Research On Gain-type AlGaN Solar-blind UV Detectors

AlGaN is a direct wide-bandgap semiconductor material,and its band gap is continuously adjustable from 3.4 e V to 6.2 e V with the change of Al composition.The absorption wavelength of AlGaN covers 200?365nm,which enables intrinsic detection of solar-blind ultraviolet light.In addition,AlGaN material has good thermal stability,chemical stability and anti-radiation energy characteristics,so it is the preferred material for the preparation of solar-blind ultraviolet(SBUV)detectors,which has important application prospects in the fields of secure communication,missile warning,corona detection,fire monitoring and so on.So far,AlGaN solar-blind UV detectors have made important progress.Metal-semiconductor-metal(MSM)and PIN-structured detectors have reached the application level in terms of achieving dose detection.However,high-gain AlGaN solar-blind UV detectors still have great challenges,and it is difficult to achieve efficient detection of weak signals.In view of this,the dissertation focuses on how to realize high-gain AlGaN solar-blind UV detectors.The gain of AlGaN solar-blind UV detectors is improved by adjusting the polarization field of AlGaN heterojunctions and designing multiple quantum well structures in the active region.The main achievements of this dissertation are as follows.1.The electrostatic shielding of polarized charges by free carriers in AlGaN heterojunctions is discovered,and the unintentionally doped hetero-intercalation layer is designed to weaken the polarization shielding phenomenon.The electric field,energy band,and carrier concentration characteristics of the device were simulated by Apsys software.It was found that when there are high concentrations of free carriers with opposite electric properties around the polarization charges of AlGaN heteromaterials,the polarization charges will be electrostatically shielded by the carriers and cannot produce effective polarization electric field regulation.By using the unintentionally doped hetero-intercalation layer,the free carrier concentration near the polarization charge can be effectively reduced,the polarization shielding effect can be reduced,and the polarization electric field regulation can be realized.2.The polarization-enhanced front-incidence P-I-P-I-N-AlGaN solar-blind UV avalanche detector(APD)is designed and developed.Through the polarization control effect of the hetero-intercalation layer,the polarization electric field strength in the multiplication region of the device is enhanced,the avalanche breakdown voltage of AlGaN-APD is reduced,the avalanche gain of the device is increased,and the overall performance of the device is improved.3.An AlGaN multiple quantum well(MQW)PIN vertical photoconductive gain solar-blind ultraviolet detector structure is proposed and developed.By introducing an AlGaN multiple quantum well(MQW)structure into the active region of the device,the trapping and confinement function of hole transport is realized,and the transit time difference between electrons and holes is increased,thereby inducing photoconductive gain in the device.The MQW-enhanced PIN-AlGaN solar-blind UV detector can be self-driven at zero bias voltage,with a peak responsivity of 0.425 A/W at the deep UV wavelength of 233 nm,and a corresponding external quantum efficiency(EQE)as high as 226%.