Modelling Of Surface Field Distribution In GaN HEMTs And The Reverse Conducting Design

Power semiconductors are exerting a deep influence on human society through thefileds like machinery controlling, power transmission, power management, etc. Sipower devices have been developing for over half a century, and their performance isapproaching the physical limits. The increasing demand for higher performance isforcing researchers to try new semiconductors. GaN HEMT, with its potential of highbreakdown, low resistance, low switching loss, and capability to withstand hightemperature, proves to be the most promising next-generation power device.However, a series of issues are awaiting solutions before GaN HEMT is ready forwide commercialization, including the control of threshold voltage, current collapse,leakage current, material growth, etc. This thesis aims at the issues for GaN HEMT as apower switch device. The main contents are as the followings.1. The thesis theoretically anylizes the device physics of both nonpolarsemiconductor based GaAs HEMT and polar semiconductor based GaN HEMT.Normally-off operation and current collapse are also discussed systematically. What’smore, based on the work in Sun Yat-sen University and the available references, thisthesis reviewed the processing of GaN HEMTs, including material growth, deviceisolation, Ohmic and Schottky contancts formation, and device passivation.3. The thesis proposes a model to predict the surface electric field arounddrain-side gate edge in GaN HEMT. The device structure is mirrored into a transformedplane, and in the transformed plane, the the Laplace equation is solved by mirror chargemethod. Computer simulations are carried out whose results have verified the proposedmodel. The model is then implemented to study the influence of barrier thickness, Alfraction, and drain voltage on surface field.3. This thesis proposes a GaN reverse conduction HEMT (RC-HEMT) byintroducing an additional Schottky contact near the drain-side gate edge and connect itto the source. Experienmental results show the reverse working voltage is around3Vwithout sacrificing the forward on-resistance. Therefore, GaN RC-HEMT provides adesirable solution for applications where reverse conduction is required, such as inverters. The cost, the systems volume, and the number of wires could be greatlyreduced.