Simulation Of Termination Techniques For Vertical GaN Schottky Barrier Diodes

The third generation of wide band gap semiconductor materials which is representedby gallium nitride(GaN)are gradually emerging.Compared with traditional semiconductor materials,GaN has good chemical stability,high breakdown voltage,low on-resistance and high operating temperature.These advantages greatly compensate the inherent shortcomings of the traditional semiconductor materials.GaN are able to work on high-temperature,high-power,high-frequency environment.Considering that GaN Schottky Barrier Diodes(SBD)have a low breakdown voltage,the use of vertical structure GaN SBD can effectively improve the breakdown voltage compared to lateral structure GaN SBD.More and more research and experiments are carried out on vertical free-standing GaN SBD,but the current experiment process is not yet mature and the manufacturing cost is too high.Considering these situations,this paper has carried out the following research through simulation software:1.This paper introduces the working principle of vertical free-standing GaN SBD devices by energy band analysis and the three basic physical equations used in this simulation software Silvaco and the five physical parameter models selected in this simulation in detail.The corresponding vertical free-standing GaN SBD structure is established through the simulation software and the problem of peak electric field in SBD is proposed by observing the location of device breakdown during the simulation.2.Considering the problem of the spiked electric field in the vertical free-standing GaN SBD,several terminal techniques are proposed to alleviate the spiked electric field phenomenon,and the working principles of the four terminal techniques and the results of the obtained simulation data are explained by combining the simulation data.The specific analysis as follows:(1)The terminal depth d and the terminal length L of the junction terminal structure are optimized;(2)The reason for the change in the field plate length L_FP leading to the peak value of the electric field is explored,which can bring two peak electric fields,one is the junction peak electric field and the other is the offset electric field due to the peak electric field shift of the device because of the change of the end position of the field plate;(3)Combine the simulation data to briefly explain the principle of the guarding ring structure;(4)Propose a composite terminal structure,replace the P⁺layer in the guarding ring structure with an oxide layer and combine with the field plate to obtain the composite terminal structure.The vertical breakdown voltage of the vertical free-standing GaN SBD with a composite terminal structure is 850 V,which higher than the 500 V of the vertical free-standing GaN SBD without a terminal structure.Composite terminal structure can improve the breakdown voltage of the SBD.3.The reverse recovery characteristics of the vertical free-standing GaN SBD structure of the composite terminal structure were studied,the recovery principle and corresponding circuit principle of the vertical free-standing GaN SBD device were analyzed in detail,and the reverse recovery time 1.6ns of the device was obtained by simulation,then continued to simulate the temperature variable reverse recovery test of the device,and found that with the temperature change,the device reverse recovery time did not change much.After that,a typical GaN SBD device is manufactured by using the existing process technology.The doping concentration obtained by C-V analysis is that the doped N_dis about 8.1×10¹⁵cm^-3,and the experimental parameter setting of this simulation is 8×10¹⁵cm^-3.The results agree with each other,which verifies that the simulation results of this paper have certain reference significance,and the I-V curves of the obtained devices are compared with the results of the same SBD established by simulation in Chapter 3,and the two turn-on voltages are basically the same.Finally,the I-V temperature analysis of the device is performed,and the temperature change curve of the reverse current is continuously increased with the increase of temperature.With the increase of temperature,the leakage of the device increases accordingly.