| The structure and chemistry of compound semiconductor surfaces during metalorganic vapor-phase epitaxy have been investigated. In particular, surface roughness, interface structure, and heterogeneous reaction kinetics of the group V precursors were studied. Moreover, the structures of the compound semiconductor surfaces have been examined using scanning tunneling microscopy, x-ray photoemission spectroscopy, and reflectance difference spectroscopy.; The surface roughness of gallium arsenide (001) films changes with the temperature and growth rate. Height-height correlation analysis of scanning tunneling micrographs reveals that the root-mean height difference on the surface follows a power law dependence on lateral separation, i.e., Γ(L) = kLα, up to a critical distance, Lc, after which it remains constant. For layer-by-layer growth, the roughness exponent, α, equals 0.25 ± 0.05, whereas the critical distance increases from 50 to 150 nm as the substrate temperature increases from 825 to 900 K. The roughness exponent jumps to 0.65 ± 0.1 upon transitioning to three-dimensional island growth. By relating the height-height correlation function to the Einstein diffusivity relationship, the activation energy for gallium surface diffusion was estimated: Ed = 1.35 ± 0.1 eV.; Exposing indium phosphide films to 10 mTorr of tertiarybutylarsine below 500°C results in the deposition of a thin indium arsenide layer from 1.5 to 5.0 atomic layers thick (2.3 to 7.5 Å). The surface of this layer remains atomically smooth independent of arsenic exposure time. However, in an overpressure of tertiarybutylarsine at or above 500°C, the arsenic atoms diffuse into the bulk, creating strained InAsP films. These films form three-dimensional island structures to relieve the built-up strain. The activation energy and pre-exponential factor for arsenic diffusion into indium phosphide was found to be: Ed = 1.7 ± 0.2 eV and Do = 2.3 ± 1.0 × 10−7 cm2/s.; The kinetics of phosphine adsorption and phosphorus desorption from gallium phosphide and indium phosphide (001) surfaces have been studied using reflectance difference spectroscopy to monitor the phosphorus coverage in real time. The adsorption and desorption processes follow first-order reactions. The rate parameters were determined by fitting the experimental data to a kinetic model. The initial sticking coefficients of phosphine on GaP (2x4), (1x1), and InP (2x4) surfaces were found to be 730.0·exp(−0.6 ± 0.2(eV)/kT), 1.6·exp(−0.4 ± 0.2(eV)/kT) and 0.0055·exp(−0.1 ± 0.2eV/kT), respectively. The desorption of phosphorus from the GaP (2x1) and (1x1) surfaces was first-order in coverage with rate constants of 5.0 × 1015(s−1)·exp(−2.6 ± 0.2(eV)/kT) and 5.0 × 1015(s−1 )·exp(−2.9 ± 0.4(eV)/kT). The results presented in this thesis illustrate how molecular-scale chemical phenomena affect the evolution of compound semiconductor nanostructures during metalorganic vapor-phase epitaxy. |
