Molecular beam epitaxy and field emission deposition for metal film growth on III–V compound semiconductors—A comparative study

Abstract

Aluminium and gold films were deposited on characterized (001) InP and GaAs surfaces under ultrahigh vacuum conditions in a molecular beam epitaxy (MBE) system both by MBE and by a novel field emission deposition (FED) technique in which ionized clusters were generated by field emission from the molten metal. Films ranging in thickness from a few hundred ångströms to 1 μm were grown by both techniques and were examined in situ by Auger electron spectroscopy and reflection high energy electron diffraction and ex situ by high resolution scanning electron microscopy (SEM), X-ray diffraction and electrical current-voltage measurements of the contacts. These studies revealed a sharp contrast between the structural properties of the films. The aluminium films deposited by MBE on oxygen- and carbon-free ion-bombarded annealed reconstructed (001) surfaces at about 40 °C were mirror smooth and epitaxial with (011) Al parallel to (001) InP, GaAs. However, the aluminium films obtained by FED at the same temperature on similarly prepared surfaces were polycrystalline with a slight preferred orientation. A similar contrast in structural properties was evident for gold deposition. In both techniques the film adhesion was good. The SEM studies indicated that the FED films were formed by accretion of liquid droplets. Current-voltage measurements showed that the metal-semiconductor contacts formed by MBE and FED had greatly reduced barrier heights which may result from the residual effects of ion bombardment and annealing.