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Abstract: Vertically coupled quantum wires (QWRs) have been made by alternately stacking nominally 3.6nm thick In0.53Ga0.47As self-organized QWR layers and 1nm thick In0.52Al0.48As barrier layers on (221)A-oriented InP substrates by molecular beam epitaxy. The surface of In0.53Ga0.47As QWR layers was corrugated at an amplitude of 1.1nm and period of 27nm, and lateral confinement potential is induced by their thickness modulation. The wavelength of photoluminescence (PL) from the stacked QWRs at 15K becomes longer from 1220 to 1327nm with increasing total number of stacked QWR layers, N SL, from 1 to 9, while PL full-width at half-maximum is reduced from 22 to 8.6meV. The PL intensity with the polarization parallel to the wire direction, I ∥, is 1.30 times larger than that with the normal polarization, I ⊥, when . The PL intensity ratio, I ∥/I ⊥, reaches as large as 4 when , indicating successful control of relative strength between vertical confinement and lateral confinement of carriers. The value of I ∥/I ⊥ obtained for the stacked QWRs with is the same value as cylindrical QWRs have. The results indicate that effectively cylindrical QWRs with the best uniformity and 1.3μm range emission were realized by stacking of self-organized QWR layers. [Copyright &y& Elsevier]

Abstract: Using a newly developed envelope function approximation model that includes interface effects, several InAs/GaSb type-II superlattices (SL) for the 4μm (around 310meV) detection threshold were designed. The model predicts that a given threshold can be obtained with progressively thinner SL periods and the thinner designs can have higher mobility and longer Auger lifetime over the thicker designs. The proposed SL structures were grown by molecular-beam epitaxy. The band gaps of SLs determined by low-temperature photoluminescence (PL) remained constant PL peak energy around 340–320meV with distinctively different designs in the period range from 50.2 to 21.2Å. Correlation between SL material quality and the full-width at half-maximum (FWHM) of the luminescence peak were made. In situ annealing after SL growth improved surface morphologies and the FWHM of the emission peak for the annealed SL samples were slightly narrower than those of non-annealed SLs. [Copyright &y& Elsevier]

Abstract: GaInNAs/GaAs quantum wells grown by molecular beam epitaxy under different arsenic pressures have been studied using photoluminescence (PL), X-ray diffraction (XRD) and secondary-ion mass spectrometry (SIMS). The best optical properties are achieved with the V/III beam equivalent pressure ratio (V/IIIBEP) of 10. The PL emission wavelength remains unchanged for 8⩽V/IIIBEP⩽12, suggesting that within this range neither the alloy composition nor the nitrogen sticking coefficient is changed. For the lower and higher V/IIIBEP ratios the PL wavelength is red-shifted or blue-shifted, respectively. The XRD results indicate that the nitrogen incorporation into the group-V sub-lattice is enhanced at low As pressures and reduced at high As pressures. The PL behaviour can thus be understood as a competition between As and N adatoms in occupying anion lattice sites. [Copyright &y& Elsevier]

We present a detailed analysis of the Ga coverage and of the post-growth annealing effects on the optical properties of very-low-density self-assembled GaAs/AlGaAs quantum dots grown by modified droplet epitaxy. Through theoretical calculation of the QD electronic states, including thermally activated Al–Ga interdiffusion processes, we were able to relate our spectroscopic observations to QD structural properties. [Copyright &y& Elsevier]

We have overgrown GaAs (0 0 1) substrates, patterned with dense square arrays of round-shaped nanometer-sized holes and trenches with stacked InAs quantum dots (QDs). Different periods of square hole arrays were overgrown at the same time and we observe a strong dependence of the evolving surface morphology on the period of the pre-pattern. QD pairs are observed only for large periods, whereas predominately single QDs form on patterns with smaller periods. We are able to assign the photoluminescence (PL) emission to specific QD layers and correlate the observed PL spectra of these QD arrays with the surface morphology. Furthermore, a comparison of the PL emission between conventionally grown and laterally ordered QDs reveals a comparable optical intensity of the ordered QDs. [Copyright &y& Elsevier]

The optimum growth conditions and strain balancing processes have been studied using molecular beam epitaxy (MBE) grown 51 A˚ InAs/40 A˚ GaSb type-II superlattices (SLs) designed to have cut-off wavelength of 10 μm. The most dominant factor in reducing the defect level in the SL structure was buffer growth temperature evidenced by transmission electron microscopy. In the study of the strain balancing process, the SLs could be lattice matched to the GaSb substrate by increasing the thickness of the InSb interfaces (IFs) from a nominal value of 1.0 to 1.4 ML, however, the structural quality degraded dramatically when the thickness of IFs reached beyond ∼1.0 ML. By optimizing the growth condition and MBE shutter sequences, micron thick InAs/GaSb SLs with a reduced lattice mismatch were routinely obtained with the full-width half-maximum of 18 arcsec, and the root mean square values of surface roughness of 2 A˚ in 5 μm area scan of atomic force microscopy demonstrating high quality. Correlation between material quality and photoresponse signal strength in photoconductivity measurements was made on SL samples with cut-off wavelength on the order of 10 μm. [Copyright &y& Elsevier]

Effect of lower growth temperature Ts on C incorporation to substitutional sites in Ge1−xCx/Si(0 0 1) grown by molecular beam epitaxy was investigated. To enhance the non-equilibrium growth condition, the temperature Ts was lowered from 600°C down to 300°C. The C incorporation into substitutional sites of GeC epilayers was very sensitive to Ts. X-ray diffraction (XRD) measurement indicated that the substitutional C composition x increased with decrease in Ts from 600°C to 400°C. At Ts⩽350°C, the estimation of x by the XRD analysis was impossible because of polycrystallization. The Raman shift measurement enables to estimate x for Ts⩽350°C, as consequently larger x than that grown at Ts=400°C was verified. The enhancement of non-equilibrium growth condition by decreasing Ts was important to increase x. [Copyright &y& Elsevier]