Control of GaAs Schottky barrier height using a thin nonstoichiometric GaAs interface layer grown by low-temperature molecular beam epitaxy

Abstract

This article proposes a novel Schottky junction structure on (100) GaAs, which has a thin nonstoichiometric GaAs interface layer. A 10- to 20-Å-thick As-rich or Ga-rich interface layer was grown by low-temperature molecular beam epitaxy at 200 °C, and placed at the metal-GaAs junction interface. Independent of metal work functions, the interlayer insertion causes a wide variation in barrier heights in the range of 0.5–1.0 eV on n-GaAs, and 0.4–0.9 eV on p-GaAs. The barrier height variation is attributed to a strong Fermi-level pinning controlled by stoichiometric defect levels in the interlayer. The levels were characterized by isothermal capacitance transient spectroscopy of a metal-insulator-semiconductor structure having a nonstoichiometric interlayer between an aluminum nitride insulating film and GaAs. High concentrations of defect levels were confirmed around 0.4 eV below the conduction band edge in the As-rich interlayer and around 0.3 eV above the valence band edge in the Ga-rich interlayer. An anomalous transient response, exhibiting what appears to be low activation energy and a small capture cross section, was found in addition to the normal response. This anomaly can be explained by variable range hopping conduction via defect sites along the interlayer. In diodes with dense interfacial defects, this relaxation process for trapped carriers is considered to proceed faster than the usual emission to the conduction or valence band, at low temperatures.