Sharp emission from single InAs quantum dots grown on vicinal GaAs surfaces

Abstract

We report on optical studies of single InAs quantum dots grown on vicinal GaAs͑001͒ surfaces. To ensure low quantum dot density and appropriate size, we deposit InAs layers 1.4 or 1.5 ML thick, thinner than the critical thickness for Stranski-Krastanov quantum dot formation. These dots show sharp and bright photoluminescence. Lifetime measurements reveal an exciton lifetime of 500 ps. Polarization measurements show an exciton fine structure splitting of 15 eV and allow to identify the exciton and charged exciton transitions with linewidth as narrow as 23 eV. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3125430͔ Self-assembled quantum dots ͑QDs͒ proved an excellent system for the implementation of quantum bits 1-3 and as sources of single 4,5 and entangled photons. [6][7][8] The most common technique for growing self-assembled QDs, the Stranski-Krastanov ͑SK͒ method, allows for the fabrication of QDs with good optical properties; nearly lifetime limited linewidth of the optical transitions in these dots makes them suitable for single spin measurement 9 and two photon interference. 10 The ability of controlling the position of selfassembled QDs would allow for more complex devices, and different attempts 11,12 have been made in this direction. In particular a growth technique similar to the SK method has been used to produce rows of QDs ͑Ref. 13͒ on vicinal GaAs substrates. Although this technique gives some control on the lateral alignment of QDs, the study of the optical properties of such vicinal QDs has been limited to ensemble measurements so far. 14,15 In this letter, we present a study of the optical properties of single InGaAs QDs, grown on a vicinal GaAs substrate by molecular beam epitaxy ͑MBE͒. The low QD density required for addressing single dots has been achieved by selecting a substrate with suitable misorientation angle and by exploring the subcritical regime of InAs island formation. 16 The high resolution spectroscopic measurements presented in this letter, combined with polarization selective and time resolved measurements, give a first contribution in identifying optical transitions in single QDs of this kind.In order to grow samples with different QD sizes and densities, four substrates were mounted in the MBE reactor, namely an exactly oriented GaAs͑001͒ substrate and three GaAs͑001͒ vicinal substrates misoriented by 3°, 5°, and 7°t oward the ͓100͔ direction. After oxide layer desorption, a GaAs buffer layer was grown at 600°C to ensure the translation of multiatomic steps according to the substrate vicinality. A 10 period GaAs/AlGaAs superlattice was then grown to block carrier diffusion to and from the substrate. After growing a 100 nm thick GaAs layer, the substrate temperature was lowered to 485°C and 1.4 or 1.5 InAs monolayers were deposited at a rate of 0.05 ML/s. The growth was then interrupted for 20 s. During this time QDs formed in the subcritical regime, as the InAs layer thickness was below the 1.7 ML critical thickness for SK dot formation. Under the thermodynamically co...

Photon Cascade from a Single Crystal Phase Nanowire Quantum Dot

“…In Figure d, a microphotoluminescence spectrum of a single crystal phase quantum dot shows bright emission with comparable intensities to type I quantum dots (measured in the same setup) and strong polarization along the nanowire growth z -axis (Supporting Information Figure S1). We measure the coherence length under above-band excitation for line X in a Michelson interferometer and extract from an exponential fit a line width of 23 ± 1 μeV.…”

Single quantum dot emission at telecom wavelengths from metamorphic InAs/InGaAs nanostructures grown on GaAs substrates

“…3 However, a surface density of a few dots per micro square meter is necessary to allow detection of single photons, requiring ad hoc growth procedures. 4,5 In molecular beam epitaxy ͑MBE͒, the deposition of subcritical InAs coverages followed by postgrowth annealing ͑PGA͒ is an useful approach, 6,7 but to match the QD emission with the 1.3 m telecom window, it is necessary to engineer the InAs/GaAs structure, for example, adding InGaAs or GaSb capping layers. 4,5,8 To extend the emission up to 1.55 m, the growth of QDs on metamorphic buffers has been useful for high density structures.…”

Low density MOVPE grown InGaAs QDs exhibiting ultra-narrow single exciton linewidths

“…Furthermore, the dephasing time of localized excitons in semiconductor QDs is inversely proportional to the linewidth of optical transitions [7], therefore narrow linewidth QDs are especially interesting for tasks in the field of quantum computation [8]. Up to now, sharp QD PL emission linewidths, as narrow as 10 μeV or even lower under resonant pumping, were reported for QDs grown by molecular-beam epitaxy (MBE) [9,10]. The linewidth of MBE grown QDs has been typically of about one order of magnitude smaller than MOVPE grown QDs, due to the low impurity incorporation, the atomic layer control of the MBE, and the fundamental differences in growth method compared to MOVPE.…”