Artificial photosynthesis relies on the availability of semiconductors that are chemically stable and can efficiently capture solar energy. Although metal oxide semiconductors have been investigated for their promise to resist oxidative attack, materials in this class can suffer from chemical and photochemical instability. Here we present a methodology for evaluating corrosion mechanisms and apply it to bismuth vanadate, a state-of-the-art photoanode. Analysis of changing morphology and composition under solar water splitting conditions reveals chemical instabilities that are not predicted from thermodynamic considerations of stable solid oxide phases, as represented by the Pourbaix diagram for the system. Computational modelling indicates that photoexcited charge carriers accumulated at the surface destabilize the lattice, and that self-passivation by formation of a chemically stable surface phase is kinetically hindered. Although chemical stability of metal oxides cannot be assumed, insight into corrosion mechanisms aids development of protection strategies and discovery of semiconductors with improved stability.

We report the realization of a new multi-band-gap semiconductor. The highly mismatched alloy Zn 1-y Mn y O x Te 1-x has been synthesized using the combination of oxygen ion implantation and pulsed laser melting. Incorporation of small quantities of isovalent oxygen leads to the formation of a narrow, oxygen-derived band of extended states located within the band gap of the Zn 1-y Mn y Te host. When only 1.3% of Te atoms is replaced with oxygen in a Zn 0.88 Mn 0.12 Te crystal (with band gap of 2.32 eV) the resulting band structure consists of two direct band gaps with interband transitions at ~1.77 eV and 2.7 eV. This remarkable modification of the band structure is well described by the band anticrossing model in which the interactions between the oxygenderived band and the conduction band are considered. With multiple band gaps that fall within the solar energy spectrum, Zn 1-y Mn y O x Te 1-x is a material perfectly satisfying the conditions for single-junction photovoltaics with the potential for power conversion efficiencies surpassing 50%.PACS numbers: 71.20.Nr; 78.66.Hf; 61.72.Vv; 89.30.Cc The unusual properties of HMAs are well explained by the recently developed band anticrossing (BAC) model [3][4][5]. The model has also predicted several new effects that were later confirmed by experiments [6][7][8]. According to this model the electronic structure of the HMAs is determined by the interaction between localized states associated with N or O atoms and the extended states of the host semiconductor matrix.As a result the conduction band splits into two subbands with distinctly non-parabolic dispersion relations [3].In most instances, e.g. N in GaAs or O in CdTe, the localized states are located within the conduction band and the anticrossing interaction results in the formation of a relatively wide lower subband [5]. The subband is shifted to lower energies leading to a reduction of the energy band gap. The BAC model predicts that a narrow band can be formed only if the localized states occur well below the conduction band edge. Such a case is realized in ZnTe, MnTe and Zn 1-y Mn y Te alloys where the O level is located roughly 0.2 eV below the conduction band edge.We have shown recently that pulsed laser melting (PLM) followed by rapid thermal annealing (RTA) is well suited for the synthesis of HMAs. The combined ion 3 beam and laser processing approach has been demonstrated as an effective approach to synthesize dilute semiconductor alloys including GaN x As 1-x [9,10] and Ga 1-x Mn x As [11].Large enhancement by a factor of five in the incorporation of N in N + -implanted GaAs was observed. This is attributed to the rapid recrystallization rate associated with this process which results in the incorporation of impurity atoms to a level well above the solubility limit [12,13].Here we report the design and synthesis of a new type of material, the highly semiconductor [20,21]. Even for this non-optimal band gap configuration we calculate a power conversion efficiency of 45%, which is higher than th...

Simultaneous increases in electrical conductivity (up to 200%) and thermopower (up to 70%) are demonstrated by introducing native defects in Bi2 Te3 films, leading to a high power factor of 3.4 × 10(-3) W m(-1) K(-2). The maximum enhancement of the power factor occurs when the native defects act beneficially both as electron donors and energy filters to mobile electrons. They also act as effective phonon scatterers.

No abstract

No abstract

We demonstrate that the introduction of an elemental beam of Mn during the molecular beam epitaxial growth of Bi 2 Se 3 results in the formation of layers of Bi 2 MnSe 4 that intersperse between layers of pure Bi 2 Se 3 . This study revises the assumption held by many who study magnetic topological insulators (TIs) that Mn incorporates randomly at Bi-substitutional sites during epitaxial growth of Mn:Bi 2 Se 3 . Here, we report the formation of thin film magnetic TI Bi 2 MnSe 4 with stoichiometric composition that grows in a self-assembled multilayer heterostructure with layers of Bi 2 Se 3 , where the number of Bi 2 Se 3 layers separating the single Bi 2 MnSe 4 layers is approximately defined by the relative arrival rate of Mn ions to Bi and Se ions during growth, and we present its compositional, structural, and electronic properties. We support a model for the epitaxial growth of Bi 2 MnSe 4 in a near-periodic self-assembled layered heterostructure with Bi 2 Se 3 with corresponding theoretical calculations of the energetics of this material and those of similar compositions. Computationally derived electronic structure of these heterostructures demonstrates the existence of topologically nontrivial surface states at sufficient thickness. New J. Phys. 19 (2017) 085002 J A Hagmann et al

No abstract

Wavelength‐tunable nano/microlasers are essential components for various highly integrated and multifunctional photonic devices. Based on the different band gap/composition of inorganic cesium lead halide perovskite materials, broad band light absorption and emission devices can be achieved. Herein, a vapor–liquid–solid route for growing cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) microcrystal structures is demonstrated. These square‐shaped microstructures exhibit strong blue, green, and red photoluminescence, indicating that their band gaps can be engineered to cover the entire visible range. Optically pumped red–green–blue whispering‐gallery mode lasers based on the controlled composition of these microcrystals are successfully realized at room temperature. Moreover, rationally designed white‐light‐emitting chips with high brightness are fabricated utilizing these metal halide perovskite microstructures grown on sapphire. All these results evidently suggest a feasible route to the design of red–green–blue lasers and white‐light emitters for potential applications in full‐color displays as well as photonic devices.