The crystal structure of aluminum layers grown by molecular beam epitaxy (MBE) on GaAs(100) was studied using high resolution transmission electron microscopy. We obtained cross-sectional images with nearly atomic resolution of the lattice structure at Al-GaAs interfaces. GaAs epitaxial layers were grown at 585 °C and cooled in the ultrahigh vacuum MBE growth chamber prior to aluminum deposition. After the desired substrate temperature had been achieved, aluminum was immediately deposited onto arsenic-rich surfaces at a rate of 1000 Å h−1.
Aluminum layers deposited onto substrates at 80 °C exhibit an Al(110)/GaAs(100) epitaxial relationship along an abrupt interface. In some regions of the interface we observed isolated arsenic crystallites which were epitaxial with the GaAs substrate. The current-voltage (I-V) and capacitance-voltage (C–V) characteristics of this material are well behaved. Barrier heights of 0.79 eV and ideality factors of 1.04 were determined from room temperature I–V measurements.
For aluminum deposited onto GaAs substrates at 400 °C, evidence of twodimensional nucleation and growth was observed. The resulting pyramid-shaped aluminum crystallites had facets along crystallographic planes. Two epitaxial relationships were observed: Al(100)/GaAs(100) and Al(110)/GaAs(100). We observed 12 Å steps along the Al(100)–GaAs(100) interface. C–V and scanning electron microscopy measurements indicate that the individual aluminum crystallites are electrically and physically separated.