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

氮化镓（GaN）是高温、大功率、高频金属氧化物半导体场效应晶体管（mosfet）的最佳候选材料之一。用氮化镓制成的功率器件有潜力提供比用硅所能达到的开关速度高500倍以上的优点。实现该技术的关键部分是开发具有低缺陷和优先迁移特性的坚固氧化物，可以生产增强模式晶体管而不是耗尽模式晶体管。然而，通过栅极氧化物的栅漏电流和介电/氮化镓界面上大量的界面态导致的费米级钉钉限制了它们在此类应用中的应用。目前，没有一种材料能够满足氮化镓的所有氧化物要求。此外，氧化物必须满足各种要求，如大的带隙，以提高击穿电压。提出的研究计划的长期目标是为GaN大功率MOSFET器件开发新型栅极氧化物，用于功率转换应用，如混合动力汽车和太阳能电池阵列。这项长期研究将与Douglas Barlage教授合作进行，Douglas Barlage教授是阿尔伯塔大学电气和计算机工程专业的器件物理学家和GaN技术专家。短期目标是对GaN上栅极氧化物的原子层沉积（ALD）生长有一个基本的了解，并开发新的GaN栅极氧化物和结构。研究的重点将是研究高k金属氧化物以纳米层合材料的形式组合，以引入GaN MOS结构栅极材料所需的所有特性，如大带隙材料和大介电常数。通过ALD沉积氧化物将受益于该技术的许多优点，包括对厚度的良好控制，低温沉积，无针孔和高保形薄膜。本文将探讨这些氧化物的化学性质、微观结构和化学计量学对原子层沉积薄膜电性能的影响。

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.