Optically Modulated III–V Nitride-Based Top-Mounted and Flip-Chip IMPATT Oscillators at Terahertz Regime: Studies on the Shift of Avalanche Transit Time Phase Delay Due to Photogenerated Carriers

Extensive simulation experiments are carried out to study the effects of optical illumination on the terahertz (>1.0 THz) characteristics of GaN-based IMPact Avalanche Transit Time (ATT) (IMPATT) oscillator. The shift of ATT phase delay, due to photogenerated carriers, in the top-mounted (TM) and flip-chip (FC) IMPATTs is also studied through a modified simulation scheme, for the first time. The study reveals that, compared to predominant electron photocurrent in TM IMPATT, hole-dominated photoleakage current in FC IMPATT is more important in modulating the high-frequency characteristics of the GaN-based terahertz device. Optically illuminated FC IMPATT shows more pronounced shift of avalanche phase delay, frequency chirping, as well as a decrease of negative conductance and total negative resistance of the device. The inequality in the magnitudes of electron and hole ionization rates in GaN has been found to be correlated with the aforementioned results.