Dresden 2009 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 7: Quantum dots: Optical properties I

HL 7.9: Talk

Monday, March 23, 2009, 16:00–16:15, BEY 118

(111)-Grown InGaAs/GaAs Quantum Dots as Ideal Source for Entangled Photon Pairs — •Andrei Schliwa, Momme Winkelnkemper, and Dieter Bimberg — IFP, Fak. II, TU-Berlin

For a number of protocols of future secure communication systems the generation of entangled photon pairs are essential. Their creation, based on the XX→ X→ 0 recombination cascade in QDs, requires necessarily a vanishing excitonic fine-structure splitting (fss). The latter is hard to achieve in a controlled way for QDs grown on (001)-substrate. Dot to dot variations of piezoelectricity and QD elongation, which induce a lateral electronic anisotropy, lead to variations of the fss. The structural anisotropy and the piezoelectricity are intrinsic characteristics of the (001) substrate orientation featuring different surface mobilities along [110] and [1-10] and polar axes with non-vanishing projections on the growth plane. Therefore, we propose the use of QDs grown on (111)-GaAs substrates. Using eight-band k·p theory in conjunction with an improved configuration interaction method we calculate the fss for (111)-grown QDs together with the biexciton binding energy as function of size, aspect ratio and chemical composition. Assuming a threefold rotational structural symmetry of the QDs, we show that the corresponding piezoelectric field does not lower this symmetry any further. Thus, the excitonic bright states remain degenerate and the XX→ X→ 0 cascade presents an intrinsically perfect source of entangled photon pairs. This result is of general character and applies to all self-organized QDs in a zinc-blende system [1].

[1] Deutsche Patentanmeldung Nr.: 10 2008 036 400.2