15 GHz GaN Hi–Lo IMPATT Diodes With Pulsed Peak Power of 25.5 W

The p+–n–n−–n+ structure, known as Hi–Lo structure, was investigated in gallium nitride (GaN) single-drift-region (SDR) impact ionization avalanche transit-time (IMPATT) diodes to improve the output power and efficiency. The 15 GHz GaN Hi-Lo IMPATT diode was designed according to the Scharfetter and Gummel model under realistic conditions, suppressing the tunneling current (<10−4 cm2) and breakdown voltage (< 400 V). Even in such conditions, the calculated efficiency was higher than that of the p+–n abrupt junction structure and the improvement of RF characteristics was expected. The fabricated GaN Hi–Lo IMPATT diodes showed a clear avalanche breakdown and a pulsed microwave oscillation in the frequency range from 15 to 17 GHz. The maximum peak output power of 25.5 W and the efficiency of 2% were achieved, showing the highest values on microwave band GaN IMPATT diodes, and we confirmed that the Hi–Lo structure is effective for the high-power and high-efficiency operation of GaN IMPATT diodes.