Role of metal d states in II-VI semiconductors

Quinary wurtzite Zn-Ga-Ge-N-O solid solutions and their photocatalytic properties under visible light irradiation

Wurtzite solid solutions between GaN and ZnO highlight an intriguing paradigm for water splitting into hydrogen and oxygen using solar energy. However, large composition discrepancy often occurs inside the compound owing to the volatile nature of Zn, thereby prescribing rigorous terms on synthetic conditions. Here we demonstrate the merits of constituting quinary Zn-Ga-Ge-N-O solid solutions by introducing Ge into the wurtzite framework. The presence of Ge not only mitigates the vaporization of Zn but also strongly promotes particle crystallization. Synthetic details for these quinary compounds were systematically explored and their photocatalytic properties were thoroughly investigated. Proper starting molar ratios of Zn/Ga/Ge are of primary importance for single phase formation, high particle crystallinity and good photocatalytic performance. Efficient photocatalytic hydrogen and oxygen production from water were achieved for these quinary solid solutions which is strongly correlated with Ge content in the structure. Apparent quantum efficiency for optimized sample approaches 1.01% for hydrogen production and 1.14% for oxygen production. Theoretical calculation reveals the critical role of Zn for the band gap reduction in these solid solutions and their superior photocatalytic acitivity can be understood by the preservation of Zn in the structure as well as a good crystallinity after introducing Ge.

(CH3NH3)2Pb(SCN)2I2: a more stable structural motif for hybrid halide photovoltaics?

Hybrid halide perovskites have recently emerged as a highly efficient class of light absorbers; however, there are increasing concerns over their long-term stability. Recently, incorporation of SCN(-) has been suggested as a novel route to improving stability without negatively impacting performance. Intriguingly, despite crystallizing in a 2D layered structure, (CH3NH3)2Pb(SCN)2I2 (MAPSI) possesses an ideal band gap of 1.53 eV, close to that of the 3D connected champion hybrid perovskite absorber, CH3NH3PbI3 (MAPI). Here, we identify, using hybrid density functional theory, the origin of the smaller than expected band gap of MAPSI through a detailed comparison with the electronic structure of MAPI. Furthermore, assessment of the MAPSI structure reveals that it is thermodynamically stable with respect to phase separation, a likely source of the increased stability reported in experiment.

Two-dimensional topological insulators with tunable band gaps: Single-layer HgTe and HgSe

Two-dimensional (2D) topological insulators (TIs) with large band gaps are of great importance for the future applications of quantum spin Hall (QSH) effect. Employing ab initio electronic calculations we propose a novel type of 2D topological insulators, the monolayer (ML) low-buckled (LB) mercury telluride (HgTe) and mercury selenide (HgSe), with tunable band gap. We demonstrate that LB HgTe (HgSe) monolayers undergo a trivial insulator to topological insulator transition under in-plane tensile strain of 2.6% (3.1%) due to the combination of the strain and the spin orbital coupling (SOC) effects. Furthermore, the band gaps can be tuned up to large values (0.2 eV for HgTe and 0.05 eV for HgSe) by tensile strain, which far exceed those of current experimentally realized 2D quantum spin Hall insulators. Our results suggest a new type of material suitable for practical applications of 2D TI at room-temperature.

Recent progress in oxynitride photocatalysts for visible-light-driven water splitting

Photocatalytic water splitting into hydrogen and oxygen is a method to directly convert light energy into storable chemical energy, and has received considerable attention for use in large-scale solar energy utilization. Particulate semiconductors are generally used as photocatalysts, and semiconductor properties such as bandgap, band positions, and photocarrier mobility can heavily impact photocatalytic performance. The design of active photocatalysts has been performed with the consideration of such semiconductor properties. Photocatalysts have a catalytic aspect in addition to a semiconductor one. The ability to control surface redox reactions in order to efficiently produce targeted reactants is also important for photocatalysts. Over the past few decades, various photocatalysts for water splitting have been developed, and a recent main concern has been the development of visible-light sensitive photocatalysts for water splitting. This review introduces the study of water-splitting photocatalysts, with a focus on recent progress in visible-light induced overall water splitting on oxynitride photocatalysts. Various strategies for designing efficient photocatalysts for water splitting are also discussed herein.

Atomic-scale origin of piezoelectricity in wurtzite ZnO

ZnO has been extensively studied by virtue of its remarkably high piezoelectric responses, especially in nanowire forms. Currently, the high piezoelectricity of wurtzite ZnO is understood in terms of the covalent-bonding interaction between Zn 3d and O 2p orbitals. However, the Zn 3d orbitals are not capable of forming hybridized orbitals with the O 2pz orbitals since the Zn ion is characterized by fully filled non-interacting 3d orbitals. To resolve this puzzling problem, we have investigated the atomic-scale origin of piezoelectricity by exploiting density-functional theory calculations. On the basis of the computed orbital-resolved density of states and the band structure over the Γ-M first Brillouin zone, we propose an intriguing bonding mechanism that accounts for the observed high piezoelectricity - intra-atomic 3dz(2)-4pz orbital self-mixing of Zn, followed by asymmetric hybridization between the Zn 3dz(2)-4pz self-mixed orbital and the O 2pz orbital along the polar c-axis of the wurtzite ZnO.

Study on the interface electronic states of chemically modified ZnO nanowires

In this work, ZnO nanowires were modified with three mercaptans.

Semiconductor-based photocatalysts and photoelectrochemical cells for solar fuel generation: a review

This perspective article describes the barrier, progress and future direction of research on the photocatalytic and photoelectrochemical solar fuel generation.

Structural trends in hybrid perovskites [Me2NH2]M[HCOO]3 (M = Mn, Fe, Co, Ni, Zn): computational assessment based on Bader charge analysis

Charge partition between the metal and the ligand governs the geometry evolution in hybrid perovskites.

Structures, electronic properties and stability phase diagrams for copper(i/ii) bromide surfaces

This study presents a comprehensive periodic slab DFT investigation into structures, electronic properties and thermodynamic stability of all plausible terminations of CuBr and CuBr₂ surfaces. We find that surfaces terminated with negatively charged bromine atoms tend to be more stable if they are accompanied by significant relaxation.

Ternary alloy nanocrystals of tin and germanium chalcogenides

Sn_xGe_1−xS, Sn_xGe_1−xSe, GeS_xSe_1−x, and SnS_xSe_1−x alloy nanocrystals were synthesized by novel gas-phase laser photolysis. Their composition-dependent lattice parameters and band gap were thoroughly characterized. The Sn_xGe_1−xS and SnS_xSe_1−x nanocrystals exhibit higher photoconversion efficiency as compared with the end members.

Electronic structure and optical properties of Cu-doping and Zn vacancy impurities in ZnTe

The geometric structures of perfect ZnTe, that with Zn vacancy (Zn0.875Te), and Cu-doped ZnTe (Zn0.875Cu0.125Te) were optimized using the pseudopotential plane wave (PP-PW) method based on the density functional theory (DFT) within generalized gradient approximation (GGA). The cohesive energy, band structure, density of states, and Mulliken populations were calculated and discussed in detail. On the other hand, an accurate calculation of linear optical functions (the dielectric function, refraction index, reflectivity, conductivity function, and energy-loss spectrum) was performed. The results demonstrated that compared to the perfect ZnTe, the lattice parameters of Zn0.875Te and Zn0.875Cu0.125Te were changed and the cell volumes decreased to some extent due to the vacancy and introduction of impurity. A vacancy acceptor level and an acceptor impurity level were produced in Zn0.875Te and Zn0.875Cu0.125Te, respectively. By comparison, Cu doping in the ZnTe system is relatively stable while the monovacancy system is not.

Origin of novel diffusions of Cu and Ag in semiconductors: the case of CdTe

It is well known in experimental studies that Cu is usually a fast diffuser in semiconductors. In some semiconductors (e.g., CdTe), Ag is also a fast diffuser. The diffusion plays an important role in many applications when Cu (Ag) is employed to tune the semiconductor's electrical or optical properties. However, the origin of why Cu (Ag) shows different diffusion behavior compared to group-IA elements is still unclear. Using first-principles method, we compare the diffusion behaviors between Cu (Ag) and group-IA elements in CdTe, and find that the novel diffusion is due to the strong coupling between Cu (Ag) d levels and unoccupied host s levels. This coupling alters the stable doping site, diffusion pathway, and diffusion energy curve from those of group-IA elements, which have no active d levels, thus making the Cu (Ag) diffusion faster in many semiconductors.

Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions

CdO in the rocksalt structure is an indirect band gap semiconductor. Thus, in order to determine its band gap one needs to calculate the complete band structure. However, in practice, the exact evaluation of the quasiparticle band structure for the large number of k-points which constitute the different symmetry lines in the Brillouin zone can be an extremely demanding task compared to the standard density functional theory (DFT) calculation. In this paper we report the full quasiparticle band structure of CdO using a plane-wave pseudopotential approach. In order to reduce the computational effort and time, we make use of maximally localized Wannier functions (MLWFs). The MLWFs offer a highly accurate method for interpolation of the DFT or GW band structure from a coarse k-point mesh in the irreducible Brillouin zone, resulting in a much reduced computational effort. The present paper discusses the technical details of the scheme along with the results obtained for the quasiparticle band gap and the electron effective mass.

Semiconductor photocatalysis--mechanistic and synthetic aspects

Preceding work on photoelectrochemistry at semiconductor single-crystal electrodes has formed the basis for the tremendous growth in the three last decades in the field of photocatalysis at semiconductor powders. The reason for this is the unique ability of inorganic semiconductor surfaces to photocatalyze concerted reduction and oxidation reactions of a large variety of electron-donor and -acceptor substrates. Whereas great attention was paid to water splitting and the exhaustive aerobic degradation of pollutants, only a small amount of research also explored synthetic aspects. After introducing the basic mechanistic principles, standard experiments for the preparation and characterization of visible light active photocatalysts as well as the investigation of reaction mechanisms are discussed. Novel atom-economic C-C and C-N coupling reactions illustrate the relevance of semiconductor photocatalysis for organic synthesis, and demonstrate that the multidisciplinary field combines classical photochemistry with electrochemistry, solid-state chemistry, and heterogeneous catalysis.

Electronic structure of transparent oxides with the Tran-Blaha modified Becke-Johnson potential

We present electronic band structures of transparent oxides calculated using the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. We studied the basic n-type conducting binary oxides In(2)O(3), ZnO, CdO and SnO(2) along with the p-type conducting ternary oxides delafossite CuXO(2) (X=Al, Ga, In) and spinel ZnX(2)O(4) (X=Co, Rh, Ir). The results are presented for calculated band gaps and effective electron masses. We discuss the improvements in the band gap determination using TB-mBJ compared to the standard generalized gradient approximation (GGA) in density functional theory (DFT) and also compare the electronic band structure with available results from the quasiparticle GW method. It is shown that the calculated band gaps compare well with the experimental and GW results, although the electron effective mass is generally overestimated.

Band structure and optical properties of hexagonal In-rich In(x)Al(1-x)N alloys

Full potential linear augmented plane wave calculations have been performed to study the electronic and optical properties of In-rich In(x)Al(1-x)N alloys in the hexagonal wurtzite structure. Compositions of x = 0.9375, 0.8125 and 0.6875 are considered which follow from replacing one, three and five In atoms by Al in the 32-atom supercell. The new form of exchange correlation, i.e. Engel-Vosko's generalized gradient approximation within density functional theory, is employed. The calculations yield the band structure and total density of states as well as the imaginary part ε(2)(ω) of the ordinary and extraordinary dielectric function. The calculated dependence of the bandgap on the composition is in good agreement with recent experimental studies. A reversal of the valence band ordering is found between x = 0.8125 and 0.6875. The absorption features in the high-energy range of ε(2)(ω) are related to critical points of the band structure. The transition energies for these van Hove singularities are determined and their bowing parameters are discussed.

Ab initio study of II-(VI)2 dichalcogenides

The structural stabilities of the (Zn,Cd)(S,Se,Te)(2) dichalcogenides have been determined ab initio. These compounds are shown to be stable in the pyrite phase, in agreement with available experiments. Structural parameters for the ZnTe(2) pyrite semiconductor compound proposed here are presented. The opto-electronic properties of these dichalcogenide compounds have been calculated using quasiparticle GW theory. Bandgaps, band structures and effective masses are proposed as well as absorption coefficients and refraction indices. The compounds are all indirect semiconductors with very flat conduction band dispersion and high absorption coefficients. The work functions and surface properties are predicted. The Te and Se based compounds could be of interest as absorber materials in photovoltaic applications.

Point defects in ZnO: an approach from first principles

Recent first-principles studies of point defects in ZnO are reviewed with a focus on native defects. Key properties of defects, such as formation energies, donor and acceptor levels, optical transition energies, migration energies and atomic and electronic structure, have been evaluated using various approaches including the local density approximation (LDA) and generalized gradient approximation (GGA) to DFT, LDA+U/GGA+U, hybrid Hartree-Fock density functionals, sX and GW approximation. Results significantly depend on the approximation to exchange correlation, the simulation models for defects and the post-processes to correct shortcomings of the approximation and models. The choice of a proper approach is, therefore, crucial for reliable theoretical predictions. First-principles studies have provided an insight into the energetics and atomic and electronic structures of native point defects and impurities and defect-induced properties of ZnO. Native defects that are relevant to the n-type conductivity and the non-stoichiometry toward the O-deficient side in reduced ZnO have been debated. It is suggested that the O vacancy is responsible for the non-stoichiometry because of its low formation energy under O-poor chemical potential conditions. However, the O vacancy is a very deep donor and cannot be a major source of carrier electrons. The Zn interstitial and anti-site are shallow donors, but these defects are unlikely to form at a high concentration in n-type ZnO under thermal equilibrium. Therefore, the n-type conductivity is attributed to other sources such as residual impurities including H impurities with several atomic configurations, a metastable shallow donor state of the O vacancy, and defect complexes involving the Zn interstitial. Among the native acceptor-type defects, the Zn vacancy is dominant. It is a deep acceptor and cannot produce a high concentration of holes. The O interstitial and anti-site are high in formation energy and/or are electrically inactive and, hence, are unlikely to play essential roles in electrical properties. Overall defect energetics suggests a preference for the native donor-type defects over acceptor-type defects in ZnO. The O vacancy, Zn interstitial and Zn anti-site have very low formation energies when the Fermi level is low. Therefore, these defects are expected to be sources of a strong hole compensation in p-type ZnO. For the n-type doping, the compensation of carrier electrons by the native acceptor-type defects can be mostly suppressed when O-poor chemical potential conditions, i.e. low O partial pressure conditions, are chosen during crystal growth and/or doping.

Native defects in oxide semiconductors: a density functional approach

We report a semilocal and hybrid Hartree-Fock density functional study of native defects in three oxide semiconductors: ZnO, SrTiO(3), and SnO. The defect that is responsible for the n-type conductivity of ZnO has been debated, in which the O vacancy, Zn interstitial, their complexes, and residual H impurity are considered candidates. Our results indicate that the O vacancy induces a deep and localized in-gap state, whereas the Zn interstitial is a shallow donor and hence can be a source of the carriers. In view of the formation energies, the O vacancy is likely to form with a substantial concentration under O-poor conditions, but the Zn interstitial is unlikely. We thus propose that the O vacancy is relevant to the nonstoichiometry of ZnO and that a source other than the native defects, such as the H impurity, needs to be considered for the n-type conductivity. For SrTiO(3), the O vacancy and its complexes have been regarded as the origins of some of the remarkable electrical and optical properties. We suggest significant roles of the Ti antisite for a new insight into the defect-induced properties. Two types of Ti antisite, both of which are off-centered from the Sr site but toward different directions, exhibit low formation energies under Ti-rich conditions as does the O vacancy. They can explain optical properties such as visible-light emission, deep-level absorption, and the ferroelectricity observed in reduced SrTiO(3). As an example of p-type conductors, SnO has been investigated with a focus on the acceptor-like native defects. Under O-rich conditions, the Sn vacancy and O interstitial are found to be energetically favorable. The Sn vacancy induces shallow acceptor levels and can therefore be a source of carriers. The O interstitial shows no in-gap levels and hence it is inactive in terms of the carrier generation and compensation. However, this defect is a key to the understanding of the structures of intermediate compounds between SnO and SnO(2).

Present status of amorphous In-Ga-Zn-O thin-film transistors

The present status and recent research results on amorphous oxide semiconductors (AOSs) and their thin-film transistors (TFTs) are reviewed. AOSs represented by amorphous In-Ga-Zn-O (a-IGZO) are expected to be the channel material of TFTs in next-generation flat-panel displays because a-IGZO TFTs satisfy almost all the requirements for organic light-emitting-diode displays, large and fast liquid crystal and three-dimensional (3D) displays, which cannot be satisfied using conventional silicon and organic TFTs. The major insights of this review are summarized as follows. (i) Most device issues, such as uniformity, long-term stability against bias stress and TFT performance, are solved for a-IGZO TFTs. (ii) A sixth-generation (6G) process is demonstrated for 32″ and 37″ displays. (iii) An 8G sputtering apparatus and a sputtering target have been developed. (iv) The important effect of deep subgap states on illumination instability is revealed. (v) Illumination instability under negative bias has been intensively studied, and some mechanisms are proposed. (vi) Degradation mechanisms are classified into back-channel effects, the creation of traps at an interface and in the gate insulator, and the creation of donor states in annealed a-IGZO TFTs by the Joule heating; the creation of bulk defects should also be considered in the case of unannealed a-IGZO TFTs. (vii) Dense passivation layers improve the stability and photoresponse and are necessary for practical applications. (viii) Sufficient knowledge of electronic structures and electron transport in a-IGZO has been accumulated to construct device simulation models.

Transferable orthogonal tight-binding parameters for ZnS and CdS

Calculations of Slater-Koster (SK) parameters appearing in the tight-binding method using sp(3)d(5) basis sets for both the cationic and anionic species are presented for ZnS and CdS. We have adjusted these parameters to match the band structures obtained from the full potential linear augmented plane wave method. This operation has been carried out for a variety of structures namely zinc blende, wurtzite, rocksalt, CsCl and for a wide range of near-neighbor distances. The SK parameters have slightly different values for the same near-neighbor distance in different structures. Therefore, a least-squares fitting has been performed separately for each parameter as a function of only the near-neighbor distance to guarantee the transferability of these parameters to different structural environments. The fitted parameters are then used to calculate the electronic structure of small-sized clusters of ZnS and CdS in given geometries and the results are compared with ab initio results. A fairly good agreement found in the one-electron energy spectrum and total energy confirms transferability of the parameters to different length scales. A detailed account of the calculation procedure and calibration results is given in the present paper. These parameters can be used to study the electronic structure of large-sized clusters where first-principles methods are computationally demanding. It may be mentioned that the SK parameters do not satisfy the R(-(l + l' + 1)) Harrison scaling law for larger values of the near-neighbor distance R.

The quasiparticle band structure of zincblende and rocksalt ZnO

We present the quasiparticle band structure of ZnO in its zincblende (ZB) and rocksalt (RS) phases at the Γ point, calculated within the GW approximation. The effect of the p-d hybridization on the quasiparticle corrections to the band gap is discussed. We compare three systems, ZB-ZnO which shows strong p-d hybridization and has a direct band gap, RS-ZnO which is also hybridized but includes inversion symmetry and therefore has an indirect band gap, and ZB-ZnS which shows a weaker hybridization due to a change of the chemical species from oxygen to sulfur. The quasiparticle corrections are calculated with different numbers of valence electrons in the Zn pseudopotential. We find that the Zn(20+) pseudopotential is essential for the adequate treatment of the exchange interaction in the self-energy. The calculated GW band gaps are 2.47 eV and 4.27 eV respectively, for the ZB and RS phases. The ZB-ZnO band gap is underestimated compared to the experimental value of 3.27 by ∼ 0.8 eV. The RS-ZnO band gap compares well with the experimental value of 4.5 eV. The underestimation for ZB-ZnO is correlated with the strong p-d hybridization. The GW band gap for ZnS is 3.57 eV, compared to the experimental value of 3.8 eV.

Strong interplay between structure and electronic properties in CuIn(S,Se){2}: a first-principles study

We present a first-principles study of the electronic properties of CuIn(S,Se){2} (CIS) using state-of-the-art self-consistent GW and hybrid functionals. The calculated band gap depends strongly on the anion displacement u, an internal structural parameter that measures lattice distortion. This contrasts with the observed stability of the band gap of CIS solar panels under operating conditions, where a relatively large dispersion of values for u occurs. We solve this apparent paradox considering the coupled effect on the band gap of copper vacancies and lattice distortions. The correct treatment of d electrons in these materials requires going beyond density functional theory, and GW self-consistency is critical to evaluate the quasiparticle gap and the valence band maximum.

Characteristic energies and shifts in optical spectra of colloidal IV-VI semiconductor nanocrystals

We investigate structural, electronic, and optical properties of colloidal IV-VI semiconductor quantum dots (QDs) using an ab initio pseudopotential method and a repeated supercell approximation. In particular, rhombo-cuboctahedral quantum dots consisting of PbSe, PbTe, and SnTe with a pseudohydrogen passivation shell are investigated for different QD sizes. The obtained dependence of the confinement energy on the QD size questions the use of three-dimensional spherical potential well models for small QD structures. The predicted band gaps are almost in agreement with measured values. The calculated Franck-Condon shifts vary significantly with the QD size. Only for PbSe they may explain the Stokes shift between optical absorption and emission. For the tellurides, spectral properties such as the oscillator strength are more important.

Sources of electrical conductivity in SnO2

SnO2 is widely used as a transparent conductor and sensor material. Better understanding and control of its conductivity would enhance its performance in existing applications and enable new ones, such as in light emitters. Using density functional theory, we show that the conventional attribution of n-type conductivity to intrinsic point defects is incorrect. Unintentional incorporation of hydrogen provides a consistent explanation of experimental observations. Most importantly, we find that SnO2 offers excellent prospects for p-type doping by incorporation of acceptors on the Sn site. Specific strategies for optimizing acceptor incorporation are presented.

Computational studies of conductivity in wide-band-gap semiconductors and oxides

The ability to control conductivity is essential for design and fabrication of (opto)electronic devices. Such conductivity control has traditionally been very difficult in wide-band-gap semiconductors, and native point defects have often been invoked to explain these problems. State-of-the-art first-principles calculations based on density functional theory have been used to elucidate these issues. Approaches for overcoming the 'band-gap problem', including the LDA+U method, allow more accurate comparisons and predictions of defect levels. The methodology is illustrated with the case of native point defects in zinc oxide. Computations reveal that the prevailing n-type conductivity cannot be attributed to native defects; it must thus be caused by impurities that are unintentionally incorporated. Hydrogen is shown to be an excellent candidate for such an impurity.

A review of the electronic and magnetic properties of tetrahedrally bonded half-metallic ferromagnets

The emergence of the field of spintronics has brought half-metallic ferromagnets to the centre of scientific research. A lot of interest was focused on newly created transition-metal pnictides (such as CrAs) and chalcogenides (such as CrTe) in the metastable zinc-blende lattice structure. These compounds were found to have the advantage of high Curie temperatures in addition to their structural similarity to semiconductors. Significant theoretical activity has been devoted to the study of the electronic and magnetic properties of these compounds in an effort to achieve a better control of their experimental behaviour in realistic applications. This paper is devoted to an overview of the studies of these compounds, with emphasis on theoretical results, covering their bulk properties (electronic structure, magnetism, stability of the zinc-blende phase, stability of ferromagnetism) as well as low-dimensional structures (surfaces, interfaces, nanodots and transition-metal delta-doped semiconductors) and phenomena that can possibly destroy the half-metallic property, like structural distortions or defects.

Correlation between ionic charge and ground-state properties in rocksalt and zinc blende structured solids

In this paper we have evaluated the ground-state properties (i.e., bulk modulus and cohesive energy) of rocksalt and zinc blende structured solids. We have presented two expressions relating the bulk modulus B (GPa) for the alkali halides, alkaline-earth chalcogenides, transition metal nitrides, rare-earth {divalent (R(2+)X) and trivalent (R(3+)X) } monochalcogenides, group IV, III-V and II-VI semiconductors and the cohesive energy E(coh) (kcal mol(-1)) for the alkali halides and alkaline-earth chalcogenides with the product of ionic charges (Z(1)Z(2)) and nearest-neighbour distance d (Å). The bulk moduli and cohesive energy of rocksalt and zinc blende type structure compounds exhibit a linear relationship when plotted on a log-log scale against the nearest-neighbour distance d (Å), but fall on different straight lines according to the ionic charge product of the compounds. We have applied the modified relation on rocksalt and zinc blende structured solids and found a better agreement with experimental data as compared to the values evaluated by earlier researchers. The results for bulk modulus differ from experimental values by the following amounts: BaO-0%, LiCl-0%, LaS-0%, SmSe-0%, ZnS-0%, CdS-0%, GaP-0%, InP-0%, MgO-0.61%, CaO-0.89%, SmS-1.7%, YbSe-1.6%, UP-1.9%, EuSe-1.9%; and the results for cohesive energy differ from experimental values by the following amounts: LiCl-0.49%, KF-0.51%, RbF-0.54%, SrO-1.2%, NaCl-1.6%, NaF-1.8%, MgSe-1.9%.

Overall Water Splitting on (Ga1-xZnx)(N1-xOx) Solid Solution Photocatalyst: Relationship between Physical Properties and Photocatalytic Activity

The physical and photocatalytic properties of a novel solid solution between GaN and ZnO, (Ga(1-x)Zn(x))(N(1-x)O(x)), are investigated. Nitridation of a mixture of Ga(2)O(3) and ZnO at 1123 K for 5-30 h under NH(3) flow results in the formation of a (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution with x = 0.05-0.22. With increasing nitridation time, the zinc and oxygen concentrations decrease due to reduction of ZnO and volatilization of zinc, and the crystallinity and band gap energy of the product increase. The highest activity for overall water splitting is obtained for (Ga(1-x)Zn(x))(N(1-x)O(x)) with x = 0.12 after nitridation for 15 h. The crystallinity of the catalyst is also found to increase with increasing the ratio of ZnO to Ga(2)O(3) in the starting material, resulting in an increase in activity.