Lateral positioning of InGaAs quantum dots using a buried stressor

We present a “bottom-up” approach for the lateral alignment of semiconductor quantum dots (QDs) based on strain-driven self-organization. A buried stressor formed by partial oxidation of (Al,Ga)As layers is employed in order to create a locally varying strain field at a GaAs(001) growth surface. During subsequent strained layer growth, local self-organization of (In,Ga)As QDs is controlled by the contour shape of the stressor. Large vertical separation of the QD growth plane from the buried stressor interface of 150 nm is achieved enabling high optical quality of QDs. Optical characterization confirms narrow QD emission lines without spectral diffusion. V C 2012 American Institute of Physics .[ http://dx.doi.org/10.1063/1.3691251] The deterministic alignment of quantum dots (QDs) during an epitaxial growth process is mandatory for electronic and optoelectronic devices 1 based on single QDs, for example, single photon detectors 2 and non-classical light emitters. 3 The self-organized formation of coherently strained islands, e.g., QDs, by the growth of strained layers in the “Stranski-Krastanow” growth regime is a consequence of the total energy minimization of the strained layer system. 4–6 QDs are formed if the strain energy relieved by island formation surpasses the energy cost associated with newly formed surfaces and edges. 7 Therefore, a selective formation of QDs on a surface will occur if the surface exhibits sites of increased strain energy, higher strain energy relief, or lower facet formation energy during growth of a strained layer. Current techniques for QD positioning generally deploy nanometer-scale lithography techniques like electron beam lithography, 8 focused ion beam lithography, 9 local oxidation, 10 or nano-imprinting 11 in order to define nanometersized areas as exclusive nucleation sites prior to the growth of quantum dots. All these “top-down” approaches share a number of difficulties, which impact the structural and optical properties of the quantum dots. First, deterministic quantum dot nucleation is possible only within very close vertical proximity to the structural patterning. An often reported problem is the missing of QDs at shallow holes patterned on a growth surface. 8,9 Since the patterning involves etching of the surface or other invasive means, the quantum dots will be surrounded by defect sites which degrade their structural and optical quality. 12 Even though sophisticated cleaning