Results, Potential and Challenges of High Power GaN-Based Transistors

Abstract

The fabrication of AlGaN/GaN high electron mobility transistors (HEMTs) employs strong spontaneous and piezoelectric polarization. The material was grown by OMVPE at 1050 °C and 75 Torr. The Hall measurements yielded ≈︂1 × 1013/cm2 electron sheet density, with 1200 to 1600 cm2/Vs electron mobility for 300 Å Al0.3Ga0.7N/GaN on sapphire at 300 K. The process steps for mesa isolation, Ohmic and Schottky contacts are presented. The frequency response and drain–source breakdown voltage have been determined experimentally. The average electron transit velocity, determined from cut-off frequency, is 1.2 × 107 cm/s, and the breakdown electric field is estimated to be 3 MV/cm. On sapphire substrates, large periphery devices yielded 1.8 W/mm at 78% power-added efficiency and small periphery devices yielded 3.3 W/mm at 36% power-added efficiency at 4 GHz. Performance limitations due to electron trapping during HEMT operation are included. Predictions of >20 W/mm microwave output power are presented for these devices on SiC substrates.