Charge Regulation Mechanism And New Structure Research Of GaN-based Power Devices

Gallium nitride(GaN)power device has the advantages of low on-resistance and high breakdown voltage,which can bring great technical breakthroughs for the power conversion systems,and have become a research hotspot in the field of power semiconductor.The research of high performance GaN power device has the important scientific significance and application value.Optimizing the on-resistance is the core issue in the development of low loss GaN power device.The on-resistance of the device is critically dependent on the Two Dimensional Electron Gas(2DEG)charges.In this dissertation,the charge regulation mechanism and new structure of GaN power device are studied.The charge regulation model is established,and the new structures of low switching loss device,low turn-on diode device,and low turn-on reverse-blocking device are proposed.The main contents and innovations of this dissertation are as follows:(1)The buffer charge regulation model of GaN power device is established.The charge regulation mechanism of GaN power device is studied.Based on Gauss’ law and electric neutral condition,the analytical relationship between the buffer doping parameters(doping concentration and doping level)and buffer charge is clarified,and the quantitative regulation effect of the buffer charge on the 2DEG charge density is revealed.The expressions of the 2DEG density and device threshold voltage are obtained,and the buffer charge regulation model is established.Compared with the conventional model,the buffer charge regulation model realizes the more accurate calculation of the 2DEG charge density and the threshold voltage,which provides a theoretical foundation for the subsequent proposal of new structure devices.(2)The dynamic charge storage GaN power device is proposed.To solve the problem of high switching loss in GaN power device,a dynamic charge storage structure is proposed.By inserting a P-type doped dynamic charge storage layer connected to the source in the device buffer,the dynamic storage of the buffer charge is realized when the device is during switching process.By utilizing the dynamic increase and decrease of the buffer charge density when the device is turned off and turned on,the depletion and recovery of the 2DEG charge is accelerated respectively.Then the device switching time is reduced,and the turn-off loss and the turn-on loss are greatly lowered.Compared with the conventional device,the dynamic charge storage device achieves a61% reduction in switching loss.Meanwhile,the dynamic charge storage device shows the non-degraded on-resistance and breakdown voltage characteristics.(3)The low barrier anode GaN power diode devices are proposed.To reduce the turn-on voltage of GaN power diode devices,the low barrier anode structures are proposed.By introducing the cascode structure composed of a Schottky and a Metal Insulator Semiconductor(MIS)into the device anode,and the gated structure to reduce the charge storage density of the p-GaN layer,the channel region barrier height is reduced.Then,the turn-on voltage of the device is lowered,and the Schottky-MIS cascode anode device with an ultralow turn-on voltage of 0.19 V and the p-GaN gated anode device with a 70% lower turn-on voltage than that of the conventional device are obtained,which optimizes the trade-off relationship between the turn-on voltage and the reverse leakage current of the diode device.(4)The alternate islands drain reverse-blocking GaN power device is proposed.To reduce the turn-on voltage of the reverse-blocking GaN power device,according to the charge regulation model and the gated anode diode device,the three-dimensional charge regulation and the barrier height reduction of the drain channel region are realized through introducing p-GaN/Schottky alternate islands structure at the drain diode of the reverse-blocking device.Then,the turn-on voltage of the device is reduced.The small gate width device with a low turn-on voltage of 0.31 V and a reverse breakdown voltage of 1092 V is obtained,and the large gate width device with a turn-on voltage of 0.41 V,a conduction current of 5.2 A,and more than 650 V forward/reverse breakdown voltages is realized.The trade-off relationship between the turn-on voltage and reverse breakdown voltage of the reverse-blocking device is optimized.