Self-assembled nanodrill technology based on droplet epitaxy growth was developed to obtain nanoholes on a GaAs(100) surface. In this technology, the gallium droplets act like “electrochemical drills” etching away the GaAs substrate beneath to give rise to nanoholes more than 10nm deep. The driving force of the nanodrill is attributed to the arsenic desorption underneath the gallium droplet at high growth temperatures and Ga-rich condition. This nanodrill technology provides an easy and flexible method to fabricate nanohole templates on GaAs(100) surface and has great potential for developing quantum dots and quantum dot molecules for quantum computation applications.

Articles you may be interested inGrowth by molecular beam epitaxy of self-assembled InAs quantum dots on InAlAs and InGaAs lattice-matched to InP

The evolution between lattice-matched GaAs/Al0.3Ga0.7As single and double ring-like nanostructures is studied, with an emphasis on the construction and destruction of the observed outer ring. Using droplet epitaxy, this was achieved by directly controlling the Ga surface diffusion on GaAs(100). Double ring-like nanostructures were observed at relatively low temperatures under a fixed As4 flux (beam equivalent pressure (BEP) of 6.4 µTorr) and at a fixed temperature under a high As4 flux. The construction of the outer ring can be controlled through surface diffusion by varying the substrate temperature or the As4 flux. Single ring-like nanostructures were realized both at relatively high temperatures under a fixed As4 flux, and at low temperatures under a relatively low As4 flux.

A growth technique combining droplet epitaxy and molecular beam epitaxy (MBE) is developed to obtain a low density of InAs quantum dots (QDs) on GaAs nanoholes. This growth technique is simple, flexible, and does not require additional substrate processing. It makes possible separate control of the QD density via droplet epitaxy and the QD quality via MBE growth. In this letter the authors report the use of this technique to produce InAs QDs with a low density of 2.7×108cm−2 as well as good photoluminescence properties. The resulting samples are suitable for single QD device fabrication and applications.

Anisotropic surface diffusion and strain are used to explain the formation of three-dimensional (In,Ga)As quantum dot lattices. The diffusion characteristics of the surface coupled with the elastic anisotropy of the matrix, provides an excellent opportunity to influence the dot positions. In particular, quantum dots that are laterally organized into long chains or chessboard two-dimensional arrays vertically organized with strict vertical ordering or vertical ordering that is inclined to the sample surface normal are accurately predicted and observed.PACS 68.35.Fx,81.15.Hi During the last decade semiconductor quantum dots (QDs) have attracted increasing attention because of potential applications as novel semiconductor devices [1,2]. Besides time consuming techniques using electron beam lithography and subsequent etching to fabricate QDs, selforganized growth techniques have captured research interest [2][3][4][5][6]. In the Stranski-Krastanow growth mode, while the growth conditions can be optimized to produce nanostructures of near identical size and shape, often only a random spatial distribution of the QD is observed for a single layer of QDs [7]. However, for multiple layers a range of different results, from near perfect QD chains to threedimensional (3D) lattices, have been reported and discussed [8][9][10][11]. In this case, it has been suggested that the anisotropy in surface diffusion for (In,Ga)As QDs on GaAs (100), which is mainly caused by the (2x4) surface reconstruction with dimer rows running along [0][1][2][3][4][5][6][7][8][9][10][11], is responsible for the formation of QD chains along the [0-11]-direction [9,12]. In particular, the surface diffusion length along [0-11] is larger than along [011]. This leads to greater strain relaxation along the [0-11]-direction, producing an elliptical strain relief that is transferred to succeeding layers. This, eventually causes an asymmetric separation between neighboring dots and consequently leads to QD chain structures. Another example of the outcome of multiple layers of QD growth is the PbSe/PbEuTe system where a nearly perfect 3D lattice is reported along with the suggestion that the self-organized result is caused by anisotropic strain transfer from QD layerto-QD layer [10,11]. In each case the explanation is qualitative and a quantitative understanding of the role of diffusion and strain and the corresponding ability to design 3D QD structures is still lacking.In this letter, we report on experiments that use natural surface steps on high index substrates to further uncover the role of both surface diffusion and strain in producing 3D ordering of QDs. In particular we examine the formation and development of 3D square-like lattices of (In,Ga)As QDs in a GaAs matrix. The square lattices are created by vertically stacking QD layers while simultaneously introducing surface steps in each layer in order to vary and control the symmetry of the diffusion and strain pattern in each layer. Our findings show that by using different high index substrates...