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We report experimental observation of optically-pumped continuous-wave lasing from self-assembled quantum dots (QDs) embedded in high-quality factor (Q) microdisk laser structures. For large diameter (4.5 μm) microdisks containing InAs QDs, the emission spectra show simultaneous lasing on one to five well separated modes (Q = 10000-17000) in the wavelength range between 920 and 990 nm. For small diameter (2 μm) microdisks containing (In,Ga)As QDs, lasing occurs even when the estimated average number of QDs inside the cavity-mode volume is unity.

We resolve spatially, spectroscopically and temporally the photoluminescence emission from single self-assembled In(Ga)As/GaAs quantum dots, The temporal evolution of the emission spectrum after pulsed excitation is measured for various excitation intensities at various ambient temperatures. The evolution of the spectrum with the increase in both steady state and pulse excitation intensities is measured as well. A multi-exciton model is used for calculating the temporal and excitation intensity dependence of the measured spectra. The quantitative agreement between the measured and calculated spectra provides an unambiguous determination of the radiative lifetime of a single quantum dot exciton. This lifetime is 4-6 ns long and is temperature independent. The reduced spatial coherence between the confined exciton and the radiation electromagnetic field quantitatively explains this long radiative time.

7 páginas, 5 figuras., We have succeeded in preparing excitons with a specific charge in single semiconductor quantum rings. Buried InAs quantum rings are loaded with electrons from a reservoir through a tunneling barrier and an additional electron–hole pair is generated by optical excitation. Single rings are addressed with nano-optical techniques. We observe abrupt shifts in the emission energy as electrons are added one by one. Furthermore, the experiments provide unique insights into the interaction of electrons in semiconductor nano-islands with their environment., We would like to thank J.P. Kotthaus for stimulating discussions. This work was funded by the DFG (Project SFB 348) and by QUEST, a NSF Science and Technology Center.

Using time correlated single photon counting combined with temperature dependent diffraction limited confocal photoluminescence spectroscopy we accurately determine, for the first time, the intrinsic radiative lifetime of single excitons confined within semiconductor quantum dots. Their lifetime is one (two) orders of magnitude longer than the intrinsic radiative lifetime of single excitons confined in semiconductor quantum wires (wells) of comparable confining dimensions. We quantitatively explain this long radiative time in terms of the reduced spatial coherence between the confined exciton dipole moment and the radiation electromagnetic field., Comment: 4 pages, 3 figures

Quantum communication relies on the availability of light pulses with strong quantum correlations among photons. An example of such an optical source is a single-photon pulse with a vanishing probability for detecting two or more photons. Using pulsed laser excitation of a single quantum dot, a single-photon turnstile device that generates a train of single-photon pulses was demonstrated. For a spectrally isolated quantum dot, nearly 100% of the excitation pulses lead to emission of a single photon, yielding an ideal single-photon source.

We resolve spatially, spectroscopically, and temporally the photoluminescence emission from single self-assembled InAs/GaAs quantum dots. The rich photoluminescence spectrum and its evolution with time after pulse excitation and with the density of excitation is experimentally measured and analyzed using a theoretical multiexciton model. The model accounts quantitatively for the dynamics of a small number of interacting electrons and holes confined in optically excited semiconductor quantum dots.

We explore electron transfer in double quantum well structures induced by femtosecond mid-infrared intersubband excitation. Spatial transfer of electrons from one quantum well to its hole filled neighbor is detected by recombination luminescence. The process results in upconversion of the mid-infrared exciting light to near-infrared luminescence. Two mid-infrared pulses with variable time delay allow us to display the field and intensity autocorrelation function for the upconverted signal and measure the electron transfer dynamics. Electron transfer between two GaAs quantum wells separated by 300 nm can be saturated and the intensity autocorrelation function exhibits a slow 18 ps recovery. Transfer between wells separated by only 25 nm is coherently controlled by the phase of the two collinear infrared pulses.

We present a novel self-assembled quantum dot structure designed to spatially separate and store photo-generated electrons and holes in pairs of strain coupled quantum dots. The spatial separation of electron–hole pairs into quantum dots and strain-induced quantum dots has been investigated and verified by photoluminescence experiments. Results from time-resolved PL demonstrates that at low temperatures (3 K) the electron–hole pair can be stored for several seconds.

6 páginas, 4 figuras.-- PACS: 78.55.−m; 71.35.−y; 73.20.Dx; 78.66.Fd.-- Trabajo presentado en el 13th International Conference on the Electronic Properties of Two-Dimensional Systems (EP2DS), Otawa del 1 al 6 de 1999., An experimental evidence of Auger-like excitation processes in InAs/GaAs quantum dots is demonstrated. Photoluminescence spectra of resonantly excited dots exhibit a rich satellite structure below the ground-state emission band. The energy position and the intensity distribution of the satellites are analyzed and an interpretation of the satellites as due to shake-up processes of the interacting carriers in the higher quantum dot states is suggested.

The primary objective of the STIR project was to investigate the feasibility of realizing graded p-type MgZnO structures, suitable for device integration, using engineered Mg concentration grading. The project was successful in demonstrating a graded MgxZn1-xO epitaxial layer on sapphire, grown by plasma-assisted molecular beam epitaxy (MBE). To realize this accomplishment, MgZnO layers were optimized to allow for up to 46% Mg with no observable phase segregation and sub-nanometer roughness. A primary enabling element of this was the development of a high temperature ZnO buffer layer, resulting in high Mg concentration with low dislocations. A graded structure with Mg concentration from 0 to 43% Mg was grown and validated with SIMS depth profiling. This work indicates that with proper control over flux sources, a graded MgZnO layer is possible and suitable for polarization doping with the proper background carrier concentration control. Future work should focus on obtaining precise control of the Mg concentration through use of a flux monitor and the potential for using nitrogen to combat background n-type carriers in order to realize a high hole density channel.

Titanium oxide (TiO2) was a commonly used anti-reflection coating (ARC) in the past, but has been displaced by silicon nitride (SiNx) due to its ability to both passivate n+ emitters and provide the appropriate optical properties required for effective ARCs (refractive index, transparency, stability over time). However, with growing interest in n-type wafers, which feature p+ emitters, and the inability of SiNx to provide effective field-effect passivation for p-type materials, other passivation materials are being actively investigated by the photovoltaics (PV) RD 20 nm) like AlOx, followed by a low cost optical material such as TiO2 with a proper refractive index for an ARC. This paper addresses the optical and microstructural properties of TiO2 films deposited at various temperatures using an in-line atmospheric chemical vapor deposition system (APCVD). The TiO2 films are investigated by spectroscopic ellipsometry, reflectance spectroscopy and cross-sectional TEM. Additionally, experimental results for the ARC performance of multi-layer ARC structures featuring AlOx/TiO2 are presented.

ZnO thin films were epitaxially grown on Zn-polar (0001) ZnO substrates by plasma-assisted molecular beam epitaxy. Surface root mean square (rms) roughness below 0.3 nm was achieved on a large range of growth temperatures by growing on ZnO substrates with 0.5 degree miscut angle toward [11¯00] axis. Surface treatment with acid etching and ozone exposure was required to remove contamination such as silica residual and carboxyl and carbonate groups on the surface. Removal of these surface impurities reduces the likelihood of extrinsic defect migration into the epitaxial films. High growth temperature (> 640°C) and oxygen rich conditions were required for films with terrace steps, but resulted in a very low growth rate (~30nm/h) and low photoluminescence (PL) lifetimes of lower than 50 ps. With moderate growth temperature (~610°C), higher growth rate and higher PL lifetime with up to 380 ps were achieved. EIT was used for the oxygen plasma to reduce reactive oxygen species etching of the surface, resulting in a higher growth rate and fewer defects in the films. Good crystalline quality was evident in Xray rocking curves with consistent narrow full width at half maximum (FWHM) of (0002), (101¯2) and (202¯1) peaks, indicating low threading dislocations. Both room-temperature and low-temperature photoluminescence indicated high optical quality of the resultant films with few non-radiative recombination centers.

InAs quantum dots (QDs) at different levels of density have been studied by means of photoluminescence, when in addition to the main laser, a second infrared (IR) laser is employed to excite the QD. It is demonstrated that the IR laser considerably affects the QD charge state as well as the emission intensity level (an increase greater than fivefold was observed). These effects are explained in terms of separate generation of excess electrons and holes provided under dual-laser excitation. However, these effects progressively vanish with increasing QD density. The results obtained unambiguously imply that the emission intensity from the QD can be effectively enhanced by purely optical means.

We report a micro-photoluminescence study on the influence of single and multi-quantum dots (QDs) on the exposure by a low-energy laser, in addition to the principal exciting laser. At low temperatures, the presence of the low-energy laser effectively quenches the single QD luminescence. This can be explained in terms of an induced screening of a built-in electric field, which plays an important role as a carrier capture mechanism. The influence of the low-energy laser is successively decreasing when the capture efficiency is increased either by elevated crystal temperature or by increased QD densities, full consistent with the proposed model.

The effect of substrate temperature (T S) and pulse duration (PD) on Mg incorporation, surface quality, and photoresponse properties of MgZnO films grown via PMOCVD were studied. Films grown at T S ranging from 500 to 700 °C but at identical PDs had band gaps varying from 3.38 to 3.87 eV, corresponding to Mg content between x = 0.06 and 0.27. The film with Mg content of 0.27 was the smoothest and achieved at 630 °C-optimal T S. Additionally, pulse time effect was studied by growing films at the same T S but different PDs. A film grown at PD of 12 s has incorporated ∼40% higher Mg than one grown in a continuous mode (PD → ∞), indicting the cruciallity of PMOCVD to realize high Mg film. The peak response spectra of photodetectors were also varied with T S and PD, in accordance with Mg content in the films.

Photoluminescence and time-resolved photoluminescence measurements of charge tunable quantum-dot heterostructures reveal that by appropriate biasing of the device, about 90% of photogenerated holes can be stored at an interface near to the nanostructures and subsequently transferred into the nanostructures in a controlled fashion. The capture dynamics are sensitive to the form of the valence band potential in the layer that caps the Stranski–Krastanow dots. The dependence of the capture rate on applied electric field suggests that the valence band confinement potential is “soft” in the capping layer, with a spatial extent of around 14 nm.

We present a practical method to determine femtosecond laser induced refractive index changes in transparent materials. Based on an iterative Fourier transform algorithm, this technique spatially resolves the refractive index of complex structures by combining the dimensions of the modified region with the corresponding phase change extracted from far-field intensity measurements. This approach is used to characterize optical waveguides written by a femtosecond laser in borosilicate glass.

One promising path to a reduced cost of crystalline silicon (c-Si) photovoltaics (PV) is to increase silicon usage efficiency by using thinner wafers. Many challenges arise when transitioning to thin wafer cells, including increased surface recombination at the rear side of the cell, increased wafer bowing, and a reduction in optical absorption due to a decreased optical path length within the silicon. Rear side passivation provides great promise in addressing these challenges. This paper addresses rear side dielectric configurations that can optimize back surface reflectance, in addition to providing excellent surface passivation. Optical modeling of various stack configurations is examined to explore the back surface reflectance at the Si-dielectric interface for different film combinations and thicknesses as a function of wavelength and internal angle of incidence. Specifically, configurations using aluminum oxide (AlO x ), silicon nitride (SiN x ), titanium dioxide (TiO 2 ), and silicon dioxide (SiO 2 ) were investigated with a focus on designing stack configurations that will also allow for high quality passivation and are compatible with a high-volume manufacturing environment.

Coupled Mode Theory analysis of a new architecture for coupled-resonance optical waveguide design is presented that enables a feedback mechanism in a photonic crystal scheme while also increasing resonant finesse from 2.77 to 10.15.

We investigate cavity-quantum electrodynamics (QED) effects in an all-semiconductor nanostructure by tuning a single self-assembled InAs quantum dot (QD) into resonance with a high quality factor microdisk whispering gallery mode (WGM). The stronger temperature dependence of the QD single-exciton (1X) resonance allows us to change the relative energy of the WGM and the 1X transitions by varying the sample temperature. The two coupled resonances exhibit crossing behavior due to the weak coupling cavity-QED regime. We demonstrate exciton lifetime reduction by 6 due to the Purcell effect by tuning the QD into resonance with the WGM. Our experiments also show that single-exciton lifetime is independent of temperature up to 50 K.

3 páginas, 4 figuras., We report how photoluminescence from self-assembled InAs quantum dots depend on pumping power and vertical electric field. The InAs dots, which are embedded in a capacitor-like structure, act as efficient trapping centers for excitons. At a high enough electric field, however, the photoexcited electrons tunnel out of the dots fast enough to quench the emission. For samples with two adjacent layers of vertically aligned dots, we find that the threshold voltage for quenching depends very strongly on the optical pumping power. In total contrast to this, we find no comparable effect for samples grown with a single layer of dots. We explain this in terms of efficient storage of electrons and holes in the double-layer samples., The work was funded by the Deutsche Forschungsgemeinschaft SFB 348, by the BMBF (Max Plank Research Award), and by QUEST, a National Science and Technology Center Grant No. DMR 20007. S. Huant was supported by the A. vHumboldt foundation.

3 páginas, 2 figuras., It is demonstrated that the photoluminescence spectra of single self-assembled InAs/GaAs quantum dots are very sensitive to excitation energy and crystal temperature. This is qualitatively explained in terms of the effective diffusivity of photogenerated particles, which affects the capture probability of the quantum dot. As a consequence, this opens the possibility of controlling the average number of excess electrons in the quantum dot by optical means. This technique may be used as a simple tool to create and study charged exciton complexes without any specially fabricated samples., One of the authors (E.S.M.) gratefully acknowledges the financial support of the Swedish Institute within the Visby Programme.

Transverse spin lifetimes of spin-polarized photogenerated carriers in InAs self-assembled quantum dots are extracted from the depolarization of their photoluminescence in a magnetic field perpendicular to the spin (the Hanle effect). Hanle measurements on a series of samples reveal that the dot dimensions influence the spin lifetime and its dependence on temperature. The spin lifetime as a function of excitation intensity is qualitatively distinct for carrier spins created in the GaAs host as compared to in the InAs wetting layer.

In an effort to engineer photonic crystal slab (PCS) devices that operate within a single slab-mode regime, the effect of increased cladding index was studied using FDTD simulation. It is known that while increased cladding index forces the light-cone to constrict in frequency, the single mode condition eases allowing for the use of thicker slabs that remain single-mode. This study shows that the behavior of the photonic band gap is similar to that of the light-cone, sweeping lower in frequency, and even widening in some cases, as cladding index increases. Band gap behavior for both even and odd polarizations over thicknesses from d/a = 0.2 to 0.6 and cladding indices from 1 to 2.5 were studied in efforts to design a single-mode, polarization insensitive, complete band gap. When graphically overlaid, the light-cone, single-mode condition, and transmission spectra represent an enabling reference for the design of realizable structures. For device applications where modal dispersion is detrimental or single mode operation is necessary, a paradigm shift away from air-bridge devices is shown to be essential as single-mode structures of this type demand slab thicknesses far too thin for adequate band gap engineering.

Oxide based compounds have been of increasing interest for wide bandgap, deep ultraviolet optoelectronics. While high Al content AlGaN has enabled many UV-DUV technologies, it suffers inherent drawbacks including difficulty achieving increasing Al incorporation, high threading dislocation densities and challenges in bandgap engineering due to polarization and piezoelectric effects. Here we present two wide bandgap cubic oxide compounds, ZnMgO and NiMgO, that offer advantages over AlGaN for deep ultraviolet (DUV) applications. NixMg1-xO and ZnxMg1-xO are both direct band gap, cubic rocksalt (B1) semiconductors with bandgaps in the UV-DUV spectral regions, offering alternatives without the aforementioned drawbacks associated with AlGaN. Here we present NixMg1-xO and ZnxMg1-xO thin films grown by plasma-assisted MBE on lattice matched MgO substrates as a novel means by which to realize DUV detection devices. In both systems we have shown the films to exhibit abrupt, continuously tunable absorptions edges over their respective bandgap ranges. NixMg1-xO films were varied compositionally from x=0 to 1, realizing bandgaps from 3.5 to 7.8 eV. ZnxMg1-xO films were similarly varied over the entire B1 range of the ternary (0

Using finite difference time domain simulations and e-beam assisted lithography we designed and fabricated high transmission transparent contacts for UV nitride devices which consist in perpendicular sets of parallel aluminum lines with a period as low as 260 nm. Transmittance values as high as 100% were predicted for aluminum meshes with the optimized periods, metal line widths and thicknesses. Simulations were compared with optical transmittance measurements. The critical parameters -such as grain size, edge roughness and mesh coating- were determined. The large aluminum grain was decreased by performing a cold aluminum deposition. The aluminum oxide layer over the aluminum mesh was found to reduce the mesh transmittance. Several alternatives were studied to overcome this issue such as coating the mesh with a thin gold or silicon dioxide layer. While the second option appeared promising the addition of the gold layer required much more improvement.

We investigate in this paper the dynamics of entanglement between a QD spin qubit and a single photon qubit inside a quantum network node, as well as its robustness against various decoherence processes. First, the entanglement dynamics is considered without decoherence. In the small detuning regime (Δ=78 μeV), there are three different conditions for maximum entanglement, which occur after 71, 93, and 116 picoseconds of interaction time. In the large detuning regime (Δ=1.5 meV), there is only one peak for maximum entanglement occurring at 625 picoseconds. Second, the entanglement dynamics is considered with decoherence by including the effects of spin-nucleus and hole-nucleus hyperfine interactions. In the small detuning regime, a decent amount of entanglement (35% entanglement) can only be obtained within 200 picoseconds of interaction. Afterward, all entanglement is lost. In the large detuning regime, a smaller amount of entanglement is realized, namely, 25%. And, it lasts only within the first 300 picoseconds.

We have studied terahertz absorption of samples containing two layers of self-aligned, self-assembled InAs quantum dots separated by a thin GaAs barrier. The vertically coupled dots were charged with electrons by applying a voltage bias between a metal gate and a doped layer beneath the dots. For a positive gate bias corresponding to flatband conditions, an absorption peak was observed near 10 meV (2.4 THz). The absorption is attributed to the inhomogeneously broadened transition between the quantum mechanically split levels (bonding and antibonding states) in the vertically coupled quantum dots.

We have investigated the far-infrared absorption in InAs/GaAs quantum dot molecules. The quantum dot molecules consist of two vertically coupled InAs self-assembled quantum dots separated by a GaAs barrier. The electronic coupling between the dot states results in an intraband absorption at THz frequencies. We show that this absorption can be bleached under high excitation intensity delivered by a free-electron laser. The saturation intensity is found to be on the order of 1 W cm−2. The electron relaxation time T1 is estimated from the saturation intensity. A lower limit for T1 of the order of 30 ps is deduced.

Using e-beam lithography on a single layer of polymethylmethacrylate (PMMA) we designed a relatively thick subwavelength aluminum mesh on top of sapphire. The 100 nm thick mesh consisted of two perpendicularly oriented sets of 100 nm wide parallel metal lines with a center to center distance as low as 260 nm. Due to the large proximity effect during e-beam exposure and the small spacing between metallic lines the use of an adhesion promoting layer appeared necessary to avoid premature peeling of the photoresist. Using a monoatomic layer of hexamethyldisilazane (HMDS) as an adhesion promoter between the sapphire and the PMMA, a 500 nm thick photoresist layer could be exposed and developed with excellent control over the features sizes. Line spacing distances from 500 nm down to 160 nm were achieved. An oxide plasma etch was found to be necessary for metal adhesion during the lift-off process. Due to the small spacing between the aluminum lines, use of a bi-layer photoresist technique to achieve undercut was not possible. Thermal evaporation of aluminum was performed and e-beam evaporation didn't help smoothing the metal surface. An additional ultrasonic bath in acetone was found necessary to ease the lift-off process.

A complete photonic band gap (PBG) in photonic crystal slab (PCS) devices is desirable for various applications, and a realizable device of this kind demands minimal transmittance in-plane as well as out of plane. While in the past much work has considered this problem, none have held transverse confinement as a prime factor. In order to achieve our goal, square and triangular hole shapes are considered. Looking at sharp featured shapes as well as their fabrication realizable rounded counterparts and an even more rudimentary triangular cluster of circles, we look to break the crystalmode symmetries for TM photonic bands and, therefore, open a complete band gap between the 1st and 2nd bands for both TE and TM light. TE/TM gap overlap is optimized for single-slab-mode operation, via the effective index method, for hole size, hole orientation, and slab thickness - all as functions of the lattice constant, a , and operational wavelength, λ. It is found that rounded triangular holes and tri-clustered circular holes of size 0.88 a and thickness d/ λ = 0.112 show identical photonic behavior that provides an optimized gap overlap of 0.0496 (ω a/2 π c = a/ λ) with a 12.81% gap figure of merit (Δω / ω 0 ).

We report on the heteroepitaxial growth of high-quality single crystal cubic ZnxMg1-xO and NiyMg1-yO thin films by radio frequency oxygen plasma-assisted molecular beam epitaxy (RF-MBE). Film compositions over the ranges x = 0 to x = 0.65 and y = 0 to y = 1 have been grown on lattice-matched MgO (100) and characterized optically, morphologically, compositionally, and electrically. Both of these ternary materials are shown to have bandgaps which vary directly as a function of transition metal (Ni or Zn) concentration. Optical transmission measurements of NiyMg1-yO show the bandgap to shift continuously over the approximate range 3.5 eV (for NiO) to 4.81 eV (for y=0.075). Similarly, the bandgap of cubic ZnxMg1-xO is shifted from about 4.9 eV (for x = 0.65) to 6.25 eV (for x=0.12). Films exhibit good morphological quality and typical roughness of NiyMg1-yO films is 5 Å while that of ZnxMg1-xO is less than 15 Å, as measured by atomic force microscopy (AFM). X-ray diffraction (XRD) is employed to confirm crystal orientation and to determine the films' lattice constants. Film compositions are interrogated by Rutherford Backscattering (RBS) and electrical characterization is made by room-temperature Hall measurements.

Storage and retrieval of excitons were demonstrated with semiconductor self-assembled quantum dots (QDs). The optically generated excitons were dissociated and stored as separated electron-hole pairs in coupled QD pairs. A bias voltage restored the excitons, which recombined radiatively to provide a readout optical signal. The localization of the spatially separated electron-hole pair in QDs was responsible for the ultralong storage times, which were on the order of several seconds. The present limits of this optical storage medium are discussed.

We present an InAs self-assembled quantum dot structure designed to spatially separate and store photo-generated electron-hole pairs. The structure consists of pairs of strain-coupled quantum dots. Separation of electron-hole pairs into the quantum dots and strain-induced quantum dots has been observed using power-dependant photoluminescence and bias-dependent photoluminescence.

Using 2D finite element modeling with the ability to solve the current continuity equations, carrier energy transport equation, Schrodinger and Poisson equations self-consistently, as well as the scalar wave equation for waveguiding devices, we have investigated the possible improvements of the device efficiencies by introducing transparent p-type contacts and multiple quantum shells (MQSs) in GaN / In 0.14 Ga 0.86 N / GaN / p-AlGaN / p-GaN core/multishell nanowires (CMS NWs). The addition of a transparent p-type current spreading contact was found to promote more uniform current injection into the CMS NWs, thus increasing the current injection efficiency. Despite the inclusion of a transparent ptype contact, the current density remained non-uniform and weighted towards the n-contact side of the NW. This asymmetry in the current density was found to be more important for higher injection current whereas it becomes much more uniform with decreasing injection current. Light generation with the transparent contact was found to become more uniformly distributed along the CMS NW, leading to more even light generation within the device in comparison to NWs without transparent p-type contacts. The replacement of single quantum shells (SQS) by MQSs in the active region of the nitride CMS NW-as has been used for conventional InGaN high brightness LEDs (HB-LEDs)-was found to be advantageous up to three quantum shells, increasing light generation from 80.47 to 94.04 W/m under a 4V bias.

A microphotoluminescence study of single InAs/GaAs quantum dots (QDs) in the presence of an applied external magnetic field is presented. Attention is focused on the redistribution between the spectral lines of a single QD observed at increasing magnetic field parallel to the growth direction (Faraday geometry). The redistribution effect is explained by considering the electron drift velocity in the QD plane that affects the probability for capture into the QD. In contrast, no redistribution is observed when applying the magnetic field perpendicular to the growth direction (Voigt geometry). Original Publication: Evgenii Moskalenko, Andréas Larsson, Mats Larsson, Per-Olof Holtz, W. V. Schoenfeld and P. M. Petroff, Effective tuning of the charge state of a single InAs/GaAs quantum dot by an external magnetic field, 2008, Physical Review B Condensed Matter, (78), 075306. http://dx.doi.org/10.1103/PhysRevB.78.075306 Copyright: American Physical Society http://www.aps.org/

Applications for photonic integrated circuit technologies based on the conditional Faraday Effect with electron spins in quantum dots are discussed. The interaction of light with the quantum confined electrons leads to a rotation of the light polarization. Design considerations for polarization multiplexing systems and plasmon resonance sensors based on polarization rotation are presented. Calculations for light of wavelengths λ=1.3 μm and λ=1.55 μm show devices with active regions of a few hundred microns are possible using InAs/GaAs quantum dots. The advantages of spin-based devices are also discussed.

A comprehensive theoretical analysis of the cavity quantum electrodynamics (QED) in single-photon Mach-Zehnder Interferometer (SMZI) based switches and single quantum gates that are intended for the processing of quantum information encoded in the polarization of single photons inside integrated photonic crystal (PC) quantum networks is presented. These devices rely on manipulating the geometrical phase of single photons by means of the Single-Photon Faraday Effect (SPFE), which can be described in terms of a detuned single mode quantum field strongly interacting with a two-level system or quantum dot (QD) inside nanocavities. The feasibility of such devices depends on the ability for the field in each arm of the interferometer to couple in their respective nanocavities, successfully interact with the quantum dot, and when the appropriate phase is accumulated couple out; all these steps being performed with minimum phase error and losses. Using the Jaynes-Cummings model, the cavity dynamics is studied for various detuning energies and coupling energies, and it is shown that the design of these devices can achieve low phase error and robustness against fabrication errors.

GaAs-based PIN detectors with mesa sizes 1, 2.5, 5, 7.5 and 10 mm were fabricated and characterized for alpha particle response using a Po-210 alpha source. By decoupling the neutron conversion process of a proximity moderator, we were able to directly probe the alpha response characteristics of the PIN detectors as a function of device area. Dark current levels in the PIN detectors ranged from 6.1 to 9.5 pA at zero bias. The dark current values were higher for larger devices and a linear relationship between mesa size and dark current was observed. The PIN detectors were found to have a strong alpha response of up to 5 nA/mm 2 with a linear relation between the response current and mesa area. The measured responsivity of the detectors was 0.014 A/W. The average device efficiency was determined to be 31.5%. Using the measured alpha response properties of the GaAs PIN diodes one is able to select the optimal device area for a given moderator and application specific neutron flux.

InAs/GaAs quantum dots have been subjected to a lateral external electric field in low-temperature microphotoluminescence measurements. It is demonstrated that the dot PL signal could be increased several times depending on the magnitude of the external field and the strength of the internal (built-in) electric field, which could be altered by an additional infrared illumination of the sample. The observed effects are explained by a model that accounts for the essentially faster lateral transport of the photoexcited carriers achieved in an electric field.

The effects of radiation damage exposure on InGaAs quantum wells and InAs quantum dots are compared using luminescence spectroscopy techniques. A large increase in the radiation resistance of the InAs quantum dots is observed and attributed to exciton localization in the quantum dots and a point defect strain gettering effect.

A photoluminescence study of self-assembled InAs/GaAs quantum dots under the influence of magnetic fields perpendicular and parallel to the dot layer is presented. At low temperatures, the magnetic field perpendicular to the dot layer alters the in-plane transport properties due to localization of carriers in wetting layer (WL) potential fluctuations. Decreased transport in the WL results in a reduced capture into the quantum dots and consequently a weakened dot-related emission. The effect of the magnetic field exhibits a considerable dot density dependence, which confirms the correlation to the in-plane transport properties. An interesting effect is observed at temperatures above approximately 100 K, for which magnetic fields, both perpendicular and parallel to the dot layer, induced an increment of the quantum dot photoluminescence. This effect is ascribed to the magnetic confinement of the exciton wave function, which increases the probability for carrier capture and localization in the dot, but affects also the radiative recombination with a reduced radiative lifetime in the dots under magnetic compression. (Less)

Single quantum dots (QDs), based on the InAs/GaAs material system have been characterized by micro-photoluminescence (μPL). The self-organized quantum dots studied are fabricated by the Stransky-Krastanov method, taking advantage of the strain caused by the lattice mismatch between InAs and GaAs. Well-defined narrow excitonic features from individual QDs are monitored in the μPL spectra, upon single or dual tunable laser excitation. The charge state of the quantum dot is revealed from these excitonic lines in the μPL spectra. However, by tuning the laser excitation energy, it is demonstrated that the charge state of the dot can be altered: The distribution of neutral and charged excitons is demonstrated to be extremely sensitive on the laser energy. In addition, with an additional infrared laser, striking changes are induced in the μPL spectra. The results achieved demonstrate the existence of two well-defined excitation energy regions for the main laser, in which the presence of the infrared laser will decrease or increase, respectively, the integrated dot μPL intensity. For excitation above the critical threshold energy of the main laser, the addition of the infrared laser will induce a considerable increase, by up to a factor 5, in the QD emission intensity. At laser excitation below the threshold energy, on the other hand, the QD emission intensity will decrease. This fact is due to reduced carrier capture efficiency into the dot as determined by the internal electric field driven carrier transport. In order to get further insight into the carrier capture process due to the electric field in the vicinity of the QD, the dots have also been subjected to an external electric field In most optical experiments with QDs, electrically injected or photoexcited carriers are primarily created somewhere in the sample outside the QDs, e.g. in the barriers or in the wetting layer. Consequently, excited carriers undergo a transport in the wetting layer and/or barriers prior to the capture into the QDs. This circumstance highlights the crucial role of the carrier transport and capture processes into the dot for the performance and operation of the dot based devices such as QD lasers, QD infrared detectors and QD memory devices. This transport effect on the optical response of the quantum dots has been investigated by subjecting the carriers to an external electric field in μPL measurements. This external field is formed by application of a lateral field between two top contacts. It is demonstrated that the QD PL signal intensity could be increased several times (>5 times) by optimizing the magnitude of this external field.