The T-gate stem height of InAlAs/InGaAs InP-based high electron mobility transistor (HEMT) is increased from 165 nm to 250 nm. The influences of increasing the gate stem height on the direct current (DC) and radio frequency (RF) performances of device are investigated. A 120-nm-long gate, 250-nm-high gate stem device exhibits a higher threshold voltage (V th) of 60 mV than a 120-nm-long gate devices with a short gate stem, caused by more Pt distributions on the gate foot edges of the high Ti/Pt/Au gate. The Pt distribution in Schottky contact metal is found to increase with the gate stem height or the gate length increasing, and thus enhancing the Schottky barrier height and expanding the gate length, which can be due to the increased internal tensile stress of Pt. The more Pt distributions for the high gate stem device also lead to more obvious Pt sinking, which reduces the distance between the gate and the InGaAs channel so that the transconductance (g m) of the high gate stem device is 70 mS/mm larger than that of the short stem device. As for the RF performances, the gate extrinsic parasitic capacitance decreases and the intrinsic transconductance increases after the gate stem height has been increased, so the RF performances of device are obviously improved. The high gate stem device yields a maximum f t of 270 GHz and f max of 460 GHz, while the short gate stem device has a maximum f t of 240 GHz and the f max of 370 GHz.

in this paper, we introduce novel surface treatments of UV/Ozone and TMAH to solve the surface problem of gate recess of InAlAs/InGaAs InP-based HEMTs. The problem of nonstoichiometric surface of InP etch stopper layer was found to be the result of donor-like surface defects brought by HF damage, bringing troubles like kink effect, high gate leakage current and deteriorated noise performance. Through the method of surface treatments, the InAlAs/InGaAs InP-based HEMTs exhibit excellent DC performances, demonstrating a low gate leakage currents of 10^-8 A/um, a peak transconductance of 1100mS/mm, an improved subthreshold swing of 92.5mV/decade at Vds = 1.0V, and a positive threshold voltage shift of Vth = 300 mV. The ft of 260GHz and fmax of 440GHz were hardly influenced by the surface treatments while the noise performances were improved obviously. Two orders of magnitude smaller input noise spectral density shows the method of surface treatment can effectively reduce the surface defects and significantly improve the surface of gate recess of InAlAs/InGaAs InP-based HEMTs.

Heterogeneous integrated InP high electron mobility transistors (HEMTs) on quartz wafers are fabricated successfully by using a reverse-grown InP epitaxial structure and benzocyclobutene (BCB) bonding technology. The channel of the new device is In0.7Ga0.3As, and the gate length is 100 nm. A maximum extrinsic transconductance g m,max of 855.5 mS/mm and a maximum drain current of 536.5 mA/mm are obtained. The current gain cutoff frequency is as high as 262 GHz and the maximum oscillation frequency reaches 288 GHz. In addition, a small signal equivalent circuit model of heterogeneous integration of InP HEMTs on quartz wafer is built to characterize device performance.