Performance dependence of InGaP/InGaAs/GaAs pHEMTs on gate metallization

Abstract

The performance of InGaP-based pHEMT's as a function of gate metallization is examined for Mo/Au, Ti/Au, and Pt/Au gates. DC and microwave performance of pHEMT's with 0.7-m gate lengths is evaluated. Transconductance, threshold voltage, f t f t f t , and f max f max f max are found to depend strongly on gate metallization. High-speed performance is achieved, with f t f t f t of 41.3 GHz and f max f max f max of 101 GHz using Mo/Au gates. The difference in performance between devices with different gate metallizations is postulated to be due to a combination of the difference in Schottky barrier heights and different gate-to-channel spacings due to penetration of the gate metal into the InGaP barrier layer.

Gate length scaling in high performance InGaP/InGaAs/GaAs pHEMTs

“…The uncertainty in permittivity arises from an 8% uncertainty in the thickness of the epitaxial layers. If this is coupled with a decrease in gate-to-channel spacing of approximately 50 Å caused by the Pt gate-sinking effect as has been previously demonstrated on this heterostructure [3], the estimate for shifts to . Within a simplified device model,…”

“…Device isolation was accomplished using selective wet chemical mesa etching, and alloyed AuGe/Ni/Au ohmic contacts with contact resistances of 0.08-0.1 -mm were used. The details of the fabrication processing were similar to those described previously [3], except for gate lithography. To achieve tight control of submicron gate lengths for this study, electron-beam lithography in a three-layer PMMA/P(MMA-MAA) resist stack was used to define gates ranging in length from 1.0-0.2 m with mushroom-shaped cross-sections.…”

DC and RF characteristics of E-mode Ga/sub 0.51/In/sub 0.49/P-In/sub 0.15/Ga/sub 0.85/As pseudomorphic HEMTs

“…When compared with present AlGaAs E-mode HEMTs, this prototype device has a large off-current at a gate-source voltage of V. The off-current may be reduced to a much lower level by replacing Ti/Au with Pt/Au as the gate metal. This is because the threshold voltage can be increased by about 0.28 V [3]. Further optimization of the device structure, such as reducing GaInP thickness and/or -doping, should be done as well to overcome this problem.…”

“…E-mode AlGaAs-InGaAs pHEMTs which exhibit high-power density and large-voltage swing have been reported [2]. Ga In P, which is lattice-matched to GaAs, is believed to be a good alternative to AlGaAs because of its advantages for high-power and low-noise applications due to its large bandgap and the absence of negatively charged DX centers [3]. In addition, Ga In P-GaAs material system has many other advantages: high etching selectivity between Ga In P and GaAs [4], high uniformity [5], high reliability [6], low microwave noise [7], low noise [8], and low frequency dispersion [5].…”

“…In addition, Ga In P-GaAs material system has many other advantages: high etching selectivity between Ga In P and GaAs [4], high uniformity [5], high reliability [6], low microwave noise [7], low noise [8], and low frequency dispersion [5]. Although depletion-mode GaInP-InGaAs pHEMTs have exhibited good electrical performance [3], [7]- [9], there is no reported electrical performance of E-mode GaInP-InGaAs pHEMTs as far as we know. Therefore, in this paper, we would like to study the E-mode Ga In P-In Ga As pHEMTs for RF applications.…”