Modelling and performance comparison of optimal AlGaAs/GaAs DMTs and multichannel HEMTs for power amplification

The theoretical characterization, fabrication, and experimental evaluation of two advanced AlGaAs/GaAs power-amplification devices are reported. The first is a doped-channel MIS-like FET (DMT) based on an i-AlGaAs/n-GaAs heterostructure; three designs are shown in diagrams along with graphs of their theoretically predicted and measured output characteristics. The most promising DMT had power density 450 mW/mm, drain efficiency 34 percent, and gain 7 dB at frequency 15 GHz. The second device is the multichannel HEMT power amplifier described by Temcamani et al. (1988). An optimized three-channel HEMT with gate length 500 nm and recess depth 800 nm had surface access resistance 0.34 ohm-mm, saturation current 400 mA/mm, breakdown voltage 18 V, output power 500 mW/mm, gain 8 dB, and power-added efficiency 33 percent at 15 GHz. (T.K.)