Session: 04-26-01: Nanoengineered, Nano Modified, Hierarchical, Multi-Scale Materials and Structures

Paper Number: 174085

Nanograined Multi-Phase Gallium Nitride Through Ultrafast Melt-Quenching: Formation Mechanism and Ultralow Lattice Thermal Conductivity 

Gallium nitride (GaN) has emerged as a pivotal semiconductor material due to its exceptional electronic and optical properties, which surpass those of conventional semiconductors, particularly silicon. With a wide direct bandgap of approximately 3.4 eV, high electron mobility, and excellent thermal and chemical stability, GaN is uniquely suited for high-power-density, high-temperature, and high-frequency applications. These attributes enable GaN-based devices to operate efficiently under extreme conditions that typically challenge or incapacitate silicon-based technologies. As a result, GaN has become indispensable in advancing power electronics, optoelectronics, radio-frequency devices, and emerging quantum technologies.

The microstructural evolution and thermal transport properties of GaN subjected to ultrafast quenching are investigated using large-scale molecular dynamics simulations. Varying cooling rates result in distinct nucleation pathways and the formation of defect-rich microstructures comprising both wurtzite (WZ) and zincblende (ZB) phases, including unique superlattice-like arrangements. Structurally, GaN crystallizes predominantly in two closely related phases: the thermodynamically stable phase WZ and the metastable ZB phase. Both phases exhibit tetrahedral coordination, where each gallium atom is bonded to four nitrogen atoms and vice versa. Despite their structural similarities, subtle differences in stacking sequences and lattice symmetries lead to distinct physical properties. The defects discussed in this study include twins, stacking faults, and dislocations. Moreover, different nucleation cores have formed during the quenching process, significantly influencing the final microstructure. The cohesive energies of WZ and ZB GaN are −4.529 eV/atom and −4.524 eV/atom, respectively, highlighting their energetic proximity. The WZ structure can be viewed as a derivative of the ZB structure via a sliding transformation of the (111) planes along the [111] direction. This close structural relationship facilitates the formation of coherent interfaces, enabling the design of novel dual-phase GaN nanostructures. Such coherent WZ/ZB interfaces, frequently observed in our simulations, are key to preserving thermal transport across phase boundaries. The results presented here provide a comprehensive atomistic picture of how ultrafast solidification processes can be harnessed to manipulate GaN’s microstructure and, consequently, tailor its thermal performance. This work contributes critical insights for the development of GaN-based devices that must operate reliably in extreme environments. Therefore, quenched GaN exhibits ultralow thermal conductivity, with reductions up to 99% compared to pristine GaN, primarily due to phonon scattering at grain and phase boundaries. Notably, coherent WZ/ZB interfaces maintain high thermal conductance owing to efficient phonon mode matching. These findings provide atomistic insights into engineering heat conduction in GaN through the controlled design and processing of microstructures.

Presenting Author: Mehrab Lotfpour University of Nevada Reno

Presenting Author Biography: My name is Mehrab Lotfpour, a fourth-year PhD student. I'm working on computational materials science, focusing on molecular dynamics simulation of materials behavior.

Authors:

Mehrab Lotfpour University of Nevada Reno
Haoran Cui University of Nevada Reno
Nolan Hagen University of Nevada Reno
Milad Nasiri University of Nevada Reno
Theodore Maranets University of Nevada Reno
Yan Wang University of Nevada Reno
Lei Cao University of Nevada Reno