Fundamental understanding and development of novel high dielectric constant ALD gate oxides on gallium nitride substrates for MOSFET power conversion applications

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Gallium Nitride (GaN) is one of the best candidates for high-temperature, high-power, and high-frequency metal-oxide-semiconductor field-effect transistors (MOSFETs). Power devices made with GaN have the potential to offer a switching speed with a figure of merit more than 500 times greater than that achievable in silicon. The critical component to enable this technology is the development of a robust oxide with low defects and preferential mobility properties that can produce an enhancement mode transistor rather than a depletion mode transistor. However, gate leakage current through the gate oxide and Fermi-level pinning due to large number of interface states at dielectric/GaN interface limit their usage in such applications. Currently, no single material has the ability to cover all the oxide requirements for GaN. Moreover, the oxides must fulfill various requirements such as a large band gap to increase the breakdown voltage. The long term objective of the proposed research program is to develop novel gate oxides for GaN high power MOSFET devices for power conversion applications such as hybrid cars and solar cell arrays. The long term research will take place in collaboration with Professor Douglas Barlage, a device physicist and expert in GaN technology, in Electrical and Computer Engineering at the University of Alberta. The shorter term objectives are to develop a fundamental understanding of the atomic layer deposition (ALD) growth of gate oxides on GaN, and to develop novel GaN gate oxides and structures. The main focus will be to investigate the combinations of high-k metal oxides in the form of nanolaminates to introduce all the required properties, such as large bandgap materials and large dielectric constant, to the gate material of GaN MOS structure. The oxides will be deposited by ALD to benefit from the many advantages of this technique, including excellent control on thickness, deposition at low temperatures, pinhole-free, and highly conformal thin films. The effect of chemistry, microstructure, and stoichiometry of these oxides on the electrical properties of atomic layer deposited films will be explored.