Interdiffusion in Semiconductor Quantum Dot Structures
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Interdiffusion in Semiconductor Quantum Dot Structures P. Lever, L. Fu, C. Jagadish, M. Gal1 and H.H. Tan Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, AUSTRALIA 1 School of Physics, University of New South Wales, Sydney, NSW 2052, AUSTRALIA ABSTRACT The potential profile of InGaAs quantum dots (QDs) was shown to be easily modified with annealing. We also demonstrate the use of spin-on-glass to create interdiffusion in QDs but the degree of interdiffusion was strongly dependent on the properties of the oxide. By using TiO2 significant suppression of thermal diffusion of the quantum dots could be achieved. On the other hand, very large additional blue shifts (in excess of 120 meV) could be obtained with both H and As implantation. The different nature of defects created by both ions and how they affect the interdiffusion of quantum dots were illustrated. In the dose and annealing temperature range studied, the degree of interdiffusion ultimately depends on the availability of free point defects or point defects liberated from clusters/extended defects to diffuse across the quantum dots. INTRODUCTION Semiconductor quantum dots (QDs) have drawn considerable interest due to their unique electrical and optical properties resulting from the 3-dimensional confinement of carriers leading to delta-function like density of states. They have found their many applications in novel devices with improved characteristics such as QD lasers and QD infrared detectors1-3. Self-organized growth techniques based on Stranski-Krastanow growth mode have been widely employed to deposit these dots. As the dots are grown at low temperatures, their thermal stability (interdiffusion) is an issue since in device structures, subsequent layers are grown at higher temperatures. Hence, the effect of interdiffusion on the properties of QDs needs to be carefully studied and controlled to improve device performance. To date there are only a handful of postgrowth interdiffusion studies of QDs as compared to the available literature on quantum wells4-9. In order for successful application of intermixing techniques for the fabrication of QD-based integrated devices, more studies are required to understand the role of defects and strain on the interdiffusion process in QDs. In this paper, the results of thermally-induced interdiffusion in InGaAs/GaAs QDs are presented. The effect of spin-on-glass and ion implantation on the interdiffusion is also presented and discussed.
EXPERIMENTAL DETAILS The QD structures used in this study were grown on semi-insulating (100) GaAs substrates by metalorganic chemical vapor deposition. Typical structure consisted of a 300nmthick buffer layer of GaAs (grown at 650°C), a 6.5 monolayer (ML) of nominally In0.5Ga0.5As dots (grown at 550°C) and a 200nm GaAs capping layer (grown at 650°C). Atomic force microscopy (Fig. 1) performed on an uncapped sample grown under the same conditions revealed that the dots w
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