Atomic scale survey of III–V epitaxial interfaces

A novel scanning tunneling microscopy technique is reported, which displays the atomically resolved lattice sites on ultrahigh vacuum cleaved (110) cross sections of epitaxially grown semiconductor multilayers. Voltage selective imaging is used to display either the group III (empty state) sites or the group V (filled state) sites on GaAs–AlGaAs and InP–InGaAsP heterojunctions grown by molecular-beam epitaxy and metalorganic vapor phase epitaxy. The interfaces can be defined to an accuracy of ±1 unit cell. Charge density maps of the group III (Al–Ga) sublattice in AlGaAs and of the group V (As–P) sublattice in InGaAsP are generated for the first time, and these reflect the composition fluctuations on the atomic scale. A tentative assignment is given to the individual Al and Ga sites and the ‘‘roughness’’ of such interfaces on the atomic scale is discussed.