We report on the role of bismuth as a surfactant in the growth of InAs quantum dots (QDs) on GaAs (001) by metal organic vapour phase epitaxy. Atomic force microscopy investigations have shown that bismuth suppresses coalescence of the InAs QDs and advances a more uniform size distribution. The photoluminescence spectra of the Bi-assisted grown QDs present several narrow peaks from the ground and the excited state transitions with full width at half maximum (FWHM) as narrow as 25 meV (both at 77 and 300 K). Due to such low values of the FWHM we were able to observe up to two well resolved excited state transitions in the photovoltage spectra measured by an electrolyte cell technique. The lowest ground transition energies observed were 0.93 eV at 77 K and 0.875 eV at 300 K (emission wavelength 1.46 µm). So using Bi-assisted growth it is possible to cover the 1.3 µm band, which is important for optoelectronic applications in the InAs/GaAs material system. Formation of such `deep' QDs without misfit dislocations was explained by the formation of a graded-composition transient InGaAs alloy layer at the GaAs/InAs hetero-interface as a result of diffusion intermixing of the components. The proposed mechanism for the effect of Bi on the QDs' morphology is that Bi decreases the surface mobility of the In atoms on the growing surface, preventing the coalescence of the QDs. Because of its rather large covalent radius (compared with that of As), Bi is not incorporated into the QDs' material segregating on the growing surface.

The possibility of controlling the photoluminescence (PL) intensity and its temperature dependence by means of in-growth and postgrowth technological procedures has been demonstrated for InAs∕GaAs self-assembled quantum dots (QDs) embedded in an InGaAs quantum well (QW). The improvement of the QD emission at room temperature (RT), achieved due to a treatment with tetrachloromethane used during the growth, is explained by the reduction of the point defect concentration in the capping layer. It is shown that the PL quenching at RT appears again if the samples are irradiated with protons, above a certain dose. These findings are accounted for by the variations in the quasi-Fermi level position of the minority carriers, which are related to the concentration of trapping centers in the GaAs matrix and have been calculated using a photocarrier statistical model including both radiative and nonradiative recombination channels. By taking into consideration the temperature dependent distribution of the majority and minority carriers between the QDs, embedding QW and GaAs barriers, our calculated results for the PL intensity reproduce very well the experimentally observed trends.

We developed high quality 2-inch GaAs/Ge/Si (100) epitaxial substrates, which may be used instead of GaAs monolithic substrates for fabrication of solar cells, photodetectors, LEDs, lasers, etc. A 200–300 nm Ge buffer layer was grown on Si substrates using the HW-CVD technique at 300°C, a tantalum strip heated to 1400°C was used as the “hotwire”. The MOCVD method was used to grow a 1 μ GaAs layer on a Ge buffer. The TDD in the GaAs layers did not exceed (1–2)∙105 cm-2 and the surface RMS roughness value was under 1 nm.

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