Large-signal microwave performance of GaN-based NDR diode oscillators

The GaN material parameters relevant to the negative differential resistanc e (NDR) devices are discussed, and their physical models based on the theor etical predictions and experimental device characteristics are introduced. Gunn diode design criteria were applied to design the GaN NDR diodes. A hig her electrical strength of the GaN allowed operation with higher doping (si milar to 10(17) cm(-3)) and at a higher bias (90 V for a 3 mu m thick diode ). The transient hydrodynamic simulations were used to carry out the harmon ic power analysis of the GaN NDR diode oscillators in order to evaluate the ir large-signal microwave characteristics. The GaAs Gunn diode oscillators were also simulated for a comparison and verification purposes. The depende nce of the oscillation frequency and output power on the GaN NDR diode desi gn and operating conditions are reported. It was found that, due to the hig her electron velocities and reduced time constants, GaN NDR diodes offered twice the frequency capability of the GaAs Gunn diodes (87 GHz vs. 40 GHz), while their output power density was 2 x 10(5) W/cm(2) compared with simil ar to 10(3) W/cm(2) for the GaAs devices. The reported improvements in the microwave performance are supported by the high value of the GaN Pf (2)Z fi gure of merit, which is 50-100 times higher than the GaAs, indicating a str ong potential of the GaN for the microwave signal generation. (C) 2000 Else vier Science Ltd. All rights reserved.