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Free Carriers (free + carrier)

Distribution by Scientific Domains
Physics and Astronomy91%

Terms modified by Free Carriers

  • free carrier concentration
    		•

    Selected Abstracts

    Organization of Organic Molecules with Inorganic Nanoparticles: Hybrid Nanodiodes,

    ADVANCED FUNCTIONAL MATERIALS, Issue 5 2008
    Kallol Mohanta
    Abstract A monolayer of inorganic nanoparticles and a monolayer of organic molecules have been electrostatically assembled in sequence. Such assemblies or organizations exhibit electrical rectification. When the sequence of the organization is reversed, the direction of rectification becomes opposite. In both n-type ZnO/organic and organic/n-ZnO assemblies, electron flow is favorable from the n-ZnO nanoparticle to the (electron-accepting) organic molecule. While the individual components do not show any rectification, substitutes of the organic molecule tune electrical rectification. Junctions between a p-type ZnO nanoparticle and an electron-donating metal phthalocyanine favor current flow in the nanoparticle-to-phthalocyanine direction. The rectification in a junction between a nanoparticle and an organic molecule is due to the parity between free carriers in the former component and the type of carrier-accepting nature in the latter one. By observing electrical rectification with the tip of a scanning tunneling microscope, organic/inorganic hybrid nanodiodes or rectifiers on the molecular/nanoscale have been established. [source]

    Highly conductive and optically transparent GZO films grown under metal-rich conditions by plasma assisted MBE

    PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 3-4 2010
    H. Y. Liu
    Abstract We demonstrate a critical effect of a metal-to-oxygen ratio on the electrical, optical, and structural properties of ZnO films heavily doped with Ga (carrier concentration in the range of 1020,1021 cm,3) grown by plasma-assisted molecular beam epitaxy. The as-grown layers prepared under the metal-rich conditions exhibited resistivities below 3 × 10,4 , cm and an optical transparency exceeding 90% in the visible spectral range as well as a large blue shift of the transmission/absorption edge attributed to the Burstein,Moss shift of the Fermi level deep into the conduction band, indicating high donor concentration. In contrast, the films grown under the oxygen-rich conditions required thermal activation and showed inferior properties. Furthermore, electrical measurements point to the nonuniform depth distribution of free carriers. An oxygen-pressure-dependent surface disordering is suggested to be responsible for the drastic effect of the metal-to-oxygen ratio on the film properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Dynamics of spin interactions in diluted magnetic semiconductor heterostructures

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007
    *Article first published online: 19 DEC 200, D. R. Yakovlev
    Abstract This paper gives an overview of the recent studies of spin dynamics in diluted magnetic semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. The spin dynamics is controlled by energy and spin transfer between systems of magnetic ions, lattice (phonon system) and free carriers. Spin,lattice relaxation time of the Mn spin system is a very strong function of the Mn content, it decreases by five orders of magnitude when the Mn content changes from 0.4 to 11%. Additionally this time can be tuned by the varying free carrier concentration and by the growth of heteromagnetic structures with inhomogeneous profile of Mn ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Effects of Si doping position on the emission energy and recombination dynamics of GaN/AlGaN multiple quantum wells

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2006
    Hamid Haratizadeh
    Abstract We report results from detailed optical spectroscopy from MOCVD grown GaN/Al0.07Ga0.93N multiple quantum wells (MQWs). Effects of Si doping position on the emission energy and recombination dynamics were studied by means of photoluminescence (PL) and time-resolved PL measurements. The samples were Si doped with the same level but different position of the dopant layer. Only the sample doped in the well shows the MQW emission redshifted compare to the GaN bandgap. The redshift is attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature the PL decay time of the sample doped in the well by a factor of two is longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Exciton relaxation in bulk wurtzite GaN: the role of piezoelectric interaction

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2003
    G. Kokolakis
    Abstract A theoretical study on the relaxation of coupled free carriers and excitons after non-resonant optical excitation in bulk wurtzite GaN is presented. In particular the effect of the acoustic piezoelectric scattering is taken under consideration, and the respective rates have been calculated, including screening effects. Results show that the piezo-acoustic rates are bigger in the wurtzite phase of GaN with respect to the cubic phase, and they are really sensitive to the background doping of the sample. Simulations of the full dynamics of the system are performed by using an Ensemble Monte Carlo method under which all the relevant scattering mechanisms are included. The set of semiclassical Boltzmann equations for electron and hole populations is complemented by an additional equation for the exciton distribution and is coupled by reaction terms describing phonon-mediated exciton binding and dissociation. The temporal evolution is studied in the short range time (100 ps) after photo-excitation. It shows that a high background doping prevents the electrons to relax toward low energy states. [source]

    Compensation of native defects in PbTe and Pb1,xSnx Te

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2008
    V. N. Babentsov
    Abstract Semi-insulation of the narrow-gap IV,VI semiconductor compounds PbTe and Pb1,xSnx Te used for infrared optoelectronic applications was investigated technologically and theoretically. Practically important cases in which the concentration of native defects greatly exceeds the intrinsic concentra- tion of free carriers due to the growth conditions are discussed. In particular, doping conditions for the semi-insulation are determined for Cd, In and Ga compensating impurities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    The performance of AlGaN solar blind UV photodetectors: responsivity and decay time

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006
    G. Cherkashinin
    Abstract The responsivity and the decay time of AlGaN solar blind UV-detectors have been studied. The photodetectors have shown a good spectral responsivity in a narrow spectral range (220 < , < 300 nm) and a short time response with the best estimated characteristic time constant of , , 30 ms measured at room temperature. Possible mechanisms responsible for the persistent photoconductivity (PPC) effect in AlxGa1,xN (x = 0.51) are analyzed. A shape of the spectral response as a function of the applied voltage is analyzed in the frameworks of the space-charge limited current model. It has been shown that the main source of PPC is traps above the Fermi level. PPC occurs when the density of free carriers equals the density of the traps. The model attributing PPC to the spatial separation of the photoexcited electrons and holes by the macroscopic potential barrier is not supported by our photocurrent studies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Magneto-optical spectroscopy of (Zn,Co)O epilayers

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006
    W. Pacuski
    Abstract We present a magneto-optical study of (Zn,Co)O layers grown by molecular beam epitaxy. We observed sharp lines related to 4A2,2E intra-ionic Co2+ transitions, and to the A , B and C excitons. Intra-ionic transitions observed by absorption and photoluminescence were used to determine the values of the parameters describing the isolated Co ions, such as the easy-plane magnetic anisotropy and the g -factor of the S = 3/2 Cobalt spin. Excitonic transitions observed in reflectivity were used to determine the giant Zeeman splitting and to estimate the effective coupling ,N0(, , , ),A ,B = 0.4 eV between excitons and Cobalt spins. Due to the electron,hole exchange within the exciton, this effective spin,exciton coupling is much weaker than the exchange integrals for free carriers, estimated to be N0|, , , | , 0.8 eV, with a positive value of (, , , ) if the normal ordering of the valence band of ZnO is assumed. The Zeeman splitting of diluted samples and the magnetic circular dichroism (for a higher Co content) are proportional to the magnetization of the paramagnetic, isolated Cobalt ions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Spin dynamics of exciton polaritons in microcavities

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2005
    I. A. Shelykh
    Abstract In this chapter we address a complex set of optical phenomena linked to the spin dynamics of exciton polaritons in semiconductor microcavities. When optically created, polaritons inherit the spin and dipole moment from the exciting light. Their state can be fully characterized by a so-called "pseudospin" accounting for both spin and dipole moment orientation. However, from the very beginning of their life in a microcavity, polaritons start changing their pseudospin state under effect of effective magnetic fields of different nature and due to scattering with acoustic phonons, defects, and other polaritons. This makes pseudospin dynamics of exciton polaritons rich and complex. It manifests itself in non-trivial changes in polarization of light emitted by the cavity versus time, pumping energy, pumping intensity and polarization. During the first years of theoretical research on exciton-polariton relaxation the polarization has been simply neglected. Later it has been understood that the energy and momentum-relaxation of exciton polaritons are spin-dependent. It is typically the case in the regime of stimulated scattering when the spin polarizations of initial and final polariton state have a huge effect on the scattering rate between these states. It appeared that critical conditions for polariton Bose-condensation are also polarization-dependent. In particular, the stimulation threshold (i.e. the pumping power needed to have a population exceeding 1 at the ground state of the lower polariton branch) has been experimentally shown to be lower under linear than under circular pumping. These experimental observations have stimulated the theoretical research toward understanding of mutually dependent polarization- and energy-relaxation mechanisms in microcavities. The authors of this chapter have been working on theoretical description of different specific effects of polariton spin-dynamics in microcavities for years. Here we attempted to put together all fragments and to formulate a general approach to the problem that would allow then to consider a variety of particular cases. We start from reminding the main spin-relaxation mechanisms known for free carriers and excitons. We then overview the most essential experimental results in this field before to present our original formalism which allowed us to interpret the key experimental findings. We are going to discuss only the strong coupling regime leaving aside all polarization effects in VCSELs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Large excitation-power dependence of pressure coefficients of InxGa1,xN/InyGa1,yN quantum wells

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
    Q. Li
    Abstract Excitation-power dependence of hydrostatic pressure coefficients (dE/dP) of InxGa1,xN/InyGa1,yN multiple quantum wells is reported. When the excitation power increases from 1.0 to 33 mW, dE/dP increases from 26.9 to 33.8 meV/GPa, which is an increase by 25%. A saturation behavior of dE/dP with the excitation power is observed. The increment of dE/dP with increasing carrier density is explained by an reduction of the internal piezoelectric field due to an efficient screening effect of the free carriers on the field. [source]

    Spin and energy transfer between magnetic ions and freecarriers in diluted-magnetic semiconductor heterostructures

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004
    D.R. Yakovlev
    Abstract In this paper we give a brief overview of our studies on dynamical processes in diluted-magnetic-semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. Presence of free carriers is an important factor which determines the energy- and spin transfer in a coupled systems of magnetic ions, lattice (the phonon system) and carriers. We report also new data on dynamical response of magnetic ions interacting with photogenerated electron-hole plasma. (Zn,Mn)Se/(Zn,Be)Se structures with relatively high Mn content of 11% provide spin-lattice relaxation time of about 20 ns, which is considerably shorter then the characterictic times of nonequilibrium phonons ranging to 1 ,s. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Free-Standing HVPE-GaN Quasi-Substrates: Impurity and Strain Distributions

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003
    T. Paskova
    Abstract We report a study of the physical properties of free-standing HVPE-GaN quasi-substrates. A variety of characterization techniques was employed in order to characterise in a comparative way the two sides of the films. The as-grown Ga-face was found to have lower density of both, structural and impurity defects. This leads to a lower concentration of free carriers and residual strain in the Ga-face compared to that in the N-face. The optical properties were found to be strongly influenced by the specific defect structure in both faces. [source]