Temperature profiling in AlGaN/GaN HEMTs with nanocrystalline diamond heat spreading layers by Raman spectroscopy

Self-heating (reduction of drain current due to lower carrier mobility caused by increased phonon scattering at high drain fields) in high electron mobility transistors (HEMTs) has been well-documented in the literature. However, attempts to alleviate it have been limited. Heat spreading schemes have involved growth of AlGaN/GaN on single crystal [1] or CVD [2] diamond, or capping of fully-processed HEMTs using nanocrystalline diamond (NCD) [3]. All approaches have suffered from reduced HEMT performance or limited substrate size. Recently, a “diamond-before-gate” approach has been successfully demonstrated to both improve the thermal budget of the process by depositing NCD before the thermally sensitive Schottky gate, and to enable large-area diamond implementation [4]. A cross-section of such a device is shown in Figure 1.