Initial Stages of InAs Quantum Dots Evolution in GaAs/AlAs Matrixes
- PDF / 206,344 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 102 Downloads / 189 Views
W13.8.1
Initial Stages of InAs Quantum Dots Evolution in GaAs/AlAs Matrixes Michael Yakimov, Vadim Tokranov, Alex Katnelson and Serge Oktyabrsky UAlbany Institute for Materials, University at Albany - SUNY, Albany NY, 12203, USA ABSTRACT We have studied the first phases of post-growth evolution of InAs quantum dots (QDs) using in-situ Auger electron spectroscopy in conjunction with Reflection High Energy Electron Diffraction (RHEED). Direct evidence for InAs intermixing with about 6ML (monolayers) of the matrix material is found from Auger signal behavior during MBE overgrowth of InAs nanostructures. Re-establishment of 2D growth mode by overgrowth with GaAs or AlAs was monitored in single-layer and multi-layer QD structures using RHEED. Decay process of InAs QDs on the surface is found to have activation energy of about 1.1 eV that corresponds to In intermixing with the matrix rather than evaporation from the surface. INTRODUCTION Quantum dots (QD) based structures are promising alternative for currently used quantum wells (QW) in various devices for light emitting [1] and detecting [2,3] applications. However, growth technology of QDs is not completely understood. Narrower size distribution is still a significant challenge for most applications. Better process control is required for commercialization of this technology. Photoluminescent (PL) properties of InAs quantum dots (QDs) embedded in a shortperiod superlattice (SPSL) depend on the surface (GaAs/AlAs) they grow on, as well as on composition and growth rate of capping layer [4]. Reflection High Energy Electron Diffraction (RHEED) monitoring of QD formation process on GaAs/AlAs in SPSL reveals its strong dependence on surface composition (GaAs or AlAs terminated SPSL). Atomic force microscopy and transmission electron microscopy results indicate that the QD density and sizes are extremely sensitive to the material of the underlying layer [4]. These facts lead to a conclusion, that QD formation process greatly depends on diffusion properties of In adatoms on the surface, which, in turn, is affected by the rate of InAs intermixing with underlying material and capping layer. One of the ways to modify the properties of the structure is to use AlGaAs alloys as matrix material, instead of pure GaAs. The structural quality of AlGaAs alloy layers is not high enough, especially when grown at temperatures below 500 °C, required for QD growth. Our general approach is to use a short period superlattice (SPSL) instead of AlGaAs alloys as a matrix material for QD structures. Parameters of SPSL can be chosen to vary the effective bandgap of SPSL anywhere between values of AlAs and GaAs. The use of SPSL is known to smoothen the surface of the structure. This effect can enhance the flatness and epitaxial quality of the upper QD sheets, especially in the multilayered stacks of QDs. The top layer of SPSL matrix can be either AlAs or GaAs, giving an additional degree of freedom to control the QD properties. In this paper we study the post-formation processes in InAs quantum dot
Data Loading...
