GOALI: Thermal Transport by Phonons in Device-Grade Nitride Nanostructures

PI：Jonathan A.MalenProposal编号：1133394氮化物半导体是用于固态照明、选择高频/电力电子和未来多结光伏的发光二极管(LED)的核心。这些技术商业化的进展需要高电流密度，以迫使改进的热管理来降低运行温度。虽然封装策略改善了散热，但初步数据显示，该器件本身具有很大的热阻。器件级氮化铝(AlN)和氮化镓(GaN)薄膜的热导率(K)测量表明，100 nm氮化铝(AlN)和100 nm氮化镓(GaN)薄膜的k值非常低。电子显微镜图像表明，这些减少是由工业增长过程中固有的结构缺陷造成的。到目前为止，还没有一个明确的科学解释。智力上的优点：这个目标建议的目标是研究由GaN、AlN和InGaN(InGaN)薄膜组成的氮化物半导体异质结(~100 nm)的热输运。卡内基梅隆大学(CMU)的一个由学术研究人员组成的跨学科团队将与Kyma Technologies合作，研究氮化物纳米结构中声子热传输的性质。有缺陷的薄膜和界面将被考虑，它们之间的距离与主体声子平均自由程相称。悬而未决的科学问题包括：器件-基板界面和氮化物层之间的热界电阻(R)是多少？高度缺陷的晶体能否以类似于无序材料的方式传递热量？生长技术如何影响薄膜的热性能？为了回答这些问题，研究将集中在一种常见的基极结构上，该结构包括具有AlN成核层的蓝宝石、碳化硅或GaN衬底，然后是InGaN缓冲层。具体的研究包括：(1)衬底对AlN成核层的R和K的影响；(2)生长工艺对AlN成核层的K和R的影响；(3)In浓度对InGaN缓冲层的K和R的影响。氮化物的受控生长和缺陷密度和结构的成像(Davis，Paskova)将被用于分子动力学模拟的原子结构信息(麦高伊)。模拟结果将与使用名为频域热反射系数(Malen)的泵浦探测光学方法对这些样品进行的k和R的直接测量进行比较。广泛的影响：与Kyma Technologies的合作使这项研究可以直接转移到工业中，在工业中，氮化物设备具有革新照明和超越硅基电子产品的潜力。Kyma认识到将热管理整合到氮化物器件结构中的迫切需要。获得Kyma的生长技术将使任何发现产生深远的影响，这些技术代表着氮化物的未来。与Cree公司和海军研究实验室在氮化物科学和技术方面的持续合作进一步支持了这项研究的需要。教育活动将通过课程开发、客座讲座和研讨会以及Kyma的暑期实习，让学生接触到行业驱动的学术研究。继而，Kyma将通过将研究主题和结果整合到学术私人投资机构教授的课程中，获得在CMU的曝光率。将为女工程师协会高中日、匹兹堡公立学校和基督教女青年会TechGyrls计划制定一个基于LED的外展活动“照明：下一代”。

PI: Jonathan A. MalenProposal Number: 1133394Nitride-based semiconductors are a centerpiece of light-emitting diodes (LEDs) for solid-state lighting, select high-frequency/power electronics, and future multi-junction photovoltaics. Progress towards commercialization of these technologies demands high current densities that compel improved thermal management to lower operating temperatures. While packaging strategies improve heat dissipation, preliminary data show that the device itself has a large thermal resistance. Thermal conductivity (k) measurements on device-grade nitride films show very low values of k in thin 100nm aluminum nitride (AlN) and 100nm gallium nitride (GaN) layers. Electron microscopy images suggest that these reductions are caused by structural imperfections inherent to industrial growth processes. As yet, a clear scientific explanation is lacking.Intellectual Merit: The objective of this GOALI proposal is to study thermal transport in nitride semiconductor heterostructures composed of GaN, AlN, and indium gallium nitride (InGaN) thin films (~100nm), fabricated by scalable growth processes. An interdisciplinary team of academic investigators at Carnegie Mellon University (CMU), in partnership with Kyma Technologies, will study the nature of thermal transport by phonons in nitride nanostructures. Defective films and interfaces separated by distances commensurate to the bulk phonon mean free paths will be considered. Open scientific questions include: What is the thermal boundary resistance (R) at the device-substrate interface and between nitride layers? Can highly defective crystals transport heat in a manner similar to disordered materials? How do growth techniques impact thin film thermal properties?To answer these questions, the investigation will focus on a common base structure that includes a sapphire, silicon carbide, or GaN substrate with an AlN nucleation layer followed by an InGaN buffer layer. Specific inquiries include: (i) the effect of the substrate on R and k of the AlN nucleation layer, (ii) the effect of growth technique on k and R of the AlN nucleation layer, and (iii) the effect of indium concentration on k and R of the InGaN buffer layer. Controlled growth of nitrides and imaging of defect density and structure (Davis, Paskova) will be used to inform the atomic structure for molecular dynamics simulations (McGaughey). Simulation results will be compared with direct measurements of k and R on these samples, made using a pump-probe optical method called Frequency Domain Thermoreflectance (Malen).Broader Impact: Partnership with Kyma Technologies makes this research directly transferable to industry, where nitride devices have the potential to revolutionize lighting and to outperform silicon-based electronics. Kyma recognizes the critical need for incorporating thermal-management into the nitride device structure. Access to Kyma's growth technologies, which represent the future of nitrides, will make any discoveries far-reaching. Continuing collaborations on nitride science and technology with the Cree Corporation and the Naval Research Laboratory further support the need for this research. The educational activities will expose students to industry-driven academic research through curriculum development, guest lectures and seminars, and summer internships at Kyma. Kyma, in turn, will receive exposure at CMU through integration of the research topics and results within courses taught by the academic PIs. An LED-based outreach activity "Lighting: The Next Generation" will be developed for the Society of Women Engineers High School Day, Pittsburgh public schools, and the YWCA TechGyrls program.