Nucleation Transitions for InGaAs Islands on Vicinal (100) GaAs

Abstract

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...

Positioning of self-assembled Ge islands on stripe-patterned Si(001) substrates

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Direct imaging of quantum wires nucleated at diatomic steps

“…[1][2][3][4][5][6][7][8][9][10][11] In particular, these steps are thought to constitute a heterogeneous source of nucleation for the formation of nano-objects and structural defects at the initial stages of the growth of many semiconductor nanostructures. 12,13 It is critically important to identify the nucleation sources for individual nano-objects such as quantum dots and wires because they constitute the fundamental blocks of future nanoelectronics and nanophotonics devices. 14 The ability to control the nucleation of these nano-objects will contribute significantly to the development of reliable single-photon sources for applications in quantum information technology.…”

Dislocation-induced changes in quantum dots: Step alignment and radiative emission

“…Islands form ''strings'' along multiatomic step edges. As seen in previous studies, 9 nucleation on steps is energetically favorable. Figures 1͑b͒ and 1͑c͒ show the surface morphology after growth of 100 InGaAs/GaAs QD layers.…”

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