Structural Design And Performance Study Of New GaN HEMT Power Devices

In recent years,with the continuous expansion of the application field of semiconductor power devices,especially on special occasions,require devices to maintain stable performance in harsh environments such as high temperature and strong radiation,so the third generation semiconductor represented by gallium nitride（GaN）have attracted increasing attention.Due to the advantages of AlGaN/GaN HEMT devices with high density of two-dimensional electron gas,high electron mobility,high critical breakdown electric field and low parasitic parameters,GaN HEMTs shine in the field of power device applications.In order to be better applied in the fields of power management,inverter and motor control,how to achieve excellent reverse conducting performance or reverse blocking performance is an urgent problem to be solved at present.Based on the existing research on GaN HEMT devices,this thesis designs a DCRC（Double Channel Reverse Conduct）-HEMT and a PHD（Hybrid Drain with P-buried layer）-HEMT.Based on Sentaurus TCAD simulation technology,the mechanisms of the proposed devices are analyzed and verified.The main research content and results of this thesis are as follows:1.The proposed DCRC-HEMT integrates a MIS channel diode（Metal-Insulator-Semiconductor Channel Diode,MCD）at the source and uses a double heterojunction structure to realize the upper and lower channels.During reverse conduction,the MCD controls the opening of the lower channel to achieve a low reverse turn-on voltage,avoiding the increase in on-resistance caused by sacrificing the forward conduction area to achieve reverse freewheeling.Compared with the traditional freewheeling scheme of integrated Schottky diode,the MCD structure acts as a MIS field plate in the off state,which effectively reduces the leakage current and increase breakdown voltage.The lower channel achieves channel pinch-off through the MIS structure,which is different from the traditional structure that needs to compromise the density of 2DEG.The lower channel of DCRC-HEMT can use a thicker barrier layer with a higher Alcomponent to reduce the reverse-conduction resistance.The proposed device achieves a low reverse turn-on voltage of 0.58 V that does not change with the gate voltage,which is 69%lower than the1.87 V of the traditional structure.2.The PHD-HEMT realizes reverse blocking by etching the drain barrier layer to form a MIS hybrid drain structure to turn off the channel.First,a shorter MIS channel length is used to reduce the forward turn-on voltage.A floating p-buried layer is introduced near the drain buffer layer to modulate the electric field distribution in the blocking state,thereby reducing the leakage current and improving the soft breakdown voltage.The critical parameters of the p-buried layer are analyzed,and the optimization interval is given.The PHD-HEMT ensures that the forward turn-on voltage V_ON is 0.6 V,and at the same time,the reverse blocking breakdown voltage is increased by more than4.29 times,which proves that the new structure has a good reverse blocking capability.