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Faraday rotation of light in microcavities is studied theoretically. The reflection and transmission spectra are calculated. It is shown that in the region of the spectrum corresponding to a characteristic mode of the cavity the Faraday rotation is strongly intensified and the polarization of the light changes substantially. [ABSTRACT FROM AUTHOR]

A quantum dot with a single magnetic ion is a perfect model system to investigate spin dynamics of a magnetic ion embedded in semiconductor matrix. In this work we present results of spin dynamics studies of Mn2+ ion embedded in CdSe quantum dot, performed under modulated excitation of the dot. In particular, the relaxation time of the Mn2+ ion in high magnetic field was determined. [ABSTRACT FROM AUTHOR]

We briefly review recent achievements in experimental and theoretical studies of the spin dynamics of electrons and trions under optical pulse-train excitation. The microscopic origin of spin coherence generation, control and detection by means of light is uncovered. The specific features of spin-Faraday, Kerr, and ellipticity signals are analyzed. We show that these effects provide complementary information about spin dynamics. The equilibrium spin dynamics probed by the spin noise spectroscopy is also discussed. [ABSTRACT FROM AUTHOR]

We report on the fabrication of a side-gate structure which enables a purely lateral electric field to be applied onto a self-assembled quantum dot. The lateral field produces an unconventional 'M'-shaped exciton energy shift-a blueshift followed by a redshift. The unconventional energy shift is reproduced by calculation. The calculation shows that only the positively charged exciton shows the unconventional shift. The origin is attributed to the field-induced hole-concentration in the bottom-corner of the dot, which strongly enhances the repulsive direct Coulomb interaction and reduces the exciton binding energy. [ABSTRACT FROM AUTHOR]

We illustrate how the linear combination of zone center bulk bands combined with the full-zone k·p method can be used to accurately compute the electronic states in semiconductor nanostructures. To this end we consider a recently developed 30-band model which carefully reproduces atomistic calculations and experimental results of bulk semiconductors. The present approach is particularly suited both for short-period superlattices and large nanostructures where a three-dimensional electronic structure is required. This is illustrated by investigating ultrathin GaAs/AlAs superlattices. [ABSTRACT FROM AUTHOR]

Crystal phase heterostructures, consisting of homogeneous composition zinc-blende inclusions in wurtzite InP and GaAs nanowires are investigated theoretically in the frame of the extended-basis tight-binding approach. Increased band gap for the wurtzite phase and staggered type II band alignment are predicted for both materials. Comparison of theoretical results with microphotoluminescence measurements on single InP nanowires yields fair semiquantitative agreement. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate that self-organized InGaAs quantum dots (QDs) grown on GaAs (111) substrate using droplet epitaxy have great potential for the generation of entangled photon pairs. The QDs show spectrally sharp luminescence lines and low spatial density. A second order correlation value of g(2)(0)<0.3 proves single-photon emission. By comparing the power dependence of the luminescence from a number of QDs we identify a typical luminescence fingerprint. In polarization dependent microphotoluminescence studies a fine-structure splitting ranging ≤40 μeV down to the determination limit of our setup (10 μeV) was observed. [ABSTRACT FROM AUTHOR]

The electric field dependence of the exciton g factor and the fine structure splitting in self-assembled InGaAs/GaAs quantum dots grown via a flush-overgrowth technique is studied by photocurrent and photoluminescence experiments. Both the fine structure and the Zeeman splitting can be tuned over a wide range via electric fields applied in growth direction of the quantum dot. For the g factor, a tunability of 250% is demonstrated from g=0.12 to 0.42. [ABSTRACT FROM AUTHOR]

We report on the experimental evidence of the manipulation of the exciton spin in InGaN quantum dots through the application of an external electric field up to room temperature. Furthermore, we have found the exciton spin relaxation to be independent of temperature. These findings are highly promising for the potential future use of nitride semiconductor quantum dots in practical spintronic devices. [ABSTRACT FROM AUTHOR]

Voltage controlled electrical charging of a single InAs quantum dot by a spin polarized electron from a ZnMnSe spin aligner is presented, and the spin information is read out optically. We demonstrate that the characteristic single quantum dot photoluminescence polarization pattern of the negative trion and the neutral exciton lines directly reflects the spin state of the electrically injected electron. [ABSTRACT FROM AUTHOR]

We apply artificial shape engineering of epitaxial semiconductor nanostructures to demonstrate InGaAs quantum rods (QRs), nanocandles, and quantum dots-in-rods on a GaAs substrate. The evolution of the QRs from a zero-dimensional to one-dimensional confinement is evidenced by systematically measuring the photoluminescence and photoluminescence decay as a function of the rod length. Lasers based on a three-stack QR active region are demonstrated at room temperature, validating the applicability of the QRs in the real devices. [ABSTRACT FROM AUTHOR]

We investigate the low-temperature upconversion electroluminescence (UCEL) in GaAs p-i-n diodes with a layer of self-assembled InAs quantum dots (QDs) in the intrinsic region (i). Injection of carriers into the QD states at an applied bias well below the flatband condition results in near-band-edge GaAs electroluminescence, i.e., emission of photons with energies much larger than that supplied by the applied voltage and the thermal energy. We attribute the UCEL to an Auger-like recombination process and discuss its influence on carrier thermalization processes and the effect of an applied magnetic field. [ABSTRACT FROM AUTHOR]

We investigated an optically created nuclear field in a single InAlAs quantum dot and demonstrated that the nuclear field can be used to discriminate whether photoluminescence lines originate from the same dot or a different dot. Since the nonlinear response of the nuclear field is sensitive to the electron g factor and correlation time of a coupled electron-nuclear spin system, the resultant Overhauser shift is their good measure for individual quantum dots. This method provides a simple and convenient alternative to the standard photon cross-correlation method. [ABSTRACT FROM AUTHOR]

The far field radiation pattern of microdisk cavities embedding a quantum well is measured through angle resolved microphotoluminescence. The radiation pattern presents two narrow lobes slightly off the disk plane, in apparent contradiction with previous theoretical predictions. The observed radiation pattern is shown to result from interferences with light reflected by the sample substrate. It can be fully reproduced given the microdisk precise geometry as well as the whispering gallery mode azimuthal number. [ABSTRACT FROM AUTHOR]

The quantum-confined Stark effect of excitonic states in self-assembled (In,Ga)As/GaAs quantum dots was studied by microphotoluminescence spectroscopy. A similar Stark-shift behavior for excitons, biexcitons, and a charged state was observed. Investigations suggest the absence of a permanent dipole moment in the lateral quantum dot plane. Values of the polarizability could be derived for all the investigated states. Furthermore, high-resolution Fabry-Pérot interferometry was applied to resolve the excitonic fine structure splitting and to investigate the influence of a lateral electric field. For a single dot, the splitting could be tuned to zero, thus affording the possibility to create electrically controlled entangled photon pairs. [ABSTRACT FROM AUTHOR]

The authors implement and demonstrate in this letter a scheme that permits to drive electroluminescence with an extremely low turn-on voltage. The device behaves like compound semiconductors, in which the electroluminescence turn-on voltage is about the same as the open circuit voltage for the photovoltaic effect. However, the electroluminescence turn-on voltage is about half of the band gap of the emitting material that cannot be explained using current models of charge injection in organic semiconductors. The authors hereby propose explanation through an Auger-type two-step injection mechanism. [ABSTRACT FROM AUTHOR]

The authors report the optical characteristics of GaSb/GaAs self-assembled quantum dots (QDs) embedded in an InGaAs quantum well (QW). Variations in the In composition of the QW can significantly alter the emission wavelength up to 1.3 μm and emission efficiency. Lasing operation at room temperature is obtained from a 2-mm-long device containing five stacked GaSb QDs in In0.13Ga0.87As QWs at 1.026 μm with a threshold current density of 860 A/cm2. The probable lasing transition involves electrons and holes confined in the QW and QDs, respectively, resulting in a large peak modal gain of 45 cm-1. A significant blueshift of the electroluminescence peak is observed with increased injection current and suggests a type-II band structure. [ABSTRACT FROM AUTHOR]

The polarization splitting of the exciton ground state in two laterally coupled quantum dots under an in-plane electric field is investigated, and its effective tuning is designed. It is found that there are significant Stark effect and anticrossing in energy levels. Due to the coupling between inter- and intradot states, the absolute value of polarization splitting is significantly reduced, and it could be tuned to zero by the electric field for proper interdot separations. The scheme of the authors is interesting for the research on the quantum dot–based entangled-photon source. [ABSTRACT FROM AUTHOR]

The authors report measurements of room temperature spin dynamics in InGaAs quantum dots using time-resolved differential transmission and Faraday rotation techniques. They observe an enhancement of the electron spin lifetime by an order of magnitude for direct optical pumping of the quantum dot ground state compared to optical pumping of the GaAs barriers. These findings indicate that the optical excitation conditions can have a critical influence on the spin kinetics, a result which may account for the wide variation of spin lifetimes reported to date. The enhancement in spin lifetime observed here is attributed to the reduction of phonon-mediated spin-flip scattering. [ABSTRACT FROM AUTHOR]

The authors report on electroluminescence measurements combined with photoluminescence excitation spectroscopy on a single InGaAs quantum well placed in the intrinsic region of a p-i-n photodiode. They show that at low current density, the spectra are dominated by the spectrally narrow excitonic emission. Moreover when increasing carrier injection, they observe the progressive transition from excitons into free electron-hole pairs. This structure meets all criteria to be integrated in a semiconductor microcavity and the present demonstration of exciton electroluminescence is the first step toward the achievement of the strong coupling regime under electrical injection. [ABSTRACT FROM AUTHOR]

The authors report measurements of hole spin relaxation in neutral InGaAs quantum dots using polarization-dependent time-resolved photoluminescence experiments. The single-particle hole spin relaxation was isolated from other spin flip processes in the electron-hole system by detecting the initial transfer of population from optically active to dark states. The results indicate that electron-hole exchange interactions play a negligible role in the carrier spin kinetics, and are consistent with a mechanism of hole spin relaxation via phonon-mediated virtual scattering between confined quantum dot states. [ABSTRACT FROM AUTHOR]

Degeneracy of the bright single exciton spin state is a prerequisite for the production of triggered polarization-entangled photon pairs from the biexciton decay of a quantum dot. Normally, however, the exciton spin states are split due to in-plane asymmetries. Here the authors demonstrate that the exciton splitting of an individual dot can be tuned through zero by thermal annealing. Repeated annealing blueshifts the exciton emission line of the dot, accompanied by a reduction and inversion in polarization splitting. Annealing is also demonstrated to control the detuning between the exciton and biexciton transitions in any selected dot. [ABSTRACT FROM AUTHOR]

The author report on a theoretical study of optical anisotropy in quantum dots. The mechanisms how shape anisotropy and strain field lead to optical anisotropy are identified by an empirical tight-binding approach. The anisotropic structure of quantum dots is shown to impose stronger confinement for the localized p orbitals aligning along the short axis. In self-assembled quantum dots, these orbitals are also seen in a higher potential produced by the strain field. As a result, the valence-band electrons prefer to occupy the orbitals aligning along the long axis, which leads to stronger optical emission polarized along that direction. [ABSTRACT FROM AUTHOR]

We linearly up convert photons from 820 to 650 nm, an energy change of ∼400 meV, using a AlGaInP/GaInP quantum well heterostructure. Current and luminescence-voltage measurements are presented at temperatures from 6 to 300 K. Photoexcited electrons are injected into the semiconductor from the Au Schottky and a forward bias across the p+-i-n heterostructure drifts electrons into the GaInP quantum well. Holes diffuse from the heavily doped substrate and radiatively recombine, emitting ∼650 nm light. Linear upconversion is verified by injecting hot electrons with a solid-state tunnel junction. This device encourages other technologies, including night-vision aids and thermal energy converters. [ABSTRACT FROM AUTHOR]

We report investigations on carrier capture and relaxation processes in undoped and modulation-doped InAs/GaAs self-assembled quantum dots (QDs) by using time-resolved spectroscopy technique with a time resolution of ∼200 fs. We find that carrier capture and relaxation in the ground state of the charged QD are faster compared to the undoped dots even at an excitation level as low as 1×1010 cm-2. It is attributed to the triggering of the vibrating polarization field induced by the presence of cold carriers in the doped dots. The rate of an electron been captured by a positively charged QD is also calculated based on our proposed model. [ABSTRACT FROM AUTHOR]

Si0.75Ge0.25/Si/Si0.5Ge0.5 trilayer asymmetric superlattices were prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 °C. The nonlinear optical response caused by inherent asymmetric interfaces in this structure predicted by theories was verified by in-plane optical anisotropy in (001) plane measured via reflectance difference spectroscopy. The results show Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice is optically biaxial and the two optical eigen axes in (001) plane are along the directions [110] and [-110], respectively. Reflectance difference response between the above two eigen axes can be influenced by the width of the trilayers and reaches as large as ∼10-4–10-3 in 15-period 2.7 nm-Si0.75Ge0.25/8 nm-Si/1.3 nm-Si0.5Ge0.5 superlattice when the normal incident light wavelength is in the range of 500–1100 nm, which is quite remarkable because the optical anisotropy does not exist in bulk Si. [ABSTRACT FROM AUTHOR]

Spin injection from a diluted magnetic semiconductor quantum well (DMS-QW) into self-assembled quantum dots (QDs) of CdSe is demonstrated via LO-phonon-assisted resonant electron tunneling. The experimental evidence for the spin injection is clearly shown by time-resolved circularly polarized exciton photoluminescence (PL) with the polarization degree up to 40% in QDs. In addition, a type II transition with the lifetime of 3.5 ns between electrons in the QDs and heavy holes in the DMS-QW is observed. These PL energies directly indicate that the electron tunneling is resonantly assisted by LO-phonon scattering, which realizes an efficient spin-injection process into QDs. [ABSTRACT FROM AUTHOR]

Carrier capture into self-organized InGaAs/GaAs quantum dots with an electronic level spacing close to optical phonon energies is studied in a two-color femtosecond transmission experiment. After resonant generation of carriers in the wetting layer, we analyze the population of both the band edge of the wetting layer and the excited states of the quantum dots. Most strikingly, the carrier capture time of 3 ps is found to be independent of the carrier density, providing that it remains small compared to the number of available electronic states in the quantum dots. Moreover, we find that the capture process is predominantly spin preserving in nature. These results suggest that phonon-mediated scattering governs the quantum dot filling. [ABSTRACT FROM AUTHOR]

By isolating quantum dots in microstructures with cleaved facets, we measure individual-quantum-dot photoluminescence emitted in the in-plane direction, in addition to the widely studied vertical direction. The emission is shown to be polarized in the plane, and the observed fine structure is found to be extremely directionally-dependent. These characteristics are attributed to exciton states with orthogonally aligned dipoles in the plane. The result suggests possibilities for single-quantum-dot devices, including side-emitting single-photon sources. [ABSTRACT FROM AUTHOR]

We report direct measurement of the spin dynamics of electrons and holes in self-assembled InAs quantum dots (QDs) through polarization-sensitive time-resolved photoluminescence experiments on modulation-doped quantum dot heterostructures. Our measured hole spin decay time is considerably longer than in bulk and quantum well semiconductor systems, indicating that the removal of near degenerate hole states with different spin quantization axes through three-dimensional confinement slows hole spin relaxation in semiconductors. The electron and hole spin decay times we observe (electrons: 120 ps; holes: 29 ps) are consistent with spin relaxation via phonon-mediated virtual scattering between the lowest two confined levels in the QDs, which have a mixed spin character due to the spin–orbit interaction. [ABSTRACT FROM AUTHOR]

We present experimental evidence of giant optical anisotropy in single InAs quantum dots. Polarization-resolved photoluminescence spectroscopy reveals a linear polarization ratio with huge fluctuations, from one quantum dot to another, in sign and in magnitude with absolute values up to 82%. Systematic measurements on hundreds of quantum dots coming from two different laboratories demonstrate that the giant optical anisotropy is an intrinsic feature of dilute quantum-dot arrays. [ABSTRACT FROM AUTHOR]

We have investigated the crystal orientation dependence of optical properties in InxGa1-xN/GaN multiple quantum wells. The spectral peaks and intensity of the microphotoluminescence signal for different crystal orientations were found to have six-fold symmetry. Quite interestingly, the refractive index, obtained from the interference pattern, also varies with the crystal orientation. The 60° periodic anisotropy of electronic transitions as well as optical parameters was interpreted in terms of the Pockels effect induced by the strong built-in field in nitride heterojunctions. The linear dependence of the change of the refractive index on electric field is consistent with the prediction of the Pockels effect. Our result provides an alternative solution to improve the designs of photonic and electronic devices based on nitride semiconductors. [ABSTRACT FROM AUTHOR]

We demonstrate that polarization-resolved ultrafast pump-probe spectroscopy can be used to measure accurately (<10%) the fraction of charged dots in quantum dot (QD) ensembles. The method is applied to study the dependence of charging levels in thermally annealed InGaAs QDs, grown both as nominally undoped and n-type modulation-doped structures. We also show that the method can be used to study the spectral distribution of charges (or charging profiles) in quantum dot ensembles. [ABSTRACT FROM AUTHOR]

The effect of small changes in GaSb layer width on the photoresponse spectrum of 20.5 Å InAs/InSb-interfaces/X Å GaSb type-II superlattice (SL) suitable for mid-infrared detection was investigated. By decreasing the GaSb width X from 27 to 18 Å, the cut-off wavelength was increased from 4.03 to 4.55 μm. This decrease of the SL bond gap and other effects of the design changes on photoresponse spectrum with narrower GaSb layers are explained by a nonperturbative, modified envelope function approximation calculation that includes the interface coupling of heavy, light, and spin orbit boles resulting from the in-plane asymmetry at InAs/GaSb interfaces. [ABSTRACT FROM AUTHOR]

We report the application of time- and polarization-resolved photoluminescence up-conversion spectroscopy to the study of spin capture and energy relaxation in positively and negatively charged, as well as neutral InAs self-assembled quantum dots. When compared to the neutral dots, we find that carrier capture and relaxation to the ground state is much faster in the highly charged dots, suggesting that electron–hole scattering dominates this process. The long spin lifetime, short capture time, and high radiative efficiency of the positively charged dots, indicates that these structures are superior to both quantum well and neutral quantum dot light-emitting diode spin detectors for spintronics applications. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Demonstrates the formation of Stark ladder quantization in semiconductor HgTe/CdTe Superlattice. Application of Wannier-Stark quantization; Coexistence of two and three dimensional electron gas in photoluminescence (PL) spectrum; Blueshift in the infrared PL spectrum.

Time‐resolved two‐photon photoemission spectroscopy (tr‐2PPE) directly probes the kinetic energy and dynamics of photoemitted electrons. At the same time, the electronic structure and temporal occupation of surface‐near states can be accessed, which allows to unravel the fundamental processes governing electron dynamics and energetics in semiconductor surfaces. Here, recent studies on epitaxial III–V semiconductors and II–VI nanostructures are reviewed and the feasibility to study electron dynamics in III–V surface quantum wells (SQW) with tr‐2PPE is demonstrated. On InP(100), for example, surface states are filled by electrons relaxing from higher energetic bulk states. In the case of nanostructured materials, these effects play an even larger role due to the high surface to bulk ratio. For CdSe quantum dots, Auger recombination strongly competes with the exploitation of the quantum size dependent phonon bottleneck. The electron cooling dynamics in CdSe platelets are extremely fast and exhibit complete independence of Auger‐like processes. Finally, an InGaAs SQW/InP structure is shown to exhibit much longer lifetime of the quantum confined states. The SQW may act as a carrier accumulation layer for bulk electrons diffusing to the surface. Implications for future use in energy material systems for photovoltaic and photocatalytic applications are discussed. [ABSTRACT FROM AUTHOR]

In III–V semiconductor nano-structures, the electron and nuclear spin dynamics are strongly coupled. Both spin systems can be controlled optically. The nuclear spin dynamics are widely studied, but little is known about the initialization mechanisms. Here, we investigate optical pumping of carrier and nuclear spins in charge tunable GaAs dots grown on 111A substrates. We demonstrate dynamic nuclear polarization (DNP) at zero magnetic field in a single quantum dot for the positively charged exciton X+ state transition. We tune the DNP in both amplitude and sign by variation of an applied bias voltage Vg. Variation of ΔVg on the order of 100 mV changes the Overhauser splitting (nuclear spin polarization) from −30 μeV (−22%) to +10 μeV (+7%) although the X+ photoluminescence polarization does not change sign over this voltage range. This indicates that absorption in the structure and energy relaxation towards the X+ ground state might provide favourable scenarios for efficient electron-nuclear spin flip-flops, generating DNP during the first tens of ps of the X+ lifetime which is on the order of hundreds of ps. Voltage control of DNP is further confirmed in Hanle experiments. [ABSTRACT FROM AUTHOR]

Long distance entanglement distribution is an important problem for quantum information technologies to solve. Current optical schemes are known to have fundamental limitations. A coherent photon-to-spin interface built with quantum dots (QDs) in a direct bandgap semiconductor can provide a solution for efficient entanglement distribution. QD circuits offer integrated spin processing for full Bell state measurement (BSM) analysis and spin quantum memory. Crucially the photo-generated spins can be heralded by non-destructive charge detection techniques. We review current schemes to transfer a polarization-encoded state or a time-bin-encoded state of a photon to the state of a spin in a QD. The spin may be that of an electron or that of a hole. We describe adaptations of the original schemes to employ heavy holes which have a number of attractive properties including a g-factor that is tunable to zero for QDs in an appropriately oriented external magnetic field. We also introduce simple throughput scaling models to demonstrate the potential performance advantage of full BSM capability in a QD scheme, even when the quantum memory is imperfect, over optical schemes relying on linear optical elements and ensemble quantum memories. [ABSTRACT FROM AUTHOR]

We report on coupling between semiconducting single-wall carbon nanotubes (s-SWNT) photoluminescence and silicon microring resonators. Polyfluorene extracted s-SWNT deposited on such resonators exhibit sharp emission peaks, due to interaction with the cavity modes of the microring resonators. Ring resonators with radius of 5 μm and 10 μm were used, reaching quality factors up to 4000 in emission. These are among the highest values reported for carbon nanotubes coupled with an integrated cavity on silicon platform, which open up the possibility to build s-SWNT based efficient light source on silicon. [ABSTRACT FROM AUTHOR]

Purcell effect is a powerful tool to efficiently collect single photons emitted by semiconductor quantum dots. However, it is common to observe a degraded single photon purity when a quantum dot is inserted in an optical microcavity. Here, we investigate the role of the cavity coupling on the single photon purity for a quantum dot deterministically coupled to a pillar cavity mode. We show that the degradation of the purity cannot be attributed to cavity feeding effects but is fully explained by recapture processes. A good single photon purity is therefore easily restored using an intra-dot excitation scheme. [ABSTRACT FROM AUTHOR]