Enabling MOCVD technology for 20 kV GaN power switches
Abstract
In order to realize GaN power switches with off-state blocking voltage approaching 20 kV andleakage current below 10-5 A, on-state current of order 100 A with on-resistance around 0.03Ohm-cm2, and die size small enough to enable hard switching at 100 kHz, and to accomplish thisat an acceptable manufacturing cost, it will be necessary to identify and develop a ~best in class~vertical device architecture. While many technical questions remain unanswered at this time,there is little doubt that an essential building block for such devices will be an n-GaN drift layerhaving low net donor concentration (less than 1.2 x 1015 cm-3) and sufficient thickness (100-125microns), combined with minimal carbon contamination (less than 7 x 1014 cm-3). Additionalrequirements are low dislocation density (less than 5 x 105 cm-2) and crystallographic surfaceswith minimal step bunching; such imperfections may degrade power device performance andreliability. In principle, all of these technical challenges may be overcome by learning how tooptimize the process of high growth rate GaN homo-epitaxy on miscut native GaN substrates.The materials specifications outlined above are well beyond the limits of present-dayMOCVD technology. The goals of this research are to develop a better understanding of thenexus between substrate properties, MOCVD parameters, and crystal growth mechanisms; and toapply this knowledge in the preparation of thick n-GaN drift layers having chemical purity andstructural quality suitable for making 20 kV vertical-geometry GaN power switches. This will beaccomplished by leveraging the ongoing collaboration between Virginia Tech (MOCVDtechnology, materials characterization) and SixPoint Materials, Inc. (bulk crystal growth viaNEAT method, wafer orientation and surface preparation). The research plan is designed toexplore the impact of crystallographic step/terrace structure on the incorporation of chemicalimpurities, and on the evolution of surface morphology, during epitaxial growth. The specificresearch objectives for this project are as follows:1. Determine MOCVD parameters enabling growth of 25 micron thick n-GaN drift layershaving well-controlled Si doping with electron density less than 1.2 x 1015 cm-3 andcarbon contamination less than 7 x 1014 cm-3.2. Identify bulk GaN wafer miscut conditions (angle, direction) promoting step-flowepitaxy, when operating within this constrained MOCVD parameter space, and realize 25micron thick n-GaN drift layers having dislocation density less than 5 x 105 cm-2 withminimal step bunching and/or meandering.3. Develop a growth interruption process to enable preparation of 100 micron thick n-GaNdrift layers having the chemical and structural properties outlined above, combined withelectrical properties (on-resistance, leakage current, breakdown voltage) not adverselyimpacted by interfaces formed via growth interruption.If successful, this research will enable GaN power devices for application on Naval shipsin medium-voltage, direct-current (MVDC) electric power distribution systems operating at 12kV with power densities approaching 1 MW/cm3.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 07, 2019
- Source ID
- N000141912069
Entities
People
- Louis Guido
Organizations
- Office of Naval Research
- United States Navy
- Virginia Tech