GaN Nanowire Schottky Barrier Diodes

A new concept of vertical gallium nitride (GaN) Schottky barrier diode based on nanowire (NW) structures and the principle of dielectric REduced SURface Field (RESURF) is proposed in this paper. High-threading dislocation density in GaN epitaxy grown on foreign substrates has hindered the development and commercialization of vertical GaN power devices. The proposed NW structure, previously explored for LEDs offers an opportunity to reduce defect density and fabricate low cost vertical GaN power devices on silicon (Si) substrates. In this paper, we investigate the static characteristics of high-voltage GaN NW Schottky diodes using 3-D TCAD device simulation. The NW architecture theoretically achieves blocking voltages upward of 700 V with very low specific on-resistance. Two different methods of device fabrication are discussed. Preliminary experimental results are reported on device samples fabricated using one of the proposed methods. The fabricated Schottky diodes exhibit a breakdown voltage of around 100 V and no signs of current collapse. Although more work is needed to further explore the nano-GaN concept, the preliminary results indicate that superior tradeoff between the breakdown voltage and specific on-resistance can be achieved, all on a vertical architecture and a foreign substrate. The proposed NW approach has the potential to deliver low cost reliable GaN power devices, circumventing the limitations of today's high electron mobility transistors (HEMTs) technology and vertical GaN on GaN devices

GALLIUM NITRIDE NANOSTRUCTURED POWER SEMICONDUCTOR DEVICES

Gallium nitride (GaN) has emerged as a promising material for development of power semiconductor devices owing to its superior material characteristics. Fabricated GaN power devices have started to outperform its silicon (Si) counterpart with low conduction and switching losses and holds the key to extremely low-loss and high efficiency power delivery circuits of the future. However, GaN power devices have been plagued with several inherent drawbacks preventing an ubiquitous adoption of GaN as the material of choice for power switches. The most critical trade-o↵ has been the choice of substrate for the growth of GaN epitaxy: a high performance, high-cost native substrate or a low-cost, non-native substrate with reliability issues. In order for GaN to thrive as a superior successor to Si, a low cost, high performance epitaxy with improved reliability is expected moving forward. A novel nanostructured approach to GaN power devices is proposed in this dissertation. The nano-GaN power devices theoretically has the potential to bypass the reliability concerns associated with a non-native substrate but still deliver comparable performance. A comprehensive model is proposed for TCAD modeling of bulk GaN power devices to accurately model the nano-GaN devices. Through extensive modeling and simulations, design guidelines for Schottky barrier diodes and field effect transistors based on the nano-GaN concept is laid out to extract the best performance out of this architecture. Dielectric and semiconductor interaction is also exploited to push these devices to perform beyond the unipolar material limit of GaN. The simulated and fabricated nano-GaN power devices show the potential to deliver equivalent or superior performance to present state of the art GaN devices but with improved reliability, ruggedness and low cost.Ph.D. in Electrical Engineering, May 201