(Invited) Understanding the Electroluminescence Signature of High-Voltage Vertical GaN Pin Diodes with Different Edge Termination Designs

Abstract

GaN has superior properties, such as a wide band gap and high critical electric field that make it promising material for future power semiconductor devices. Edge termination for GaN power devices remains a subject of significant interest. In this work, different edge termination designs were systematically evaluated and compared by utilizing broadband electroluminescence technique under various reverse bias conditions. Edge termination is a crucial step in power devices fabrication process, using nitrogen implant is a common step in GaN PiN diode. In this work, Nitrogen ion implantation was used to form junction termination extension (JTE) and Guard Rings (GR). A full 2” wafer was fabricated in a foundry process to build a high current 1.2kV class GaN vertical diodes on non-homogenous GaN substrate. In silicon power devices, a smooth tapered implanted doping profiles are often achieved through a controlled diffusion of the implanted dopant island during activation. Activation and diffusion of acceptor dopants via ion implantation is neither well controlled nor understood in GaN. In this work, based JTE terminations, GR termination and a combination of both were compared. We are comparing several devices on the same wafer type and same fabrication process but with different edge termination designs; and spatially resolving their spectrum, by utilizing the electroluminescence mapping technique to acquire a series of broadband images under high voltage reverse bias. There is a clear difference in the electroluminescence signature. This is the first time we show the impact of edge termination on the evolution of these defects and the transport path of the leakage current. The leakage current, and hence the electroluminescence signature is changing as well with the termination design. All the termination and guard ring designs were based on Nitrogen implant. The nitrogen implant doses and energy are chosen to create enough damage in the p-type region. Stress testing is in-progress to evaluate the impact of these defects on failure mechanisms. JTE only design show a leakage current as a bright ring on the outer perimeter of the device active region closer to trench isolation while a GR only design brings the leakage current near the anode. A combination of both termination designs results in scattered leakage points on the outer perimeter of the device. Simulation results of the filed profiles of the different structures and hyperspectral EL and Raman spectroscopy are in progress along with temperature stressing to understand the nitrogen diffusion mechanisms in GaN. This study will have an impact on the future of GaN power devices and mature its process to compete with SiC technology. Figure 1