An exclusive advantage of semiconductor spintronics is its potential for opto-spintronics, which will allow integration of spin-based information processing/storage with photon-based information ...transfer/communications. Unfortunately, progress has so far been severely hampered by the failure to generate nearly fully spin-polarized charge carriers in semiconductors at room temperature. Here we demonstrate successful generation of conduction electron spin polarization exceeding 90% at room temperature without a magnetic field in a non-magnetic all-semiconductor nanostructure, which remains high even up to 110 °C. This is accomplished by remote spin filtering of InAs quantum-dot electrons via an adjacent tunnelling-coupled GaNAs spin filter. We further show that the quantum-dot electron spin can be remotely manipulated by spin control in the adjacent spin filter, paving the way for remote spin encoding and writing of quantum memory as well as for remote spin control of spin–photon interfaces. This work demonstrates the feasibility to implement opto-spintronic functionality in common semiconductor nanostructures.An electron spin polarization of 90% is achieved in a non-magnetic nanostructure at room temperature without magnetic field. This is accomplished by remote spin filtering of InAs quantum-dot electrons via an adjacent tunnelling-coupled GaNAs spin filter.
A Tm-doped mixed sesquioxide ceramic laser is mode-locked near 2 µm using InGaAsSb quantum-well semiconductor saturable absorber and chirped mirrors for dispersion compensation. Maximum average ...output power of 175 mW is achieved for a pulse duration of 230 fs at a repetition rate of 78.9 MHz with a 3% output coupler. Applying a 0.2% output coupler pulses as short as 63 fs are generated at 2.057 µm.
Herein, we present experimental data on the record length uniformity within the ensembles of semiconductor nanowires. The length distributions of Ga-catalyzed GaAs nanowires obtained by ...cost-effective lithography-free technique on silicon substrates systematically feature a pronounced sub-Poissonian character. For example, nanowires with the mean length ⟨L⟩ of 2480 nm show a length distribution variance of only 367 nm2, which is more than twice smaller than the Poisson variance h⟨L⟩ of 808 nm2 for this mean length (with h = 0.326 nm as the height of GaAs monolayer). For 5125 nm mean length, the measured variance is 1200 nm2 against 1671 nm2 for Poisson distribution. A supporting model to explain the experimental findings is proposed. We speculate that the fluctuation-induced broadening of the length distribution is suppressed by nucleation antibunching, the effect which is commonly observed in individual vapor–liquid–solid nanowires but has never been seen for their ensembles. Without kinetic fluctuations, the two remaining effects contributing to the length distribution width are the nucleation randomness for nanowires emerging from the substrate and the shadowing effect on long enough nanowires. This explains an interesting time evolution of the variance that saturates after a short incubation stage but then starts increasing again due to shadowing, remaining, however, smaller than the Poisson value for a sufficiently long time.
We report the formation and phase transformation of Bi-containing clusters in Bi epilayers upon annealing. The Bi layers were grown by molecular beam epitaxy under low (220 ) and high (315 ) ...temperatures and subsequently annealed using different temperatures and annealing times. Bi-containing clusters were identified only in the annealed samples that were grown at low temperature, revealing a relatively homogeneous size distribution. Depending on the annealing temperature and duration, the clusters show different sizes ranging from 5 to 20 nm, as well as different crystallographic phase, being coherently strained zincblende Bi (zb Bi-rich Ga(As, Bi)) clusters or rhombohedral pure Bi (rh-Bi) clusters. We found that: (1) the formation of the zb Bi-rich Ga(As, Bi) clusters is driven by the intrinsic tendency of the alloy to phase separately and is mediated by the native point defects present in the low temperature grown epilayers; (2) the phase transformation from zb Bi-rich Ga(As, Bi) to rh-Bi nucleates in zincblende {111} planes and grows until total consumption of Bi in the GaAs matrix. We propose a model accounting for the formation and phase transformation of Bi-containing clusters in this system. Furthermore, our study reveals the possibility to realize self-organized zb Bi-rich Ga(As, Bi) clusters that can exhibit QD-like features.
High-power and narrow-linewidth laser light is a vital tool for atomic physics, being used for example in laser cooling and trapping and precision spectroscopy. Here we produce Watt-level laser ...radiation at 457.75 nm and 460.86 nm of respective relevance for the cooling transitions of cadmium and strontium atoms. This is achieved via the frequency doubling of a kHz-linewidth vertical-external-cavity surface-emitting laser (VECSEL), which is based on a novel gain chip design enabling lasing at > 2 W in the 915-928 nm region. Following an additional doubling stage, spectroscopy of the 1 S 0 → 1 P 1 cadmium transition at 228.87 nm is performed on an atomic beam, with all the transitions from all eight natural isotopes observed in a single continuous sweep of more than 4 GHz in the deep ultraviolet. The absolute value of the transition frequency of 114 Cd and the isotope shifts relative to this transition are determined, with values for some of these shifts provided for the first time.
The use of vertical-cavity-surface-emitting lasers with ability to operate at cryogenic temperatures (Cryo-VCSELs) is a promising path to implement optical data links between superconducting ...processors maintained in cryogenic environments (4 K range) and room temperature (RT) computing hardware. In order to achieve energy-efficient operation of a cryo-VCSEL, whether by passing current through the mirrors or utilizing intra-cavity contacts, a critical bottleneck for improving the operation is related to the p-doped distribute Bragg Reflectors (DBRs). This is because holes exhibit lower mobility and lower thermal conductivity compared to their n-side counterparts. To determine the actual temperature of an operating p-doped DBR and its impact on the behavior of the DBRs and the cryo-VCSEL, a thermal simulation using the finite-element method was conducted and validated with experimental results. Furthermore, we explored different mirror geometries to optimize both current flow and the growth complexity of the DBR. DBR layers with various interface shapes, such as uni-parabolic grading and three to five steps with different Al mole fractions, have been investigated. As a result of the study, we achieved more efficient operation at cryogenic temperatures, with a 60% reduction of the series resistance and a 39% reduction of the voltage penalty related to the p-doped DBR.
PDF
