Differences in InGaAs island nucleation on vicinal (100) GaAs surfaces as a function of miscut angle are presented. Arrhenius plots of saturation island densities show changes in activation energy and critical cluster size, which are interpreted as resulting from nucleation through different mechanisms: homogeneously (on terraces) and heterogeneously on monatomic and multiatomic steps. Furthermore, a link between step separation and island uniformity is observed.Step availability is found to be a major determinant of island uniformity at temperatures where clusters are not mobile. [S0031-9007 (97)03426-1] PACS numbers: 61.16.Ch, 68.35.Rh, 81.15.Gh, 85.40.Ux The rapidly expanding interest in Stranski-Krastanow (S-K) [1] island growth using compound semiconductors stems from their potential applications as quantum boxes. Three-dimensional quantum confinement has been achieved for various materials, including InAs and InGaAs on GaAs [2,3], InAlAs on AlGaAs [4], InP on InGaP͞ GaAs [5], and InAs on AlInAs͞InP [6], and has been demonstrated with a range of experimental techniques [7-11].Understanding surface processes in semiconductors has been beneficial in the growth formation of quantum wires [12,13]. Since island nucleation on surfaces is the foundation for self-assembled quantum dots (QDs), such understanding seems crucial in order to control the morphology of InGaAs islands used in QD applications.Saturation island densities ͑N s ͒ have been used in several heteroepitaxial systems [14-17] to determine surface kinetics coefficients. Such studies involved both Volmer-Weber (V-W) [18] and S-K growth modes. Studies of the evolution of InAs͞GaAs island densities confirm that, just as in V-W systems, island density increases exponentially until saturation, when adhesion to preformed islands becomes more probable than new island nucleation. Force microscopy investigations of island concentrations as a function of coverage found a sharp exponential increase in concentrations after the onset of the S-K transition [19].Achieving optimum uniformity in self-assembled nanostructures is considered a major issue from both a technological and basic science perspective. A recent theoretical study [20] has associated the fortuitous small size dispersion in these islands with the precursor formation of monolayer (ML) step platelets [21]. However, until now, no explanation has been provided for the large differences in size dispersity observed for S-K islands within any one material system.In this study, the influence of miscut angle on InGaAs͞ GaAs island nucleation is examined. Many analytical studies of island nucleation tend to treat surfaces as homo-geneous and consider surface defects, such as steps, as minor nonidealities in the process of surface nucleation. Here, it is shown that vicinal orientation is a decisive factor in the nucleation behavior of strained InGaAs islands in (100) GaAs, having an effect on island densities, diameters, and uniformity.Substrates chosen for this study were semi-insulating GaAs nominally orien...

Tunability in the concentration and average dimensions of self-forming semiconductor quantum dots (QDs) has been attained. Three of the approaches examined here are: variations with temperature, group V partial pressure and with substrate miscut angle. Thermally activated group III adatom mobilities result in larger diameters and lower concentrations with increasing deposition temperatures. These variations are presented for InGaAs/GaAs and AlInAs/AlGaAs, where striking differences were seen. Tunability in the InGaAs/GaAs QD concentration was also obtained in metalorganic chemical vapor deposition by varying the arsine flow. The latter gave widely varying concentrations and similar sizes. Substrate orientation was found to also be a key factor in island nucleation: Changes in vicinal orientation near (100) can be used to exploit the preferential step edge nucleation at mono and multi-atomic steps, so varying miscut angle (θm) can be used to change island densities and sizes. Anisotropies in island nucleation producing n-dot strings aligned with multiatomic step edges are observed for θm⩾0.75° and up to 2°. Quantum mechanical coupling from such island strings result in non-Gaussian shapes in the inhomogeneously broadened photoluminescence peaks. The effects of some of the other morphological differences presented here on the luminescence emission from QD ground states is discussed for InGaAs/GaAs QDs.

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We report the optical characterization of high-quality 1.55μm GaxIn1−xNyAs1−y multiquantum wells (MQWs), grown on GaAs with Ga(In)N0.01As spacer layers. The transitions between the quantized QW states of the electrons and holes have been identified using photoluminescence excitation spectroscopy. Their energies are consistent with theoretical fitting based on the band anticrossing model. It is also confirmed by detailed spectroscopic measurements that the addition of even a small amount of In to GaN0.01As barriers remarkably improves the optical characteristics of the QWs. The results imply that although strain-compensated GaInNAs MQWs provide a feasible approach to realizing 1.55μm optical emission, the relative lattice mismatch between the wells and barriers is critical to the optical quality of the related QWs.

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