InAlAs/InGaAs/InP MODFETIs with short gatelength suffer from a high output conductance, Go, and low breakdown voltage. In addition, the devices often show a kink effect in the I-V curve. We show for the first time, by numerical calculations, that weak impact ionization occurs in the In 53Ga 4 7 A~ channel under relatively moderace fields. The high Go and the kink are mainly caused by mechanisms associated with weak impact ionization. our calculations also show that the low breakdown voltage of the device is caused by the drain-source breakdown in the InGaAs channel. The occurrence of impact ionization process in the channel was experimentally verified by detection of photons from the device under moderate drain bias.
We report the design, fabrication and excellent linear power performance at mm-wave frequency range of a modified InGaAs channel pseudomorphic MODFET structure. This structure replaced the conventional n + AlGaAs carrier supply layer by n + GaAs carrier supply layer. g., was improved at high gate bias due to the superior carrier transport property of n + GaAs compared to that of n + AlGaAs.This g., improvement results in relatively flat and broad fT and f.. .x versus gate bias curves.Consequently, record high P ldB of 0.68 W Imm with G'dB of 12.9 dB and power-added efficiency of 45% were achieved at 25 GHz on a 0.33 x 120 /lm2 device.This linear power performance, to our knowledge, is the best reported in the literature for mm-wave InGaAs pseudomorphic MODFETs of this gate length. The Pout at maximum-power-added-efficiency point was as high as 0.81 W Imm with 10.9 dB gain and power added-efficiency of 59%.
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