| Gallium nitride(GaN)high electron mobility transistor(HEMT)has the advantages of high breakdown voltage,high switching speed,and low loss,and has broad application prospects in the field of power electronics.However,some power conversion systems require devices to have reverse protection and bidirectional switching capabilities,and the current research on the theoretical analysis and structural design of high-voltage and low-loss GaN reverse blocking power devices is not complete,which is not conducive to GaN reverse blocking power devices design and fabrication.In addition,the turn-on voltage introduced by the reverse blocking dependent drain Schottky barrier increases the conduction loss,and there is a trade-off optimization relationship between the reverse breakdown voltage and the conduction loss.In addition,the internal defect ionization causes the deterioration of device conduction and withstand voltage characteristics,which hinders the design and industrial application of high-reliability GaN reverse blocking power devices.Given the above problems,this thesis takes the design and fabrication of GaN reverse blocking devices with high breakdown voltage and low loss the as the purpose,and makes the following research:1.Based on the semiconductor physics and the working mechanism of GaN reverse blocking power devices,the conduction loss composition was analyzed,the mathematical relationship between the electrical characteristics of the device and the structural design is established,and the direction of the device optimization design is given.The results show that the turn-on voltage of HEMT with Schottky drain(S-HEMT)is affected by the contact area of the drain,metal work function,and interface defects.The turn-on voltage of reverse blocking HEMT with P-type doped GaN(p-GaN)cap drain(P-HEMT)is closely related to the heterojunction polarization boundary charge density,and the thick barrier,high Al content,low p-GaN layer doping,low buffer layer defect ionization are conducive to optimizing channel resistance and turn-on voltage.It provides theoretical support for device optimization design.2.The influence of the device structure and trap on the electrical performance of GaN reverse blocking power devices was studied.The results show that increasing the drain area,using drain metal with low work function and Al GaN barrier layer with low Al content is conducive to the design of low turn-on voltage.At the same time,the introduction of a field plate or p-GaN cap layer into the drain of the device can improve the reverse blocking capability.The influence of the static characteristics and dynamic resistance of the device by the buffer layer defect ionization was explored,and the internal high electric field promoted the ionization of the defect during the high-voltage,accelerating channel carrier depletion and leading to the transfer of electric field peak.The forward breakdown voltage of the device first increases and then decreases with the increase of the donor defect concentration of the buffer layer.When the device is switched at high speed,defect ionization is enhanced at the off-state high field,leading to the reduction of channel carrier density and increasing the on-resistance of the device.The resistance degradation is most significant in the regions where the electric field is crowded,such as gates and field plates.It reveals the influence mechanism of device structure design on the electrical performance of the device,and a numerical basis is provided for device development.3.A novel reverse blocking p-GaN HEMT with multi-column p-GaN/Schottky alternate-island drain(MPS-HEMT)is proposed and fabricated,which improves the conduction and blocking capabilities of the device through the modulation of channel charge and electric field by the p-GaN island and Schottky island.The experimentally fabricated MPS-HEMT exhibited a turn-on voltage of 0.31 V,a high forward and reverse breakdown voltage of more than 1000 V was achieved,along with a specific on-resistance of 8.3 mΩ·cm~2.The MPS-HEMT reduces the turn-on voltage by 41.51%and 91.19%,respectively,compared with the synchronous S-HEMT and P-HEMT.The reverse breakdown voltage of MPS-HEMT is increased by 253.40%relative to S-HEMT,and decreased by 27.87%relative to P-HEMT,The trade-off between conduction loss and break voltage has been optimized. |
