Low density InAs quantum dots with control in energy emission and top surface location (original) (raw)

In-situ height engineering of InGaAs / GaAs quantum dots by chemical beam epitaxy

Journal of Nanophotonics, 2016

This special section of the Journal of Nanophotonics is focused on optics, spectroscopy, and nanophotonics of quantum dots. The study of optical properties of colloidal quantum dots (QDs) and nanostructures, which are formed based on them, is actual for modern nanophotonics. Interest in these structures is caused by the widest range of practical applications in various fields. The most actual applications of photonics of QDs are fluorescent labeling of biological objects, biosensors, and minimally invasive biomedical technology, including thermal and photodynamic therapy of severe human diseases. 1-3 Primarily, the unique optical properties of colloidal QDs are sizedependent optical absorption and photoluminescence spectra, a wide range of luminescence excitation, high photostability of nanocrystals, etc. These properties of colloidal QD spectroscopy provide opportunities for the development of optically distinguishable codes, identifying various diseases, markers of diseased cells, tissues, and organs with its subsequent visualization. The possibility of specific binding of bioconjugated QDs with different targets provide opportunities for labeling of cells and a variety of protein molecules both in vitro and in vivo. The basis of marked applications is fundamental processes. They are 1-3 : absorption of light by colloidal QDs; the formation of excitons; radiative and nonradiative annihilation of excitons; radiative recombination of localized excitons; relations of processes of recombination luminescence with QD size and their composition (special in the case of substitutional solid solutions); the exchange of electronic excitations between colloidal QDs and organic structures, which interact with interface of quantum dots. Thus, the authors' papers 1-3 develop these important areas of optics and spectroscopy of colloidal quantum dots. A simple model of a quasi-zero-dimensional structure in the form of a spherical QD of radius a and permittivity ε 2 , embedded in a medium with permittivity ε 1 , was discussed in Ref. 4. An electron (e) and a hole (h) with effective masses m e and m h were assumed to travel within the QD. We assume that the permittivities satisfy the relation ε 2 ≫ ε 1 and that the conduction and valence bands are parabolic. The theory of exciton states in QDs under conditions of dominating polarization interaction of an electron and a hole with a spherical (QDdielectric matrix) interface are developed in Ref. 4. It is shown that the energy spectrum of a heavy hole in the valence band QD is equivalent to the spectrum of a hole carrying out oscillator vibrations in the adiabatic electron potential. 5 It is shown that the absorption and emission edge of QDs is formed by two transitions of comparable intensity from different hole size-quantization levels and into a lower electron size-quantization level. 6 The interband absorption of light in QDs was studied theoretically in Ref. 6 using the dipole approximation in the framework of the model [4] considered here, and under the assumption that the absorption length λ ≫ a. An expression for the quantity Kðs; ωÞ defined by the hole optical transition from the energy level t h ¼ 2n h (t h is the hole main quantum number, n h , is the hole radial quantum number) to the lowest electron level (n e ¼ 1, l e ¼ m e ¼ 0)

Triggered Single‐Photon Emission of Resonantly Excited Quantum Dots Grown on (111)B GaAs Substrate

physica status solidi (RRL) – Rapid Research Letters

With the present development in the emerging field of photonic quantum technologies, including, for instance, exciting progress in quantum key distribution, [1-4] quantum teleportation, [5,6] and boson sampling, [7-10] the interest in high-performance single and entangled photon-pair sources is ever increasing. A variety of systems such as atoms, dye molecules, diamond color centers, semiconductor impurities, and quantum dots (QDs) have been used to demonstrate single-photon and entangled photon pair emission. [11-17] Among them, self-assembled QDs are of particular importance due to their robustness and compatibility with semiconductor nanotechnology. Single QDs show sharp luminescence lines, high quantum efficiency, and excellent quantum properties. [10,18-22] Regarding the optical properties it is important to note that in contrast to QDs on (001) GaAs substrate, for QDs grown on (111) GaAs substrate the piezoelectric field is directed along the growth direction [111] and does not lower the symmetry below C 3V along the QDs base. [23] As a result, they are expected to feature diminishing fine-structure splitting (FSS). [23,24] This being a prerequisite for the generation of polarization-entangled photon pairs based on the radiative biexciton-exciton (XX-X) cascade, [25] QDs grown on (111) GaAs substrate are attractive candidates for this application, as has been confirmed for (111)-grown pyramidal site-controlled QDs. [14,26] In the well-explored (001) GaAs material system, coherent control has proven to be a key component for high-quality photons leading to close to perfect values for the multi-photon suppression, [27] as well as the generation of entangled photon pairs. [15,16,20,28] The latter using either advanced and more challenging growth techniques, such as droplet-etching, [29] or a rather complicated device design to control the QDs strain have to be applied. [16,30] Furthermore, it is naturally desirable to enhance the outcoupling efficiency of the source. Popular approaches are the use of solid immersion lenses, [19] which suffer from limited scalability, and micropillar cavities, [31,32] the latter featuring a high quality, yet very narrowband enhancement, hindering the simultaneous coupling to the cavity of both XX and X due to typical finite binding energies of a few meV in InGaAs or GaAs-based QDs. Especially in recent years, circular Bragg gratings (CBG) have become a powerful alternative for overcoming the aforementioned issues, [20,33-35] however demanding a high processing accuracy. Another well-established and efficient technique is the in situ integration of suitable QDs in monolithic microlenses. [36] While

Formation and optical characterization of single InAs quantum dots grown on GaAs nanoholes

Applied Physics Letters, 2007

We present a study of the structural and optical properties of InAs quantum dots formed in a low density template of nanoholes fabricated by droplet epitaxy on GaAs ͑001͒. The growth conditions used here promote the formation of isolated quantum dots only inside the templated nanoholes. Due to the good optical quality and low density of these nanostructures, their ensemble and individual emission properties could be investigated and related to the particular growth method employed and the quantum dot morphology.

An intentionally positioned (In,Ga)As quantum dot in a micron sized light emitting diode

Applied Physics Letters, 2010

We have integrated individual ͑In,Ga͒As quantum dots ͑QDs͒ using site-controlled molecular beam epitaxial growth into the intrinsic region of a p-i-n junction diode. This is achieved using an in situ combination of focused ion beam prepatterning, annealing, and overgrowth, resulting in arrays of individually electrically addressable ͑In,Ga͒As QDs with full control on the lateral position. Using microelectroluminescence spectroscopy we demonstrate that these QDs have the same optical quality as optically pumped Stranski-Krastanov QDs with random nucleation located in proximity to a doped interface. The results suggest that this technique is scalable and highly interesting for different applications in quantum devices.

Growth and characterization of single quantum dots emitting at 1300 nm

Applied Physics …, 2005

We have optimized the molecular-beam epitaxy growth conditions of self-organized InAs/ GaAs quantum dots ͑QDs͒ to achieve a low density of dots emitting at 1300 nm at low temperature. We used an ultralow InAs growth rate, lower than 0.002 ML/ s, to reduce the density to 2 dots/ m 2 and an InGaAs capping layer to achieve longer emission wavelength. Microphotoluminescence spectroscopy at low-temperature reveals emission lines characteristic of exciton-biexciton behavior. We also study the temperature dependence of the photoluminescence, showing clear single QD emission up to 90 K. With these results, InAs/ GaAs QDs appear as a very promising system for future applications of single photon sources in fiber-based quantum cryptography.

Self‐Assembled InAs/GaAs Coupled Quantum Dots for Photonic Quantum Technologies

Advanced Quantum Technologies, 2019

Coupled quantum dots (CQDs) that consist of two InAs QDs stacked along the growth direction and separated by a relatively thin tunnel barrier have been the focus of extensive research efforts. The expansion of available states enabled by the formation of delocalized molecular wavefunctions in these systems has led to significant enhancement of the already substantial capabilities of single QD systems and have proven to be a fertile platform for studying light–matter interactions, from semi‐classical to purely quantum phenomena. Observations unique to CQDs, including tunable g‐factors and radiative lifetimes, in situ control of exchange interactions, coherent phonon effects, manipulation of multiple spins, and nondestructive spin readout, along with possibilities such as quantum‐to‐quantum transduction with error correction and multipartite entanglement, open new and exciting opportunities for CQD‐based photonic quantum technologies. This review is focused on recent CQD work, highlig...