The Growth of Unintentional- and Sulphur-Doped Indium Phosphide by Molecular Beam Epitaxy

[摘要] This thesis describes a detailed and systematic investigation of those factors which influence the properties of InP grown by Molecular Beam Epitaxy. The growth of any semiconductor material for device applications requires that the growth process is reproducible, and its capabilities characterised. Both the published literature and the analysis of epitaxial InP grown at the start of this programme indicated that neither of these criteria were satisfied for the MBE growth of InP. A detailed assessment of InP grown using an existing MBE chamber and involving Photoluminescence (PL), Secondary Ion Mass Spectroscopy (SIMS) and residual carrier concentration profiles is presented. This assessment and particularly the results of the SIMS analysis was able to identify a significant concentration of impurities in the epitaxial layers and, more importantly, enabled the source of these impurities to be determined. Further experiments which involved deliberate changes in the growth conditions (growth temperature, growth rate, and V:III flux ratio) during the growth of single epitaxial layers are reported. The results from the SIMS and residual carrier concentration profiles of these layers are shown to identify limitations imposed by the construction of the existing growth chamber. Such limitations were overcome by the design and commissioning of a second growth chamber. The significant improvement in both the purity and the growth control achieved using this second chamber enabled a detailed and systematic analysis of the influence of growth conditions on the properties of epitaxial InP to be undertaken. The results of PL, SIMS, Hall and residual carrier profiles of an extensive series of layers are presented. From these results the purity and properties of unintentionally doped InP grown from solid sources are shown to be dominated by a single extrinsic impurity. The origin of this impurity is unequivocally identified as the red phosphorus source material and it is believed that this impurity is responsible for the universal n-type behaviour of InP grown by solid source MBE to date. The role of Calcium shown by SIMS to be present in the epitaxial InP is also discussed. The intentional doping of InP using Sulphur from an electrochemical source has been characterised. No evidence of Sulphur diffusion has been observed but a previously unsuspected temperature sensitivity of the electrochemical cell has been identified. The use of Sulphur as an n-type dopant in the MBE growth of InP is shown to be an attractive alternative to Si, especially when the improved morphology at high doping concentrations and the reduced dependence of incorporation rate on the group V flux are considered. In the light of the limitation on the purity of InP grown by MBE from solid sources which is identified in this study, a detailed assessment of the routes available for reducing this impurity concentration is presented. Results from a comparison of different batches of nominally high purity red phosphorus source material reveal a variation in impurity concentration of over 2 orders of magnitude, while optimisation of the growth conditions is shown only to be viable at reduced growth temperatures. However, it is clear that using the appropriate phosphorus source high purity (ND+NA < 5x10e14cm-3) InP with reproducible properties can be obtained using molecular beam growth techniques.

[发布机构] University:University of Glasgow

[关键词] Materials science, Condensed matter physics