Phase Transitions, Vol. 79, Nos. 9–10, September–October 2006, 765–770 Quantum dot electrons as controllable scattering centers in the vicinity of a two-dimensional electron gas M. RUSSy, C. MEIER*y, B. MARQUARDTy, A. LORKEy, D. REUTERz and A. D. WIECKy yExperimental Physics, University of Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany zLehrstuhl fu¨r Angewandte Festko¨rperphysik, Ruhr-Universita¨t Bochum, Universita¨tsstr. 150, D-44780 Bochum, Germany (Received 9 August 2006; in final form 17 October 2006) Self-assembled InAs quantum dots can be controllably charged with a defined number of electrons per dot. We report on conductivity measurements of Al x Ga 1x As/GaAs heterostructures, where such quantum dots are embedded in the direct vicinity of a two-dimensional electron gas (2DEG). We demonstrate the controlled enhancement of the scattering rate in the 2DEG induced by charging the quantum dots with additional electrons. The resulting transport lifetimes are in good agreement with theoretical values for Coulomb scattering in two dimensions. Keywords: Quantum dots; two-dimensional electron gas; scattering; GaAs 1. Introduction Almost immediately after the first fabrication of uniformly sized InAs quantum dots on GaAs [1], it was realized that these islands can be used as controllable scattering centers for a two-dimensional electron gas (2DEG). The first experiments showed a drastic reduction of the 2DEG mobility with decreasing distance between the dots and the 2DEG [2]. Since then, several authors successfully used self-assembled quantum dots for novel transport experiments in the quantum Hall regime of highly disordered 2DEG [3–5]. However, the reason of the strong scattering by self assembled quantum dots is still unclear. One of the main candidates for the origin of the reduction of the mobility are the quantum dot electrons and their associated Coulomb potential. However, by comparing capacitance and transport data, Zhukov et al. and Kawazu et al. demonstrated that the charging of the quantum dots can even lead to an enhancement of the mobility [6, 7]. Zhukov et al. argue that in these experiments the quantum dot electrons are not the dominant source of scattering and in certain cases effectively screen other potential inhomogeneities. Here, we report on capacitance and conductivity measurements which show a reduction of the mobility whenever additional electrons are charged in the quantum *Corresponding author. Email: cedrik.meier@uni-due.de Phase Transitions ISSN 0141-1594 print/ISSN 1029-0338 online # 2006 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/01411590600960893