Piezoelectric Effects in Misfit-Strained Iii-V Compound Heterostructures

Elasticity and piezoelectricity are anisotropic properties of a crystal. In pseudomorphic strained layers, these properties will depend critically on the orientation of growth relative to the crystallographic orientation. Microscopically, the state of strain modifies the crystal Hamiltonian, changes the optical selection rules, and produces splittings of otherwise degenerate states. Macroscopically, the elastic accommodation of misfit-strain in (hkk) growth oriented heterostructures, unlike the conventional (001) growth axis, induces a homogeneous electric polarization in the strained layer via the piezoelectric effect. Large internal electric fields result, which can approach the dielectric breakdown field. To date, our understanding of the microscopic properties has come from a rich resource of literature on the (001) oriented III-V compounds. This fact is in no small part due to the inherent ease of achieving stoichiometric growth on this surface. Conversely, the achievement of stoichiometric growth on the (111) oriented III-V compounds has not been so successful. By employing vicinal substrates, and with the aid of the in-situ surface analysis in the MBE growth chamber, excellent morphology of GaAs and strained GaInAs on the (111) orientation are demonstrated in this thesis. With this achievement, the macroscopic piezoelectric effect has been demonstrated in a (111) growth axis zincblende heterostructure, for the first time. Misfit-strained (hkk) heterostructures provide an important new class of piezoelectrically active materials for use in designing novel structures with unique electronic and optical properties. The modelling of these properties, the MBE crystal growth of (111) strained III-V compound films, and the first direct experimental evidence of misfit-strain generated electric fields, are the subject of this thesis.