Charged exciton emission at 1.3μm from single InAs quantum dots grown by metalorganic chemical vapor deposition

Abstract

We have studied the emission properties of self-organized InAs quantum dots (QDs) grown in an InGaAs quantum well by metalorganic chemical vapor deposition. Low-temperature photoluminescence spectroscopy shows emission from single QDs around 1300 nm; we clearly observe the formation of neutral and charged exciton and biexciton states, and we obtain a biexciton binding energy of 3.1 meV. The dots exhibit an s-p shell splitting of approximately 100 meV, indicating strong confinement.Semiconductor self-assembled quantum dots (QDs) are of considerable interest for future telecommunication applications, such as low-threshold lasers and non-classical light sources for quantum key distribution systems. Efficient single-photon emission has recently been demonstrated at visible wavelengths using semiconductor QD structures, 1,2,3 and there have been many detailed investigations into the low-temperature optical characteristics of QDs emitting at 1150 nm or less. 4,5,6 However, to date there have been only a small number of spectroscopic experiments on single QDs emitting in the important telecommunications window around 1300 nm: 7 biexcitonic features have been identified in low-temperature photoluminescence (PL) from QDs grown by molecular beam epitaxy (MBE), 8 whereas similar investigations for QDs fabricated by metalorganic chemical vapor deposition (MOCVD) show an unclear power dependence in the emission. 9Quantum dot structures grown by MOCVD have potentially a large commercial value due to the high growth rates achievable; however, for applications at telecommunication wavelengths the growth is complicated by large strain effects and complex surface dynamics within the dot layers. 10 Therefore, there is a strong motivation for studying the optical characteristics of these structures in relation to other fabrication techniques. Here, we report on the emission properties of single QDs in a novel dotsin-well (DWELL) heterostructure grown by MOCVD. We present low-temperature PL spectra from individual QDs with an emission wavelength of 1300 nm; powerdependent measurements clearly reveal the formation of an exciton-biexciton system, with a biexciton binding energy of more than 3 meV. We also identify recombination from charged exciton and biexciton complexes, and we observe a large energy difference between s-and p-shell states.The QDs were fabricated using conventional lowpressure MOCVD on a (100) GaAs substrate: an InAs(:Bi) dot layer was deposited in a 5 nm In 0.12 Ga 0.88 As(:Bi) quantum well (QW), and the DWELL heterostructure grown between GaAs barrier layers and InGaP cladding layers. Bismuth doping was found to significantly improve the PL intensity and emission wavelength of the dots. The DWELL structure results in a pronounced red-shift relative to similar InAs/GaAs systems due to effects such as strain relaxation 11 and alloy decomposition. 12 Atomic force microscopy (AFM) measurements on similar samples suggest a dot size of < 15 nm with elongation along the [011] axis; the QD sheet density is estimated as 2 ...

Fine structure and magneto-optics of exciton, trion, and charged biexciton states in single InAs quantum dots emitting at1.3μm

“…At low powers the spectra are composed of four narrow lines (<100 µeV, resolution limited); we have verified that all of these emission lines originate from a single dot in the mesa by comparing the PL spectra from many different mesas. 24 These lines show a linear increase in intensity over low excitation powers before saturating at ∼10 W cm −2 (2P 0 ), and they are attributed to recombination from the exciton X and trion X ± states. The exciton line shows a linearly polarized fine-structure splitting of approximately 300 µeV; this will be discussed further in the next section.…”

“…In all cases, the X − (X + ) line appears at a lower (higher) energy than the exciton, which implies that the lateral extent of the single-particle wavefunction is smaller for the hole l h than for the electron l e . 21,32 A semi-quantitative analysis of the binding energies of the exciton complexes has been performed: as the quantization energy is large for these dots (giving a total s-p shell splitting of ∼90 meV), 24 it is possible to describe the charged excitons by treating the Coulomb interactions as perturbations to the singleparticle states. Using the exchange integrals calculated by Warburton et al 32 for a symmetric parabolic confinement potential, we find a reasonable agreement with the observed X ± binding energies for l e ≈ 7.5 nm and l e /l h ≈ 1.3.…”

Single quantum dot spectroscopy using a fiber taper waveguide near-field optic

“…1͑b͒. Of particular benefit in this assignment is the recent work of Cade et al, 14 who study a DWELL material very similar to that investigated here. In Fig.…”

Selective optical pumping of charged excitons in unintentionally doped InAs quantum dots

“…7 The charge state can also be controlled by optical injection, and different charging schemes have been proposed using above or below barrier excitation. 8,9,10,11,12 In this work, we demonstrate the selective formation of charged exciton complexes in initially empty QDs under the presence of unintentional acceptor and donor impurities. Furthermore, the optical pumping mechanism is investigated for two ensembles of InAs QDs with very different size present in the same sample: small QDs emitting below 970 nm and large QDs emitting at 1165 nm at 4 K.…”