Study of the vertical transport in p-doped superlattices based on group III-V semiconductors

The electrical conductivity σ has been calculated for p-doped GaAs/Al0.3Ga0.7As and cubic GaN/Al0.3Ga0.7N thin superlattices (SLs). The calculations are done within a self-consistent approach to the k→⋅p→ theory by means of a full six-band Luttinger-Kohn Hamiltonian, together with the Poisson equation in a plane wave representation, including exchange correlation effects within the local density approximation. It was also assumed that transport in the SL occurs through extended minibands states for each carrier, and the conductivity is calculated at zero temperature and in low-field ohmic limits by the quasi-chemical Boltzmann kinetic equation. It was shown that the particular minibands structure of the p-doped SLs leads to a plateau-like behavior in the conductivity as a function of the donor concentration and/or the Fermi level energy. In addition, it is shown that the Coulomb and exchange-correlation effects play an important role in these systems, since they determine the bending potential

Theoretical luminescence spectra in p-type superlattices based on InGaAsN

In this work, we present a theoretical photoluminescence (PL) for p-doped GaAs/InGaAsN nanostructures arrays. We apply a self-consistent method in the framework of the effective mass theory. Solving a full 8 x 8 Kane's Hamiltonian, generalized to treat different materials in conjunction with the Poisson equation, we calculate the optical properties of these systems. The trends in the calculated PL spectra, due to many-body effects within the quasi-two-dimensional hole gas, are analyzed as a function of the acceptor doping concentration and the well width. Effects of temperature in the PL spectra are also investigated. This is the first attempt to show theoretical luminescence spectra for GaAs/InGaAsN nanostructures and can be used as a guide for the design of nanostructured devices such as optoelectronic devices, solar cells, and others.CNPq [564.739/2010-3/NanoSemiCon, 302.550/2011-9/PQ, 470.998/2010-5/Univ, 472.312/2009-0/PQ, 303578/2007-6/PQ, 577.219/2008-1/JP]CNPqCAPESCAPESFACEPEFACEPE [0553-1.05/10/APQ]FAPESPFAPESPMaterials Science, Engineering and Commercialization Program of Texas State UniversityMaterials Science, Engineering and Commercialization Program of Texas State Universit

Microscopic Properties of the SiO2/Si Interface Growth Based on Numerical Simulations

To improve the understanding of the microscopic properties of the silicon oxidation process, we perform numerical simulations of thermal SiO2 thin film growth. Therefrom, we analyze the growth kinetics as well as the evolution of the SiO2/Si interface formation. The oxidation rate in the early stages of growth is governed by two processes : the rapid initial formation of the oxidation front, and its subsequent diffusion. The corresponding oxidation kinetics, arising from the simulations, provides a rather good description of a large variety of experimental data, with the minimum number of variable parameters. The effect of external parameters, such as temperature and pressure, can be explained in terms of scaling concepts. It is found that the temporal evolution of SiO2 concentration at a given fixed crystalline cross section is continuous, while the spatial distribution at any given time shows abrupt (step like) behavior, decaying from 100 % to zero concentration within just a few lattice constants. The results of the simulations suggest a very simple phenomenological approach for modeling of microstructural aspects of the SiO2/Si syste

Microscopic Properties of the SiO2/Si Interface Growth Based on Numerical Simulations

To improve the understanding of the microscopic properties of the silicon oxidation process, we perform numerical simulations of thermal SiO2 thin film growth. Therefrom, we analyze the growth kinetics as well as the evolution of the SiO2/Si interface formation. The oxidation rate in the early stages of growth is governed by two processes : the rapid initial formation of the oxidation front, and its subsequent diffusion. The corresponding oxidation kinetics, arising from the simulations, provides a rather good description of a large variety of experimental data, with the minimum number of variable parameters. The effect of external parameters, such as temperature and pressure, can be explained in terms of scaling concepts. It is found that the temporal evolution of SiO2 concentration at a given fixed crystalline cross section is continuous, while the spatial distribution at any given time shows abrupt (step like) behavior, decaying from 100 % to zero concentration within just a few lattice constants. The results of the simulations suggest a very simple phenomenological approach for modeling of microstructural aspects of the SiO2/Si syste

Spin-polarization effects in homogeneous and non-homogeneous diluted magnetic semiconductor heterostructures

Spin polarization is a key characteristic in developing spintronic devices. Diluted magnetic heterostructures (DMH), where subsequent layers of conventional and diluted magnetic semiconductors (DMS) are alternate, are one of the possible ways to obtain it. Si being the basis of modern electronics, Si or other group-IV DMH can be used to build spintronic devices directly integrated with conventional ones. In this work we study the physical properties and the spin-polarization effects of p-type DMH based in group-IV semiconductors (Si, Ge, SiGe, and SiC), by performing self-consistent (k) over right arrow . (p) over right arrow calculations in the local spin density approximation. We show that high spin polarization can be maintained in these structures below certain values of the carrier concentrations. Full spin polarization is attained in the low carrier concentration regime for carrier concentrations in the DMS layer up to similar to 2.0 x 10(19) cm(-3) for Si and up to similar to 6.0 x 10(19) cm(-3) for SiC. Partial, but still important spin polarization can be achieved for all studied group-IV DMH, with the exception of Ge for carrier concentrations up to 6.0 x 10(19) cm(-3). The role played by the effective masses and the energy splitting of the spin-orbit split-off hole bands is also discussed throughout the paper.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq[550.126/05-8/CTPETRO]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq[303.817/05-4/PQ]CNPq[304936/2009-0/PQ]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq[303578/2007-6/PQ]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq[577.219/2008-1/JP]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CAPESCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)FACEPE[1077-1.05/08/APQ]Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco (FACEPE)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPES

Effect of gamma radiation on the electrical properties of polyaniline/silicon carbide heterojunctions

Polyaniline thin films have been deposited by a very simple technique on p-type Silicon Carbide (SiC) substrates to fabricate heterojunctions devices with good electrical properties. In this work two heterojunctions devices of Polyaniline (PANI) on p-type 4H–SiC and 6H–SiC substrates were electrically characterized using current- voltage (I-V) in the temperature range 20–430 K Capacitance–frequency (C-f) measurements. Furthermore, impedance and capacitance measurements are carried out to study the effect of gamma irradiation on these devices. Additionally, we demonstrate not only the ease of fabrication of PANI/p-SiC heterostructures, but also we show strong indication that these heterostructures have potential applications as sensors of gamma irradiation

Theoretical study of the influence of vacancies in the magnetic stability of V-, Cr-, and Mn-doped SnO2

In this work we study, theoretically, the magnetic properties of transition metals (TMs)-doped SnO2 (with TM = V, Cr, and Mn) in a diluted magnetic oxide configuration, focusing in particular in the role played by the presence of O vacancies, VO, nearby the TM. We present the results of first-principles electronic structure calculations of Sn0.96TM0.04O2 and Sn0.96TM0.04O1.98(VO)0.02 alloys. The calculated total energy as a function of the total magnetic moment per cell shows a magnetic metastability, corresponding to a high-spin (HS) ground state, respectively, with 2 and 3 μB/cell, for Cr and Mn, and a metastable low-spin (LS) state, with 0 (Cr) and 1 (Mn) μB/cell. For vanadium, only a state with 1 μB/cell was found. The spin-crossover energy (ESCO) from the LS to the HS is 114 meV for Cr and 42 meV for Mn. By creating O vacancies close to the TM site, we show that the metastability and ESCO change. For chromium, a new HS state appears (4 μB/cell), with an energy barrier of 32 meV relative to the 2 μB/cell state. For manganese, the metastable LS state of 1 μB/cell disappears, while for vanadium the HS state of 1 μB/cell remains. In all cases, the ground state corresponds to the expected HS. These findings suggest that these materials may be used in applications that require different magnetization states