Nucleation and strain relaxation at the InAs/GaAs(100) heterojunction

The techniques of molecular beam epitaxy have been used to investigate the nucleation and growth of InAs heteroepitaxial thin films lattice mismatched to GaAs(100) substrates. Our previous observations have been that optimum structural and electrical properties are obtained only if the heteroepitaxial nucleation sequence is carried out under experimental conditions leading to the indium stabilized (4×2) InAs(100) surface reconstruction. In this work, reflection electron diffraction, Auger electron spectroscopy and x-ray diffraction have been used to determine the InAs(100) surface phase diagram. The InAs/GaAs(100) heterojunction grown by MBE is abrupt and smooth surfaces are obtained only under indium stabilized nucleation conditions. A residual compressive strain at the crystalline interface occurs which is somewhat relieved by a tetragonal distortion in the direction normal to the film plane. Results of investigations by reflection electron diffraction show that the nucleation of InAs/GaAs(100) occurs via island formation and coalescence, and that the initial in-plane lattice constant observed for InAs at 520 °C is 5.9 Å. The unstrained lattice constant is obtained only after ∼2000 Å of growth under indium stabilized conditions. If the InAs bond length in the vicinity of the interface is estimated from the experimental data, the agreement between our previously measured (via XPS) value for the heterojunction valence-band discontinuity and the calculation based on Harrison’s model (LCAO) is improved.