3 GHz RF measurements of AlGaN/GaN transistors transferred from silicon substrates onto single crystalline diamond

The integration of AlGaN/GaN thin film transistors onto diamond substrates enables the efficient dissipation of device heat, thus providing a boost in performance and reliability of current high-frequency GaN power amplifiers. In this paper, we show 3 GHz load-pull measurements of GaN transistors on silicon (Si) and single crystalline diamond (SCD) as fabricated by our recently presented direct low-temperature bond process. After the transfer onto SCD, the efficiency and output power are increased by 15%, which is explained by a calculated temperature difference of ∼100 K. In addition, the temperature between individual gate fingers is reduced such that the output power density (Pout) is independent of the amount of fingers. A drawback of our GaN epilayer is identified in the huge thermal resistance of the buffer layer so that the heat spreading performance of our technology is significantly impaired. Nevertheless, we demonstrate a large GaN-on-diamond output power of 14.4 W at a Pout of 8.0 W/mm.