A new FDSOI spin qubit platform with 40nm effective control pitch

Coupled semiconductor quantum dot (QD) arrays emerged recently as promising structures for the next generation of high efficiency intermediate band solar cell (IBSC), because of their ability to facilitate the formation of minibands. The quantum coupling effect that exists between states in QDs in an array influences the electronic and optical properties of such structures. So far, great experimental and theoretical efforts have been devoted to study the vertically coupled QD arrays. We present here a method based on multi‐band k ⋅ p Hamiltonian combined with periodic boundary conditions, applied to predict the electronic and optical properties of InAs/GaAs QDs‐based lateral QD arrays. Formation of the intermediate band (IB) in all cases was achieved via delocalisation of the electron ground state (e0). We show that the IB in a laterally coupled QD‐IBSC is more robust against external electric field from the solar cell's pn junction than that in a vertically coupled arrangement. Because of symmetry of the QD array lattice and QD states itself, which are C2v for the zinc blend QDs, the electronic and absorption structures were obtained via sampling throughout the reciprocal space in the first Brillouin zone of QD arrays. Copyright © 2014 John Wiley & Sons, Ltd.

Dense arrays of quantum wires and quantum dots with large confinement energy and very uniform size distributions are needed for realistic device applications. Significant progress has been achieved by combining self-organized growth on high-index substrates with lithographic patterning and atomic hydrogen assistance. We report here on the fabrication of GaAs quantum wire and quantum dot arrays with superior electronic properties by molecular beam epitaxy. Our new method additionally allows to precisely position the wires and dots on specific wafer areas.

We develop a detailed theoretical investigation of the effect of Coulomb\ninteraction on electron transport in arrays of chaotic quantum dots and\ndiffusive metallic wires. Employing the real time path integral technique we\nformulate a new Langevin-type of approach which exploits a direct relation\nbetween shot noise and interaction effects in mesoscopic conductors. With the\naid of this approach we establish a general expression for the Fano factor of\n1D quantum dot arrays and derive a complete formula for the interaction\ncorrection to the current which embraces all perturbative results previously\nobtained for various quasi-0D and quasi-1D disordered conductors and extends\nthese results to yet unexplored regimes.\n

Issues of Ge hut cluster array formation and growth at low temperatures on the Ge/Si(001) wetting layer are discussed on the basis of explorations performed by high resolution STM and in-situ RHEED. Dynamics of the RHEED patterns in the process of Ge hut array formation is investigated at low and high temperatures of Ge deposition. Different dynamics of RHEED patterns during the deposition of Ge atoms in different growth modes is observed, which reflects the difference in adatom mobility and their ‘condensation’ fluxes from Ge 2D gas on the surface for different modes, which in turn control the nucleation rates and densities of Ge clusters. Data of HRTEM studies of multilayer Ge/Si heterostructures are presented with the focus on low-temperature formation of perfect films.Heteroepitaxial Si p–i–n-diodes with multilayer stacks of Ge/Si(001) quantum dot dense arrays built in intrinsic domains have been investigated and found to exhibit the photo-emf in a wide spectral range from 0.8 to 5 μm. An effect of wide-band irradiation by infrared light on the photo-emf spectra has been observed. Photo-emf in different spectral ranges has been found to be differently affected by the wide-band irradiation. A significant increase in photo-emf is observed in the fundamental absorption range under the wide-band irradiation. The observed phenomena are explained in terms of positive and neutral charge states of the quantum dot layers and the Coulomb potential of the quantum dot ensemble. A new design of quantum dot infrared photodetectors is proposed.By using a coherent source spectrometer, first measurements of terahertz dynamical conductivity (absorptivity) spectra of Ge/Si(001) heterostructures were performed at frequencies ranged from 0.3 to 1.2 THz in the temperature interval from 300 to 5 K. The effective dynamical conductivity of the heterostructures with Ge quantum dots has been discovered to be significantly higher than that of the structure with the same amount of bulk germanium (not organized in an array of quantum dots). The excess conductivity is not observed in the structures with the Ge coverage less than 8 Å. When a Ge/Si(001) sample is cooled down the conductivity of the heterostructure decreases.

Formation of laterally ordered single InAs quantum dot (QD) arrays by self-organized anisotropic strain engineering of InGaAs/GaAs superlattice templates on GaAs (311)B by molecular beam epitaxy is achieved through optimization of growth temperature, InAs amount, and annealing. Directed self-organization of these QD arrays is accomplished by coarse substrate patterns providing absolute QD position control over large areas. Due to the absence of one-to-one pattern definition the site-controlled QD arrays exhibit excellent optical properties revealed by resolution limited (80 μeV) linewidth of the low-temperature photoluminescence from individual QDs.

Linear arrays of quantum dots are predicted to show localization effects for light traveling along the linear dimension quite similar to the case of the Anderson localization phenomenon known for electron transport. A basic requirement is to have stable arrays of such quantum dots at hand that might be incorporated into potential devices. To prepare such linear arrays, we dispersed ZnSe quantum dots in a polymer solution and used this solution in a first approach to electrospin polymer nanofibers from this solution using polystyrene and polylactide as polymer matrix. Nanofibers with quantum dots with dimensions ranging from several 100 nm to about 10 nm were achieved in this way. Using frame type and cylindrical rotating electrodes, an enhanced mutual orientation of these fibers was achieved. In a second approach, we used the wetting assisted template approach based on porous alumina templates to obtain parallel sets of polystyrene nanorods containing quantum dots.

ABSTRACTWe investigated the behavior of carrier populations generated at the interface of an n‐Si wafer to an Si quantum dot (QD) array embedded in SiO2 with a photon flux ranging from 1.24 to 2.48 eV (1000 to 500 nm). The optically assisted IV method was used with the Si wafer as hot carrier (HC) absorber and the Si QD array as energy selective contact (ESC). Charge carriers obtain excess energy from photons with energies significantly exceeding the band gap, resulting in an HC population. This reduces the bias field required to provide kinetic energy by field emission. The ESC can collect HCs at lower bias voltages. Tunneling resonances show the energy selective behavior under illumination at 80 K and room temperature (295 K). The data at 80 K can arguably be interpreted as an HC population in Si within the range of the ballistic mean free path from the QD array. We discovered a correlation between the energetic shift of the average hot hole temperature near the valence band edge and the energy of the photons impinging on the mesa structures. The optically assisted IV technique delivers a proof of principle for operation of an Si QD array as an ESC at room temperature, and furthermore for an HC solar cell with one ESC at 80 K. Copyright © 2013 John Wiley & Sons, Ltd.

An experimental study of carrier relaxation mechanisms andcarrier distribution in InAs-InGaAs-GaAs quantum dot (QD)arrays is presented. The structures were investigated byresonant photoluminescence (PL) at different temperatures. For asample with low confinement energy for electrons and holes ina QD the carrier distribution within the QD array changes fromnon-Fermi (random) to Fermi (equilibrium) when temperatureincreases from 20 to 300 K. In contrast, for the sample withhigh QD confinement energy the carrier distribution remainsrandom even at room temperature. Near-resonantPL at 20 K reveals a series of broad phononreplicas ascribed to multiphonon relaxation processes involvingLO phonons in the QD, in the wetting layer, at the interface and inGaAs as well as acoustic phonons. The complex distribution ofInGaAs in QDs formed by activated alloy phase separation isbelieved to cause a dispersion of QD phonon energies and tolead to a further broadening of phonon lines.

We present a theory for understanding the exchange interaction between electron spins in neighboring quantum dots, either by changing the detuning of the two quantum dots or independently tuning the tunneling barrier between quantum dots. The Hubbard model and a more realistic confining-potential model are used to investigate how the tilting and barrier control affect the effective exchange coupling and thus the gate fidelity in both the detuning and symmetric regimes. We show that the exchange coupling is less sensitive to the charge noise through tunnel barrier control (while allowing for exchange coupling operations on a sweet spot where the exchange interaction has zero derivative with respect to the detuning). Both GaAs and Si quantum dots are considered and we compare our results with experimental data showing qualitative agreements. Our results answer the open question of why barrier gates are preferable to tilt gates for exchange-base gate operations.

Electrons and holes confined in quantum dots define excellent building blocks for quantum emergence, simulation, and computation. Silicon and germanium are compatible with standard semiconductor manufacturing and contain stable isotopes with zero nuclear spin, thereby serving as excellent hosts for spins with long quantum coherence. Here, we demonstrate quantum dot arrays in a silicon metal-oxide-semiconductor (SiMOS), strained silicon (Si/SiGe), and strained germanium (Ge/SiGe). We fabricate using a multi-layer technique to achieve tightly confined quantum dots and compare integration processes. While SiMOS can benefit from a larger temperature budget and Ge/SiGe can make an Ohmic contact to metals, the overlapping gate structure to define the quantum dots can be based on a nearly identical integration. We realize charge sensing in each platform, for the first time in Ge/SiGe, and demonstrate fully functional linear and two-dimensional arrays where all quantum dots can be depleted to the last charge state. In Si/SiGe, we tune a quintuple quantum dot using the N + 1 method to simultaneously reach the few electron regime for each quantum dot. We compare capacitive crosstalk and find it to be the smallest in SiMOS, relevant for the tuning of quantum dot arrays. We put these results into perspective for quantum technology and identify industrial qubits, hybrid technology, automated tuning, and two-dimensional qubit arrays as four key trajectories that, when combined, enable fault-tolerant quantum computation.

We demonstrated highly selective growth and positioning of Si quantum dots (QDs) on SiO₂ patterns by controlling reactive area whose surface is terminated with OH bonds for the Si nucleation in low–pressure chemical vapor deposition (LPCVD) using SiH₄, and evaluated effects of line and space pattern width on QD growth. Although hemispherical QDs were predominantly formed when the line width was ~50 nm or greater, elliptical QD shapes became more prevalent as the line width decreased to ~30 nm or less, resulting in reduced size uniformity. However, it was found that one–dimensional arrays of elliptical QDs with good size uniformity can be realized with line widths of ~25 nm and space widths of ~50 nm. Furthermore, by designing a line and space pattern considering the migration length of the Si precursor during the SiH₄–LPCVD, we successfully formed two–dimensional self–aligned Si–QDs with high uniformity to form a closest–packing structure.

We describe a novel approach to grow Si nanostructures embedded into crystalline rare earth oxides using molecular beam epitaxy. By efficiently exploiting the growth kinetics during growth one could create nanostructures exhibiting various dimensions, ranging from three dimensionally confined quantum dots to the quantum wells, where the particles are confined in of the dimensions. The crystalline rare earth oxide that has been used in this study is epitaxial gadolinium oxide (Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ). The room temperature quantum confinement effects characterized by the strong intensity and narrow photoluminescence peak in an array of Si quantum dots embedded in Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , indicates high crystalline quality and narrow size distribution range of quantum dots. The Si quantum dots with dimension about 3-5 nm exhibited quantum confinement, which was observed in the photoluminescence and photoionization studies. The embedded Si-nanoclusters exhibit excellent charge storage capacity with competent retention and endurance characteristics;, and demonstrate their potential in future nonvolatile memory devices.

Electron states in a inhomogeneous Ge/Si quantum dot array with groups of closely spaced quantum dots were studied by conventional continuous wave ($cw$) ESR and spin-echo methods. We find that the existence of quantum dot groups allows to increase the spin relaxation time in the system. Created structures allow us to change an effective localization radius of electrons by external magnetic field. With the localization radius close to the size of a quantum dot group, we obtain fourfold increasing spin relaxation time $T_1$, as compared to conventional homogeneous quantum dot arrays. This effect is attributed to averaging of local magnetic fields related to nuclear spins $^{29}$Si and stabilization of $S_z$-polarization during electron back-and-forth motion within a quantum dot group.

Semiconductor quantum dot arrays defined electrostatically in a 2D electron gas provide a scalable platform for quantum information processing and quantum simulations. For the operation of quantum dot arrays, appropriate voltages need to be applied to the gate electrodes that define the quantum dot potential landscape. Tuning the gate voltages has proven to be a time-consuming task, because of initial electrostatic disorder and capacitive cross-talk effects. Here, we report on the automated tuning of the inter-dot tunnel coupling in gate-defined semiconductor double quantum dots. The automation of the tuning of the inter-dot tunnel coupling is the next step forward in scalable and efficient control of larger quantum dot arrays. This work greatly reduces the effort of tuning semiconductor quantum dots for quantum information processing and quantum simulation.

We report an analysis of a two-dimensional variable-range hopping conductance in doped and gated Ge/Si heterostructures with arrays of Ge quantum dots. We found that the conductivity $\ensuremath{\sigma}$ versus temperature T follows the Efros-Shklovskii behavior $\ensuremath{\sigma}={\ensuremath{\sigma}}_{0}\mathrm{exp}[\ensuremath{-}{(T}_{0}{/T)}^{1/2}]$ with the temperature-independent prefactor ${\ensuremath{\sigma}}_{0}\ensuremath{\sim}{e}^{2}/h.$ A strong reduction of the measured value of the characteristic temperature ${T}_{0}$ from that calculated for single-particle hopping was observed. The data provide evidence for interaction-driven many-electron excitations in dense arrays of quantum dots.