Electrical control of the exciton–biexciton splitting in self-assembled InGaAs quantum dots

Abstract

We report on single InGaAs quantum dots embedded in a lateral electric field device. By applying a voltage we tune the neutral exciton transition into resonance with the biexciton using the quantum confined Stark effect. The results are compared to theoretical calculations of the relative energies of exciton and biexciton. Cascaded decay from the manifold of single exciton-biexciton states has been predicted to be a new concept to generate entangled photon pairs on demand without the need to suppress the fine structures splitting of the neutral exciton.The controlled next generation of entanglement is an important concept in both quantum information science [1] and quantum cryptography [2]. Benson et al. [3] proposed the use of biexciton-exciton cascade in semiconductor quantum dots (QDs) to generate such nonclassical states of light. Subsequently, many groups [4][5][6] worldwide have demonstrated the generation of entangled photon pairs via this process. Creating polarization entangled, rather than classically correlated [7], photon pairs has been achieved by tuning the exciton fine structure splitting to zero [8]. Recently, this has been achieved by several groups [9][10][11] by applying an electric field in a lateral geometry in the base plane of the QD. An alternative approach for realizing an entangled photon source, proposed by Avron et al. [12], requires the exciton to be tuned into resonance with the biexciton in order to exploit time reordering of the emitted photon pairs.In this Letter we demonstrate tuning of exciton and biexciton states of a single InGaAs QD into resonance by applying an electric field parallel to the QD layer. Comparison with theory shows that the sign of the energy shift arising from the quantum confined Stark effect [13] is opposing for the exciton and biexciton states. This allows us to bring both transitions into resonance at electric fields of F∼17 kV/cm. Such devices are promising candidates for realizing an electrically tunable source of entangled photon pairs. The samples investigated were grown by molecular beam epitaxy and consist of the following layer sequence: starting with a semi-insulating (100) GaAs wafer we deposited a 300 nm thick GaAs buffer layer, followed by 25 periods of a AlAs (2.5 nm)/GaAs (2.5 nm) superlattice. We grew a 200 nm thick GaAs waveguide, into the center of which a single layer of nominally In 0.5 Ga 0.5 As QDs was incorporated. The areal density of the QDs was varied during the growth by stopping the rotation of the wafer and samples with a density of ∼10 µm −2 , as revealed by atomic force microscope measurements (not shown here), were chosen for further processing. Using a combination of optical lithography and electron beam metalization we established back-to-back Ti/Au Schottky gates on the surface of the sample. In a first evaporation step we deposit a 20 nm titanium undercoating, followed by a 60 nm gold layer. In a second lithography step we produced larger Ti/Au bonding pads with a layer thickness of 20 nm and 200 nm, respectively. In t...

Radio frequency occupancy state control of a single nanowire quantum dot

“…This strain field and its corresponding hydrostatic pressure (p) tunes the QD emission due to deformation potential coupling [47]. At such low acoustic amplitudes the contribution of SAW-induced lateral electric fields are weak [48] and the observed spectral shift is dominated by the strain contribution. [49,30] The extracted relative spectral tuning ∆E strain of 1X 0 and 1X − are plotted as a function of φ in Fig.…”

Relative stability of excitonic complexes in quasi-one-dimensional semiconductors

“…Optical properties of semiconducting carbon nanotubes (CNs), in particular, are largely determined by excitons [4,5], and can be tuned by electrostatic doping [6][7][8], or by means of the quantum confined Stark effect [9][10][11]. Trions and biexcitons, though not detectable in bulk materials at room temperature, play a significant role in quantum confined systems of reduced dimensionality such as quantum wells [12][13][14][15][16], nanowires [17][18][19][20][21], nanotubes [22][23][24][25][26][27][28][29][30][31][32][33], and quantum dots [34][35][36].…”

Shape of recombination lines for exciton complexes in quantum dots with in-plane electric field

“…Recently, quite a lot of attention is paid to the confined Stark effect for the electric field F which is oriented within the quantum dot plane of confinement [4][5][6][7]. In contrast to the vertical orientation of the electric field, the in-plane field segregation of charge carriers within a single dot leads to a significant modulation of recombination energies.…”