Study On UV Phototransistor Based On P-GaN HEMT Structure

With the rapid development of UV detection technology,it has been widely used in civil and military fields,such as missile warning,flame detection,biomedical detection and UV communication.As the third group nitride is a direct band gap semiconductor,it has excellent photoelectric properties.In addition,the third group nitride can cover the UV band according to the adjustable band gap width of different material components.The third group nitride also has excellent properties such as high electron saturation drift rate,high breakdown electric field,high thermal conductivity and strong radiation resistance.It is the preferred material for the preparation of semiconductor UV detector.The research object of this paper is a UV phototransistor based on p-Ga N HEMT structure.It mainly focuses on the simulation performance calculation of the detector,the optimization of the device structure parameters through simulation calculation,the optimization of the device process,mainly the ohmic contact annealing process,and the performance analysis of the final device.The main research results are as follows:?1?The UV phototransistor based on p-Ga N HEMT structure was simulated by Silvaco TCAD.The structure of the device is composed of p-Ga N gate and Al Ga N/Ga N heterostructure.The length of p-Ga N gate is 1.4?m,the thickness is 110nm,the distance between source and drain is 8.4?m,the thickness of Al Ga N is 15nm,the composition of Al is 0.23,and the thickness of Gan is 2?m.The results show that when the source drain bias voltage is less than 10V,the dark current of the device can be less than50n A/mm,the photocurrent is more than 10m A/mm?@1m W/cm²light intensity?,the light response can reach 2.93×10⁵A/W,and the light/dark current ratio is more than 10⁵.?2?The influence of different device structure parameters on the performance of p-Ga N HEMT is studied.The performance of the Al Ga N barrier layer with different thickness?12nm,15nm,18nm?and different aluminum components?0.21,0.23,0.25?is calculated.It is found that the photocurrent and dark current of the device increase with the increase of the Al component and the thickness of the Al Ga N layer,especially when the thickness of the Al Ga N layer increases to 18nm,the dark current increases to more than 10^-4A/mm.When the thickness of Al Ga N layer exceeds 18 nm,it is difficult for p-Ga N to deplete the two-dimensional electron gas in the lower channel,which results in the sudden increase of dark current.In addition,the influence of doping concentration(1×10¹⁷/cm3,3×10¹⁷/cm³,1×10¹⁸/cm³)of p-Ga N layer on the performance of the device is calculated.It is found that the dark current and photocurrent of the device decrease with the increase of doping concentration of p-Ga N,but the variation is within an order of magnitude.?3?We prepared the UV phototransistor and then its performance was characterized.The annealing process of ohmic contact was optimized.We tested the annealing of Al Ga N ohmic contact at different annealing temperatures from 810?to890?,and analyzed the relationship between the measured resistance and distance through the rectangular TLM model.The relationship between annealing temperature and contact resistance of ohmic contact is obtained and finally,the optimal annealing condition of 840?is obtained,the contact resistance is 2.69?·mm.We characterized the spectral response of the device and the I-V characteristic curve under the condition of illumination and no illumination.The light dark current ratio of the device is more than 10²,and the main reason for the difference between the simulation results and the device is that the dark current is too large.Then,we analyze the reason for the larger dark current of the device,and propose a further improvement scheme.