Mechanisms of Self-Ordering of Quantum Nanostructures Grown on Nonplanar Surfaces

Abstract

We present an analytic model that explains the self-ordering of quantum nanostructures grown on nonplanar surfaces. Self-limiting growth in these structures results from the interplay among growthrate anisotropy, curvature-induced capillarity, and, for alloys, entropy of mixing effects. Experimental results on self-limiting organometallic chemical vapor deposition on corrugated surfaces are in quantitative agreement with the model. The implications of the self-limiting growth characteristics on the self-ordering of quantum wells, wires, and dots are discussed. [S0031-9007(98)07220-2] PACS numbers: 68.65. + g, 81.10.Bk, 82.65.Dp Two-or three-dimensionally quantum-confined semiconductor structures have attracted much attention because of their interesting physical properties and potential device applications [1]. To overcome limitations in size and interface quality related to traditional lithography techniques, many efforts have been devoted to study their formation during the epitaxial process [2]. This can be accomplished if a suitable driving force is introduced to yield the desired lateral heterostructure patterning. A widely used approach in this direction is to exploit self-ordering processes on planar surfaces, as for strained-induced Stranski-Krastanow growth of quantum dots (QDs) [3,4]. Such techniques have the advantage that self-ordering is achieved without any surface patterning prior to growth; however, they suffer from a limited control on uniformity and deposition site due to the intrinsic random nature of the nucleation process.Self-ordering of nanostructures on nonplanar surfaces has the potential for solving these problems, as the corrugated surface can provide a template for the nucleation sites. In fact, organometallic chemical vapor deposition (OMCVD) and molecular beam epitaxy (MBE) on substrates patterned with corrugations (see Fig. 1) [5,6] or with pyramidal patterns [7] have been successfully employed to fabricate uniform arrays of quantum wires (QWRs) and QDs. Despite the accurate structural control demonstrated with this approach, the understanding of the self-limiting growth mechanism on such corrugated surfaces has been essentially phenomenological [8]. Existing models can, in fact, predict only constant growth rates of thick layers on mm-sized facets, depending on their orientation and environment, as a result of gas-phase and surface diffusion [9,10]. The growth behavior of facets in the 10-nm scale, relevant to the self-ordering of quantum nanostructures, cannot be explained with such models, since facet-size dependent surface diffusion fluxes should be invoked to account for the self-limiting growth [11].In this Letter we address the self-limiting growth of a corrugated surface, and establish a model that quantitatively describes the self-ordering of quantum wells (QWs), QWRs, and QDs on such patterned substrates.The formation of surface patterns during growth relies on lateral gradients in the surface chemical potential m. Considering, for simplicity, variations in only one dim...

Morphological, compositional, and geometrical transients of V-groove quantum wires formed during metalorganic vapor-phase epitaxy

“…The appearance of a self-limiting width along the bottom of the groove, together with the segregation of the most mobile adatom species along the vertical axis (perpendicular to the bottom facet) of the recess, produces two-dimensional lateral carrier confinement. Our model, which focusses exclusively on kinetics, in contrast to previous studies, 11,12 provides a complete explanation of the observed behavior in V-groove recesses (e.g., modulation of the self-limiting profile width and Ga segregation) based on (i) different rates of precursor and adatom surface kinetics on each facet plane and (ii) interfacet mass transport, which accounts for growth rate anisotropy and capillarity.…”

“…Cross-sectional transmission electron microscopy (TEM) 11 has demonstrated the presence of a transient regime during which the profile of the recess and the Ga segregation evolve toward stationary values determined by the growth conditions and alloy composition. We reproduce the experimentally observed geometric and compositional transients based on reaction-diffusion equations for each facet of the V-groove template, and we explain our results in terms of the surface kinetics established by the geometry and growth conditions.…”

(In,Ga)As sidewall quantum wires on shallow-patterned InP (311)A

“…[4][5][6] A variety of theoretical and experimental work has been performed to improve the quality of V-groove and ridge-type QWires and QDots. 7 Both techniques rely on sharp corners or tips and, hence, relatively deep ͑typically several hundreds of nanometers͒ patterns, which are rounded in the case of V-grooves and sharpened in the case of ridges due to adatom migration from the adjacent slow-growing side facets towards the corners or tips for QWire and QDot formation. This requires reshaping of the pattern during growth of the buffer and barrier layers with considerable thickness for well-defined QWire and QDot formation and stacking in multilayers.…”

Magneto-optical properties of single site-controlled InGaAsN quantum wires grown on prepatterned GaAs substrates

“…15,18 Their distinctive V-shaped cross section (typically having sub-μm width) is defined by two mirroring {111}A crystal planes, exposed by the etching procedure. Due to a combination of growthrate anisotropy, curvature-induced capillarity, and entropy of mixing effects, [21][22][23] MOCVD of a thin layer of InGaAs on a GaAs substrate patterned with V grooves results in the formation of a QWR along the main axis of each groove. Figure 1(a) displays a sketch of the grown QWR structure, characterized by a crescent-shaped cross section.…”

“…[17][18][19][20][21] Such V grooves are relatively long (up to several hundreds of microns) linear recesses, oriented along the [110] crystallographic direction and obtained through a combination of electron-beam lithography and wet chemical etching. 15,18 Their distinctive V-shaped cross section (typically having sub-μm width) is defined by two mirroring {111}A crystal planes, exposed by the etching procedure.…”