Ballistic Thermal Transport at Sub‐10 nm Laser‐Induced Hot Spots in GaN Crystal

Abstract

Ballistic thermal transport at nanoscale hotspots will greatly reduce the performance of a Gallium nitride (GaN) device when its characteristic length reaches the nanometer scale. In this work, the authors develop a tip‐enhanced Raman thermometry approach to study ballistic thermal transport within the range of 10 nm in GaN, simultaneously achieving laser heating and measuring the local temperature. The Raman results show that the temperature increase from an Au‐coated tip‐focused hotspot up to two times higher (40 K) than that in a bare tip‐focused region (20 K). To further investigate the possible mechanisms behind this temperature difference, the authors perform electromagnetic simulations to generate a highly focused heating field, and observe a highly localized optical penetration, within a range of 10 nm. The phonon mean free path (MFP) of the GaN substrate can thus be determined by comparing the numerical simulation results with the experimentally measured temperature increase which is in good agreement with the average MFP weighted by the mode‐specific thermal conductivity, as calculated from first‐principles simulations. The results demonstrate that the phonon MFP of a material can be rapidly predicted through a combination of experiments and simulations, which can find wide application in the thermal management of GaN‐based electronics.

Gallium Nitride Based Electrode for High‐Temperature Supercapacitors

“…It obviously manifested that the cycling stability of porous GaN-based heterostructure dramatically ameliorated by incorporating porous GaN conductive substrate. [38] The improvement of cycling performance in the initial stage is attributed to electrode activation. [39] In general, the superior electrochemistry performance of the GaN/NCO-2 heterostructure originates from the synergistic effect of porous GaN and NCO NSs.…”

A brief review on the recent development of phonon engineering and manipulation at nanoscales

“…On the experimental side, advances in thermometry, such as the 3ω method [33,34], T-type method [35,36], H-type method [37,38], Raman thermometry [39][40][41][42][43][44][45][46], time-domain and frequency-domain thermoreflectance (TDTR and FDTR) [4,[47][48][49][50][51][52][53], have enabled the characterization of heat transport processes and thermal properties on smaller spatial and temporal scales. Raman thermometry is a non-contact optical temperature measurement technology that utilizes Raman scattering.…”

“…In 2019, Fan et al [43] pointed out that dualwavelength flash Raman method can be used for the characterization of anisotropic thermal properties. The emergence of tip-enhanced Raman scattering has significantly improved the spatial resolution of Raman thermometry [44,45], allowing for measurements and imaging at sub-10 nm scales [47,48]. This advanced technique can be utilized to explore ballistic thermal transport at nanoscale hotspots [48].…”

“…The emergence of tip-enhanced Raman scattering has significantly improved the spatial resolution of Raman thermometry [44,45], allowing for measurements and imaging at sub-10 nm scales [47,48]. This advanced technique can be utilized to explore ballistic thermal transport at nanoscale hotspots [48]. TDTR and FDTR are also non-contact measurement technologies for thermal properties, which measure the temperature change of nanomaterials through the change of surface reflectance of metal films on nanomaterials.…”