Optically controlled characteristics of III–V Nitride based MM-wave transit-time devices

Extensive simulation experiments are carried out for the first time, to study the photo-irradiation effects on the high frequency characteristics of III-V GaN (Gallium Nitride) based Top-Mounted and Flip-Chip IMPATT oscillators at MM-wave window frequency (140.0 GHz). MM-wave properties of un-illuminated GaN IMPATTs are compared with those of conventional Si, GaAs and InP IMPATTs, under similar operating conditions. Superiority of GaN based IMPATTs at D-band is established. It is found that the un-illuminated GaN IMPATT is capable of delivering a output power of 5.6 W with an efficiency of 23.5% at 145.0 GHz. Frequency up-chirping of 6.0 GHz and a degradation of power output by almost 15.0 % are further observed in case of photo-illuminated FC IMPATT. The study reveals that compared to predominate electron photocurrent in Top-Mounted IMPATT, photo-generated leakage current dominated by hole in Flip-Chip IMPATT has more pronounced effect on the GaN based device as regards the frequency chirping and decrease of negative conductance and total negative resistance per unit area of the device. The inequality in the magnitudes of electron and hole ionization rates in the Wide Band Gap semiconductor have been found to be correlated with the above results. The study reveals that GaN IMPATT is a potential candidate for replacing conventional IMPATTs at high frequency operation. These results are useful for practical realization of optically modulated GaN based high power IMPATTs for application in MM-wave communication systems.