High thermal conductivity and ultrahigh thermal boundary conductance of homoepitaxial AlN thin films

Gustavo Alvarez-Escalante,Debdeep Jena,Huili Grace Xing,Ryan Page,Renjiu Hu,Zhiting Tian

doi:10.1063/5.0078155

Abstract

Wurtzite aluminum nitride (AlN) has attracted increasing attention for high-power and high-temperature operations due to its high piezoelectricity, ultrawide-bandgap, and large thermal conductivity k. The k of epitaxially grown AlN on foreign substrates has been investigated; however, no thermal studies have been conducted on homoepitaxially grown AlN. In this study, the thickness dependent k and thermal boundary conductance G of homoepitaxial AlN thin films were systematically studied using the optical pump–probe method of frequency-domain thermoreflectance. Our results show that k increases with the thickness and k values are among the highest reported for film thicknesses of 200 nm, 500 nm, and 1 μm, with values of 71.95, 152.04, and 195.71 W/(mK), respectively. Our first-principles calculations show good agreement with our measured data. Remarkably, the G between the epilayer and the substrate reported high values of 328, 477, 1180, and 2590 MW/(m2K) for sample thicknesses of 200 nm, 500 nm, 1 μm, and 3 μm, respectively. The high k and ultrahigh G of homoepitaxially grown AlN are very promising for efficient heat dissipation, which helps in device design and has advanced applications in micro-electromechanical systems, ultraviolet photonics, and high-power electronics.

Highlights

The high k and ultrahigh G of homoepitaxially grown aluminum nitride (AlN) are very promising for efficient heat dissipation, which helps in device design and has advanced applications in micro-electromechanical systems, ultraviolet photonics, and high-power electronics
We investigated the cross-plane thermal conductivity k and thermal boundary conductance G of thin homoepitaxially grown AlN films by implementing the optical pump–probe method of frequency-domain thermoreflectance (FDTR)
The samples were prepared with an aluminum-assisted surface cleaning method using molecular beam epitaxy, which results in AlN films with unprecedentedly high crystalline quality

Summary

Introduction

Proper control and mitigation of heat is vital for high-power and high-temperature operation. Wide-bandgap (WBG) semiconductors, such as gallium nitride (GaN), and ultrawide-bandgap (UWBG) semiconductors, such as gallium oxide (Ga2O3) and aluminum nitride (AlN), have gained attention due to their potential integration in deep-ultraviolet photonics and in power and radio frequency (RF) electronics. The high-power density sustaining hundreds to thousands of volts causes power devices to exhibit high operating temperatures due to Joule heating, potentially diminishing the device performance and lifetime. Among UWBG semiconductors, the combination of high piezoelectricity, ultrawide bandgap [∼6.1 eV, almost as twice as silicon carbide (SiC) and GaN], and one of the largest thermal conductivities k of 340 W/(mK) makes AlN a leading material for advancing applications in micro-electromechanical systems (MEMS), ultraviolet photonics, and high-power electronics needed to sustain their viability at high temperatures and harsh environments. AlN stands out for its high dielectric strength, ease of deposition and processing (involving low temperatures and nontoxic precursors), and its potential for integration with CMOS devices, MEMS contour mode filters, and film bulk-wave acoustic filters.3Since Slack’s pioneering work on k of AlN crystals, there has been a follow-up work on k of AlN single crystals and AlN epilayers on a foreign substrate. no thermal studies have been conducted on homoepitaxially grown AlN. Wide-bandgap (WBG) semiconductors, such as gallium nitride (GaN), and ultrawide-bandgap (UWBG) semiconductors, such as gallium oxide (Ga2O3) and aluminum nitride (AlN), have gained attention due to their potential integration in deep-ultraviolet photonics and in power and radio frequency (RF) electronics.. Among UWBG semiconductors, the combination of high piezoelectricity, ultrawide bandgap [∼6.1 eV, almost as twice as silicon carbide (SiC) and GaN], and one of the largest thermal conductivities k of 340 W/(mK) makes AlN a leading material for advancing applications in micro-electromechanical systems (MEMS), ultraviolet photonics, and high-power electronics needed to sustain their viability at high temperatures and harsh environments.. High k and ultrahigh G values were observed, highlighting the importance of using homoepitaxy for efficient thermal management of AlN-based devices

Methods

Results

Conclusion