Abstract
A composite-channel metamorphic high electron mobility transistor (MHEMT) was developed for low noise high linearity application. The MHEMT was grown by molecular beam epitaxy (MBE) on GaAs substrates with InAlAs graded buffer. The composite-channel layers in the MHEMT include a top In/sup 0.55/Ga/sup 0.45/As layer, a middle In/sup 0.67/Ga/sup 0.33/As layer, and a bottom In/sup 0.55/Ga/sup 0.45/As layer. The design of this structure provides better electron confinement in the channel with less impact ionization as compared to conventional dual delta doped MHEMTs. This results in devices with higher linearity and drain to gate voltage as compared to the conventional metamorphic HEMTs. The 0.25/spl times/160/spl mu/m/sub 2/ device with the novel channel structure exhibits a maximum frequency of oscillation f/sup max/ of 290 GHz and a current gain cut-off frequency f/sup t/ of 110 GHz. The noise figure of the device at 6 GHz is 0.23db and an associated gain was 15.06dB. The IP3 of the device at 6 GHz is 18.67dBm. The composite channel metamorphic HEMT shows great potential for high linearity and low noise application at high frequencies.
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