HIGH-ELECTRON-MOBILITY transistors (HEMTs) and heterojunction bipolar transistors (HBTs) have attracted many attentions in high speed and power applications due to the superior transport properties. As compared to AlGaAs pseudomorphic HEMTs (PHEMTs), InGaP-related devices with the following advantages, such as higher band gaps, higher valence-band discontinuity [1], negligible deep-complex (DX) centers [2], excellent etching selectivity between InGaP and GaAs, good thermal stabilities, higher Schottky barrier heights [3], and so on. Particularly, the use of an undoped InGaP insulator takes the advantages of its low DX centers and low reactivity with oxygen [4], [5], which may still suffer from a high gate leakage issue. In order to inhibit the gate leakage issue, increase the power handling capabilities, and improve the breakdown voltages, a MOS structure has been widely investigated. However, there is still a lack of reliable native oxide films growing on InGaP, and very few papers have reported on InGaP/InGaAs MOS-PHEMTs. Over the past few years, an alternative technique named liquid-phase chemical-enhanced oxidation (LPCEO) to growreliable native oxide films on GaAs [6], [7], Si [7], InP [7],
AlGaAs [8], and InGaAs [9] has been reported. This is an easy, low-cost, and low-temperature (30 C–70 C) technique to grow uniform and smooth native oxide films on GaAs-based materials. Moreover, in the liquid-phase oxidation system, neither anodic equipment nor an assisting energy source is needed. According to the preliminary studies of this technique, some issues were addressed [10], [11]. In this work, a thin InGaP native oxide layer prepared by the liquid-phase oxidation as the gate dielectric for InGaP/InGaAs MOS-PHEMT application is demonstrated.
EXPERIMENTAL
The details of the oxidation system were reported earlier in [6] and [7]. Although liquid-phase oxidation on InGaP material has a much slower oxidation rate, less than 10 nm/h, compared with that of the GaAs material, it is still feasible to grow a thin oxide film. The oxidation rate becomes significantly saturated when the oxidation time is longer than an hour, which is measured using a Veeco Instrument DEKTAK and confirmed by scanning electron microscopy (SEM). The oxide film is mostly composed of InPO -like and Ga oxide, which is confirmed by the values of the peak energy and energy separations of X-ray photoelectron spectroscopy (XPS) between main core levels schematically shows the PHEMT structure grown by the metal–organic chemical vapor deposition (MOCVD) on a semi-insulating GaAs substrate. Hall measurement indicates that the electron mobility is 4000 cm /V s and the electron sheet density is cm at room temperature. The device isolation was accomplished by mesa wet etching down to the buffer layer. Ohmic contacts of the Au-Ge-Ni metal were deposited by evaporation and then patterned by lift-off processes, followed by rapid thermal annealing. The depth of gate recess is 110 nm for the reference PHEMT and 100 nm for the MOS-PHEMT. After etching the capping layer and partial Schottky layer, a LPCEO growth solution was used to generate the gate oxide for the MOS-PHEMT at 50 C for 30 min. Finally, the gate electrode was formed with Au. Moreover, the oxide, as illustrated in the figure, also selectively and simultaneously passivated the isolated surface sidewall.
By Edgar Alberto Servita 18.856.338
CAF
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