Zinc-blende AlN Research Articles

Electronic and magnetic properties of V- and Cr-doped zinc-blende AlN

The electronic and magnetic properties of the zinc-blende aluminum nitride doped with V and Cr are studied using the density functional theory (DFT), namely the KKR-CPA-PBE method. Pure AlN is found to be a wide band gap semiconductor, and doping V and Cr single impurities generate ferromagnetic half-metallic behavior. Moreover, the values of the formation energy reveal that these compounds are stable systems for all dopant concentrations. A self-consistent energy minimization scheme determines the ferromagnetic state as the stable magnetic state for V- and Cr-doping AlN. A double exchange mechanism is identified as the mechanism responsible for magnetism in our systems. When increasing doping impurities, the total magnetic moments increase linearly and the Curie temperature T C , calculated using the mean-field approximation, shows a significant change. The present findings reveal Cr- and V-doped zinc-blende AlN as potential candidates for high Curie temperature ferromagnetic materials.

Mapping the mechanical properties in nitride coatings at the nanometer scale

We report on a multilayered structure comprising of rock-salt (rs) structured CrN layers of constant thickness and AlN layers of varying thicknesses, which surprisingly enables the growth of metastable zinc-blende (zb) AlN layers for certain layer-thickness combinations. The multilayer exhibits an atomic and electronic structure gradient as revealed using advanced electron microscopy and electron spectroscopy. Gradient structures are also accompanied by a modulation of the chemical compositions. A combined experimental analysis based on valence electrons and inner shell electrons allowed mapping the mechanical properties of the multilayer at the nanometer scale and further unveiled the effect of oxygen impurities on the bulk modulus. We found that the presence of oxygen impurities causes a remarkable reduction of the bulk modulus of rs-CrN while having no significant effect on the bulk modulus of the stable wurtzite structure wz-AlN layers. The findings are unambiguously validated by theoretical calculations using density functional theory.

Fully analytic valence force field model for the elastic and inner elastic properties of diamond and zincblende crystals

Using a valence force field model based on that introduced by Martin, we present three related methods through which we analytically determine valence force field parameters. The methods introduced allow easy derivation of valence force field parameters in terms of the Kleinman parameter $\zeta$ and bulk properties of zincblende and diamond crystals. We start with a model suited for covalent and weakly ionic materials, where the valence force field parameters are derived in terms of $\zeta$ and the bulk elastic constants $C_{11}$, $C_{12}$, and $C_{44}$. We show that this model breaks down as the material becomes more ionic and specifically when the elastic anisotropy factor $A = 2C_{44}/(C_{11}-C_{12}) > 2$. The analytic model can be stabilised for ionic materials by including Martin's electrostatic terms with effective cation and anion charges in the valence force field model. Inclusion of effective charges determined via the optical phonon mode splitting provides a stable model for all but two of the materials considered (zincblende GaN and AlN). A stable model is obtained for all materials considered by also utilising the inner elastic constant $E_{11}$ to determine the magnitude of the effective charges used in the Coulomb interaction. Test calculations show that the models describe well structural relaxation in superlattices and alloys, and reproduce key phonon band structure features.

Electronic distribution and elastic properties of zinc-blende AlN and GaN

The density-functional theory (DFT) and density-functional perturbation theory (DFPT) are employed to study the electronic distributions and elastic properties of zinc-blende AlN and GaN. The linear charge density distributions along the [111] direction and charge density distribution of (001) planes for zinc-blende AlN and GaN are calculated. The total state of density and partial state of density of AlN and GaN are also calculated. Based on the optimized lattice parameters, the elastic constants and the internal strain parameters of zinc-blende AlN and GaN are calculated. The elastic tensors and compliance tensors are used to calculate Young’s modulus of (101) planes.

Comparative Study on the Interatomic Force Constants and Elastic Properties of Zinc-Blende AlN, AlP, and AlAs

The lattice constants, interatomic force constants and elastic constants of zinc-blende AlN, AlP and AlAs are calculated by ab initio pseudopotential plane wave method. The calculated lattice constants are underestimated owing to local density approximation itself and thermal expansion effect. Based on the density functional perturbation theory, the elastic properties of these materials are studied. The calculated values are affected by lattice constant, selection of pseudopotential and exchange-correlation energy. Based on the calculated elastic constants, Young's modulus diagrams on (101) sides of these materials are drawn, which provides an important reference for the future research on the mechanics of such materials.

Elastic, piezoelectric and thermal properties of zinc-blende AlN under pressure

The present work aims to investigate the elastic constants and their related mechanical parameters, acoustic wave speeds, piezoelectric coefficients and thermal properties of cubic zinc-blende AlN and their pressure dependence up to 5 GPa. The calculations are performed using the pseudopotential plane-wave method within the frame work of the density functional perturbation theory in the local density approximation for the exchange–correlation functional. The accord between our results and the experimental and previous theoretical data reported in the literature is found to be generally reasonably good. It is found that the surface acoustic wave speeds decrease with increasing pressure for both [100] and [110] crystallographic directions, while both elastic stiffness constants and piezoelectric coefficients increase under applied pressure. The variation of the features of interest as a function of pressure shows almost a linear behavior.

Density Functional Investigation for Electronic Properties of Zinc Blende GaN and AlN

Density Functional Investigation for Electronic Properties of Zinc Blende GaN and AlN

A theoretical calculation of the electronic and magnetic behaviour of C-doped zincblende AlN

Based on structural spin-polarized density functional theory, the electronic and magnetic properties of carbon-doped zincblende AlN were investigated. The calculations were carried out by means of the pseudopotential method employed exactly as implemented in Quantum Espresso code. For 0.625% C-doped AlN, we found a ferromagnetic and half-metallic behaviour. Per supercell, the AlC0.0625N0.9375 has a net magnetic moment of 1.0μβ. The main contribution to the magnetic moment comes from the 2p-C orbitals, with a lesser contribution of the 2p-N and 2p-Al orbitals. Our results suggest that C-doped AlN has potential applications in semiconductor spintronic devices.

Review: mechanical behavior of metal/ceramic interfaces in nanolayered composites—experiments and modeling

Recent experimental and modeling studies in nanolayered metal/ceramic composites are reviewed, with focus on the mechanical behaviors of metal/nitrides interfaces. The experimental and modeling studies of the slip systems in bulk TiN are reviewed first. Then, the experimental studies of interfaces, including co-deformation mechanism by micropillar compression tests, in situ TEM straining tests for the dynamic process of the co-deformation, thickness-dependent fracture behavior, and interrelationship among the interfacial bonding, microstructure, and mechanical response, are reviewed for the specific material systems of Al/TiN and Cu/TiN multilayers at nanoscale. The modeling studies reviewed cover first-principles density functional theory-based modeling, atomistic molecular dynamics simulations, and mesoscale modeling of nanolayered composites using discrete dislocation dynamics. The phase transformation between zinc-blende and wurtzite AlN phases in Al/AlN multilayers at nanoscale is also reviewed. Finally, a summary and perspective of possible research directions and challenges are given.

Ab initio modeling of zincblende AlN layer in Al-AlN-TiN multilayers

An unusual growth mechanism of metastable zincblende AlN thin film by diffusion of nitrogen atoms into Al lattice is established. Using first-principles density functional theory, we studied the possibility of thermodynamic stability of AlN as a zincblende phase due to epitaxial strains and interface effect, which fails to explain the formation of zincblende AlN. We then compared the formation energetics of rocksalt and zincblende AlN in fcc Al through direct diffusion of nitrogen atoms to Al octahedral and tetrahedral interstitials. The formation of a zincblende AlN thin film is determined to be a kinetically driven process, not a thermodynamically driven process.

Growth and Stress-induced Transformation of Zinc blende AlN Layers in Al-AlN-TiN Multilayers.

AlN nanolayers in sputter deposited {111}Al/AlN/TiN multilayers exhibit the metastable zinc-blende-structure (z-AlN). Based on density function theory calculations, the growth of the z-AlN is ascribed to the kinetically and energetically favored nitridation of the deposited aluminium layer. In situ nanoindentation of the as-deposited {111}Al/AlN/TiN multilayers in a high-resolution transmission electron microscope revealed the z-AlN to wurzite AlN phase transformation through collective glide of Shockley partial dislocations on every two {111} planes of the z-AlN.

Active zinc-blende III–nitride photonic structures on silicon

We use a layer transfer method to fabricate free-standing photonic structures in a zinc-blende AlN epilayer grown by plasma-assisted molecular beam epitaxy on a 3C-SiC pseudosubstrate and containing GaN quantum dots. The method leads to the successful realization of microdisks, nanobeam photonic crystal cavities, and waveguides integrated on silicon (100) and operating at short wavelengths. We assess the quality of such photonic elements by micro-photoluminescence spectroscopy in the visible and ultraviolet ranges, and extract the absorption coefficient of ZB AlN membranes (α ∼ (2–5) × 102 cm−1).

Self-assembling of impurity clusters in AlN:(Ga, BV, CV), (BV, CV = P, As; P, Sb; As, Sb)

The self-assembling conditions of arrays of tetrahedral impurity clusters of two types in zinc blende AlN:(Ga, BV, CV), (BV, CV=P, As; P, Sb; As, Sb) are represented. Doping with one cation and two anion isoelectronic impurities transforms AlN into AlN-rich GaxAl1−xBVyCVzN1−y−z alloy of GaBV, GaCV, GaN, AlBV, AlCV and AlN. The cause of self-assembling is the preference of GaBV, GaCV and AlN bonding over that of GaN, AlBV, AlCV. The conditions are considered from 0°C to 1000°C in the dilute and ultra dilute limits for the cation and anion impurities, correspondingly. The temperature ranges between the cluster occurrence and self-assembling completion when the same anion impurities are in clusters are very small. 1P4Ga and 1As4Ga cluster occurrence temperatures are equal, correspondingly, to 797°C and 736°C at Ga content 2% and P and As contents 0.01%. 1P4Ga and 1Sb4Ga cluster occurrence temperatures are equal, correspondingly, to 976°C and 736°C at the same impurity contents. The cluster densities in AlN:(Ga, As, Sb) are close to those in AlN:(Ga, P, Sb). The results demonstrate that studied semiconductors are promising materials to produce arrays of identical ∼1nm low band gap objects of two types embedded in the wide band gap matrix.

Thermodynamic Properties of Wurtzite and Zinc-Blende AlN

In this paper, we carry out linear response calculation to determine the phonon density of states and the thermodynamic properties of the wurtzite and zinc-blende AlN by using the norm-conserving pseudo-potential method. The optimized lattice constant is in good agreement with the available experimental data. The internal energies increase almost linearly with temperature and the phonon free energy curves move down with increasing temperature in both structures. The zero value of the lattice vibration free energy appears at temperature 707K in wurtzite and 728K in zinc-blende AlN respectively. The specific heat capacity of the wurtzite AlN is higher than that of the zinc-blende AlN at room temperature owing to the difference of the phonon spectra.

First-Principles Study on Elastic Properties of AlN

Structural and elastic properties of AlN are investigated by using First-principles. Both of wurtzite and zinc-blende structures are investigated, respectively. The bulk moduli of the wurtzite structure and zinc blende AlN are 194.2GPa and 187GPa, which obtained by the elastic stiffness constants respectively. Shear moduli are 136GPa and 124GPa. Young's moduli are 331GPa and 305GPa. Poisson's ratio and Pugh criterion suggests that both of them are brittle material. The brittleness of wurtzite AlN is higher than that of zinc-blende AlN. The elastic anisotropy of the bulk moduli and shear moduli were discussed. Three-dimensional anisotropic of the young's modulus were analyzed.

Schottky barrier at the AlN/metal junction

We report a first princples study of the Schottky barrier of zinc blende (zb) AlN to Pt, Au, Al, W, In, and Cs. We find good agreement with the Schottky model for Pt, Au, Al, W, and In contacts. However, in the case of Cs, a spatially extended interface dipole formation results in significant deviation from the Schottky rule. Moreover, for the “cesiated” AlN surface, the electron affinity shifts from positive 2.0 eV for clean AlN to negative 1.8 eV in qualitative agreement with recent experiments by Wu and Kahn [C. I. Wu and A. Kahn, Appl. Surf. Sci. 162, 250 (2000)].

Cubic GaN quantum dots embedded in zinc-blende AlN microdisks

Microresonators containing quantum dots find application in devices like single photon emitters for quantum information technology as well as low threshold laser devices. We demonstrate the fabrication of 60nm thin zinc-blende AlN microdisks including cubic GaN quantum dots using dry chemical etching techniques. Scanning electron microscopy analysis reveals the morphology with smooth surfaces of the microdisks. Micro-photoluminescence measurements exhibit optically active quantum dots. Furthermore this is the first report of resonator modes in the emission spectrum of a cubic AlN microdisk.

Hybrid functional study of the elastic and structural properties of wurtzite and zinc-blende group-III nitrides

We present a complete set of elastic and structural parameters for wurtzite and zinc-blende group-III nitrides, GaN, InN and AlN, calculated ab initio. A high degree of accuracy is ensured using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional approach. Both lattice and elastic constants are obtained by means of the stresses acting on the crystal, rather than by a minimization of the lattice energy. Our results show very good agreement with available experimental data. Furthermore, all the independent internal strain parameters of the wurtzite nitrides are reported.

Surface energies of AlN allotropes from first principles

In this letter we present first-principles calculations of the surface energies of rock-salt (B1), zinc-blende (B3) and wurtzite (B4) AlN allotropes. Of several low-index facets, the highest energies are obtained for monoatomic surfaces (i.e. of only either Al or N atoms): and . The difference between Al- and N-terminated surfaces in these cases is less then 20 meV/Å2. The stoichiometric facets have energies lower by 100 meV/Å2 or more. The obtained trends could be rationalized by a simple nearest-neighbour broken-bond model.

FERROMAGNETIC PROPERTIES IN V-DOPED AlN FROM FIRST PRINCIPLES

Using the first-principles method based on the density functional theory, we have calculated electronic structure of zinc blende AlN doped with 6.25% of V. The V dopants are found spin polarized and the calculated band structures suggest a 100% polarization of the conduction carriers. The ferromagnetic ground state in V-doped AlN can be explained in terms of double-exchange mechanism, and a Curie temperature above room temperature can be expected. These results suggest that the V-doped AlN may present a promising dilute magnetic semiconductor and find applications in the field of spintronics.