Systematic study of magnetic linear dichroism and birefringence in (Ga,Mn)As

Magnetic linear dichroism and birefringence in (Ga,Mn)As epitaxial layers is investigated by measuring the polarization plane rotation of reflected linearly polarized light when magnetization lies in the plane of the sample. We report on the spectral dependence of the rotation and ellipticity angles in a broad energy range of 0.12-2.7 eV for a series of optimized samples covering a wide range on Mn-dopings and Curie temperatures and find a clear blue shift of the dominant peak at energy exceeding the host material band gap. These results are discussed in the general context of the GaAs host band structure and also within the framework of the k.p and mean-field kinetic-exchange model of the (Ga,Mn)As band structure. We find a semi-quantitative agreement between experiment and theory and discuss the role of disorder-induced non-direct transitions on magneto-optical properties of (Ga,Mn)As.Comment: 18 page

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

Hole confinement theory of delta-doping semiconductor heterostructures

Poços e super-redes delta-doping tipo são sistemas semicondutores de interesse considerável tanto para a pesquisa básica como para aplicações em dispositivos. Neste trabalho desenvolvemos um novo método para o cálculo de potenciais e estruturas de bandas deste tipo de sistemas. O método baseia-se na expansão em ondas planas da equação da massa efetiva multibandas, usa matrizes de energia cinética de qualquer tamanho e leva em conta o potencial de troca e correlação de uma maneira mais rigorosa do que em trabalhos anteriores. São calculados perfis de potencial e estrutura de minibandas e subbandas bem como a posição do nível de Fermi de uma série de poços isolados e super-redes delta-doping tipo p. São estudadas também as diferenças entre super-redes delta-doping tipo p e tipo n. A partir deste método foi desenvolvido ainda um procedimento de cálculo de espectros de fotoluminescência dos poços estudados. Este procedimento baseia-se nas forças de oscilador das transições entre os buracos confinados no interior do poço e os elétrons livres da banda de condução. Ele é utilizado para calcular funções envelope, integrais de superposição e espectros de transições diretas e indiretas. Por fim, comparamos espectros calculados teoricamente com resultados experimentais extraídos da literatura.p-type ro-doping quantum wells and superlattices are semiconductor systems of considerable interest for basic research and device applications. In this work, a method for calculating potentials and band structures of such systems is developed. The method relies on a plane wave expansion of the multiband effective mass equation, uses kinetic energy matrices of any size, and takes exchange correlation into account in a more rigorous way than this was done before. The method is used to calculate potential profiles, subband and miniband structures as well as Fermi level positions for a series of p-type delta-doping quantum wells and superlattices. The differences between n- and p-type delta-doping structures are studied. In addition to this we developed a procedure within this method to ca1culate photoluminescence (PL) spectra of the wells studied. It depends on the oscillator strength between the holes inside the wells and the free electrons on the conduction band. We use this procedure to calculate envelope functions, overlap integrals and direct and indirect transitions spectra. Finally, we compare our theoretical calculations of PL spectra with experimental results extracted from the literature

Hole confinement theory of delta-doping semiconductor heterostructures

Poços e super-redes delta-doping tipo são sistemas semicondutores de interesse considerável tanto para a pesquisa básica como para aplicações em dispositivos. Neste trabalho desenvolvemos um novo método para o cálculo de potenciais e estruturas de bandas deste tipo de sistemas. O método baseia-se na expansão em ondas planas da equação da massa efetiva multibandas, usa matrizes de energia cinética de qualquer tamanho e leva em conta o potencial de troca e correlação de uma maneira mais rigorosa do que em trabalhos anteriores. São calculados perfis de potencial e estrutura de minibandas e subbandas bem como a posição do nível de Fermi de uma série de poços isolados e super-redes delta-doping tipo p. São estudadas também as diferenças entre super-redes delta-doping tipo p e tipo n. A partir deste método foi desenvolvido ainda um procedimento de cálculo de espectros de fotoluminescência dos poços estudados. Este procedimento baseia-se nas forças de oscilador das transições entre os buracos confinados no interior do poço e os elétrons livres da banda de condução. Ele é utilizado para calcular funções envelope, integrais de superposição e espectros de transições diretas e indiretas. Por fim, comparamos espectros calculados teoricamente com resultados experimentais extraídos da literatura.p-type ro-doping quantum wells and superlattices are semiconductor systems of considerable interest for basic research and device applications. In this work, a method for calculating potentials and band structures of such systems is developed. The method relies on a plane wave expansion of the multiband effective mass equation, uses kinetic energy matrices of any size, and takes exchange correlation into account in a more rigorous way than this was done before. The method is used to calculate potential profiles, subband and miniband structures as well as Fermi level positions for a series of p-type delta-doping quantum wells and superlattices. The differences between n- and p-type delta-doping structures are studied. In addition to this we developed a procedure within this method to ca1culate photoluminescence (PL) spectra of the wells studied. It depends on the oscillator strength between the holes inside the wells and the free electrons on the conduction band. We use this procedure to calculate envelope functions, overlap integrals and direct and indirect transitions spectra. Finally, we compare our theoretical calculations of PL spectra with experimental results extracted from the literature

Band structure calculations of InP wurtzite/zinc-blende quantum wells

Semiconductor nanowhiskers (NWs) made of III-V compounds exhibit great potential for technological applications. Controlling the growth conditions, such as temperature and diameter, it is possible to alternate between zinc-blende (ZB) and wurtzite (WZ) crystalline phases, giving origin to the so called polytypism. This effect has great influence in the electronic and optical properties of the system, generating new forms of confinement to the carriers. A theoretical model capable to accurately describe electronic and optical properties in these polytypical nanostructures can be used to study and develop new kinds of nanodevices. In this study, we present the development of a wurtzite/zinc-blende polytypical model to calculate the electronic band structure of nanowhiskers based on group theory concepts and the k.p method. Although the interest is in polytypical superlattices, the proposed model was applied to a single quantum well of InP to study the physics of the wurtzite/zinc-blende polytypism. By the analysis of our results, some trends can be predicted: spatial carriers' separation, predominance of perpendicular polarization (xy plane) in the luminescence spectra, and interband transition blueshifts with strain. Also, a possible range of values for the wurtzite InP spontaneous polarization is suggested. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4767511]Brazilian funding agency CAPESBrazilian funding agency CAPESBrazilian funding agency CNPqBrazilian funding agency CNPqBrazilian funding agency FAPESPBrazilian funding agency FAPES

Electronic band structure of polytypical nanowhiskers

AbstractIII-V compound nanowhiskers have attracted much attention recently due to their distinguished electronic and optical properties. In these nanostructures it was observed a phenomenon called polytypism, i. e., a phase alternation between zinc-blend and wurtzite structure. Although the polytypical effect is now well controlled, a more detailed band structure model is not still done, especially in the vicinity of the band edges. In this theoretical study we propose a model to calculate the electronic band structure in the vicinity of the band edges for polytypical nanowhiskers. Relying on group theory concepts and on the k p method we connected the irreducible representations at the Γ-point of the two crystal structures and described them in a single matrix. Our results for InP show the carriers’ spatial separation which agrees with reported experiments

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

Spin-polarized transport in II-VI diluted magnetic semiconductors superlattices

We studied the spin-polarized charge densities in II-VI-based diluted magnetic superlattices formed of p-doped ZnTe:Mg/ZnTe:TM/ZnTe:Mg non-magnetic/magnetic/non-magnetic layers, with TM standing for transition metal. The calculations were performed within a self-consistent k.p method, in which are also taken into account the exchange correlation effects in the local density approximation. Our results show a limit for the width of the non-magnetic layer for which the difference between the opposite spin charge densities is maximized, indicating the best conditions to obtain full polarization by varying the TM content. We also discuss these effects in the calculated photoluminescence spectra. Our findings point to the possibility of engineering the spin-polarized charge distribution by varying the widths of the magnetic and non-magnetic layers and/or varying the TM concentration in the magnetic layers, thus providing a guide for future experiments. (c) 2012 Elsevier B.V. All rights reserved.CNPqCNPq [564.739/2010-3/NanoSemiCon, 303.880/2008-2/PQ, 470.998/2010-5/Univ, 472.312/2009-0/Univ, 304936/2009-0/PQ, 303578/2007-6/PQ, 577.219/2008-1/JP]CAPESCAPESFACEPE [0553-1.05/10/APQ]FACEPEFAPESPFAPES

Luminescence studies on nitride quaternary alloys double quantum wells

We present theoretical photoluminescence (PL) spectra of undoped and p-doped Al(x)In(1-xy)Ga(y)N/Al(X)In(1) (X) (Y)Ga(Y)N double quantum wells (DQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange-correlation effects within the local density approximation. Strain effects due to the lattice mismatch are also taken into account. We show the calculated PL spectra, analyzing the blue and red-shifts in energy as one varies the spike and the well widths, as well as the acceptor doping concentration. We found a transition between a regime of isolated quantum wells and that of interacting DQWs. Since there are few studies of optical properties of quantum wells based on nitride quaternary alloys, the results reported here will provide guidelines for the interpretation of forthcoming experiments. (C) 2008 Elsevier B.V. All rights reserved.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqCAPESCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)FAPESPFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP