*Review* **Diamond/GaN HEMTs: Where from and Where to?**

**Joana C. Mendes 1,\* , Michael Liehr <sup>2</sup> and Changhui Li <sup>2</sup>**


**\*** Correspondence: joanacatarina.mendes@ua.pt

**Abstract:** Gallium nitride is a wide bandgap semiconductor material with high electric field strength and electron mobility that translate in a tremendous potential for radio-frequency communications and renewable energy generation, amongst other areas. However, due to the particular architecture of GaN high electron mobility transistors, the relatively low thermal conductivity of the material induces the appearance of localized hotspots that degrade the devices performance and compromise their long term reliability. On the search of effective thermal management solutions, the integration of GaN and synthetic diamond with high thermal conductivity and electric breakdown strength shows a tremendous potential. A significant effort has been made in the past few years by both academic and industrial players in the search of a technological process that allows the integration of both materials and the fabrication of high performance and high reliability hybrid devices. Different approaches have been proposed, such as the development of diamond/GaN wafers for further device fabrication or the capping of passivated GaN devices with diamond films. This paper describes in detail the potential and technical challenges of each approach and presents and discusses their advantages and disadvantages.

**Keywords:** diamond; GaN; HEMT; thermal management; GaN-on-diamond; CVD

**Citation:** Mendes, J.C.; Liehr, M.; Li, C. Diamond/GaN HEMTs: Where from and Where to? *Materials* **2022**, *15*, 415. https://doi.org/10.3390/ ma15020415

Academic Editor: Fabrizio Roccaforte

Received: 8 October 2021 Accepted: 30 December 2021 Published: 6 January 2022

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