Bridging the Miscibility Gap in InGaN Alloys

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。技术上的。该项目解决了整个成分范围内高晶体质量的InGaN的外延生长问题。目的是为了更好地了解混溶GaN的性质，并探索能够始终如一地提供单相InGaN薄膜的方法。理论研究表明，界面平行于c轴的层(如a面或m面InGaN)的相分离被显著抑制。因此，该方法是开发MOCVD工艺，通过不同的外延层模板(AlN、GaN和InN)在a平面上生长InGaN外延层。了解生长取向和应变对InGaN混溶带隙的基本影响的研究有望为获得单相器件质量的InGaN外延层提供一种新的途径。然后，这些薄膜将允许研究InGaN在以前无法进入的成分范围内的基本光学和传输性质。关于InxGa1-xN在混溶带隙区域(0.45×0.75)的光学和输运性质的详细研究是不可能的，因为这些InxGa1-xN薄膜的结晶质量通常很低，并且表现出微弱的或可以忽略不计的光致发光。预计将通过这些研究来表征InxGa1-xN在混溶带隙区域的许多重要的物理性质(结构、光学和电学)。非技术性。该项目涉及具有技术相关性的电子/光子材料科学专题领域的基础研究问题。在更完整的合金范围内实现器件质量的InGaN外延层将为许多基于III-氮化物的光电子器件带来显著的好处。InGaN的禁带宽度从0.7 eV扩展到3.4 eV，覆盖了整个太阳光谱。原则上，基于不同In含量的多层InGaN的多结太阳能电池或光电化学电池在捕获穿过电池的不同波长的太阳光方面具有很高的效率。InGaN合金也可能是潜在的重要热电材料，并可能成为开发新一代汽车中直接将热电转换为电能的热电发生器、航天器中的放射性同位素发电机或冷却模块的其他材料的有吸引力的替代材料，以提高微纳传感器网络的效率和寿命。在先前预测的混溶带隙区域获得高质量的InGaN也将极大地促进波长大于550 nm的高效率LED的发展。高效绿色/黄色InGaN LED的成功实现将使通过R-G-B三色芯片集成方法实现白光LED的技术成为可能，为普通照明提供高效光源。富In的InGaN的带隙也可以被设计成与光纤通信波长匹配，大约在1.5um左右。博士后和研究生将积极参与一个具有高度跨学科性质的研究项目，包括最先进的光子材料和结构的外延研究，到先进的材料表征和微/纳米规模的光子/光电子器件原型研究。本科生也将使用惠塔克捐赠基金参与这项研究。教育和外展计划包括与交通大学工程外展中心开展的活动一起，向高中教师和学生团队介绍“纳米光子学”的实践活动。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." Technical. This project addresses the epitaxial growth of high crystalline quality InGaN across the complete composition range. The aim is to gain greater understanding of the properties of the miscibility gap and to explore methods that can consistently provide single phase InGaN films. Theoretical studies suggest that phase separation in layers having the interface oriented parallel to the c-axis (such as a- or m-plane InGaN) is dramatically suppressed. Thus, the approach is to develop MOCVD processes for the growth of InGaN epilayers on a-plane through different epilayer templates (AlN, GaN, and InN). Studies to understand fundamental effects of growth orientation and strain on the miscibility gap in InGaN are expected to lead to a new approach for achieving single phase device quality InGaN epilayers. These films will then allow for studies of fundamental optical and transport properties of InGaN in composition ranges which were previously inaccessible. Detailed studies concerning the optical and transport properties of InxGa1-xN in the miscibility gap region (0.45 x 0.75) have not been possible because these InxGa1-xN films generally have been of very low crystalline quality and exhibit weak or negligible photoluminescence. It is anticipated that many of the important physical properties (structural, optical, and electrical) of InxGa1-xN in the miscibility gap region will be characterized through these studies. Non-Technical. The project addresses fundamental research issues in a topical area of electronic/photonic materials science having technological relevance. The realization of device quality InGaN epilayers over a more complete alloy range would yield significant benefits for many III-nitride based optoelectronic devices. The bandgap of InGaN expands from about 0.7 eV to 3.4 eV, which covers the entire solar spectrum. In principle, a multijunction solar cell or photoelectrochemical cell based on multi-layers of InGaN with different In-contents is highly efficient at capturing different wavelengths of the sunlight passing through the cell. InGaN alloys could also be potentially important thermoelectric (TE) materials and may be an attractive alternative to other materials for the development of TE generators that are able to directly convert heat to electricity in new generation automobiles, radioisotope TE generators in spacecraft or cooling modules for enhanced efficiency and lifetime of micro/nano-scale sensor networks. Attainment of high quality InGaN in the previously predicted miscibility gap region would also significantly benefit the development of high efficiency LEDs with wavelengths longer than 550 nm. The successful attainment of highly efficient green/yellow InGaN LEDs would then enable the technology for white LEDs through the R-G-B three color chip integration approach providing highly efficient light sources for general illumination. The bandgap of In-rich InGaN could also be engineered to match the fiber optic communication wavelength around 1.5 um. Postdoctoral and graduate students will be actively involved in a research program that is highly interdisciplinary in nature including state-of-the-art epitaxial research of photonic materials and structures to advanced materials characterization and micro/nano-scale prototype photonic/optoelectronic device research. Undergraduates will also participate in this research using Whitacre Endowment funds. Plans for education and outreach include the development of hands-on activities to be presented to teams of high school teachers and students on 'Nanophotonics' in conjunction with activities conducted by the Center of Engineering Outreach at TTU.