We investigated the electronic and magnetic properties of a series of zinc-blend II-V compounds by carrying out density-functional-theory calculations including spin-orbit couplings. Contrary to the case of CaN and CaP, the half-metallic characteristics of the II-V compounds such as CaSb and CaBi were found to be destroyed. Our analysis of the valence band structures of CaAs, CaSb, and CaBi revealed a critical role of the spin-orbit coupling interactions on the exchange-split band structure, thereby leading to breakdown of the half-metallic ferromagnetism for the systems with heavier group V elements in the zinc-blend II-V compounds.
We report first-principles calculations of zinc-blende half-metals, identifying systems for epitaxial growth with semiconductors, and present calculations for CrAs/GaAs multilayers. We find that half-metallicity is conserved troughout the heterostructure, making this a good candidate for spintronics applications.
We report a new biphasic crystalline wurtzite/zinc-blende homostructure in gallium nitride nanowires. Cathodoluminescence was used to quantitatively measure the wurtzite and zinc-blende band gaps. High resolution transmission electron microscopy was used to identify distinct wurtzite and zinc-blende crystalline phases within single nanowires through the use of selected area electron diffraction, electron dispersive spectroscopy, electron energy loss spectroscopy, and fast Fourier transform techniques. A mechanism for growth is identified.
We report systematic first-principles calculations for ordered zinc-blende compounds of the transition metal elements V, Cr, Mn with the sp elements N, P, As, Sb, S, Se, Te, motivated by recent fabrication of zinc-blende CrAs, CrSb, and MnAs. They show ferromagnetic half-metallic behavior for a wide range of lattice constants. We discuss the origin and trends of half-metallicity, present the calculated equilibrium lattice constants, and examine the half-metallic behavior of their transition element terminated (001) surfaces.
The properties of perfect screw dislocations have been investigated for several zinc-blende materials such as diamond, Si, $β$-SiC, Ge and GaAs, by performing first principles calculations. For almost all elements, a core configuration belonging to shuffle set planes is favored, in agreement with low temperature experiments. Only for diamond, a glide configuration has the lowest defect energy, thanks to an sp$^2$ hybridization in the core.
The structure of the pseudo-binary mercury chalcogenide alloy HgSe0.7S0.3 has been studied by means of X-ray and neutron powder diffraction at pressures up to 8.5 GPa. A phase transition from the cubic zinc blende structure to the hexagonal cinnabar structure was observed at P ~ 1 GPa. A phenomenological model of this reconstructive phase transition based on the displacement mechanism is proposed. The analysis of the geometrical relationship between the zinc blende and the cinnabar phases has shown that the possible order parameter for the zinc blende - cinnabar structural transformation is th…
Existence of ferromagnetism in bulk calcium compounds is discovered theoretically. First-principles calculations of calcium phosphide, calcium arsenide and calcium antimonide in the zinc-blende structure have been performed to show the half-metallic ground state in each optimized stable structure. Magnetism comes from spin-polarization of electrons in $p$-orbitals of P, As or Sb and $d$-orbitals of calcium atoms. The half-metallicity is analogous to the half-metallic zinc-blende compounds, {\it e.g.} CrAs or CrSb, but the predicted compounds become ferromagnetic without transition metals. In (…
Ground state properties of SiC, AlN, GaN and InN in the zinc-blende and wurtzite structures are determined using an ab initio scheme. For the self-consistent field part of the calculations, the Hartree-Fock program Crystal has been used. Correlation contributions are evaluated using the coupled-cluster approach with single and double excitations. This is done by means of increments derived for localized bond orbitals and for pairs and triples of such bonds. A comparison between the ground state energies of the zinc-blende and wurtzite structure is made: At the Hartree-Fock level, it turns out …
We report on first-principles calculations of multilayers of zinc-blende half-metallic ferromagnets CrAs and CrSb with III-V and II-VI semiconductors, in the [001] orientation. We examine the ideal and tetragonalised structures, as well as the case of an intermixed interface. We find that, as a rule, half-metallicity can be conserved throughout the heterostructures, provided that the character of the local coordination and bonding is not disturbed. At the interfaces with semiconductors, we describe a mechanism that can give also a non-integer spin moment per interface transition atom, and deri…
For analyzing quantum transport in semiconductor devices, accurate electronic structures are critical for quantitative predictions. Here we report theoretical analysis of electronic structures of all III-V zinc-blende semiconductor compounds. Our calculations are from density functional theory with the semi-local exchange proposed recently [F. Tran and P. Blaha, Phys. Rev. Lett. 102, 226401 (2009)], within the linear muffin tin orbital scheme. The calculated band gaps and effective masses are compared to experimental data and good quantitative agreement is obtained. Using the theoretical schem…
We develop a nucleation-based model to explain the formation of the wurtzite (WZ) crystalline phase during the vapor-liquid-solid growth of free-standing nanowires of zinc-blende (ZB) semiconductors. We first show that, in nanowires, nucleation generally occurs at the outer edge of the solid/liquid interface (the triple phase line) rather than elsewhere at the solid/liquid interface. In the present case, this entails major differences between ZB and WZ nuclei. Depending on the pertinent interface energies, WZ nucleation is favored at high liquid supersaturation. This explains our systematic ob…
The electronic structure of AlN in wurtzite and zinc-blende phases is studied experimentally and theoretically. By using x-ray emission spectroscopy, the Al 3p, Al 3s and N 2p spectral densities are obtained. The corresponding local and partial theoretical densities of states (DOS), as well as the total DOS and the band structure, are calculated by using the full potential linearized augmented plane wave method, within the framework of the density functional theory. There is a relatively good agreement between the experimental spectra and the theoretical DOS, showing a large hybridization of t…
It is demonstrated that the nearest neighbor Mn pair on the GaAs (001) surface has a lower energy for the [-110] direction comparing to the [110] case. According to the group theory and the Luttinger's method of invariants, this specific Mn distribution results in bulk uniaxial in-plane and out-of-plane anisotropies. The sign and magnitude of the corresponding anisotropy energies determined by a perturbation method and ab initio computations are consistent with experimental results.
In this letter we present an expression relating the cohesive energy for the A3B5 and A2B6 semiconductors with the product of their ionic charges and nearest neighbor distance. The cohesive energy values of these solids exhibits a linear relationship when plotted on a log-log scale against the nearest neighbor distance, but fall on different straight lines according to the ionic charge product of the solids. A good agreement has been found between the experimental and calculated values of the cohesive energy for A3B5 and A2B6 semiconductors.
New materials are currently sought for use in spintronics applications. Ferromagnetic materials with half metallic properties are valuable in this respect. Here we present the electronic structure and magnetic properties of binary compounds consisting of 3d transition metals and group V elements viz. P, Sb and As in the zinc-blende structure. We demonstrate that compounds of V, Cr and Mn show half metallic behavior for appropriate lattice constants. By comparing the total energies in the ferromagnetic and antiferromagnetic structures, we have ascertained that the ferromagnetic phase is stable …
The density-functional theory (DFT) and density-functional perturbation theory (DFPT) are employed to study the pressure dependence of elastic and dynamical properties of zinc-blende ZnS and ZnSe. The calculated elastic constants and phonon spectra from 0 GPa to 15 GPa are compared with the available experimental data. Generally, our calculated values are overestimated with experimental data, but agree well with recent other theoretical values. The discrepancies with experimental data are due to the use of local density approximation (LDA) and the effect of temperature. In this work, in order …
An accurate density-functional method is used to study systematically half-metallic ferromagnetism and stability of zincblende phases of 3d-transition-metal chalcogenides. The zincblende CrTe, CrSe, and VTe phases are found to be excellent half-metallic ferromagnets with large half-metallic gaps (up to 0.88 eV). They are mechanically stable and approximately 0.31-0.53 eV per formula unit higher in total energy than the corresponding nickel-arsenide ground-state phases, and therefore would be grown epitaxially in the form of films and layers thick enough for spintronic applications.
We present an extended study of single impurity atoms and atomic swaps in half-metallic CrAs, CrSb and CrSe zinc-blende compounds. Although the perfect alloys present a rather large gap in the minority-spin band, all defects under study, with the exception of void impurities at Cr and sp sites and Cr impurities at sp sites (as long as no swap occurs), induce new states within the gap. The Fermi level can be pinned within these new minority states depending on the lattice constant used for the calculations and the electronegativity of the sp atoms. Although these impurity states are localized i…
We study the transport of spin polarized electrons in n-GaAs using spatially resolved continuous wave Faraday rotation. From the measured steady state distribution, we determine spin relaxation times under drift conditions and, in the presence of strain, the induced spin splitting from the observed spin precession. Controlled variation of strain along [110] allows us to deduce the deformation potential causing this effect, while strain along [100] has no effect. The electric field dependence of the spin lifetime is explained quantitatively in terms of an increase of the electron temperature.
We present a technique to calculate the spin relaxation of hot electrons during their energy thermalization in the Gamma-valley of zinc-blende semiconductors. The results of this model match recent experimental data and they can be used to check the applicability of spin related boundary conditions across a semiconductor/ferromagnet junction in reverse bias conditions (spin injection).
The ground state structures of the A$_x$B$_{1-x}$C wurtzite (WZ) alloys with $x=$0.25, 0.5, and 0.75 are revealed by a ground state search using the valence-force field model and density-functional theory total energy calculations. It is shown that the ground state WZ alloy always has a lower strain energy and formation enthalpy than the corresponding zinc-blende (ZB) alloy. Therefore, we propose that the WZ phase can be stabilized through alloying. This novel idea is supported by the fact that the WZ AlP$_{0.5}$Sb$_{0.5}$, AlP$_{0.75}$Sb$_{0.25}$, ZnS$_{0.5}$Te$_{0.5}$, and ZnS$_{0.75}$Te$_{0…
The diamond and zinc-blende semiconductors are well-known and have been widely studied for decades. Yet, their electronic structure still surprises with unexpected topological properties of the valence bands. In this joint theoretical and experimental investigation we demonstrate for the benchmark compounds InSb and GaAs that the electronic structure features topological surface states below the Fermi energy. Our parity analysis shows that the spin-orbit split-off band near the valence band maximum exhibits a strong topologically non-trivial behavior characterized by the $\mathcal{Z}_2$ invari…
In a recent publication [Galanakis I et al 2006 \PR B \textbf{74} 140408(R)] we have shown that in the case of CrAs and related transition-metal chalcogenides and pnictides, crystallizing in the zinc-blende structure, the excess of the transition-metal atoms leads to half-metallic ferrimagnetism. The latter property is crucial for spintronic applications with respect to ferromagnets due to the lower stray fields created by these materials. We extend this study to cover the case where the transition-metal atoms sitting at antisites are not identical to the ones in the perfect sites. In Cr-based…
Determining accurate absolute surface energies for polar surfaces of semiconductors has been a great challenge in decades. Here, we propose pseudo-hydrogen passivation to calculate them, using density functional theory approaches. By calculating the energy contribution from pseudo-hydrogen using either a pseudo molecule method or a tetrahedral cluster method, we obtained (111) surfaces energies of Si, GaP, and ZnS with high self-consistency. This method quantitatively confirms that surface energy is determined by the number and the energy of dangling bonds of surface atoms. Our findings may gr…
Using the accurate first-principle method within density-functional theory, we systematically study CrSb in the zincblende (zb) structure. The zb CrSb is predicted of robust half-metallic ferromagnetism (HMFM) with a magnetic moment of 3.000 $μ_B$ per formula. It is much better than other zb compounds with HMFM because its spin-flip gap reaches 0.774 eV at the equilibrium volume and persists nonzero with its volume changing theoretically from -21% to +60%. It is found there may be a common mechanism for the HMFM in all the zb Cr- and Mn-pnictides. Since being compatible with the III-V semicond…
We calculate the lattice thermal conductivity ($κ$) for cubic (zinc-blende) and hexagonal (wurtzite) phases for 8 semiconductors using $\textit{ab initio}$ calculations and solving the Phonon Boltzmann Transport Equation, explaining the different behavior of the ratio $κ_{\rm hex}/κ_{\rm cub}$ between the two phases. We show that this behavior depends on the relative importance of two antagonistic factors: anharmonicity, which we find to be always higher in the cubic phase; and the accessible phase space, which is higher for the less symmetric hexagonal phase. Based on that, we develop a metho…
Using first-principles calculations within generalized gradient approximation, the electronic and magnetic properties of zinc blende (zb) CrP/MnP superlattice are investigated. The equilibrium lattice constant is calculated to be $5.33\,$Å. The stability of ferromagnetic zb CrP/MnP superlattice against antiferromagnetism is considered and it is found that the ferromagnetic CrP/MnP superlattice is more stable than the antiferromagnetic one. It is shown that at the equilibrium lattice constant the CrP/MnP superlattice does not show any half metallicity mainly due to the minority $t_{2g}$ states …
We report calculated, electronic and related properties of wurtzite and zinc blende gallium nitrides (w-GaN, zb-GaN). We employed a local density approximation (LDA) potential and the linear combination of atomic orbital (LCAO) formalism. The implementation of this formalism followed the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). The calculated electronic and related properties, for both structures of GaN, are in good agreement with corresponding, experimental data, unlike results from most previous ab initio calculations utilizing a density function…
The structural, electronic, dielectric and vibrational properties of zinc-blende (ZB) InAs were studied within the framework of density functional theory (DFT) by employing local density approximation and norm-conserving pseudopotentials. The optimal lattice parameter, direct band gap, static dielectric constant, phonon frequencies and Born effective charges calculated by treating In-4d electrons as valence states are in satisfactory agreement with other reported theoretical and experimental findings. The calculated band gap is reasonably accurate and improved in comparison to other findings.
Here, we show that we control the crystal structure of indium phosphide (InP) nanowires by impurity dopants. We have found that zinc decreases the activation barrier for 2D nucleation growth of zinc-blende InP and therefore promotes the InP nanowires to crystallise in the zinc blende, instead of the commonly found wurtzite crystal structure. More importantly, we demonstrate that we can, by controlling the crystal structure, induce twinning superlattices with long-range order in InP nanowires. We can tune the spacing of the superlattices by the wire diameter and the zinc concentration and prese…
A simple theoretical method for deducing the effective bond-orbital model (EBOM) of III-nitride wurtzite (WZ) semiconductors is presented. In this model, the interaction parameters for zinc-blende (ZB) structures are used as an initial guess for WZ structure based on the two-center approximation. The electronic band structure of III-nitride WZ semiconductors can hence be produced by utilizing this set of parameters modified to include effects due to three-center integrals and fitting with first-principles calculations. Details of the semi-empirical fitting procedure for constructing the EBOM H…
Material structures containing tetrahedral FeAs bonds, depending on their density and geometrical distribution, can host several competing quantum ground states ranging from superconductivity to ferromagnetism. Here we examine structures of quasi two-dimensional (2D) layers of tetrahedral Fe-As bonds embedded with a regular interval in a semiconductor InAs matrix, which resembles the crystal structure of Fe-based superconductors. Contrary to the case of Fe-based pnictides, these FeAs/InAs superlattices (SLs) exhibit ferromagnetism, whose Curie temperature (Tc) increases rapidly with decreasing…
We review pitfalls in recent efforts to make a conventional semiconductor, namely ZnO, ferromagnetic by means of doping with transition metal ions. Since the solubility of those elements is rather low, formation of secondary phases and the creation of defects upon low temperature processing can lead to unwanted magnetic effects. Among others, ion implantation is a method of doping, which is highly suited for the investigation of those effects. By focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that there are manifold sources for ferromagnetism in this material which can …
First-principles density-functional method is used to study the recently high-pressure synthesized compound PtC. It is confirmed by our calculations that the platinum carbide has a zinc-blende ground-state phase at zero pressure and the rock-salt structure is a high-pressure phase. The theoretical transition pressure from zinc-blende to rock-salt is determined to be 52GPa. Furthermore, our calculation shows the possibility that the experimentally synthesized PtC by Ono et al. under high pressure condition might undergo a transition from rock-salt structure to zinc-blende after the pressure que…
Employing first-principles calculations we study the structural, electronic and magnetic properties of the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x}$V$_x$]Si alloys. In their equilibrium rocksalt structure all alloys are non-magnetic. The zincblende and wurtzite structures are degenerated with respect to the total energy. For all concentrations the alloys in these lattice structures are half-metallic with the gap located in the spin-down band. The total spin moment follows the Slater-Pauling behavior varying linearly between the -1 $μ_B$ of the perfect ScC and ScSi alloys and the +1 $μ_B$ of the perfe…
The structural and optical properties of 3 different kinds of GaAs nanowires with 100% zinc-blende structure and with an average of 30% and 70% wurtzite are presented. A variety of shorter and longer segments of zinc-blende or wurtzite crystal phases are observed by transmission electron microscopy in the nanowires. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV when the percentage of wurtzite is increased. The downward shift of the emission peaks can be understood by carrier confinement at the interfaces, in quantum wells and in random sh…
Large spin splitting in the conduction band (CB) and valence band (VB) of ferromagnetic semiconductors (FMSs), predicted by the influential mean-field Zener model[1,2] and assumed in many spintronic device proposals[3-8], has never been observed in the mainstream p-type Mn-doped FMSs[9-15]. Here using tunnelling spectroscopy in Esaki-diode structures, we report the observation of such a large spontaneous spin-splitting energy (ΔE = 31.7 - 50 meV) in the CB bottom of n-type FMS (In,Fe)As, which is surprising considering the very weak s-d exchange interaction reported in several zinc-blende (ZB)…
Developing a valence force field model for wurtzite semiconductors by exploiting similarities with [111]-oriented zinc blende systems: The case of wurtzite boron nitride, III-N materials and (B,In,Ga)N alloys
he correct estimation of thermal properties of ultra-scaled CMOS and thermoelectric semiconductor devices demands for accurate phonon modeling in such structures. This work provides a detailed description of the modified valence force field (MVFF) method to obtain the phonon dispersion in zinc-blende semiconductors. The model is extended from bulk to nanowires after incorporating proper boundary conditions. The computational demands by the phonon calculation increase rapidly as the wire cross-section size increases. It is shown that the nanowire phonon spectrum differ considerably from the bul…
Electronic structure and band characteristics for zinc monochalcogenides with zinc-blende- and wurtzite-type structures are studied by first-principles density-functional-theory calculations with different approximations. It is shown that the local-density approximation underestimates the band gap and energy splitting between the states at the top of the valence band, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field-splitting energy. Regardless of the structure type considered, the spin-orbit-coupling energy is found to be overestimated for ZnO and underesti…
Polarization dependent Raman scattering experiments realized on single GaAs nanowires with different percentages of zinc-blende and wurtzite structure are presented. The selection rules for the special case of nanowires are found and discussed. In the case of zinc-blende, the transversal optical mode E1(TO) at 267 cm-1 exhibits the highest intensity when the incident and analyzed polarization are parallel to the nanowire axis. This is a consequence of the nanowire geometry and dielectric mismatch with the environment, and in quite good agreement with the Raman selection rules. We also find a c…
Here, we clarify the central role of the miscut during group III-V/ group IV crystal growth. We show that the miscut first impacts the initial antiphase domain distribution, with two distinct nucleation-driven and terraces-driven regimes. It is then inferred how the antiphase domain distribution mean phase and mean lateral length are affected by the miscut. An experimental confirmation is given through the comparison of antiphase domain distributions in GaP and GaSb/AlSb samples grown on nominal and vicinal Si substrates. The antiphase domain burying step of GaP/Si samples is then observed at …
A density functional theory study of substitutional carbon impurities in ZnO has been performed, using both the generalized gradient approximation (GGA) and a hybrid functional (HSE06) as exchange-correlation functional. It is found that the non-spinpolarized C$_\mathrm{Zn}$ impurity is under almost all conditions thermodynamically more stable than the C$_\mathrm{O}$ impurity which has a magnetic moment of $2μ_{\mathrm{B}}$, with the exception of very O-poor and C-rich conditions. This explains the experimental difficulties in sample preparation in order to realize $d^{0}$-ferromagnetism in C-…
Ab-initio, self-consistent electronic energy bands of zinc blende CdS are reported within the local density functional approximation (LDA). Our first principle, non-relativistic and ground state calculations employed a local density potential and the linear combination of atomic orbitals (LCAO). Within the framework of the Bagayoko, Zhao, and Williams (BZW) method, we solved self-consistently both the Kohn-Sham equation and the equation giving the ground state density in terms of the wave functions of the occupied states. Our calculated, direct band gap of 2.39 eV, at the point, is in accord w…
The deformation potentials of cubic semiconductors are re-examined from the point of view of the extended-basis $sp^3d^5s^*$ tight-binding model. Previous parametrizations had failed to account properly for trigonal deformations, even leading to incorrect sign of the acoustic component of the shear deformation potential {\it d}. The strain-induced shifts and splittings of the on-site energies of the p- and d-orbitals are shown to play a prominent role in obtaining satisfactory values of deformation potentials both at the zone center and zone extrema. The present approach results in excellent a…
In this work we study the structural stability and electronic properties of the Beryllium sulphide nanowires (NWs) in both zinc blende (ZB) and wurtzite (WZ) phases with triangle and hexagonal cross section, using first principle calculations within plane-wave pseudopotential method. A phenomenological model is used to explain the role of dangling bonds in the stability of the NWs. In contrast to the bulk phase, ZB-NWs with diameter less than 133.3 (angstrom) are found to be less favorable over WZ-NWs, in which the surface dangling bonds (DBs) on the NW facets play an important role to stabili…
e have calculated the spin-orbit (SO) splitting $Δ_{SO}=ε(Γ_{8v}) - ε(Γ_{7v})$ for all diamond-like group IV and zinc-blende group III-V, II-VI, and I-VII semiconductors using the full potential linearized augmented plane wave method within the local density approximation. The SO coupling is included using the second variation procedure, including the $p_{1/2}$ local orbitals. The calculated SO splittings are in very good agreement with available experimental data. The corrections due to the inclusion of the $p_{1/2}$ local orbital are negligible for lighter atoms, but can be as large as $\sim…
We employ first-principles techniques tailored to properly describe semiconductors (modified Becke-Johnson potential added to the exchange-correlation functional), to obtain the electronic band structures of both the zinc-blende and wurtzite phases of GaAs, GaSb, InAs, and InSb. We extract the spin-orbit fields for the relevant valence and conduction bands at zone center, by fitting the spin-splittings resulting from the lack of space inversion symmetry of these bulk crystal structures, to known functional forms---third-order polynomials. We also determine the orientations of the spin-orbit ve…
The mechanical properties of Cadmium Selenide (CdSe) nanowire is an emerging issue due to its application in semiconductor and optoelectronics industries. In this paper, we conducted molecular dynamics (MD) simulations to investigate the temperature-dependent mechanical properties and failure behavior of Zinc-Blende (ZB) CdSe nanowire under uniaxial tensile deformation. We employed Stillinger-Weber (SW) potential to describe the inter-atomic interactions. The effect of variation of temperatures (100 K-600 K), sizes, and crystal orientation on the tensile response of the CdSe nanowires is inves…
Most III-V semiconductors, which acquire the zinc-blende phase as bulk materials, adopt the metastable wurtzite phase when grown in the form of nanowires. These are new semiconductors with new optical properties, in particular, a different electronic band gap when compared with that grown in the zinc-blende phase. The electronic gap of wurtzite InAs at the Gamma-point of the Brillouin zone (E0 gap) has been recently measured, E0 = 0.46 eV at low temperature. The electronic gap at the A point of the Brillouin zone (equivalent to the L point in the zinc-blende structure, E1) has also been obtain…
Room-temperature ferromagnetism is observed in (110) oriented ZnO films containing 5 at % of Sc, Ti, V, Fe, Co or Ni, but not Cr, Mn or Cu ions. There are large moments, 1.9 and 0.5 muB/atom for Co- and Ti-substituted oxides, respectively. Sc-substituted ZnO shows also a moment of 0.3 muB/Sc. Magnetization is very anisotropic, with variations of up to a factor three depending on the orientation of the applied field relative to the R-cut sapphire substrates. Results are interpreted in terms of a spin-split donor impurity band model, which can account for ferromagnetism in insulating or conducti…
GaN based high electron mobility transistors show promise in numerous device applications which elicits the need for accurate models of bulk, surface, and interface electronic properties. We detail here a hybrid density functional theory study of zinc blende (zb) GaN and diamond bulk and surface properties, and zb GaN on diamond interfaces using slab supercell models. Details are provided on the dependence of electronic properties with respect to supercell size, the use of pseudo-hydrogen to passivate the bottom GaN layer, and dipole corrections. The large bulk modulus of diamond provides a te…
Ultrathin semiconductor nanocrystals (NCs) with at least one dimension below their exciton Bohr radius receive a rapidly increasing attention due to their unique physicochemical properties such as strong quantum confinement, large surface-to-volume ratio, and giant oscillator strength. These superior properties highly depend on the shape and crystal phase of semiconductor NCs. Slight changes in the shape and phase of NCs can cause significant changes in their properties. Therefore, it is crucial to controllably synthesize semiconductor NCs. Here, we demonstrate not only the synthesis of robust…
We present calculations of the exchange interactions and Curie temperatures in Cr-based pnictides and chalcogenides of the form CrX with X=As, Sb, S, Se and Te, and the mixed alloys CrAs$_{50}$X$_{50}$ with X=Sb, S, Se, and Te. The calculations are performed for Zinc Blende (ZB) structure for 12 values of the lattice parameter between 5.44 and 6.62 Å, appropriate for some typical II-VI and III-V semiconducting substrates. Electronic structure is calculated via the linear muffin-tin-orbitals (LMTO) method in the atomic sphere approximation (ASA), using empty spheres to optimize ASA-related erro…
We present a Hamiltonian in real space which is well suited to study numerically the behavior of holes introduced in III-V semiconductors by Mn doping when the III$^{3+}$ ion is replaced by Mn$^{2+}$. We consider the actual lattice with the diamond structure. Since the focus is on light doping by acceptors, a bonding combination of III and V p-orbitals is considered since the top of the valence band, located at the $Γ$ point, has p character in these materials. As a result, an effective model in which the holes hop between the sites of an fcc lattice is obtained. We show that around the $Γ$ po…
Semiconductor nanocrystals (NCs) experience stress and charge transfer by embedding materials or ligands and impurity atoms. In return, the environment of NCs experiences a NC stress response which may lead to matrix deformation and propagated strain. Up to now, there is no universal gauge to evaluate the stress impact on NCs and their response as a function of NC size $d_{\mathrm{NC}}$. I deduce geometrical number series as analytical tools to obtain the number of NC atoms $N_{\mathrm{NC}}(d_{\mathrm{NC}}[i])$, bonds between NC atoms $N\mathrm{_{bnd}}(d_{\mathrm{NC}}[i])$ and interface bonds …
