Carrier Density (carrier + density)

Distribution by Scientific Domains

Kinds of Carrier Density

  • charge carrier density
  • sheet carrier density


  • Selected Abstracts


    Control of Carrier Density by a Solution Method in Carbon-Nanotube Devices,

    ADVANCED MATERIALS, Issue 20 2005
    T. Takenobu
    A new method for controlling the hole density in single-walled carbon nanotube field-effect transistors (SWCNT-FETs) by solution-based chemical doping is presented. The use of organic molecules that adsorb onto SWCNTs from solution is investigated. The transfer characteristics of the SWCNT-FETs exhibit continuous and precise shifts in threshold voltages (see Figure) upon doping with F4TCNQ molecules, even in air. [source]


    Determination of carrier diffusion coefficient and lifetime in single crystalline CVD diamonds by light-induced transient grating technique

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2010
    T. Malinauskas
    Abstract We report on a contactless, all-optical study of carrier diffusion and recombination kinetics in single-crystalline diamond layers using the light-induced transient grating (LITG) technique. Decay times of transient diffraction grating yielded carrier lifetime of ,R,,,3,ns and bipolar diffusion coefficient Da,=,12,cm2/s at 300,K. The latter value of Da was found to be 4,5 times lower than the ambipolar diffusivity based on electron and hole mobilities, measured by photo-electrical time-of-flight (ToF) technique. This discrepancy was attributed to the bandgap renormalization at high excess carrier densities and its impact on carrier diffusion. The significant decrease of low temperature diffusivity pointed out to a contribution of many-body effects which are tentatively attributed to the formation of electron,hole liquid (EHL) at T,<,150,K. [source]


    Strain-engineered novel III,N electronic devices with high quality dielectric/semiconductor interfaces

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
    M. Asif Khan
    Abstract Since the early demonstration of 2D-electron gas [M. A. Khan et al., Appl. Phys. Lett. 60, 3027 (1992)] and a heterojunction field effect transistor (HFET) [M. Asif Khan et al., Appl. Phys. Lett. 63, 1214 (1993)] in III,N materials, rapid progress has been made to improve the DC and RF performance of GaN,AlGaN based HFETs. Stable and impressive microwave powers as high as 4,8 W/mm have been reported for device operation frequencies from 10 to 35 GHz. The key reason for these high performance numbers is an extremely large sheet carrier densities (>1 × 1013 cm,2) that can be induced at the interfaces in III,N hetereojunction [A. Bykhovsk et al., J. Appl. Phys. 74, 6734 (1993); M. Asif Khan et al., Appl. Phys. Lett. 75, 2806 (1999)]. These are instrumental in screening the channel dislocations thereby retaining large room temperature carrier mobilities (>1500 cm2/Vs) and sheet resistance as low as 300 ,/sq. These numbers and the high breakdown voltages of the large bandgap III,N material system thus enable rf-power approximately 5,10 times of that possible with GaAs and other competitor's technologies. We have recently introduced a unique pulsed atomic layer epitaxy approach to deposit AlN buffer layers and AlN/AlGaN superlattices [J. Zhang et al., Appl. Phys. Lett. 79, 925 (2001); J. P. Zhang et al., Appl. Phys. Lett. 80, 3542 (2002)] to manage strain and decrease the dislocation densities in high Al-content III,N layers. This has enabled us to significantly improve GaN/AlGaN hetereojunctions and the device isolation. The resulting low defect layers are not only key to improving the electronic but also deep ultraviolet light-emitting diode devices. For deep UV LED's they enabled us to obtain peak optical powers as high as 10 mW and 3 mW for wavelengths as short as 320 nm and 278 nm. Building on our past work [M. Asif Khan et al., Appl. Phys. Lett. 77, 1339 (2000); X. Hu et al., Appl. Phys. Lett. 79, 2832 (2001)] we have now deposited high quality SiO2/Si3N4 films over AlGaN with low interface state densities. They have then been used to demonstrate III,N insulating gate transistors (MOSHFET (SiO2) and MISHFET (Si3N4) with gate leakage currents 4,6 order less than those for conventional GaN,AlGaN HFETs. The introduction of the thin insulator layers (less then 100 Ĺ) under the gate increases the threshold voltage by 2,3 V. In addition, it reduces the peak transconductance gm. However the unity cut-off frequency, the gain and the rf-powers remain unaffected as the gm/Cgs (gate-source capacitance) ratio remains unchanged. In addition to managing the defects and gate leakage currents we have also employed InGaN channel double heterojunction structures (AlInGaN,InGaN,GaN) to confine the carriers thereby reducing the spillover into trappings states. These InGaN based MOS-DHFETs exhibited no current-collapse, extremely low gate leakage currents (<10,10 A/mm) and 10,26 GHz rf-powers in excess of 6 W/mm. We have also demonstrated the scalability and stable operation of our new and innovative InGaN based insulating gate heterojunction field effect transistor approach. In this paper we will review the III,N heterojunction field-effect transistors progress and pioneering innovations including the excellent work from several research groups around the world. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Modulation of mobility in homoepitaxially-grown AlGaN/GaN heterostructures

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    J. A. Grenko
    Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c-axis GaN substrates. Room temperature Hall mobilities up to 1805 cm2/Vs at sheet carrier densities of 0.77x1013 cm,2 have been measured. By varying the GaN buffer layer thickness in these homoepitaxially-grown Al0.25Ga0.75N/GaN heterostructures, we observed a buffer-induced modulation of the room temperature 2DEG sheet carrier densities and Hall mobilities. The increase in sheet carrier density and corresponding decrease in mobility as the GaN buffer layer thickness is reduced below 0.75 ,m is related to the presence of Si impurities at the bulk GaN substrate/epitaxial interface. Capacitance-voltage measurements and SIMS analysis confirm the presence of Si impurities at the surface prior to and after epitaxial growth. The factor of 2 reduction in the room temperature mobility is consistent with a predicted theoretical mobility reduction based on intersubband scattering. We have also been able to separate the contributions to the 2DEG carrier density from the ionized donors and the polarization field; the magnitude of each is ,5x1012 cm,2. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Transport mechanism in the quantum well embedded with quantum dots

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2009
    E. S. Kannan
    Abstract Electron transport in single and double quantum well system embedded with InAs quantum dots is investigated by carrying out magnetoresistance measurements at 1.2 K. At low carrier densities, the electrons are strongly localized due to disorder and undergo magnetic field induced insulator to quantum Hall liquid transitions characterized by temperature independent crossing points. At higher carrier densities no such magnetic field induced transition are observed. The potential induced by the electrons in the quantum dots were found to enhance the scattering between the edge states resulting in the substantial reduction of the width of the Hall plateau in the single quantum well system. In the double quantum well system, instead of plateaus abrupt increase in the Hall resistance is observed at integer filling factors. On sweeping the gate bias at fixed magnetic field, hysteresis effect was observed in the double quantum well system due to the charge trapping in the defect levels. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    A comparative study of defect states in evaporated and selenized CIGS(S) solar cells

    PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2005
    P. K. Johnson
    Abstract Current-voltage, admittance spectroscopy, and drive-level capacitance profiling measurements were taken on Cu(In1,xGax)(Se1,ySy)2 solar cell devices. The devices were made using two different types of absorbers. One set of absorbers was deposited via physical vapor deposition, while the other set of absorbers was made by selenization of metal precursors. Additionally, each type of absorber was completed with one of two different types of buffer treatments: a CdS layer or a cadmium partial electrolyte surface modification. The devices with the evaporated absorbers had larger values of VOC, higher carrier densities, lower densities of trapping defects, and likely shallower gap states. Results were qualitatively similar for the CdS and partial electrolyte buffers. Copyright © 2005 John Wiley & Sons, Ltd. [source]


    Microstructural, thermal, and electrical properties of Bi1.7V0.3Sr2Ca2Cu3Ox glass-ceramic superconductor

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2004
    T. S. Kayed
    Abstract A glass-ceramic Bi1.7V0.3Sr2Ca2Cu3Ox superconductor was prepared by the melt-quenching method. The compound was characterized by scanning electron microscopy, x-ray diffraction, differential thermal analysis, current-voltage characteristics, transport resistance measurements, and Hall effect measurements. Two main phases (BSCCO 2212 and 2223) were observed in the x-ray data and the values of the lattice parameters quite agree with the known values for 2212 and 2223 phases. The glass transition temperature was found to be 426 °C while the activation energy for crystallization of glass has been found to be Ea = 370.5 kJ / mol. This result indicates that the substitution of vanadium increased the activation energy for the BSCCO system. An offset Tc of 80 K was measured and the onset Tc was 100 K. The Hall resistivity ,H was found to be almost field-independent at the normal state. A negative Hall coefficient was observed and no sign reversal of ,H or RH could be noticed. The mobility and carrier density at different temperatures in the range 140-300 K under different applied magnetic fields up to 1.4 T were also measured and the results are discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Controllable Molecular Doping and Charge Transport in Solution-Processed Polymer Semiconducting Layers

    ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009
    Yuan Zhang
    Abstract Here, controlled p-type doping of poly(2-methoxy-5-(2,-ethylhexyloxy)- p -phenylene vinylene) (MEH-PPV) deposited from solution using tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) as a dopant is presented. By using a co-solvent, aggregation in solution can be prevented and doped films can be deposited. Upon doping the current,voltage characteristics of MEH-PPV-based hole-only devices are increased by several orders of magnitude and a clear Ohmic behavior is observed at low bias. Taking the density dependence of the hole mobility into account the free hole concentration due to doping can be derived. It is found that a molar doping ratio of 1 F4-TCNQ dopant per 600 repeat units of MEH-PPV leads to a free carrier density of 4,×,1022,m,3. Neglecting the density-dependent mobility would lead to an overestimation of the free hole density by an order of magnitude. The free hole densities are further confirmed by impedance measurements on Schottky diodes based on F4-TCNQ doped MEH-PPV and a silver electrode. [source]


    High-Density Carrier Accumulation in ZnO Field-Effect Transistors Gated by Electric Double Layers of Ionic Liquids

    ADVANCED FUNCTIONAL MATERIALS, Issue 7 2009
    Hongtao Yuan
    Abstract Very recently, electric-field-induced superconductivity in an insulator was realized by tuning charge carrier to a high density level (1,×,1014 cm,2). To increase the maximum attainable carrier density for electrostatic tuning of electronic states in semiconductor field-effect transistors is a hot issue but a big challenge. Here, ultrahigh density carrier accumulation is reported, in particular at low temperature, in a ZnO field-effect transistor gated by electric double layers of ionic liquid (IL). This transistor, called an electric double layer transistor (EDLT), is found to exhibit very high transconductance and an ultrahigh carrier density in a fast, reversible, and reproducible manner. The room temperature capacitance of EDLTs is found to be as large as 34,µF cm,2, deduced from Hall-effect measurements, and is mainly responsible for the carrier density modulation in a very wide range. Importantly, the IL dielectric, with a supercooling property, is found to have charge-accumulation capability even at low temperatures, reaching an ultrahigh carrier density of 8×1014 cm,2 at 220,K and maintaining a density of 5.5×1014 cm,2 at 1.8,K. This high carrier density of EDLTs is of great importance not only in practical device applications but also in fundamental research; for example, in the search for novel electronic phenomena, such as superconductivity, in oxide systems. [source]


    Silicon Nanowires: A Review on Aspects of their Growth and their Electrical Properties

    ADVANCED MATERIALS, Issue 25-26 2009
    Volker Schmidt
    Abstract This paper summarizes some of the essential aspects of silicon-nanowire growth and of their electrical properties. In the first part, a brief description of the different growth techniques is given, though the general focus of this work is on chemical vapor deposition of silicon nanowires. The advantages and disadvantages of the different catalyst materials for silicon-wire growth are discussed at length. Thereafter, in the second part, three thermodynamic aspects of silicon-wire growth via the vapor,liquid,solid mechanism are presented and discussed. These are the expansion of the base of epitaxially grown Si wires, a stability criterion regarding the surface tension of the catalyst droplet, and the consequences of the Gibbs,Thomson effect for the silicon wire growth velocity. The third part is dedicated to the electrical properties of silicon nanowires. First, different silicon nanowire doping techniques are discussed. Attention is then focused on the diameter dependence of dopant ionization and the influence of interface trap states on the charge carrier density in silicon nanowires. It is concluded by a section on charge carrier mobility and mobility measurements. [source]


    Comparison of the Mobility,Carrier Density Relation in Polymer and Single-Crystal Organic Transistors Employing Vacuum and Liquid Gate Dielectrics

    ADVANCED MATERIALS, Issue 21 2009
    Yu Xia
    The mobility of polymer and single-crystal transistors using a universal test-bed where the injected carrier density can vary more than four orders of magnitude are investigated and compared. A striking difference in the mobility,carrier density relationship was observed, revealing a fundamentally different charge-transport mechanism between polymer and single-crystal transistors. [source]


    Dielectric modeling of transmittance and ellipsometric spectra of thin In2O3:Sn films

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2010
    Zhaohui Qiao
    Abstract Thin ITO films with thickness between 0.05 and 0.4,µm were deposited on quartz substrates by direct-current magnetron-sputtering. The films' ellipsometric and transmittance spectra between 280 and 2500,nm were simulated simultaneously with a computer program based on dielectric modeling. The dielectric function used is the sum of three types of electronic excitations: intraband transitions of free electrons (extended Drude model), band gap transitions, and interband transitions into the upper half of the conduction band. A successful fit of the simulated to the experimental curves was obtained with a two-layer model (bulk and surface layers) and applying the Bruggeman effective-medium approach. From the simulation, film thickness, refractive index, band gap, and free carrier density can be obtained. The thickness of the surface layer is comparable with the surface roughness determined by AFM measurements. [source]


    Passivation study of the amorphous,crystalline silicon interface formed using DC saddle-field glow discharge

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010
    Barzin Bahardoust
    Abstract The DC saddle-field (DCSF) glow discharge method was used to deposit intrinsic a-Si:H onto c-Si to passivate the c-Si surface. The effective minority carrier lifetime in the heterostructures as a function of the excess minority carrier density in the c-Si wafers was measured. The results were then analyzed in the context of recombination associated with interface defect states using three known recombination models. The defect density and the charge density at the interface are inferred. In addition subsequent annealing of the samples was studied. It is shown that for our intrinsic a-Si:H samples improvements in surface passivation are directly correlated with the reduction of interface defects and not the reduction of minority carrier concentration at the interface due to electric field. We have achieved excellent surface passivation with effective carrier lifetime >4,ms for an intrinsic a-Si:H sample deposited at a process temperature of 200,°C and thickness of about 30,nm. It is also demonstrated that subsequent annealing, at 240,°C, of the samples which were prepared at process temperatures <240,°C greatly increases the effective lifetime. [source]


    Hole,polar phonon interaction scattering mobility in chain structured TlSe0.75S0.25 crystals

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2009
    A. F. Qasrawi
    Abstract In this study, the electrical resistivity, charge carriers density and Hall mobility of chain structured TlSe0.75S0.25 crystal have been measured and analyzed to establish the dominant scattering mechanism in crystal. The data analyses have shown that this crystal exhibits an extrinsic p-type conduction. The temperature-dependent dark electrical resistivity analysis reflected the existence of three energy levels located at 280 meV, 68 meV and 48 meV. The temperature dependence of carrier density was analyzed by using the single donor,single acceptor model. The carrier concentration data were best reproduced assuming the existence of an acceptor impurity level being located at 68 meV consistent with that observed from resistivity measurement. The model allowed the determination of the hole effective mass and the acceptor,donor concentration difference as 0.44m0 and 2.2 × 1012 cm,3, respectively. The Hall mobility of the TlSe0.75S0.25 crystal is found to be limited by the scattering of charged carriers over the (chain) boundaries and the scattering of hole,polar phonon interactions above and below 300 K, respectively. The value of the energy barrier height at the chain boundaries was found to be 261 meV. The polar phonon scattering mobility revealed the high-frequency and static dielectric constants of 13.6 and 15.0, respectively. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Properties of post-annealed ZnO films grown with O3

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2008
    H. S. Kim
    Abstract The properties of ZnO thin films grown with ozone are examined. Annealing studies were performed on ZnO films grown by pulsed-laser deposition using either O2 and an O2/O3 gas mixture as the oxidant. The carrier density of ZnO films grown with pure O2 generally decreases upon annealing in 1 atm O2. In contrast, the n-type carrier density for ZnO films grown with O2/O3 mixture gas increased with O2 annealing. The results indicate that acceptor states, created via growth in ozone, are annihilated with post-annealing. This suggests that the ozone-related acceptor states are metastable. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Charge carrier density dependence of the hole mobility in poly(p -phenylene vinylene)

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2004
    C. Tanase
    Abstract The hole transport in various poly(p -phenylene vinylene) (PPV) derivatives has been investigated in field-effect transistors (FETs) and light-emitting diodes (LEDs) as a function of temperature and applied bias. The discrepancy between the experimental hole mobilities extracted from FETs and LEDs based on a single disordered polymeric semiconductor originates from the strong dependence of the hole mobility on the charge carrier density. The microscopic charge transport parameters are directly related to the chemical composition of the analysed polymers. By chemically modifying the PPV, the hole mobility in both FETs and LEDs can be changed by orders of magnitude. For highly disordered PPVs it is demonstrated that the exponential density of states (DOS), which is used to describe the charge transport in FETs, is a good approximation of the tail states of the Gaussian DOS, which describes the charge transport in LEDs. Increase of the directional order in the PPV film enhances the mobility but also induces a strong anisotropy in the charge transport, thereby obscuring a direct comparison between sandwich and field-effect devices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Cathodoluminescence properties of zinc oxide nanoparticles

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2004
    M. R. Phillips
    Abstract Zinc oxide nano-particles (25 nm) have been investigated by cathodoluminescence spectroscopy (300 nm,1700 nm) at 80 K and 300 K following thermal annealing in high purity H2/N2, N2, O2 and Ar gaseous atmospheres. The intensity of the ZnO near band edge peak was significantly increased after heat treatment in hydrogen. Conversely, thermal annealing in the other gas types decreased this emission. This effect is attributed to hydrogen passivation of competitive non-radiative defect centers, most likely bulk zinc vacancy centers. The appearance of a strong green emission centered at 2.4 eV following thermal annealing in all gas atmospheres is ascribed to the formation of bulk oxygen vacancy defects. A strong red shift of the near band edge emission with increasing beam current at 300 K is accredited to electron beam heating rather than to an increase in the carrier density. Electron beam heating is evidenced by the occurrence of a strong black body emission in the near infrared spectral region. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Nonadiabatic electron,phonon effects in low carrier density superconductors

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2005
    E. Cappelluti
    Abstract Different families of unconventional superconductors present a low charge carrier density as a common trait, suggesting that the low charge density can be at the basis of a unifying picture for different superconductors. In the past years we have suggested that the electron,phonon interaction can be responsible for a high- Tc superconducting pairing in a nonadiabatic regime, where nonadiabatic effects are triggered on by the small electronic Fermi energy associated with the low charge density character. A coherent picture of such a framework requires however reconciling the low charge density and the small Fermi energy with a finite metallic character (sizable density of states and large Fermi surfaces). In this paper we investigate the peculiar conditions which are needed to be encountered in order to fulfill these requirements. We discuss the specific case of fullerenes, cuprates and MgB2 alloys by analyzing their specific structural and electronic properties The comparison between these materials and simple instructive models permits to underline the different routes to reconcile these characteristics in different compounds. In cuprates and fullerenes the interplay between small Fermi energies and large Fermi surface is strictly connected with strong electronic correlation effects. A comprehensive understanding of these issues can be useful to the future search for new nonadiabatic high- Tc materials. (© 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]


    Scanning capacitance microscopy as a tool for the assessment of unintentional doping in GaN

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    Rachel A. Oliver
    Abstract Scanning capacitance microscopy (SCM) is a technique based on atomic force microscopy which provides information about the concentration and distribution of charge carriers in a semiconducting sample. As an imaging technique it provides an advantage over more conventional approaches such as secondary ion mass spectrometry and depth-profiling Hall voltage measurement since it provides a two-dimensional dataset rather than a one dimensional line profile. Here, we demonstrate the utility of SCM for GaN-based materials by assessing the unintentionally doped layer at the GaN/sapphire interface in a series of samples in which the growth conditions initially favoured the formation of three-dimensional islands, which later coalesced to form a two-dimensional film. Using SCM we observe that the width of the resulting conductive layer at the GaN/sapphire interface depends on the time taken to achieve coalescence but that the carrier density does not. We also assess and attempt to explain the roughness of the top surface of the conductive interface layer, which can only be addressed using an imaging technique. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Modulation of mobility in homoepitaxially-grown AlGaN/GaN heterostructures

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009
    J. A. Grenko
    Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c-axis GaN substrates. Room temperature Hall mobilities up to 1805 cm2/Vs at sheet carrier densities of 0.77x1013 cm,2 have been measured. By varying the GaN buffer layer thickness in these homoepitaxially-grown Al0.25Ga0.75N/GaN heterostructures, we observed a buffer-induced modulation of the room temperature 2DEG sheet carrier densities and Hall mobilities. The increase in sheet carrier density and corresponding decrease in mobility as the GaN buffer layer thickness is reduced below 0.75 ,m is related to the presence of Si impurities at the bulk GaN substrate/epitaxial interface. Capacitance-voltage measurements and SIMS analysis confirm the presence of Si impurities at the surface prior to and after epitaxial growth. The factor of 2 reduction in the room temperature mobility is consistent with a predicted theoretical mobility reduction based on intersubband scattering. We have also been able to separate the contributions to the 2DEG carrier density from the ionized donors and the polarization field; the magnitude of each is ,5x1012 cm,2. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Monte Carlo simulation of surface charge effects in T-branch nanojunctions

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008
    T. González
    Abstract We analyze the influence of the surface charge on the operation of ballistic T-branch junctions based on InAlAs/InGaAs layers by means of a semi-classical 2-D Monte Carlo simulator. A new self-consistent model in which the local value of the surface charge is dynamically adjusted depending on the surrounding carrier density is used in the calculations. The rectifying behaviour exhibited by these devices (down-bending shape of the output voltage VC as a function of the applied voltage VR = -VL =V) is found to be much influenced by the surface charge. A satisfactory agreement is achieved between simulated results and experimental measurements. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Predominant point defects in tellurium saturated CdTe

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006
    P. Fochuk
    Abstract High temperature Hall effect measurements at 570,1070 K under well defined Te vapor pressure in CdTe single crystals grown by THM and Bridgman techniques were made. Both the free carrier density versus Te vapour pressure value and temperature dependencies were studied. At heating up till ,870 K the hole density was Te vapor pressure independent, but it varied in different samples from 1 × 1016 to 1 × 1017 cm,3. At higher temperatures the conductivity becomes of intrinsic type, turning then into n-type one. A theoretical analysis of native point defects contents at different conditions in the framework of Krögers quasichemical formalism was performed. It resulted in the impossibility of mutual compensation of native donors and acceptors proposed by different authors. The results were explained assuming the presence of an electrically active foreign point defect , the oxygen interstitial acceptor. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Charge-carrier mobilities in disordered semiconducting polymers: effects of carrier density and electric field

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2006
    K.D. Meisel
    The cover picture of this issue of physica status solidi (c) has been taken from the article [1]. [source]


    The evolution of the electric field in an optically excited semiconductor superlattice

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2005
    Alvydas Lisauskas
    Abstract We report on time-resolved photocurrent spectroscopy of an intrinsic GaAs/Al0.3Ga0.7As superlattice subsequent to femtosecond optical excitation. Information on the spatio-temporal evolution of the densities of electrons and holes and on the internal electric field is obtained by tracing Wannier-Stark photocurrent spectra as a function of delay time for various bias fields and pump excitation intensities. The experimental results are supplemented by simulations. We employ the combined information to define the conditions to be met for succesful pump-probe Bloch gain experiments. In particular, we find that field screening sets on upper limit for the carrier density of 1016 cm,3, and that the time window during which gain should be found is defined by the duration of the sweep-out of the optically injected electrons from the superlattice which occurs within about 10 ps after excitation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Effect of hydrostatic pressure on the transport properties in magnetic semiconductors

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004
    M. Csontos
    Abstract The effect of pressure on the ferromagnetic phase transition has been studied in manganese doped III-V semiconductors by electrical conductance and Hall measurements. We found that the application of hydrostatic pressure shifts the transition temperature upwards both in (In,Mn)Sb and (Ga,Mn)As. The anomalous-Hall coefficient shows a dramatic increase in the hysteresis loops in the ferromagnetic phase and an enhanced magnetization both below and above the phase transition. As the normal-Hall results suggest that the pressure does not change the carrier density [in (In,Mn)Sb] or rather decreases it [in (Ga,Mn)As], all the above observations are indicative of a pressure-induced enhancement of magnetic coupling. [source]


    Persistent photoconductivity in quantum dot layers in InAs/GaAs structures

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003
    V. A. Kulbachinskii
    Abstract We synthesized InAs/GaAs structures with quantum dot layers and investigated electron (Si doping) lateral transport in the temperature interval 0.05 K < T < 300 K in the dark and under illumination by light over a wide interval of wavelengths in magnetic fields up to 6 T. All the samples exhibited a positive persistent photoconductivity at T < 250 K. Without illumination in the high carrier density samples the Shubnikov,de Haas effect and the quantum Hall effect were observed. Low carrier density samples showed a 2D Mott variable range hopping conductivity. The morphology of the quantum dot layers was investigated by atomic force microscopy (AFM). The length of localization exceeds the average quantum dot size and correlates very well with the quantum dot cluster size obtained by AFM. [source]


    Hole,polar phonon interaction scattering mobility in chain structured TlSe0.75S0.25 crystals

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2009
    A. F. Qasrawi
    Abstract In this study, the electrical resistivity, charge carriers density and Hall mobility of chain structured TlSe0.75S0.25 crystal have been measured and analyzed to establish the dominant scattering mechanism in crystal. The data analyses have shown that this crystal exhibits an extrinsic p-type conduction. The temperature-dependent dark electrical resistivity analysis reflected the existence of three energy levels located at 280 meV, 68 meV and 48 meV. The temperature dependence of carrier density was analyzed by using the single donor,single acceptor model. The carrier concentration data were best reproduced assuming the existence of an acceptor impurity level being located at 68 meV consistent with that observed from resistivity measurement. The model allowed the determination of the hole effective mass and the acceptor,donor concentration difference as 0.44m0 and 2.2 × 1012 cm,3, respectively. The Hall mobility of the TlSe0.75S0.25 crystal is found to be limited by the scattering of charged carriers over the (chain) boundaries and the scattering of hole,polar phonon interactions above and below 300 K, respectively. The value of the energy barrier height at the chain boundaries was found to be 261 meV. The polar phonon scattering mobility revealed the high-frequency and static dielectric constants of 13.6 and 15.0, respectively. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]