HEMT technology gains on mm-waves

In a high-electron-mobility transistor (HEMT), a silicon-doped AlGaAs layer grown on top of an undoped GaAs layer brings about the formation, on the GaAs side, of a 150-A thick two-dimensional electron gas layer which moves between doped and undoped material layers and forms the carrier channel to link the device source with the drain. A HEMT device, based on a 0.25-micron gate length geometry and operating at 38 GHz was shown to produce a minimum noise figure of 2.2 dB. When the transistor was cooled to 200 K, the noise figure dropped to 1.3 dB. With power-added efficiency of 26 percent at 30 GHz the HEMT appears to be well suited to space-based systems, where power supplies are at a premium. Tables and graphs illustrating the performance of various HEMT devices are included.