This thesis describes how a scanning tunnelling microscope (STM) can be utilised for <I>in situ </I>analysis of molecular beam epitaxially grown III-V semiconductors. The initial research required the integration of an STM into an <I>in situ </I>III-V processing facility which included two growth chambers and a focused ion beam (FIB) lithography chamber. By minimising vibrations from the rest of the system, post growth STM observations of GaAs(100) with a vicinal surface showed that the STM produced reliable atomic scale images. This was extended to show how, as the substrate temperature increased from 630°C to 645°C, growth changed from an island growth regime to a step flow regime, thus preserving the vicinal structure. If there is a lattice mismatch in heterostructure growth then misfit dislocations form at the interface. The growth of GaSb on GaAs(100) was studied to determine the effect on surface morphology of a 7% lattice mismatch. It was found that the misfit dislocations propagate with continued growth and terminate at the surface as a screw dislocation, thereby inducing spiral growth. The rms surface roughness resulting from this spiral growth increased with decreasing substrate temperature, however the dislocation density decreased. Photoluminescence (PL) experiments were undertaken to determine whether the surface roughness translates to interface roughness in a single quantum well. A similar lattice mismatch was observed to produce sub-micron coherent islands of InAs on GaAs(100) substrates. The evolution of these islands for given parameters was studied, noting the formation of a wetting layer and the critical thickness (1.6 monolayers) at which island nucleation occurred. These islands were very uniform in width (+/- 10% size variation) yet had two height regimes. PL experiments detected emission at 1.2 eV suggesting that there is structural coherency of the islands which is confining the band energies. The interaction of a 30 keV Ga<SUP>+</SUP> FIB with GaAs(100) was studied for line doses of 1x10<SUP>8</SUP> ions cm<SUP>-2</SUP>. Topographic analysis showed there was little surface damage, however, electrically active defect sites were spatially resolved using the spectroscopic mode of the STM. These sites were found to lie below the conduction band as determined from I-V measurements.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:596957 |
| Date | January 1997 |
| Creators | Brown, S. J. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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