Low leakage current density (as low as 10/sup -8/ A/cm/sup 2/ at an applied voltage of 5 V) and high breakdown electrical field (larger than 4.5 MV/cm) of the liquid phase chemical-enhanced oxidized GaAs insulating layer enable application to the GaAs MOSFET. The oxide layer is found to be a composite of Ga/sub 2/O/sub 3/, As, and As/sub 2/O/sub 3/. The n-channel depletion mode GaAs MOSFET's are demonstrated and the I-V curves with complete pinch-off and saturation characteristics can be seen. A transconductance larger than 30 mS/mm can be achieved which is even better than that of MESFET's fabricated on the same wafer structure.

A GaAs MOSFET with a liquid phase oxidized gate

We have investigated the oxide growth kinetics of near-room-temperature liquid phase chemical enhanced oxidation on differently oriented and doped GaAs substrates. Oxidation reactions have been studied by analyzing their activation energies and have been found to depend on the bond configuration of crystal planes. Experimental results indicate that the activation energies are independent of the doping of GaAs. The oxidation rates are dopant selective (n−:p+-GaAs∼4:1 at 30 °C under illumination) and sensitive to illumination (without:with illumination∼1:25 at 30 °C for a n+-doped GaAs). In the oxidation reactions, photogenerated holes are found to play an important role. Finally, we have proposed a mechanism based on the band bending and the carrier transport near the oxide-GaAs interface to interpret the experimental observations.

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Effect of crystal orientation and doping on the activation energy for GaAs oxide growth by liquid phase method

The N-channel depletion-mode GaAs MOSFETs with a liquid phase chemical enhanced selective gate oxide grown at low temperature are demonstrated. The proposed selective oxidation method makes the fabrication process of GaAs MOSFETs more reliable and self side-wall passivation possible. The fabricated GaAs MOSFETs exhibit current-voltage characteristics with complete pinch-off and saturation characteristics. The 2 /spl mu/m gate-length MOSFETs with a gate oxide thickness of 35 nm show transconductance larger than 80 mS/mm and maximum drain current density of 380 mA/mm. In addition, microwave characteristics with f/sub T/ of 1.8 GHz and f/sub max/ of 5.2 GHz have been achieved from the 3 /spl mu/m/spl times/60 /spl mu/m GaAs MOSFETs.

GaAs MOSFETs fabrication with a selective liquid phase oxidized gate

Growth of passivating UV/ozone oxides on InP: Correlations between chemical composition and interfacial electrical properties

The gate dielectrics of Ga2O3(As2O3) of the GaAs MOSFET were prepared by a low-cost and low-temperature liquid-phase chemically enhanced oxidation method. The temperature and oxide thickness dependence of gate dielectric films on GaAs MOSFET have been investigated. The leakage current and dielectric breakdown field were both studied. Both gate leakage current density and breakdown electrical field were found to depend on the oxide thickness and operating temperature. The increasing trend in gate leakage current and the decreasing trend in breakdown electrical field were observed upon reducing oxide thickness from 30 to 12 nm and increasing operating temperature from −50°C to 200°C.

Temperature effect on gate leakage currents in gate dielectric films of GaAs MOSFET

A low‐temperature (∼250 °C) high‐pressure oxidation technique is used for the thermal oxidation of gallium arsenide in an ambient of oxygen and water vapor. It is shown that a uniform and chemically stable oxide with high band‐gap energy can be grown on GaAs by this process. The role of water vapor and oxygen is studied in detail to obtain information on the oxidation mechanism. The electrical characteristics and the composition of this oxide are presented to demonstrate its suitability for surface passivation and metal‐oxide–semiconductor devices.

Nandita Basu

Papers

High‐pressure thermal oxidation of n‐GaAs in an atmosphere of oxygen and water vapor