The relationship between low-frequency dispersion and the intermodulation performance of AlGaAs/GaAs HBTs has been demonstrated for thc first time. The theoretical analysis and experimenf a1 results indicate that IM3 wil I depend strongly on the frequency spacing (Af = j 2 -f i ) in the two-tone measurement.

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Excellent noise (0.41 dB minimum noise figure with 11.5 dB associated gain at 18 GHz) and linearity (third order intercept point of 37.6 dBm at 42.5 mW DC power giving a linearity figure of merit (LFOM) of 137) have been obtained for a InAlAsAnGaAs metamorphic HEMT on a GaAs substrate. These devices have been used to design and fabricate microwave and millimeter wave amplifiers. Amplifier results will be presented.

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MHEMT devices with 60% indium channels gave transport characteristics similar to An excellent 0.61 dB minimum noise figure and 11.8 dB associated gain at 26 GHz, have been obtained for a InP-based HEMTs with room-temperature sheet InAlAsAnGaAs metamorphic HEMT on a GaAs densities and mobilities of 3 . 2~1 0 '~ cm-2 and substrate. 10,500 cm2N.s. Atomic force microscopy Low-noise amplifiers show under 1.8 dB noise figure showed an RMS surface roughness of 11 W. The with gain greater than 24 dB across 27 -32 GHz. excellent channel transport properties and surface morphology are indicative of the high