Formation of diluted III–V nitride thin films by N ion implantation

iluted III–Nₓ–V₁ˍₓ alloys were successfully synthesized by nitrogen implantation into GaAs,InP, and AlyGa1−yAs. In all three cases the fundamental band-gap energy for the ion beam synthesized III–Nₓ–V₁ˍₓ alloys was found to decrease with increasing N implantation dose in a manner similar to that observed in epitaxially grownGaNₓAs1−x and InNₓP₁ˍₓalloys. In GaNₓAs₁ˍₓ the highest value of x (fraction of “active” substitutional N on As sublattice) achieved was 0.006. It was observed that NAs is thermally unstable at temperatures higher than 850 °C. The highest value of x achieved in InNₓP₁ˍₓ was higher, 0.012, and the NP was found to be stable to at least 850 °C. In addition, the N activation efficiency in implantedInNₓP₁ˍₓ was at least a factor of 2 higher than that in GaNₓAs₁ˍₓ under similar processing conditions. AlyGa1−yNₓAs₁ˍₓ had not been made previously by epitaxial techniques. N implantation was successful in producing AlyGa1−yNₓAs₁ˍₓalloys. Notably, the band gap of these alloys remains direct, even above the value of y (y>0.44) where the band gap of the host material is indirect.This work was supported by the ‘‘Photovoltaic Materials Focus Area’’ in the DOE Center of Excellence for the Synthesis and Processing of Advanced Materials, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences under U.S. Department of Energy Contract No. DE-ACO3-76SF00098. The work at UCSD was partially supported by Midwest Research Institute under subcontractor No. AAD-9-18668-7 from NREL

Deterministic Assembly of Arrays of Lithographically Defined WS2 and MoS2 Monolayer Features Directly from Multilayer Sources into Van der Waals Heterostructures

One of the major challenges in the van der Waals (vdW) integration of two-dimensional (2D) materials is achieving high-yield and high-throughput assembly of predefined sequences of monolayers into heterostructure arrays. Mechanical exfoliation has recently been studied as a promising technique to transfer monolayers from a multilayer source synthesized by other techniques, allowing the deposition of a wide variety of 2D materials without exposing the target substrate to harsh synthesis conditions. Although a variety of processes have been developed to exfoliate the 2D materials mechanically from the source and place them deterministically onto a target substrate, they can typically transfer only either a wafer-scale blanket or one small flake at a time with uncontrolled size and shape. Here, we present a method to assemble arrays of lithographically defined monolayer WS2 and MoS2 features from multilayer sources and directly transfer them in a deterministic manner onto target substrates. This exfoliate-align-release process - without the need of an intermediate carrier substrate - is enabled by combining a patterned, gold-mediated exfoliation technique with a new optically transparent, heat-releasable adhesive. WS2/MoS2 vdW heterostructure arrays produced by this method show the expected interlayer exciton between the monolayers. Light-emitting devices using WS2 monolayers were also demonstrated, proving the functionality of the fabricated materials. Our work demonstrates a significant step toward developing mechanical exfoliation as a scalable dry transfer technique for the manufacturing of functional, atomically thin materials

Ariel - Volume 2 Number 7

Editors Richard J. Bonanno Robin A. Edwards Associate Editors Steven Ager Stephen Flynn Shep Dickman Tom Williams Lay-out Editor Eugenia Miller Contributing Editors Michael J. Blecker W. Cherry Light James J. Nocon Lynne Porter Editors Emeritus Delvyn C. Case, Jr. Paul M. Fernhof

Si photocathode with Ag-supported dendritic Cu catalyst for CO2 reduction

Si photocathodes integrated with Ag-supported dendritic Cu catalysts are used to perform light-driven reduction of CO2 to C2 and C3 products in aqueous solution. A back illumination geometry with an n-type Si absorber was used to permit the use of absorbing metallic catalysts. Selective carrier collection was accomplished by a p+ implantation on the illumination side and an n+ implantation followed by atomic layer deposition of TiO2 on the electrolyte site. The Ag-supported dendritic Cu CO2 reduction catalyst was formed by evaporation of Ag followed by high-rate electrodeposition of Cu to form a high surface area structure. Under simulated 1 sun illumination in 0.1 M CsHCO3 saturated with CO2, the photovoltage generated by the Si (∼600 mV) enables C2 and C3 products to be produced at -0.4 vs. RHE. Texturing of both sides of the Si increases the light-limited current density, due to reduced reflection on the illumination side, and also deceases the onset potential. Under simulated diurnal illumination conditions photocathodes maintain over 60% faradaic efficiency to hydrocarbon and oxygenate products (mainly ethylene, ethanol, propanol) for several days. After 10 days of testing, contamination from the counter electrode is observed, which causes an increase in hydrogen production. This effect is mitigated by a regeneration procedure which restores the original catalyst selectivity. A tandem, self-powered CO2 reduction device was formed by coupling a Si photocathode with two series-connected semitransparent CH3NH3PbI3 perovskite solar cells, achieving an efficiency for the conversion of sunlight to hydrocarbons and oxygenates of 1.5% (3.5% for all products)

Structural and Electronic Properties of Amorphous and Polycrystalline In2Se3 Films

Structural and electronic properties of amorphous and single-phase polycrystalline films of gamma- and kappa-In2Se3 have been measured. The stable gamma phase nucleates homogeneously in the film bulk and has a high resistivity, while the metastable kappa phase nucleates at the film surface and has a moderate resistivity. The microstructures of hot-deposited and post-annealed cold-deposited gamma films are quite different but the electronic properties are similar. The increase in the resistivity of amorphous In2Se3 films upon annealing is interpreted in terms of the replacement of In-In bonds with In-Se bonds during crystallization. Great care must be taken in the preparation of In2Se3 films for electrical measurements as the presence of excess chalcogen or surface oxidation may greatly affect the film properties.Comment: 23 pages and 12 figure

Chemical Vapor Deposition Model of Polysilicon in a Trichlorosilane and Hydrogen System

The traditional polysilicon processes should be refined when addressing the low energy consumption requirement for the production of solar grade silicon. This paper addresses the fluid dynamic conditions required to deposit polysilicon in the traditional Siemens reactor. Analytical solutions for the deposition process are presented, providing information on maximizing the rate between the amount of polysilicon obtained and the energy consumed during the deposition process. The growth rate, deposition efficiency, and power-loss dependence on the gas velocity, the mixture of gas composition, the reactor pressure, and the surface temperature have been analyzed. The analytical solutions have been compared to experimental data and computational solutions presented in the literature. At atmospheric pressure, the molar fraction of hydrogen at the inlet should be adjusted to the range of 0.85–0.90, the gas inlet temperature should be raised within the interval of 673 and 773 K, and the gas velocity should reach the Reynolds number 800. The resultant growth rate will be between 6 and 6.5 _m min−1. Operation above atmospheric pressure is strongly recommended to achieve growth rates of 20 _m min−1 at 6 atm

High fidelity quantum memory via dynamical decoupling: theory and experiment

Quantum information processing requires overcoming decoherence---the loss of "quantumness" due to the inevitable interaction between the quantum system and its environment. One approach towards a solution is quantum dynamical decoupling---a method employing strong and frequent pulses applied to the qubits. Here we report on the first experimental test of the concatenated dynamical decoupling (CDD) scheme, which invokes recursively constructed pulse sequences. Using nuclear magnetic resonance, we demonstrate a near order of magnitude improvement in the decay time of stored quantum states. In conjunction with recent results on high fidelity quantum gates using CDD, our results suggest that quantum dynamical decoupling should be used as a first layer of defense against decoherence in quantum information processing implementations, and can be a stand-alone solution in the right parameter regime.Comment: 6 pages, 3 figures. Published version. This paper was initially entitled "Quantum gates via concatenated dynamical decoupling: theory and experiment", by Jacob R. West, Daniel A. Lidar, Bryan H. Fong, Mark F. Gyure, Xinhua Peng, and Dieter Suter. That original version split into two papers: http://arxiv.org/abs/1012.3433 (theory only) and the current pape

Ariel - Volume 2 Number 6

Editors Richard J. Bonanno Robin A. Edwards Associate Editors Steven Ager Stephen Flynn Shep Dickman Tom Williams Lay-out Editor Eugenia Miller Contributing Editors Michael J. Blecker W. Cherry Light James J. Nocon Lynne Porter Editors Emeritus Delvyn C. Case, Jr. Paul M. Fernhof