-interface.The polarization electric field has two sides,it is helpful to improve the performance of the detector by taking advantage of its favorable side and weakening its disadvantage.In this paper,we focus on improving the responsivity and reducing the dark current of AlGaN-based UV detector based on regulating the polarization electric field at the hetero-interface.The main results are as follows:1.Proposing a method to reduce the dark current of the detector by introducing a grading n-AlGaN layer to adjust the polarization field.The photoelectric characteristics of hetero-junction pin-AlGaN based UV detectors with different polarization charge density are studied,it is found that the dark current increases and the responsivity decreases with the increase of the polarization charge density,and the results show that the polarization electric field will have a negative influence on the photoelectric characteristics of the detector.To solve this problem,an Al component grading n-AlGaN layer is inserted into the hetero-interface,the effect of polarization electric field on the dark current is reduced and the spectral response of the detector is improved.2.Improving the performance of Schottky AlGaN-based UV detector obviously by using polarized electric field.A polarization electric field is introduced into the Schottky structure by introducing a low Al component into the Schottky contact interface,the quantum efficiency has been more than 50% for the first time under zero bias.The direction of the polarization electric field is the same as that in the Schottky junction,thus,the effective electric field intensity in the depletion region is enhanced,and the collection efficiency of the detector is improved,at the same time,the polarization field increases the height of the Schottky barrier and improves the rectification effect.3.Evaluating the average energy for impact ionization by holes in Al0.4Ga0.6N alloy by the experimental method by optimizing the structure of the device to suppress the polarization electric field.The variation of the quantum efficiency under different reverse bias in backilluminated homo-junction separate absorption and multiplication(SAM)structure Al0.4Ga0.6N avalanche ultraviolet photo-detector with different thickness of the multiplication layer are studied,and considering the law of conservation of energy in the course of impact ionization,the average threshold energy of hole induceing impact ionization in Al0.4Ga0.6N materials is obtained.This study pave a way for the further optimization of the design of AlGaN-based avalanche detectors.