Characterization of Thick Epitaxial GaN for Power Electronics Applications
Abstract
This proposed research will investigate defects in thick GaN epitaxial layers, doped and undoped and to understand what influences defect propagation from the substrate into the epilayer. The research to be carried out will investigate the electrical activity of defects in thick (10s~100s of ~m) epilayers as well as the influence of defects on the epi/dielectric interface. The research focus will also be to investigate the spatial statistical distribution of defects through experimental defect distribution investigates as well as to develop the appropriate probability density functions for spatial distribution as well as thickness distributions. This need will be met for ONR through a program which involves material from ONR contractors, the power electronics section at NRL, as well as epitaxial layers purchased directly from commercial vendors. The proposed research is separated into three inter related tasks in order for a systematic understanding of defects to be achieved. The research to be carried out in Task 1 will evaluate the role of material defects in thick GaN epitaxial materials, through a variety of test structures which will be designed andfabricated in the UMD NanoCenter Fabrication Laboratory Facility. Individual test structures will be designed to monitor bulk material and interfacial material properties that are expected to evolve under specific high voltage conditions. Such stress conditions include high temperatures, and high electric and magnetic fields. The test structures that will be utilized are low-voltageand high-voltage (up to 1 kV) p-n junction and Schottky barrier diodes, and MOScapacitors. The experimental data will be used to validate the appropriate physics phenomena caused by the applied stress. Through an iterative approach, the results from Task 1 evaluation will allow the researchers of ONR~s 6.1 program to further refine material synthesis approaches in order to mitigate the role of material defects in thick epitaxial layers. In Task 2, the investigations will encompass advanced defect spectroscopic techniques to thick epi materials and two-terminal test structures. These include: deep level transientspectroscopy (DLTS), photoconductivity spectroscopy, photo-induced current transient spectroscopy (PICTS), and photoluminescence (PL) spectroscopy. Optical defect spectroscopic techniques are especially useful for WBG semiconductors since they can access a wide range of defects with energies deep within the bandgap, not accessible by thermal ionization. Furthermore, these techniques can detect defects as the low as the part per billion level. Defect energy level, concentration and capture cross-section will be determined. The proposed research will undertake an in situ study of defect dynamics under electric field stress using synchrotron radiation spectroscopy. Changes in defect configuration will be correlated with changes in electrical characteristics which will be simultaneously monitored using an automated electrical data acquisition test set up. In the proposed Task 3, defect distributions, both spatial and vertically (thickness) as well as crystal quality in these thick films will be characterized. The defect distribution techniques which will be investigated as part of the proposed research for characterizing dislocation density and behavior in thick epilayers will be: (1) electron backscatter diffraction, (2) cross-sectionalTEM, (3) two-photon photoluminescence for mapping dislocations in 3D and (4)cathodoluminescence (CL) measurements. Conventional top-down CL characterization can only probe to depths of approximately 1 ~m. The proposed research will target application of these physical and optical measurements in order to obtain a three dimensional distribution map of defects and will collaborate with NRL to obtain correlations with electrical characteristics.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 23, 2019
- Source ID
- N000141912022
Entities
People
- Aristos Christou
Organizations
- Office of Naval Research
- United States Navy
- University of Maryland