GOALI: Strained Layer Heterostructures for GaN-on-Si Epitaxy

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Non-technical Description: Gallium nitride is an important semiconductor due to its wide ranging applications in solid-state lighting and power electronics. Pennsylvania State University and Efficient Power Conversion (EPC) Corporation are partnering in this GOALI project to develop materials growth technology to integrate gallium nitride thin films with silicon wafers, which are the standard substrates used for integrated circuit fabrication. The ability to directly combine these two materials would allow flexibility in circuit design for a variety of applications. However, the hexagonal crystal structure of gallium nitride is incompatible with the cubic crystal structure of (100) silicon. This project seeks to overcome these limitations by intentionally introducing strain into the silicon to alter the surface structure and thereby reduce the crystal mismatch. Real-time wafer curvature measurements are used to directly measure strain in the silicon substrate and study dynamic changes in film stress during gallium nitride deposition. Post-growth structural characterization is used to elucidate mechanisms of stress generation and relaxation. The project supports the Ph.D. thesis work of two graduate students at Penn State University who are exposed to issues relevant to process scale-up and manufacturing in a global semiconductor foundry through the collaboration with EPC. Undergraduates and high-school students from underrepresented groups and economically challenged regions of Pennsylvania are participating in the research through summer programs at Penn State University. Technical Description: This GOALI project is on the epitaxial growth of AlGaN/GaN heterostructures on on-axis (100) Si substrates for hybrid power electronics circuits. Strained Si/SiGe virtual substrates are being explored as a route to control the dominant reconstruction of the (100) Si surface and thereby reduce the in-plane rotational misalignment of AlN nuclei. In-situ wafer curvature measurements are used to monitor stress relaxation in the SiGe layers and measure tensile strain in the Si layer at the growth temperature and study its impact on GaN/AlN heteroepitaxy. The effects of n-type dopant chemistry on stress evolution in GaN are also being examined. The project seeks a fundamental understanding of the role of Si surface strain on GaN/AlN epitaxy, which can then be exploited to develop AlGaN/GaN two-dimensional electron gas heterostructures on (100) Si for power devices. The project team has complementary expertise in group III-nitride heteroepitaxy on Si substrates (Penn State University) and process scale-up and commercialization of GaN-on-Si for power field-effect transistors (EPC). In addition, EPC is well positioned to capitalize on hybrid circuit designs that will be enabled by the GaN on (100) Si growth technology developed in this project.