We report on high-resolution photoluminescence (PL) and photocurrent (PC) spectroscopies of a single self-assembled InAs/GaAs quantum dot (QD) embedded in an n-i-Schottky device with an applied magnetic field in Faraday and Voigt geometries. The single-QD PC spectrum of neutral exciton (X$^0$) is obtained by sweeping the bias-dependent X$^0$ transition energy to achieve resonance with a fixed narrow-bandwidth laser through quantum-confined Stark effect. With a magnetic field applied in Faraday geometry, the diamagnetic effect and the Zeeman splitting of X$^0$ are observed both in PL and PC spectra. When the magnetic field is applied in Voigt geometry, the mixture of bright and dark states results in an observation of dark exciton states, which are confirmed by the polarization-resolved PL and PC spectra.

A high-gain photodetector based on junctionless MOSEFT has been presented in this work. Tri-gate junctionless nanowire phototransistors were fabricated on (100) silicon-on-insulator wafers with a buried oxide of thickness 145 nm and top silicon layer of thickness 10 nm. The gate stack consisted of a 10 nm SiO2 dielectric and a 50 nm poly-Si gate electrode. The channel length and doping concentration of junctionless n-MOSFETs was 1 μm and 3 × 1019 cm−3, respectively. The dark current of this device measured at room temperature was less than 1 pA. The measured internal gain of the device was about 35 for 860 nm light illumination. The photocurrent was 300 times larger than the dark current for only 30 nW incident power on the nanowire at 300 mV drain bias.

For the first time, long coherence times (T 2 ) up to tens of microseconds were observed in a silicon-based charge quantum bit (qubit) device at 4.2 K. The coherence times demonstrated in this paper are two orders of magnitude longer, and the operating temperature is two orders of magnitude higher than the reported semiconductor charge qubit systems (see Table 1). In contrast to other approaches, in this work the qubits are formed by trench isolation instead of surface gate-defined. The qubits were fabricated on P-doped silicon-on-insulator (SOI) wafers through current industrial semiconductor manufacturing technology. We have demonstrated the accurate readout of the qubits' electronic states by using a single electron transistor (SET) as an electrometer. The first observation of the interaction between two sets of capacitively coupled charge movements was achieved by using our charge detection technique.

Normally, wave functions in single quantum dots can be tuned transversely by a perpendicular magnetic field because of the cyclotron energy. In this work, we are presenting a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field, the hole wave function shrinks in the base plane, resulting in that the center of effective mass moves towards apex. For electrons, however, the center of effective mass does not move much. This induces a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots. Additionally, the many-body exciton states in a coupled system with a single self-assembled quantum dot and a wetting layer are observed by strong anomalous diamagnetic shifts. A tremendous positive diamagnetic coefficient is observed when an electron in the wetting layer combines with a hole in quantum dot, which is nearly one order of magnitude larger than that of the excitonic states confined in quantum dots. When the electrons recombine with holes within quantum dot in the coupled system, a peculiar negative diamagnetic effect is observed. The properties of emitted photons depending on the large electron wave function extents in wetting layer indicate the coupling between the systems in different dimensionality, which was also verified by a magnetic field applied in different configurations.

We report the direct observation of coupling between a single self-assembled InAs quantum dot and a wetting layer, based on strong diamagnetic shifts of many-body exciton states using magneto-photoluminescence spectroscopy. An extremely large positive diamagnetic coefficient is observed when an electron in the wetting layer combines with a hole in the quantum dot; the coefficient is nearly one order of magnitude larger than that of the exciton states confined in the quantum dots. Recombination of electrons with holes in a quantum dot of the coupled system leads to an unusual negative diamagnetic effect, which is five times stronger than that in a pure quantum dot system. This effect can be attributed to the expansion of the wavefunction of remaining electrons in the wetting layer or the spread of electrons in the excited states of the quantum dot to the wetting layer after recombination. In this case, the wavefunction extent of the final states in the quantum dot plane is much larger than that of the initial states because of the absence of holes in the quantum dot to attract electrons. The properties of emitted photons that depend on the large electron wavefunction extents in the wetting layer indicate that the coupling occurs between systems of different dimensionality, which is also verified from the results obtained by applying a magnetic field in different configurations. This study paves a new way to observe hybrid states with zero- and two-dimensional structures, which could be useful for investigating the Kondo physics and implementing spin-based solid-state quantum information processing.

We report the charge sensing of two isolated double quantum dots (IDQDs) at 4.2 K. The structure is fabricated through trench isolation of highly doped n-type silicon on silicon-on-insulator wafer. Each device contains one pair of IDQDs and one single electron transistor (SET) which serves as an electrometer. We detect the charge motion in each IDQD and the results are consistent with the simulation.

We demonstrate the initialization of a single quantum-dot hole spin with high fidelity ( lower bound > 97%), on picosecond time scales, and without the need for magnetic fields. Using the initialization scheme based on rapid electric-field ionization of a resonantly excited exciton, this is achieved by employing a self-assembled quantum dot with a low conduction-to-valence band offset ratio, allowing control of the relative electron and hole tunneling rates over three orders of magnitude. This large difference in tunneling rates could permit spin-storage efficiencies >99.5% by fast-switching to a low electric-field condition. Our results may provide a practical route towards ultrafast high-fidelity initialization of individual quantum-dot hole spins for the implementation of quantum error correction in a scalable spin-based quantum computer.

In this paper we investigate the mode splitting in a photonic molecule consisting of two coupled photonic crystal cavities separated by an optical well in a photonic crystal waveguide. We show experimentally, by using a confocal microphotoluminescence mapping technique, that fine control of the coupling between the cavities can be achieved by the addition of an optical well. Our results demonstrate that an increase in the depth of the well leads to an increased mode splitting and a strongly red shifted symmetric supermode (the ground mode).

We report a photoluminescence (PL) spectroscopy study of charge state control in single self-assembled InAs/GaAs quantum dots by applying electric and/or magnetic fields at 4.2 K. Neutral and charged exciton complexes were observed under applied bias voltages from −0.5 V to 0.5 V by controlling the carrier tunneling. The highly negatively charged exciton emission becomes stronger with increasing pumping power, arising from the fact that electrons have a smaller effective mass than holes and are more easily captured by the quantum dots. The integrated PL intensity of negatively charged excitons is affected significantly by a magnetic field applied along the sample growth axis. This observation is explained by a reduction in the electron drift velocity caused by an applied magnetic field, which increases the probability of non-resonantly excited electrons being trapped by localized potentials at the wetting layer interface, and results in fewer electrons distributed in the quantum dots. The hole drift velocity is also affected by the magnetic field, but it is much weaker.

This paper presents a novel fabrication process to realize high density silicon based quantum dot devices with close proximity Al and Si gates on ultrathin silicon-on-insulator for spin qubit applications. Al gates surrounding a Si nanowire channel can adjust tunnelling barrier height electrically, while Si plunger side gates enable precise control of the quantum dots potential. This device is fabricated using a multi-layer electron beam lithography process that is fully compatible with metal oxide semiconductor technology. Low temperature electrical measurements and Coulomb oscillation characteristics have demonstrated the capability of this structure to electrostatically define two coupled single electron transistors, one to be used as a turnstile device and the other as an electrometer.

144 highly tuneable high density lithographically defined Si double quantum dots (DQDs) are fabricated for the first time in parallel via a scalable VLSI compatible fabrication process for the realisation of single electron qubits for quantum computing. 25 nm DQDs with less than 5 nm in dimensional variation are achieved via the use of Hydrogen silsesquioxane resist and electron beam lithography. Repeatable coulomb oscillations and coulomb diamonds signifying single electron tunneling are observed in the electrical characteristics of a Si DQD structure. This demonstrates the viability and dimensionality of our system and paves the way for single electron spin manipulation in scalable Si based systems.

The electro-optic properties of strained GaInAsSb/GaAs quantum wells (QWs) are investigated. A single QW p-i-n sample was grown by molecular beam epitaxy with antimony (Sb) pre-deposition technique. We numerically predict and experimentally verify a strong quantum confined Stark shift of 40 nm. We also predict a fast absorption recovery times crucial of high-speed optoelectronic devices mainly due to strong electron tunneling and thermionic emission. Predicted recovery times are corroborated by bias and temperature dependent time-resolved photoluminescence measurements indicating (≤30 ps) recovery times. This makes GaInAsSb QW an attractive material particularly for electroabsorption modulators and saturable absorbers.

This paper presents the realization of a FinFET double quantum dots transistor on ultrathin silicon-on-insulator. In this platform, three Al FinFET gates surround the Si device layer channel forming electrically tunable potential barriers; Si plunger side gates are included to enable precise control of the quantum dots potential. This device is fabricated using a multi-layer electron beam lithography process that is fully compatible with metal oxide semiconductor technology. Low temperature electrical measurements and coulomb oscillation characteristics have demonstrated the capability of this structure to form double quantum dots with adjustable interdot coupling.

We have fabricated lithographically-defined Si quantum dots (QDs) within a metal-oxide-semiconductor field-effect transistor (MOSFET) structure. In this architecture, the top gate is used to tune the carrier density whereas side gates control the potentials of the QDs and tunneling barriers. These lithographically-defined and electrically-tunable Si QDs were successfully realized without unintentional localized potentials.

We report on the observation of Coulomb oscillations from localized quantum dots superimposed on the normal hopping current in ZnO nanowire transistors. The Coulomb oscillations can be resolved up to 20 K. Positive anisotropic magnetoresistance has been observed due to the Lorentz force on the carrier motion. Magnetic field-induced tunneling barrier transparency results in an increase of oscillation amplitude with increasing magnetic field. The energy shift as a function of magnetic field indicates electron wavefunction modification in the quantum dots.

We report the design and fabrication of InAs quantum dot gated transistors, which are normally-on, where the channel current can be switched off by laser illumination. Laser light at 650 nm with a power of 850 pW switches the channel current from 5 mu A to 2 pA, resulting in an on/off ratio of more than 60 dB. The switch-off mechanism and carrier dynamics are analyzed with simulated band structure.