Thermal Characterization of Buried Interfaces in Multilayer Heterostructures via TDTR with Periodic Waveform Analysis

TL;DR

This paper introduces a frequency-tunable periodic waveform analysis TDTR technique for depth-resolved thermal measurements of buried interfaces in multilayer heterostructures, revealing insights into phonon transport and thermal bottlenecks.

Contribution

The work develops PWA-TDTR, enabling non-destructive, depth-specific thermal characterization of buried interfaces with broadband frequency probing and sensitivity-guided fitting.

Findings

Buried Ga2O3/SiC interface shows weak phonon transmission due to acoustic mismatch.

Transition layers in GaN/Si act as phonon-impedance gradients redistributing heat.

GaN/diamond boundary remains the main thermal bottleneck despite diamond's high conductivity.

Abstract

Accurate evaluation of buried thermal interfaces is vital for understanding and optimizing heat dissipation in wide- and ultra-wide-bandgap (WBG/UWBG) semiconductor devices. Conventional time-domain thermoreflectance (TDTR) typically probes only near-surface transport due to its restricted modulation frequency range. Here, we employ a frequency-tunable periodic waveform analysis TDTR (PWA-TDTR) technique to perform depth-resolved thermal measurements on three representative systems: epitaxial {\epsilon}-Ga2O3/SiC, GaN/Si, and mechanically bonded GaN/diamond. By combining broadband multi-frequency probing with sensitivity-guided joint fitting, we quantitively determine interfacial thermal conductance, layer-specific thermal conductivity, and volumetric heat capacity, without requiring destructive sample preparation. The results reveal that the buried Ga2O3/SiC interface exhibits weak phonon transmission due to acoustic mismatch; the transition layers in GaN/Si act as phonon-impedance gradients that redistribute heat flux; and the GaN/diamond boundary remains the dominant thermal bottleneck despite diamond's ultrahigh bulk conductivity. These findings demonstrate that the modulation frequency in PWA-TDTR functions as a tunable probe of depth-dependent phonon transport, directly linking frequency-domain thermal response to interfacial energy transmission. Overall, this work positions PWA-TDTR as a versatile platform for investigating buried nonmetal-nonmetal interfaces in next-generation high-power and optoelectronic materials.