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High-temperature stable and smooth gate materials are required for self-aligned GaAs metal-semiconductor field effect transistor devices processing. Furthermore, the high Schottky barrier is beneficial to the GaAs digital logic circuits based on the enhancement mode field effect transistors. We report the high-temperature (up to 900 °C) stable MoAl2.7 Schottky contacts to n-GaAs with enhanced barrier heights from 0.67 to 0.98 V and low values of ideality factors after annealing. The surface of annealed contact is lustrous and smooth. The epitaxial AlxGa1−xAs layer, which induces the enhanced barrier height, at the interface of MoAl2.7/n-GaAs contact, has been clearly identified by the high-resolution cross-sectional transmission electron microscopy.

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The interfacial stability, surface morphology and electrical characteristics of MoAl contacts to n-GaAs have been investigated by using x-ray diffraction, scanning electron microscopy, sheet resistance and current-voltage measurements. The compositions of rf-cosputtered MoAl. films were x = 0.35, 2.7, and 7.0, respectively. The contacts were annealed by rapid thermal processing in the temperature range 500-1000 "C for 20 s. The interfaces of MoA10. 3 5/GaAs and MoA12. 7 /GaAs were stable up to 900 °C, while the interfaces of MoA1 7 .0/GaAs were less stable and reactions occurred above 800 *C. The variations of sheet resistances and the barrier heights of the Schottky diodes as a function of annealing temperatures can be well correlated to the interfacial stability. The MoA1 2 . 7 /n-GaAs diodes exhibited the best stability and were characterized by the highest barrier height (0.98 V) and nearly unit ideality factor (1.11) after annealing at 900 *C. For all thermally stable MoAlx/n-GaAs Schottky diodes, the barrier heights increased with annealing temperature.

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