Power Saturation Characteristics of GaAs/AlGaAs High Electron Mobility Transistors

High electron mobility transistors (HEMTs) employing both single and quadruple GaAs/AIGaAs heterojunctions have been fabricated and tested for power at 10 GHz. The multiple heterojunction layer, with a two-dimensional electron gas (2-DEG) sheet carrier density of 3.2 x 10/sup12/ cm^-2 significantly higher current capability (as required for microwave power devices) than the conventional structure where the 2-DEG density is limited to <= 10¹² cm^-2. HEMTs with gate dimensions of 0.5 µm x 200 µm were mounted in X-band FET packages for rf evaluation. The QHJ HEMTs yielded a saturated power of 21 dBm (0.63 W/mm), small signal gain of 14.5 dB, power added efficiency of 39%, and third order IMD product of -19 dBc at saturation. The corresponding figures for the SHJ HEMTs were 18 dBm (0.32 W/mm), 15 dB, 43% and -14 dBc, respectively. These are the highest power densities yet reported for a HEMT.