Characterization of indium phosphide and indium gallium arsenic phosphide grown by helium-plasma-assisted GSMBE

Abstract

<p>This thesis involved the characterization of InP and InGaAsP grown by He-plasma-assisted gas source molecular beam epitaxy. Samples were typically grown under standard GSMBE conditions, in terms of growth rate and substrate temperature, except for the presence of a low energy helium plasma generated from an electron-cyclotron resonance source. These materials exhibit increased resistivity and faster optical response times with respect to standard materials grown without the plasma. The unusual properties are believed to be caused by the impact of the plasma particles during growth. Samples were characterized under various doping and anneal conditions using Hall effect measurements, temperature-dependent resistivity studies, positron annihilation spectroscopy, photoluminescence and SIMS analysis. Undoped He-InP was weakly n-type as-grown, with a carrier concentration much lower than that of standard InP, suggesting that electron traps were present. On anneal, the carrier concentration decreased further, implying that donor-like defects had been removed. The sample doped with 3 × 1017 cm-3 Be was also n-type; the Be was found to be compensated by donor-like defects. Positron annihilation measurements indicated the presence of single and divacancy defects, which enlarged upon anneal. The characterization of the quaternary constituted the core of the experimental work. He-InGaAsP exhibited the wane trends as the binary He-InP. The undoped and Si-doped samples exhibited low carrier concentrations, indicating the presence of electron traps. Annealing removed these electron traps. The samples doped with <2 × 1018 cm-3 Be were weakly n-type as-grown, but became p-type on anneal, suggesting the removal of donor-like compensating defects. Samples doped with >2 × 10 18 cm-3 Be were p-type as grown, but the hole concentration was lower than expected. As for the He-InP, positron annihilation spectroscopy indicated the presence of neutral or negatively-charged open volume defects that increased in size on anneal. None of the He-InGaAsP samples exhibited photoluminescence until annealed at temperatures of ∼600°C. To estimate the energy levels and concentrations of the defects responsible for the unusual properties of the quaternary, a Fermi-Dirac model was fitted to the Hall effect data. Two donor-like and two acceptor-like levels were identified.</p>