GOALI: Thermal transport in AlGaN alloys: effect of point and structural defects

North Carolina State University, Raleigh NC

Investigators

Abstract

CBET-1336464 PI: Paskova, Tania M. (NCSU) The objective of this GOALI research effort is to perform a systematic study of thermal conductivity of AlGaN alloys in the entire composition range with variable defect density achieved by using hydride vapor phase epitaxy on different substrates and to explore the role of point and structural defects on the thermal transport in these materials. In partnership with Kyma Technologies, our interdisciplinary team of academic PIs seeks to gain understanding of the thermal transport sensitivity to defect present and to develop a proper analytical model applicable to alloy layers with variable ratio of substrate/layer thermal conductivities. Currently, there is a considerable interest in developing compact and highly efficient devices based on III-Nitride materials for variety of electronic and optoelectronic applications. However, the presence of large number of defects reduces the device efficiency, light output and lifetimes while contributing to overheating. Despite their enormous practical importance, the thermal management of AlGaN-based devices is not well developed and the studies of thermal conductivity and their dependences on defects, typically present, are very limited. In order to enhanced our knowledge about that and to accelerate the device development this research project is focused on: (i) growth optimization, aiming to control the defect density by varying growth conditions, substrates, buffers, and layer thickness; (ii) determining the accurate values of thermal conductivity of AlGaN alloys and its dependence on the Al mass fraction, elucidating the effect of alloy scattering; (iii) establishing the thermal conductivity dependencies on both dislocation and point defect densities; (iv) theoretical modeling of thermal conductivity in nitride alloys, aiming to validate or refine the existing models. Variety of techniques is employed for the microstructure characterization, and the 3-omega method is used for the thermal conductivity measurements of the AlGaN materials. The knowledge gained can guide technological developments of highly desired nitride layers and substrates based on AlGaN ternary alloys to enable better thermal management of the device structures, and thus improving their performance and lifetime, being critically important for multiple high-power, high-frequency electronic and high-efficient optoelectronic applications. The PIs of this project are strongly committed to the integration of research and education. The project provides training of graduate students by exposing them to comprehensive, application-driven academic research through curriculum development, guest lectures, seminars and summer internships at Kyma. The project intends to involve and support women and underrepresented minorities, as well as high school students conducting summer science research. Kyma in turn will continue to receive exposure at NCSU through integration of the research topics and results.