Dr. Piner's group is principally focused on research and technology development in the growth and characterization, semiconductor fabrication, and performance optimization of wide bandgap materials for solid-state device applications.
Heteroepitaxy, i.e., epitaxy of one material on a substrate of another material, is a proven approach for commercializing new device technologies such as GaN-based photonic (LEDs and LDs), and electronic (FETs) devices. However, it also inherently creates crystal defects. Thin film crystal quality improvement is an on-going area of scientific pursuit by Dr. Piner's group, performed on two state-of-the-art growth systems, termed "reactor", based on the metalorganic chemical vapor deposition (MOCVD) process. The MOCVD reactors are located in the R.F. Mitte Building on the Texas State campus. Both have multiple ports for metal and/or dopant species, two reactive gases (ammonia and silane), process gases (H2 and N2), and can attain a process temperature in excess of 1100 °C. The first reactor (donated by TriQuint Semiconductor in 2010) is designed to hold 150 mm diameter wafers while the second reactor (donated by Nitronex, LLC, a subsidiary of M/A-COM Technology Solutions Inc., in 2014) has 100 mm diameter capacity; critical capabilities for commercial collaboration and technology transfer. In that regard, the second reactor has been incorporated into the Advanced Functional Materials Research Service Center which means it is accessible to the Texas State community as well as to external collaborators.
Thermal impedance is a key hindrance to realizing the full performance potential of many semiconductor device technologies. For example, only ~10% of the lab performance demonstrated by GaN RF devices has been realized in commercial products. Coupling wide bandgap devices with CVD diamond is an exciting approach for addressing thermal limitations. To that end, an EV Group wafer bonding system, the EVG501, is installed in the R.F. Mitte Cleanroom, and a CVD diamond reactor designed by Crystallume Inc., is operated by Dr. Piner's research team. With this toolset, Texas State has all the capabilities necessary to pursue this research and close this performance gap.