Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 16: Quantum dots and wires: Optical properties I

HL 16.4: Vortrag

Montag, 25. Februar 2008, 14:45–15:00, ER 164

Controlled Optical Charging of Single InGaAs Quantum Dots — •Dominik Heiss, Vase Jovanov, Max Bichler, Gerhard Abstreiter, and Jonathan J. Finley — Walter Schottky Institut, Garching, Deutschland

We propose an all optical spin readout concept for individual electron spins in single self assembled quantum dots (QDs). By employing the spin-conditional absorption of a circularly polarized light pulse tuned to the X⁻¹ absorption line, we propose to convert the spin information of the resident electron to charge information. Subsequent non-resonant photoluminescence (PL) then directly reveals the charge state of the quantum dot and, therefore, the spin orientation of the resident electron. We have applied time gated PL to confirm that efficient optical charging and non invasive measurement of the charge state can be performed in the same dot. The structures investigated are n-Schottky photodiodes with a dilute ensemble of In_0.5Ga_0.5As QDs in the intrinsic region. A 20 nm Al_0.3Ga_0.7As barrier below the dot layer inhibits electron tunnelling escape, whilst holes are efficiently removed when a high electric field (|E| > 20 kV/cm) exists in the intrinsic region. This leads to electron accumulation and X⁻ⁿ transitions are prominent in the readout phase of the measurement and our results are in good agreement with a rate equation model of the optical charging process. In contrast, for |E| < 20 kV/cm the optical charging rate becomes very low (∼ 390 s⁻¹W⁻¹cm²) demonstrating that the charge and spin state of the dot can be tested via PL over millisecond timescales, without altering it.