structural and electrical characterization of defect annihilation in thick gan layers on si, gan, and cte matched substrates
Name: Atsunori Tanaka
Grad Year: 2019
As Gallium Nitride (GaN) has quickly accomplished the commercialization of high-brightness blue LED and related optical devices, GaN has been also expected to be a strong contender for next-generation high power devices with high frequency of operation due to its superb material characteristics. The development of GaN devices has been attributed to the improvement of material quality by several growth techniques but defects in heteroepitaxial GaN layers still remain a critical issue for many applications especially for reliable high power devices. While GaN LEDs are relatively resilient to defects compared to other III-V material systems, leakage current and breakdown voltage are strongly related to GaN material quality. Thanks to recent works on bulk GaN substrate growth such as Na-flux, Hydride Vapor Phase Epitaxy and ammonothermal methods, GaN devices with thick drift layer and low dislocation densities are becoming feasible; however cost, reliability and uniformity over large areas remain challenging for market adoption of technologies based on these substrates. Therefore, the growth of thick and high quality GaN on cheap substrates is a crucial subject for GaN power devices commercialization. For typical GaN layer grown on Si, since the GaN layer typically cannot be grown thicker than 3-4 Ám on Si, the dislocation density at the GaN surface cannot be lowered below 10^8 cm^-2 because the transition layers/GaN interface suffers from the generation of large dislocation densities due to lattice and thermal mismatches. In this study, with our ability to grow over 20 Ám thick GaN on Si, we were able to carry out systematic studies on GaN Schottky barrier diode characteristics with different thicknesses of 5 Ám to 20 Ám unintentionally doped GaN layers on Si substrates. We observed correlation of Schottky diode ideality factor and barrier height with density of dislocations and were able to improve the device characteristics by growing thick GaN on Si and annihilating the threading dislocations under the contact. We have also carried out similar studies on GaN substrate to compare the result with Si, where the starting dislocation densities were very low and consequently the device characteristics were superior to those we obtained on Si. A similar analysis is being conducted on a newly commercialized CTE matched substrate.
Industry Application Area(s)
Electronics/Photonics | Materials | Semiconductor