PH.D. STUDENT

Recent activities

Robert’s recent work has been focused on wide/ultrawide bandgap (WBG/UWBG) semiconductors, especially gallium oxide (Ga2O3), silicon carbide (SiC), and diamond. The EMDD Lab at ARL grows diamond by Microwave Plasma Chemical Vapor Deposition (MPCVD) and SiC epi-layers by Chemical Vapor Deposition (CVD) and Physical Vapor Transport (PVT) methods. SiC has become a critical material for high power electronics, especially with increasing demand within the electric vehicle (EV) market. In particular, Robert’s SiC work has included radiation hardened devices and sensors, depositing high-quality gate dielectrics, and growth and characterization of thick (>100 microns) epi-layers. Single crystal (SC) diamond is sometimes referred to as the “ultimate semiconductor” due to its exceptionally large electronic bandgap, critical field strength, and thermal conductivity, among other properties. However, device applications are still limited due to the difficulty in producing high-quality, large area substrates. Robert’s research has included innovative solutions for meeting this challenge as well as synthesizing doped diamond layers. Over the last several years, Ga2O3 has generated considerable excitement as an UWBG semiconductor for power electronics and radio frequency (RF) devices. In particular, Ga2O3 is currently the only UWBG semiconductor capable to crystallization from a melt at an industrial scale. The implication is commercial availability of large area, native substrates, which has been difficult to achieve with gallium nitride (GaN). Robert’s work on Ga2O3 has been largely focused on substrate fabrication, chemi-mechanical polishing (CMP), and materials characterization. Developing an efficient, high-yield fabrication and CMP process that produces an epi-ready surface with minimal subsurface damage and an excellent surface finish is a critical step toward commercializing the technology. Robert also characterizes and maps defects in Ga2O3 which are important to understand for producing next-generation electronic devices. This includes spectroscopy and diffraction techniques as well as transmission electron microscopy (TEM) with Dr. Nasim Alem’s research group to improve the semiconductor community’s understanding of the material at the atomic scale. Robert and the rest of the EMDD team also work directly with U.S. Ga2O3 suppliers, leading Ga2O3 epi growers, DoD and government labs, and foundries to facilitate rapid process improvements in establishing and scaling up commercial Ga2O3 products.

Highlighted publications

• Cheng, H., Yi, N., Gao, Y., Lo Verso, A., Zhu, J., Erdely, D., Xue, C., and Lavelle, R. “Fabricating functional circuits on 3D freeform surfaces via intense PLD zinc mass transfer,” Materials Today. (2021).

• Malakoutian, M., Song, Y., Yuan, C., Ren, C., Lundh, J., Lavelle, R., Brown, J., Snyder, D., Graham, S., Choi, S., and Chowdhury, S. “Polycrystalline diamond growth on β-Ga2O3 for thermal management,” Appl. Phys. Exp. 14 (2021).

• Han, S., Song, J., Yoo, S., Ma, Z., Lavelle, R., Snyder, D., Redwing, J., Jackson, T., and Chu, R. “Experimental demonstration of charge-balanced GaN super-heterojunction Schottky barrier diode capable of 2.8 kV switching,” IEEE Electron. Device Letters. 41 [12] 1758-1761 (2020).