Molecular-beam epitaxial growth of NiAl on GaAs(001)

Abstract

High-quality, single-crystal overlayers of NiAl that create a Schottky barrier height of 0.90 eV have been grown on semi-insulating GaAs(001) by molecular-beam epitaxy and characterized by high-energy resolution x-ray photoelectron spectroscopy, low-energy electron diffraction, and high-energy x-ray photoelectron diffraction. Thin Al interlayers were grown between the NiAl and the substrate in order to test the possibility that an ultrathin AlxGa1−xAs layer of higher band gap than the substrate forms at the interface and is the cause of the high barrier height. It has been found that such a layer does indeed form when the Al prelayer is deposited near room temperature and annealed at 500 °C, or if the deposition is carried out at a substrate temperature of 500 °C. Moreover, the presence of this prelayer correlates with the appearance of a high barrier height at the interface. Virtually identical results are obtained when layers of Ni and Al are deposited sequentially at room temperature and then annealed at 500 °C to alloy and recrystallize the metal. The realization of a 0.9-eV barrier height occurs independently of the removal of any excess As from the interface, which according to the advanced unified defect model, is thought to cause the high barrier height by virtue of a change in the balance of antisite defects.