Abstract Extended Hückel theory calculations are carried out for interstitial hydrogen atoms in silicon model crystals without and with vacancies. The energetically stable positions the hydrogens appear to be tetrahedral site vacancies; case of vacancies favor dangling bonds 0.35 bond lengths away from vacancy nearest neighbors. vibrational frequencies all defect types considered very close agreement infrared bands observed after proton irradiation silicon. increase number a vacancy....

Porous silicon (PS) with its distribution of crystallite sizes is a highly disordered material. We present theoretical formulation to explain the photoluminescence (PL) spectra porous silicon. base our formalism on quantum confinement model using methods similar those Kane and Lifshitz. A minimal set parameters employed whose numerical values are obtained from independent experiments and/or microscopic theories. Our work demonstrates (i) downshift in PL peak due size distribution, thus...

Path integrals with a periodic constraint ∫θ̇ ds =Θ̄+2πn (n=integer) are studied. In particular, the path integral for string entangled around singular point in two dimensions is evaluated polar coordinates. Applications made polymers and without interactions, Aharonov–Bohm effect, angular momentum projection of spinning top.

Abstract Mutliferroic and magnetoelectric gallium ferrite (GaFeO 3 ) is plagued by substantial electrical leakage in polycrystalline form. Here, we report on understanding the conduction mechanism ceramic samples vis‐à‐vis processing conditions. The results show that oxygen annealed exhibit minimum as compared to air or nitrogen suggesting role of oxy3gen vacancies conduction. Detailed time temperature‐dependent impedance spectroscopy analysis showed higher activation energy than samples....

We describe the elements of electronic structure and chemical trends in cation-substitutional Cr, Mn, Fe, Co, Ni, Cu, Zn impurities GaP Fe InP. First, using recently developed method Fazzio, Caldas, Zunger, we deconvolute observed acceptor, donor, intracenter d\ensuremath{\rightarrow}${d}^{\mathrm{*}}$ excitation energies into a one-electron mean-field contribution many-electron multiplet correction. Then, self-consistent quasiband crystal-field Green's-function Lindefelt show that theory...

The Aharonov-Bohm effect is investigated in the Feynman path-integral formulation of quantum mechanics. We consider an idealized situation with electron moving a magnetic-field-free region outside solenoid whose radius to length ratio very small. nonvanishing vector potential term Lagrangian written as angular-velocity-dependent potential. In order account for singularity due presence itself, periodic constraint imposed on path integral. propagator can then be evaluated using...

Student difficulties regarding the angular velocity () and acceleration of a particle have remained relatively unexplored in contrast to their linear counterparts. We present an inventory comprising multiple choice questions aimed at probing misconceptions eliciting ill-suited reasoning patterns. The development was based on interactions with students, teachers experts. report misconceptions, some which are parallel those found earlier kinematics. Fixations inappropriate prototypes were...

We develop a manifest supertwistor space formalism for three dimensional $\mathcal{N}=1, 2,3,4$ superconformal field theories. This simultaneously makes the supersymmetry, conformal invariance and conservation. solve two point correlators of (half) integer spin conserved supercurrents using graded supergroup generators. Apart from generators, we find that superhelicity operators are necessary to fix their functional form in this setup. The can be recast into first order Euler equations which...

The size $(d)$ dependence of photoluminescence from nanocrystalline semiconductors is examined. overall luminescence determined by two distinct physical mechanisms: (i) the variation semiconductor gap with $d$ (typically $\ensuremath{\sim}{1/d}^{\ensuremath{\alpha}},$ $\ensuremath{\alpha}>1),$ and (ii) oscillator strength ${f}_{\mathrm{osc}}$ ${1/d}^{\ensuremath{\beta}},$ $5<~\ensuremath{\beta}<~6).$ We present an analytical framework to understand line shape based on above...

We study the hydrogenic impurity in a quantum dot (QD). employ effective mass theory with realistic barrier and variable mass. The model is simple, but it predicts features not previously observed. observe that shallow becomes deeper as size (R) reduced further reduction of at times resonant conduction band. Such shallow-deep (SHADE) transition investigated critical terms Bohr radius (aI*) identified. A relevant aspect QD dielectric constant, ε, its decreases. Employing dependent ε(R), we...

The temperature dependence of the luminescence intensity in nanocrystalline semiconductors, amorphous and chalcogenides has been reported to be Berthelot type $\mathrm{exp}{(T/T}_{B}),$ where ${T}_{B}$ is some characteristic temperature. A similar behavior for transport properties certain semiconductors porous silicon. We propose a simple microscopic model origin term. assume that arises from competition between radiative hopping processes. process modeled by assuming carrier tunnels through...

We present the development, administration, and analysis of a focused inventory on rotational kinematics rigid body around fixed axis. The inventory, which is made up 13 multiple-choice questions, was developed basis interactions with students teachers. systematic iterative aspects construction are illustrated. were validated, administered to set teachers (N = 25) two groups preuniversity 74 905) in India. Students, as well teachers, exhibited difficulties applying operational definition...

We outline a simple framework to explain the vast amount of data on photoluminescence (PL) behavior porous silicon. Our model involves competition between an activated radiative process and Berthelot-type nonradiative process. successfully explains wide range observations by various groups temperature, pressure emission energy dependence PL. The temperature luminescence intensity decay time as predicted this is observed for variety materials such amorphous silicon chalcogenide glasses....

We report the results of a first-principles calculation electronic structure substitutional, unrelaxed, and neutral chalcogen impurities (O, S, Se) in silicon. have employed recently developed quasi band crystal-field defect Green's-function method. find that whereas atomistic models predict binding energies donor levels semi-conductors increase with ionization potential free impurity atoms, special enhancement screening solid predicts, for silicon, reversal this order. Our are excellent...

Spin waves in a model of an amorphous Heisenberg ferromagnet are studied by means effective medium approximation (EMA) for comparison with observations transition metal–metalloid alloys. For long wave length and low energy the EMA agrees quasicrystalline spin energy, but gives larger density states than extended chain corresponds to conventional theory. The also finite vector structure spectral weight function.

A deep trap in the fundamental gap of a semiconductor has sharp (delta function) character. In alloy presence disorder introduces distribution activation energies. The authors have undertaken detailed analytical and numerical exercise to examine effect such broadening on capacitance transient deep-level spectroscopy (DLTS) analysis traps. general standard DLTS negligible error except cases severe where it overestimates energy. They illustrate their by considering both simulated actual...

The crossing points of the first-principles nonlocal screened atomic pseudopotentials elements were shown previously to constitute a sensitive anisotropic atomic-size scale. This scale allows systematization crystal structure as many 565 binary compounds A. Zunger, [Phys. Rev. B 22, 5839 (1980)]. In this paper we apply same coordinates for systematizing trends in solid solubilities divalent solvents Be, Mg, Zn, Cd, Hg, and semiconductor Si Ge (192 data points), well location ion-implantation...

It is shown that the empirical correlation between infrared (IR) stretching frequency of Si–H bond in substituted silane molecules (SiH3R1, SiH2R1R2, and SiHR1R2R3 with Ri molecular fragment) can be understood on a fundamental basis as dependence order (S component) bond.

Relaxation of deep levels in semiconductors is studied through capacitance transients. We explore the temperature-time duality relationship which inherent such thermal relaxation processes. Using considerations we show existence four distinct spectroscopies. demonstrate that techniques for spectroscopic evaluation transients are based on differential operators and provide a novel interpretation to spectroscopy. extend this approach higher order Two families spectroscopy analyzed using...

Rectilinear motion of a particle with constant velocity is one the simplest situations can envisage in mechanics. We discuss rotational kinematics associated this and find that they are pedagogical relevance. have constructed small inventory consisting conceptual multiple-choice questions after consultation content experts feedback from students. This was administered to group physics teachers responses reveal interesting misconceptions harbored even by teachers. A brief discussion pitfalls...

Carrier-mediated ferromagnetism in a dilute magnetic semiconductor has been studied using (i) single-impurity based generalized Ruderman-Kittel-Kasuya-Yosida (RKKY) approach which goes beyond linear response theory, and (ii) mean-field-plus-spin-fluctuation within (purely fermionic) Hubbard-model representation of the impurities, incorporates dynamical effects associated with finite frequency spin correlations ordered state. Due to competition between magnitude carrier polarization its...

The authors have investigated the electronic structure of an amorphous metal within a s band tight-binding framework. Their investigations were based on number effective medium theories proposed in recent years. These purport to describe systems with short-range order. aim these was compare 'exact' calculation performed recently by Fujiwara and Tanabe (1979) same model. They establish that approximation (EMA) Roth (1974) provides most satisfactory description structure. Useful insight into...

The results of a combined study the temperature variation photoluminescence (PL) and dc conductivity from high optical-quality free-standing porous silicon films are presented. PL spectra samples have been studied in range 10–300 K. Dc (σ) on these 90 to 300 K voltage 0.25–1.5 V. We attempt understand luminescence transport data terms recently proposed unified model. exhibits Berthlot-type [≅exp(T/TB)]. can be explained competition between an activated radiative process [≅ exp−(Tr/T)]...

We have studied the nature of eigenstates on a Fibonacci chain. A careful study averaged density states reveals highly structured density. also eigenfunctions at band center and find that charge as well quantity related to entropy possess same fractal dimension.