Electrorefraction in Quantum Dots. R.Prasanth, J.E.M. Haverkort and J.H. Wolter COBRA Inter-University Research Institute, Eindhoven University of Technology, Physics Department P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands; E-mail: R.Prasanth@tue.nl We developed a model to calculate the electrorefraction due to the Quantum Confined Stark Effect in strained cylindrical QDs. We followed a numerical matrix diagonalization method using an expansion in plane-wave states. The correct polarization dependence is obtained by using the 4X4 Luttinger-Kohn Hamiltonian for the valence band. The exciton wavefunction is also calculated using a diagonalization approach. We will present the absorption spectra as a function of applied electric field and dot dimensions and discuss the implications for the electrorefraction. Introduction Electro-absorption modulators and Mach-Zehnder Interferometric (MZI) space switches [1] have mainly been developed using bulk or quantum well materials. In bulk semiconductor materials, the length of the phase shifting section is usually 2-4 mm. We have recently shown that this length can be decreased down to 0.46 mm in quantum well material by combining carrier depletion and the Quantum Confined Stark Effect (QCSE) in an asymmetric MZI switch [2]. This results shows that reducing the dimensionality of the semiconductor structure, provides improved performance phase shifters. In this contribution, we will investigate the possibility of quantum dot (QD) material for providing electrorefraction in the phase shifter of an MZI. The conceptual advantage of QDs is the discrete density of states, resulting in narrow absorption peaks which shift with the applied electric field due to the QCSE. Bandfilling will decrease the oscillator strength of the QD absorption peaks. When choosing the operating wavelength to coincide with the peak of such a discrete absorption peak, both the QCSE and bandfilling result in a quickly decreasing absorption strength, resulting in electro-absorption. On the other hand, when choosing the operating wavelength just outside the discrete absorption peak, a clear electro-refraction effect is expected. In this contribution, we will present a model to calculate the electro-absorption and electro- refraction in QD material. In particular we will investigate the influence of the QD size on the QCSE and exciton oscillator strength [3]. The final goal of this work is to identify the potential of QD material for realistic electro-absorption modulators, electro-refraction based MZI’s as well as for all-optical signal processing based on bandfilling. Theoretical approach In our model we treat cylindrical InAs quantum dots with radius R and height h within a GaAs matrix. We assume a parabolic conduction mass with effective mass m e *. For the valence band, we use the 4X4 Luttinger-Kohn Hamiltonian with respect to the {|3/2,+3/2>,|3/2,-3/2>, |3/2,+1/2>, |3/2,-1/2>} basis and allow for strain as well as for the QCSE by adding the interaction with the electric field F [4] eFz z y x a z y x V z y x m H hy c e e e + + + ∇ ∇ = ) , , ( ) , , ( ) ) , , ( 2 1 ( * 2 ε