# Interface-Driven Electrothermal Degradation in GaN-on-Diamond High Electron Mobility Transistors

## TL;DR

This paper shows that interface quality, not just material properties, is key to managing heat in GaN-on-diamond transistors.

## Contribution

The study reveals interface thermal resistance has a stronger impact than substrate conductivity in GaN-on-diamond HEMTs.

## Key findings

- Increasing thermal boundary layer thickness or decreasing its conductivity worsens device performance.
- Interface thermal boundary resistance dominates over substrate thermal conductivity in determining device behavior.
- Optimized interfaces can make low-conductivity substrates outperform high-conductivity ones with poor interfaces.

## Abstract

Diamond is an attractive substrate candidate for GaN high-electron-mobility transistors (HEMT) to enhance heat dissipation due to its exceptional thermal conductivity. However, the thermal boundary resistance (TBR) at the GaN–diamond interface poses a significant bottleneck to heat transport, exacerbating self-heating and limiting device performance. In this work, TCAD simulations were employed to systematically investigate the effects of thermal boundary layer (TBL) thickness (dTBL) and thermal conductivity (κTBL) on the electrothermal behavior of GaN-on-diamond HEMTs. Results show that increasing the TBL thickness (5–20 nm) or decreasing its thermal conductivity (0.1–1.0 W/(m·K)) leads to elevated hotspot temperatures and degraded electron mobility, resulting in a notable deterioration of I–V characteristics. The nonlinear dependence of device performance on κTBL is attributed to Fourier’s law, where heat flux is inversely proportional to thermal resistance. Furthermore, the co-analysis of substrate thermal conductivity and interfacial quality reveals that interface TBR has a more dominant impact on device behavior than substrate conductivity. Remarkably, devices with low thermal conductivity substrates and optimized interfaces can outperform those with high-conductivity substrates but poor interfacial conditions. These findings underscore the critical importance of interface engineering in thermal management of GaN–diamond HEMTs and provide a theoretical foundation for future work on phonon transport and defect-controlled thermal interfaces.