Bridging the Miscibility Gap in InGaN Alloys

“这项奖励是根据2009年美国复苏和再投资法案（公法111-5）资助的。”技术。该项目致力于在整个组成范围内实现高结晶质量InGaN的外延生长。目的是为了更好地了解混相间隙的性质，并探索能够持续提供单相InGaN薄膜的方法。理论研究表明，在具有平行于c轴的界面层（如-或m平面InGaN）中，相分离被显著抑制。因此，该方法是开发MOCVD工艺，通过不同的脱膜模板（AlN， GaN和InN）在平面上生长InGaN脱膜。了解生长取向和应变对InGaN中混相间隙的基本影响的研究有望为实现单相器件质量的InGaN薄膜提供新的方法。这些薄膜将允许在组成范围内研究InGaN的基本光学和输运性质，这是以前无法达到的。由于这些InxGa1-xN薄膜通常具有非常低的晶体质量，并且表现出微弱或可忽略的光致发光，因此不可能详细研究InxGa1-xN在混相间隙区域（0.45 x 0.75）的光学和输运性质。预计这些研究将对混相隙区InxGa1-xN的许多重要物理性质（结构、光学和电学）进行表征。非技术。本项目旨在解决电子/光子材料科学中具有技术相关性的主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脱膜将为许多iii -氮化物基光电器件带来显着的好处。InGaN的带隙从0.7 eV扩大到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通过电池的不同波长的阳光方面效率很高。InGaN合金也可能是潜在的重要热电（TE）材料，并且可能是其他材料的有吸引力的替代品，用于开发能够在新一代汽车中直接将热转化为电的热电发生器，航天器中的放射性同位素TE发生器或冷却模块，以提高微/纳米级传感器网络的效率和寿命。在先前预测的混相间隙区域获得高质量的InGaN也将大大有利于波长长于550nm的高效led的发展。成功实现高效的绿色/黄色InGaN led将使白光led技术通过R-G-B三色芯片集成方法为一般照明提供高效光源。富铟InGaN的带隙也可以设计成与1.5 um左右的光纤通信波长相匹配。博士后和研究生将积极参与高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，先进材料表征和微/纳米尺度的原型光子/光电器件研究。本科生也将使用惠塔克捐赠基金参与这项研究。教育和推广计划包括开发实践活动，向高中教师和学生团队展示“纳米光子学”，并与TTU工程推广中心开展的活动相结合。

"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.