Within this work we present optical and structural properties of InP quantum dots embedded in ͑Al x Ga 1−x ͒ 0.51 In 0.49 P barriers. Atomic force microscopy measurements show a mainly bimodal height distribution with aspect ratios ͑ratio of width to height͒ of about 10:1 and quantum dot heights of around 2 nm for the smaller quantum dot class ͑type A͒ and around 4 nm for the larger quantum dot class ͑type B͒. From ensemblephotoluminescence measurements we estimated thermal activation energies of up to 270 meV for the type-A quantum dots, resulting in a 300 times higher luminescence intensity at 200 K in comparison to our InP quantum dots in Ga 0.51 In 0.49 P at the same emission wavelength. Photon statistic measurements clearly display that InP quantum dots in ͑Al 0.20 Ga 0.80 ͒ 0.51 In 0.49 P emit single photons up to 80 K, making them promising candidates for high-temperature single-photon emitters.
Systematic excitation power and temperature-dependent measurements on the emission lines of single self-assembled InP/(Al 0.20 Ga 0.80) 0.51 In 0.49 P quantum dots embedded in micropillars have been performed. The quantum dots were excited optically via a pulsed laser and their luminescence was collected using a micro-photoluminescence setup. The exciton and biexciton intensity, linewidth, and spectral position was investigated in a temperature range from 4 K up to 130 K. Singlephoton emission from the quantum dots is presented up to a temperature of 100 K, confirmed by photon-statistics measurements. V
Direct detection of biomarkers from unpurified whole blood has been a challenge for label-free detection platforms, such as photonic crystal slabs (PCS). A wide range of measurement concepts for PCS exist, but exhibit technical limitations, which render them unsuitable for label-free biosensing with unfiltered whole blood. In this work, we single out the requirements for a label-free point-of-care setup based on PCS and present a wavelength selecting concept by angle tuning of an optical interference filter, which fulfills these requirements. We investigate the limit of detection (LOD) for bulk refractive index changes and obtain a value of 3.4 E-4 refractive index units (RIU). We demonstrate label-free multiplex detection for different types of immobilization entities, including aptamers, antigens, and simple proteins. For this multiplex setup we detect thrombin at a concentration of 6.3 µg/ml, antibodies of glutathione S-transferase (GST) diluted by a factor of 250, and streptavidin at a concentration of 33 µg/ml. In a first proof of principle experiment, we demonstrate the ability to detect immunoglobulins G (IgG) from unfiltered whole blood. These experiments are conducted directly in the hospital without temperature control of the photonic crystal transducer surface or the blood sample. We set the detected concentration levels into a medical frame of reference and point out possible applications.
We report on the epitaxial growth of vertically stacked InP and In(Ga)As quantum dot (QD) layers to realize a triple dot quantum gate structure consisting of an asymmetric control double dot and a single target dot suitable for a CNOT gate structure. Structural analysis as well as studies on the optical properties are presented. For studies on control dot structures we analyze the growth of InP islands in a GaInP barrier on (100) GaAs substrates. By stacking InP QD layers with intentional asymmetric design in QD size of each layer and adjustment of the barrier width between the double dots, coupling and control of the coupling via barrier layer width-design can be demonstrated. For defined gate action single dot spectra of aligned dots are indispensable. Therefore QD density reduction is studied. We study two possibilities to affect the QD density and control the dot site by manipulating the surface potential of InP island nucleation. (i) Growth of InP islands on top of a low density In(Ga)As QD seed layer (ii) Growth of InP islands on patterned (100) GaAs substrates. We present microsphere photolithography in combination with wet chemical etching as a fast and low-cost method to produce regular hole arrays in a GaAs surface, which are suitable for controlled nucleation of self-assembled InP islands.1 Introduction During the last decades the growth of semiconductor quantum dots (QDs) by metal-organic vaporphase epitaxy (MOVPE) has highly improved and linewidths as well as luminescence efficiencies are reported, e.g., for the InAs/GaAs system [1] reaching the quality of samples grown by molecular beam epitaxy [2,3]. This allows for the fabrication of atom-like structures due to a three-dimensional charge carrier confinement even on a mass production scale. The epitaxial growth process enables a relatively easy implementation of QDs in electronic systems and therefore makes semiconductor QDs to promising building blocks for single-photon and single-electron devices suitable for applications in quantum information processing (QIP) [4,5]. Today, research is focusing on the functionalization of QDs, including the implementation in resonator and electronic structures. For the realization of quantum gate structures also the coupling of QDs forming a quantum dot molecule
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