Research On Mechanism Of Photoelectrochemical Etching And Device Process Of Gallium Nitride

Compared with other semiconductor materials,the main advantages of GaN lie in the larger band gap and higher electron mobility and saturation rate,which make it have broad application prospects in the field of power electronics.Recent studies have found that a novel photoelectrochemical(PEC)wet etching process can efficiently and nondestructively etch GaN materials,and has the potential to replace the traditional dry etching process.However,the current research on GaN PEC etching is not sufficient,the systematic etching theory has not been established.In addition,the electric field concentration phenomenon existing in conventional GaN HEMT devices during withstand voltage will lead to early breakdown of the device,and the actual performance of the final device is far from the theoretical limit.In order to solve the above-mentioned key problems,in-depth research has been carried out on the photoelectrochemical etching mechanism of GaN materials and the exploration of new structures of GaN HEMT devices.The main research results are as follows.First,after studying various existing PEC etching schemes,thesis designs and builds a GaN PEC wet etching process platform for research.Based on this,the corresponding etching process flow of electrode PEC etching and electrodeless ELPEC etching was developed,and the etching mechanism was studied in depth.By using different experimental methods and changing experimental parameters,the principle of etching is verified and the general etching law is mastered.The study found that the PEC etching rate is limited by the two-step reaction of GaN oxidation and Ga₂O₃ dissolution.In addition,a relatively well-established etching mechanism for chopped UV ELPEC etching is also presented in thesis.Secondly,by adjusting the process parameters,a larger etching rate is achieved.In the PEC etching experiment with electrodes,after etching for 2h with 0.025mol/L Na OH solution and 1V bias voltage,the etching depth reached about 3?m,and the etching rate was about 25nm/min.In the experiment of electrodeless ELPEC etching,by using 1KHz chopper UV,the etching rate was increased while the etching surface roughness was reduced.The etching rate increased from 7.4 nm/min using continuous UV etching to16.8 nm/min,the normalized Ra/De(surface roughness/etching depth)decreased from0.175 to 0.051,and the depth reached 1010 nm after 1h of etching,the surface roughness Ra is 52nm.Finally,based on the conventional P-GaN back-barrier GaN HEMT,a novel GaN HEMT with a Hybrid Semiconductor Layer above substrate has been proposed.By inserting a compound semiconductor layer on the substrate,the electric field distribution inside the device can be effectively modulated,the peak electric field near the gate and drain can be reduced,and the breakdown voltage of the device can be significantly improved while maintaining low on-resistance.Studies have shown that when the gate-drain pitch is 6?m,the breakdown voltage of the structure is 1319 V,which is 172%higher than that of the conventional HEMT of 485 V,and the specific on-resistance is only 0.39 m?·cm~2.When the gate-drain pitch is 20?m,the breakdown voltage of the device is 3480 V,and the power figure of merit reaches 5.24 GW/cm~2.