Hydrogen in the Ultrawide Bandgap Semiconductor beta-Ga203

Lehigh University, Bethlehem PA

Investigators

Abstract

Nontechnical description: Semiconductors with bandgaps larger than those of gallium nitride and silicon carbide are emerging as a new class of ultra-wide-bandgap electronic materials for high-power, deep-ultraviolet, and extreme-environment applications. Despite the tremendous potential of the ultra-wide-bandgap semiconductors for device applications, with orders of magnitude improvement over devices made from more conventional semiconductors, the fundamental underlying mechanisms of their electrical properties are poorly understood. This project is focused particularly on gallium oxide, a semiconducting oxide with a bandgap of 4.9 eV, that is an attractive candidate for high-power devices. In spite of its promising applications, gallium oxide remains underexplored, and the defects and impurities that affect its electrical properties remain controversial, opening exciting opportunities for fundamental research that impacts technology. Hydrogen impurities and their chemical reactions strongly affect the electronic properties of gallium oxide and are of particular interest in this project. Experimental studies of defects and impurities in gallium oxide provide an excellent opportunity for students to solve important problems in materials physics, igniting excitement that leads to a successful career in science and engineering. The recruiting of students from groups that are under-represented in physics is expanded in the present project. Technical description: This project is focused on experimental investigation of the hydrogen impurity in gallium oxide, a semiconducting oxide with an ultra-wide bandgap of 4.9 eV. Hydrogen is an important impurity in oxide semiconductors where it can give rise to n-type conductivity and can also compensate deep acceptors. While there are a few theoretical predictions for the properties of hydrogen in gallium oxide, the research in this area is in its infancy. Gallium oxide promises to show new behaviors and to reveal new defect physics. The research involves a complementary set of experimental methods, aiming to determine how hydrogen impurities affect the electronic properties of gallium oxide and to test the theoretical predictions. For example, the combination of vibrational spectroscopy with free-carrier absorption provides a powerful strategy for studying hydrogen centers that relates specific defects with the conductivity they cause. Furthermore, the interactions of hydrogen with other defects such as gallium vacancy are investigated to probe the passivation of these deep acceptors by hydrogen. The addition of Raman scattering and photo-thermal ionization spectroscopies provide access to additional types of hydrogen species that do not have infrared absorption lines (such as molecular hydrogen) but that, nonetheless, play an important role in defect reactions that affect the conductivity of gallium oxide and its thermal stability. The expected outcome of this research is fundamental understanding of which hydrogen centers are n-type dopants in gallium oxide and investigates how hydrogen interacts with other defects that also affect electronic properties. The fundamental science of these defects and their reactions needs to be understood so that the conductivity of gallium oxide can be reliably controlled and engineered. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.