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A δ-doped In0.425Al0.575As∕In0.425Ga0.575As∕GaAsmetamorphic high electron mobility transistor with an In0.425Ga0.575Aschannel to effectively relieve the impact-ionization effects has been successfully fabricated by the molecular beam epitaxy system. With the designs of an In0.425Ga0.575Aschannel layer and a wide-bangap In0.425Al0.575AsSchottky-contact layer, good carrier confinement, improved breakdown, low output conductance, and high voltage gain with good linearity have been simultaneously achieved. We have also comprehensively investigated the microwave and power performances as a function of VGSand VDS, respectively. Experimentally, the unity-gain cutoff frequency (ft)and the maximum oscillation frequency (fmax)slightly decrease with VDSof above 2V. However, the power gain and the output power increase as VDSincreases from 1 to 5V. Furthermore, the proposed device has also demonstrated good intermodulation distortion characteristics at lower biases, indicating its promise for the large-scale and low-voltage millimeter-wave integrated circuit applications.

A GaAs-based In0.1Al0.25Ga0.65As∕In0.22Ga0.78As∕In0.1Al0.25Ga0.65Ashigh-electron mobility transistor with a quaternary In0.1Al0.25Ga0.65Asstrain-relaxed layer (SR-HEMT) has been fabricated successfully. The lower lattice mismatch between In0.1Al0.25Ga0.65Asand In0.22Ga0.78Asyields high-electron mobility and good carrier confinement. Experimental results indicate that the SR-HEMT exhibits a peak gmof 300mS∕mm, a maximum drain-current density of 576mA∕mm, a high breakdown voltage of 15.9V, a cut-off frequency of 34.6GHz, a maximum oscillation frequency of 55.1GHz, a small-signal power gain of 20dB, and a saturated power of 15.8dBmat 2.4GHzwith the gate dimension of 0.65×100μm2. Furthermore, the SR-HEMT exhibits a temperature-insensitive threshold voltage shift of −0.667mV∕K.