Wide Band Gap Semiconductors for Flexible Power Applications

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This discovery grant proposal describes a comprehensive research and education program of wide-band gap semiconductors for power applications in diversified mediums. Two semiconductors of focus are gallium nitride (GaN) and zinc oxide (ZnO), both which offer very distinct advantages over silicon (Si) over their respective application space. The development and commercialization of these material systems are the underlying motivation for this work. The GaN device offers performance advantages on traditional single crystal substrates that currently cannot be realized with Si or silicon carbide (SiC). The envisioned goal is seeing the discrete MOSFET component to its completion for eventual implementation in large-scale power systems. The immediate advantages of GaN is the potential higher speed operation. Power management systems operating at higher frequency allow the use of smaller passive components with higher efficiency thus leading to a positive environmental impact. ***The ZnO device does not offer the raw performance advantage of the GaN device because of the lower inherent mobility. However, its potential application space is much wider due to its strong transistor performance with locally deposited semiconductors. We first achieved this using a source-gated FET (SGT) with comparable performance to state-of-the-art and commercially available indium gallium zinc oxide (IGZO) thin-film transistors (TFTs). Recently, we also built a novel transistor architecture that can be described fully as a "thin-film bipolar tunneling emitter junction transistor" (TJT). The first iteration of the TJT fully built below 150 °C outperforms all known TFTs with respect to power management. The ZnO approachs are currently being tested for integration into biomedical applications. This benchmark achievement, will enable high current and power applications for flexible and printable devices previously not possible. ***Students are held to one common theme that enables exploration into a broad variety of applications within this multidisciplinary program. Students participate in theoretical and fabricated device design with the aid of industry standard design and simulation packages. Within the successful program proposed here, theory is used alongside measurements of fabricated devices to determine the impact of new material systems on electronic systems. Currently, as part of this program we will continue to explore a number of circuits in power (GaN) and biomedical (ZnO) applications with this unique device architecture. Further research enables a wide variety of applications in the area of energy harvesting. The approach mimics the process in high-tech manufacturing development. In this process, students are immersed in solid state devices, nano physics, material science and advanced circuit design principles to address the needs of today's high-tech engineering market place. **