Performance of Al_0.24Ga_0.76As/In_0.22Ga_0.78As double-heterojunction HEMTs with an as deposited and a buried gate

Depletion-mode Al0.24Ga0.76As/In0.22Ga0.78As double-heterojunction high electron mobility transistors (DH-HEMTs) were fabricated with an as deposited gate to compare with those with a buried gate by annealing. Instead of a recessed gate, a buried gate used to control the distance between the gate and channel (and hence the aspect ratio) improves the series resistance. Measured transconductance of 150 mS mm−1 and an open-drain voltage gain of 136 for the DH-HEMT with an as deposited gate are enhanced to 175 mS mm−1 and 160 for the DH-HEMT with a 330 °C annealed gate. Good device linearity is also obtained with a low second harmonic to fundamental ratio of 3.55%. The measured maximums fts (fmaxs) are 13.5, 13.5 and 14.5 (35, 37, and 37.5) GHz for DH-HEMTs with an as deposited gate, and with 280 °C and 330 °C annealed gates, respectively. At a measured frequency of 2.4 GHz, the DH-HEMT with a 330 °C annealed gate exhibits the highest PAE = 44.8% at VDS = 3 V and VGS = −1.0 V and the lowest Fmin = 1.89 dB at VDS = 3 V and ID = 200 mA mm−1.