Most electronic devices are made using silicon, but silicon is not suitable for high-temperature and high-power applications that are needed for many applications in the military (e.g., all electric ships), the electrical distribution grid, etc. Other semiconductors, notably gallium nitride (GaN) and silicon carbide (SiC) are more suitable, but devices fabricated using materials degrade under operating conditions. Atomic-scale defects such as impurities or missing atoms are responsible. Such defects are often rendered benign by hydrogen atoms that are bound to the defects. Under operating conditions, "hot electrons" can kick the hydrogens off these defects. Much progress has been achieved in identifying the pertinent defects, but device-design engineers need modeling software that can predict the lifetime of devices. The Principal Investigators have extensive experience in the device reliability and degradation area. Pantelides and Zhang recently developed a theory for the calculation of the rates of defect activation by hot electrons, while Pantelides and Schrimpf have been working on the identification of defects through electrical measurements and quantum mechanical calculations, developing simple engineering-level models. The objective of this proposal is to fully implement the newly-developed theory for the rates of hot-electron defect activation, to perform pertinent calculations, and combine them with available and new electrical data on real devices in order to develop more sophisticated engineering-level models for hot-electron degradation of power devices. The proposed research is also relevant to the degradation of light-emitting diodes (LEDs) and solar cells. Engineering-level models will be made available to the engineering community and software developers. Students and post-docs will be trained on the bridge area between physics and electrical engineering. An annual workshop for high-school teachers will make them aware of the new developments and their significance. We will also participate in the NSF-funded Tennessee Louis Stokes Alliance for Minority Participation (TLSAMP) by funding one minority undergraduate every summer to participate in our research program.
High-electron-mobility transistors (HEMTs) based on wide-gap materials such as GaN hold great promise for high-power, high-temperature applications, but their use is currently limited by reliability issues. Device-reliability modeling is currently done by phenomenological models that rely primarily on correlations between device failure and device parameters. Modeling based on physical phenomena re-quires knowledge of the underlying physical processes. In recent work by the lead-PI and collaborators, parameter-free quantum-mechanical calculations were combined with electrical stress data to demonstrate that hot-electron degradation of III-V high electron mobility transistors (HEMTs) is caused by either the release of H from specific defects or by a reconfiguration of specific impurities. A simple engineering-level model was developed to fit stress data and predict long-term degradation under operating conditions. The model relies on sophisticated Monte-Carlo solutions of the Boltzmann equation in the real device to get electron densities in space and energy, but uses a crude step function for the capture cross section for hydrogen release. The Principal Investigators have had extensive experience in these areas. Pantelides and Zhang recently developed a theory for the calculation of inelastic scattering cross sections of hot electrons by defects, while Pantelides and Schrimpf have worked on the identification of defects through electrical measurements and quantum mechanical calculations, developing simple engineering-level models. The objective of this proposal is to fully implement the newly-developed theory of cross sections and perform pertinent calculations that can be used to model available and new experimental data on device degradation. The objective will be to develop accurate, validated, engineering-level models to describe and predict short term and long-term hot-electron-induced device degradation. The results will also be useful for understanding and modeling the role of defects in the performance and degradation of solar cells and light-emitting diodes.
