Research On GaN-based Photoelectrochemical Etching Technology And New Device Structure

GaN has been widely used in the field of electrical electronics with its large band gap,high breakdown electric field strength,and high electron mobility.Although the GaN power device has been vigorously developed,there are still many problems that need to be solved。For example,the damage caused by dry etching and the introduction of defects will lead to the increase of device leakage current,and the device breakdown in advance due to the large electric field peak at the gate edge of GaN power devices.In order to solve the above problems,this thesis focuses on GaN photochemical etching process（PEC）and the novel voltage resistance structure of GaN HEMT devices.First of all,aiming at the surface damage caused by dry etching,this article conducted a series of experiments by using the self-built PEC etching process platform.By changing the relevant experimental parameters,the law of etching is studied and the principle of etching is verified.The changing parameters are etching time,chopper frequency and Na₂S₂O₈ solution concentration.When the etching time is 120min,the etching depth reaches 2886nm,and the etching roughness reaches 146nm.In order to reduce the effect of dislocation,an optical chopper is introduced and the influence of chopper frequency is studied.The results of step profiler and SEM show that the etched bottom was obviously improved after adding chopper.Finally,the influence of Na₂S₂O₈solution is also studied.After adding Na₂S₂O₈solution,the etching depth increases from600nm to 900nm,and the etching roughness decreases from 32nm to 11.7nm.Secondly,in view of the existing problems of the original experimental platform,the experimental platform was improved.UVREF400 filter,DT365 filter and ZWB2 filter were added to the original platform,and a three-electrode working system was adopted.The improved experimental platform was used to carry out the etching experiment,and the etching depth reached 3500nm after 2h.Then,three-dimensional SEM image analysis was carried out on the M-type alignment mark,and it was found that the clear three-dimensional pattern was presented.Finally,a novel GaN HEMT structure（HP-HEMT）with a mixed P-type doping layer on the substrate is proposed to address the low voltage resistance of GaN HEMTs.This structure can effectively improve the peak electric field at the gate edge and drain edge,and overall increase the channel average electric field intensity with little influence on the DC characteristics.By optimizing the key parameters,the breakdown voltage of HP-HEMT structure reached 1625V when the distance between gate and drain was 6μm,N_p+=8×10¹⁷ cm^-3,N_p=1×10¹⁷cm^-3,L_di=1μm,which was much higher than 405V of Conv-HEMT and 905V of AP-HEMT.Its specific on-off resistance is only 0.4mΩ·cm².At the same time,when the distance between gate and drain is 20μm,the optimal value of the device reaches 10.15GW/cm².The input capacitance,output capacitance and reverse capacitance are all reduced compared to conventional structures.Meanwhile,the HP-HEMT device has a higher on-off speed（376V/ns）and a higher turn-off speed（103V/ns）.