Effect of an additional infrared excitation on the luminescence efficiency of a single InAs/GaAs quantum dot

Abstract

Microphotoluminescence ͑PL͒ spectra of a single InAs/GaAs self-assembled quantum dot ͑QD͒ are studied under the main excitation of electron-hole pairs in the wetting layer ͑WL͒ and an additional infrared ͑IR͒ laser illumination. It is demonstrated that the IR laser with fixed photon energy well below the QD ground state induces striking changes in the spectra for a range of excitation energies and powers of the two lasers. For the main excitation above a threshold energy, defined as the onset of transitions between shallow acceptors and the conduction band in GaAs, the addition of the IR laser will induce a considerable increase in the QD emission intensity. This is explained in terms of additional generation of extra electrons and holes into the QD by the two lasers. For excitation below the threshold energy, the carrier capture efficiency from the WL into the QD is suggested to be essentially determined by the internal electric-field-driven carrier transport in the plane of the WL. The extra holes, generated in the GaAs by the IR laser, are supposed to effectively screen the built-in field, which results in a considerable reduction of the carrier collection efficiency into the QD and, consequently, a decrease of the QD PL intensity. A model is presented which allows estimating the magnitude of the built-in field as well as the dependence of the observed increase of the QD PL intensity on the powers of the two lasers. The use of an additional IR laser is considered to be helpful to effectively manipulate the emission efficiency of the quantum dot, which could be used in practice in quantum-dot-based optical switches.

Photoneutralization and slow capture of carriers in quantum dots probed by resonant excitation spectroscopy

“…For larger C-doping densities, the QD occupancy increases more slowly with increasing n A , while at the same time the depletion length rapidly decreases below it maximum value. For the typical acceptor densities of the order of 10 13 − 10 14 cm −3 [58], the QD is nearly populated by three holes, which is more than the two holes occupancy considered in our work hypothesis (see section IV A). However, excepting an average value of the typical acceptor densities, we do not have a precise knowledge of the C-doping in the QD vicinity.…”

Magnetic field effects on optical and transport properties inInAs∕GaAsquantum dots

“…The distance between the dots is consequently smaller than the diffusion length of the photoinduced carriers. Our previous study revealed an exciton diffusion length in the WL of approximately 1 m. 7 Since only a very limited WL contribution can be observed in the low-temperature PL spectrum, we roughly estimate a dot separation of about 1 m and a dot density of approximately 10 8 cm −2 .…”

“…Our previous work based on lateral electric field dependence studies on single dot related PL indicates a depth of the potential fluctuations of approximately 3 meV. 14 Furthermore, PLE measurements reveal a Stokes shift of about 5 meV, 7,15 which also gives a rough estimate of the depth of the local WL potential fluctuations. Based on these different experimental observations, the depth of the WL potential fluctuations is estimated to be 3 -5 meV.…”

Manipulating the spin polarization of excitons in a single quantum dot by optical means

“…11,12 In contrast to single laser excitation, which only results in X 0 , when adding a second infrared ͑IR͒ laser excitation X + is formed, as was demonstrated by us earlier. 13 An even higher polarization is measured for X + , c =73%, which is considered to be an upper bound for spin polarization of electrons captured into the QD from the wetting layer ͑WL͒.…”

“…Detailed descriptions of the sample and of the experimental setup are given elsewhere. [11][12][13] c was determined as c = ͑I co − I cross ͒ / ͑I co + I cross ͒, where I co ͑I cross ͒ corresponds to the spectrally integrated PL signal of the co͑cross-͒circular components.…”