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1 Feb 2006

Volume 99, Issue 3, Articles (03xxxx)

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Diffusion length and junction spectroscopy analysis of low-temperature annealing of electron irradiation-induced deep levels in 4H-SiC

A. Castaldini, A. Cavallini, L. Rigutti, S. Pizzini, A. Le Donne, and S. Binetti

J. Appl. Phys. 99, 033701 (2006); http://dx.doi.org/10.1063/1.2160708 (4 pages) | Cited 1 time

Online Publication Date: 1 February 2006

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The effects of low-temperature annealing in 8.2 MeV electron-irradiated 4H-SiC Schottky diodes were investigated. Deep-level transient spectroscopy and minority-carrier diffusion length (Ld) measurements were carried out on not-irradiated samples and on irradiated samples before and after thermal treatments up to T = 450 °C. We found that several deep levels in the upper half band gap (S1 with enthalpy ET = 0.27 eV, S2 with ET = 0.35 eV, S4 with ET = 0.71 eV, and S5 with ET = 0.96 eV) anneal out or modify at temperature values lower or equal to T = 450 °C, whereby their progressive annealing out is accompanied by a net increase of Ld, up to 50% of the value in the as-irradiated sample. We drew some conclusions regarding the microscopic nature of the defects related to the deep levels, according to their annealing behavior.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Fe Electron and positron radiation effects
66.30.-h Diffusion in solids
71.55.Ht Other nonmetals
85.30.Kk Junction diodes
65.40.G- Other thermodynamical quantities

Subband and transport calculations in double n-type δ-doped quantum wells in Si

I. Rodriguez-Vargas and L. M. Gaggero-Sager

J. Appl. Phys. 99, 033702 (2006); http://dx.doi.org/10.1063/1.2168024 (7 pages) | Cited 4 times

Online Publication Date: 2 February 2006

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The Thomas-Fermi approximation is implemented in two coupled n-type δ-doped quantum wells in Si. An analytical expression for the Hartree-Fock potential is obtained in order to compute the subband level structure. The longitudinal and transverse levels are obtained as a function of the impurity density and the interlayer distance. The exchange-correlation effects are analyzed from an impurity density of 8×1012 to 6.5×1013 cm−2. The transport calculations are based on a formula for the mobility, which allows us to discern the optimum distance between wells for maximum mobility.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
61.72.uf Ge and Si
71.55.Cn Elemental semiconductors
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Kinetics of low-temperature activation of acceptors in magnesium-doped gallium nitride epilayers grown by metal-organic vapor-phase epitaxy

E. Litwin-Staszewska, R. Piotrzkowski, L. Dmowski, P. Prystawko, R. Czernecki, and L. Konczewicz

J. Appl. Phys. 99, 033703 (2006); http://dx.doi.org/10.1063/1.2168232 (5 pages) | Cited 4 times

Online Publication Date: 3 February 2006

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The annealing process of magnesium-doped gallium nitride (GaN:Mg) epilayers grown by metal-organic vapor-phase epitaxy was investigated by in situ measurements of electrical transport properties. The resistivity ρ and the Hall effect were studied as functions of time and temperature in the range of 20–600 °C. A time-dependent p-type conductivity was observed at temperatures as low as 350 °C. Activation energy of about Eact = 1.5 eV was found for the magnesium acceptor (Mg) from the isothermal measurements of ρ(t) kinetics in the range of 350–550 °C. This value corresponds well to the theoretical prediction for the thermal dissociation of magnesium-hydrogen complexes (Mg–H). The annealing at temperatures higher than 600 °C leads obviously to the activation of Mg acceptors, but the final resistivity of the sample is higher than the result obtained after annealing at 520 °C. The ionization energy of electrically active Mg acceptor level of about EA = 170 meV was found from the temperature dependences of the resistivity ρ(T).
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Computational study of Ge and Sn doping of CdTe

John E. Jaffe

J. Appl. Phys. 99, 033704 (2006); http://dx.doi.org/10.1063/1.2168237 (4 pages) | Cited 2 times

Online Publication Date: 7 February 2006

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The formation and ionization energies of substitutional Ge and Sn dopants in CdTe are calculated in a supercell model within the local-density approximation to density-functional theory. Doping on both the Cd and Te sublattices is considered, but the formation energy of both defects is predicted to be much lower on the Cd site under most growth conditions. The Ge and Sn on the Cd sites are predicted to be deep donors and hole traps with defect ionization levels near the midgap, with Ge slightly lower than Sn, in good agreement with experiments. The Ge and Sn on the Te sites are predicted to be shallow acceptors.
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61.72.uf Ge and Si
71.55.Gs II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

One-dimensional postwetting layer in InGaAs/GaAs(100) quantum-dot chains

Zh. M. Wang, Yu. I. Mazur, J. L. Shultz, G. J. Salamo, T. D. Mishima, and M. B. Johnson

J. Appl. Phys. 99, 033705 (2006); http://dx.doi.org/10.1063/1.2169868 (5 pages) | Cited 8 times

Online Publication Date: 8 February 2006

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Long chains of quantum dots formed in InGaAs/GaAs(100) multiple layers have been systematically investigated by scanning electron, transmission electron, and atomic force microscopies. In addition to the usual two-dimensional wetting layer involved in the Stranski-Krastanov growth, we have directly observed a one-dimensional postwetting layer along the [01−1] direction that strings together the quantum dots in each chain. In sharp contrast with the two-dimensional wetting layer, which exists before the quantum-dot chains form, this one-dimensional postwetting layer develops during the GaAs capping of the existing dot chains. This one-dimensional layer forms through the anisotropic surface diffusion of In atoms that accompanies the change in strain profile during capping and therefore produces the steady-state material distribution that includes a one-dimensional postwetting layer as a result.
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68.08.Bc Wetting
68.65.Hb Quantum dots (patterned in quantum wells)
68.35.Ct Interface structure and roughness
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)

Electron scattering due to threading edge dislocations in n-type wurtzite GaN

Jeong Ho You, Jun-Qiang Lu, and H. T. Johnson

J. Appl. Phys. 99, 033706 (2006); http://dx.doi.org/10.1063/1.2168028 (10 pages) | Cited 15 times

Online Publication Date: 9 February 2006

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The effect of electrically active VGa–ON threading edge dislocations on drift and Hall mobilities in n-type epitaxial wurtzite (WZ) GaN is investigated theoretically. The charge distribution along the dislocation core is first obtained by means of a density-functional theory atomistic calculation; the two N atoms near the missing Ga atom at the dislocation core are found to be electron acceptors. An accurate analytical expression for dislocation electrostatic strength is then derived for the case of up to −2q charge per structural unit of the threading dislocation core. This strength factor is determined by minimizing the total increase of free energy per site of the partially charged dislocation line. Two different models of scattering potentials for charged dislocation lines are then used to determine the dislocation effect on in-plane electron mobility, and closed-form solutions for the dislocation contribution to drift and Hall mobilities are derived for the more accurate potential. By estimating the effects of other scattering mechanisms, the total mobility is then compared with available experimental data. It is found that for free-carrier concentrations higher than 1016 cm−3, reducing dislocation density below ndis = 108 cm−2 has little beneficial effect on total mobility for typical WZ GaN samples.
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72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
71.55.Eq III-V semiconductors

Bipolar carrier transport in a conjugated polymer by complex admittance spectroscopy

Dmitry Poplavskyy and Franky So

J. Appl. Phys. 99, 033707 (2006); http://dx.doi.org/10.1063/1.2149495 (9 pages) | Cited 37 times

Online Publication Date: 9 February 2006

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We report the bipolar transport properties of the LUMATION™ (Sumitomo Chemical) 1300 Series green-emitting polymer investigated by means of admittance spectroscopy. Analysis of the inductive response in single-carrier polymer diodes yields electron and hole mobilities which are in excellent agreement with the results of independent measurements. Admittance measurements in dual injection diodes, in combination with the analysis of current-voltage characteristics, provide evidence that the dual injection diodes operate in space-charge-limited regime, indicative of strong recombination within the material. Our results provide strong evidence that the space-charge-related admittance response of dual-carrier diodes is dominated by combined electron-hole response, which corresponds to the sum of electron and hole mobilities. This implies that electron and hole mobilities cannot be obtained separately from admittance measurements in space-charge-limited dual-carrier devices.
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85.60.Jb Light-emitting devices

Influence of lateral current spreading on the apparent barrier parameters of inhomogeneous Schottky diodes

J. Osvald

J. Appl. Phys. 99, 033708 (2006); http://dx.doi.org/10.1063/1.2169879 (5 pages) | Cited 4 times

Online Publication Date: 10 February 2006

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The influence of the series resistance of inhomogeneous Schottky diodes on the apparent barrier parameters in three different arrangements was studied. It is shown that when there is a total current spreading in the semiconductor substrate the ideality factor of the diode remains unity and the extracted series resistance is equal to the real value. On the other hand a lack of current spreading in the substrate results in the different voltage drops on the particular series resistances which causes different actual voltages on the particular diodes. The ideality factor nonequal to unity and the apparent series resistance different from the real value of the resistances are then the results of the barrier parameter extraction.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices

Comparison of blended versus layered structures for poly(p-phenylene vinylene)-based polymer photovoltaics

S. V. Chasteen, J. O. Härter, G. Rumbles, J. C. Scott, Y. Nakazawa, M. Jones, H.-H Hörhold, H. Tillman, and S. A. Carter

J. Appl. Phys. 99, 033709 (2006); http://dx.doi.org/10.1063/1.2168046 (10 pages) | Cited 13 times

Online Publication Date: 14 February 2006

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We characterize and compare blended and bilayered heterojunctions of polymer photovoltaic devices using poly[oxa-1,4-phenylene-1,2-(1-cyano)-ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)-ethenylene-1,4-phenylene] (CN-ether-PPV) and poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-1,2-ethenylene] (M3EH-PPV) as electron- and hole-transporting polymers, respectively. We find that both blended and bilayered structures have substantially improved current densities (>3 mA/cm2) and power efficiencies ( ∼ 1% under white light) over neat films. Improved exciton dissociation at multiple interfaces and reduced recombination due to energy and charge transfers increases the charge-carrier collection in both types of heterojunction devices, but low electron mobilities in the polymers lead to low fill factors and reduced quantum efficiency ( ∼ 20%) that limit the power efficiency. Time-resolved photoluminescence reveals that for blended structures both the hole and electron-transporting polymers undergo efficient quenching with the exciton decay being dominated by the existence of two fast decay channels of 0.12 and 0.78 ns that are assigned to interspecies charge transfer and account for the increased short-circuit current observed. For layers, these components are not as prevalent. This result indicates that greater exciton generation at the dissociating interface and more efficient charge collection in the thin layers is primarily responsible for the improved short-circuit current, a conclusion that is further supported by numerical simulations of the exciton generation rate and charge collection. We also report evidence for an intermediate exciplex state in both types of structures with the greatest yield for blends with 50 wt % of CN-ether-PPV. Overall, the improved performance is due to different processes in the two structures; efficient bulk exciton quenching and charge transfer in blends and enhanced exciton generation and charge collection in layers. The optimization of each photovoltaic heterostructured device relies on this understanding of the mechanisms by which each material architecture achieves high power efficiencies.
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85.60.Bt Optoelectronic device characterization, design, and modeling

Nondispersive hole transport in carbazole- and anthracene-containing polyspirobifluorene copolymers studied by the charge-generation layer time-of-flight technique

Frédéric Laquai, Gerhard Wegner, Chan Im, Heinz Bässler, and Susanne Heun

J. Appl. Phys. 99, 033710 (2006); http://dx.doi.org/10.1063/1.2168590 (7 pages) | Cited 8 times

Online Publication Date: 14 February 2006

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Nondispersive hole transport in two polyspirobifluorene copolymers containing either 10% anthracene or 10% carbazole was studied in detail by the charge-generation layer time-of-flight (TOF) technique over a wide range of electric fields and temperatures. The TOF transients of both polymers showed a clear plateau indicating nondispersive transport of charge carriers. Zero-field mobilities were found to be in the order of 10−6 cm2/V s at room temperature. Results were analyzed within the framework of the Gaussian disorder model to extract the parameters of the charge-carrier transport. The width of the transport density of states was determined to be 83 meV for the polyspirobifluorene-anthracene copolymer and 89 meV for the polyspirobifluorene-carbazole copolymer. At lower temperatures a change of slope in the temperature dependence of the zero-field mobility was observed. At higher temperatures the TOF transients were modified by a cusp. Both phenomena can be explained within the framework of the Gaussian disorder model.
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72.20.Fr Low-field transport and mobility; piezoresistance
71.20.Rv Polymers and organic compounds

Electronic properties of H-terminated diamond in electrolyte solutions

C. E. Nebel, B. Rezek, D. Shin, H. Watanabe, and T. Yamamoto

J. Appl. Phys. 99, 033711 (2006); http://dx.doi.org/10.1063/1.2171805 (4 pages) | Cited 18 times

Online Publication Date: 15 February 2006

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The electronic properties of hydrogen-terminated single-crystalline chemical-vapor deposited diamond in electrolyte solutions between pH 2 and 12 have been characterized by cyclic voltammetry experiments and pH-sensitive measurements using ion-sensitive field-effect transistor structures. The data show the formation of surface conductivity in diamond if immersed into electrolytes. The drain-source conductivity is pH dependent, with about 66 mV/pH. Due to strong Coulomb repulsion between positive ions in the electrolyte (hydronium ions) and the H+-surface termination of diamond, an enlarged tunneling gap is established which prevents electronic interactions between the electrolyte and diamond. This gap is the “virtual gate insulator” of diamond ion-sensitive field-effect transistor structures, with an interface resistance of about 108 Ω. The application of potentials larger than the oxidation threshold of +0.7 V (pH 13) to +1.6 V (pH 1) gives rise to strong leakage currents and to partial surface oxidation.
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73.25.+i Surface conductivity and carrier phenomena
82.80.Fk Electrochemical methods
73.40.Mr Semiconductor-electrolyte contacts
85.30.Tv Field effect devices

Enhanced magnetoresistance in a magnetic-particle chain

C. Xu, F. Q. Tong, and Y. Q. Ma

J. Appl. Phys. 99, 033712 (2006); http://dx.doi.org/10.1063/1.2171808 (5 pages)

Online Publication Date: 15 February 2006

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We study the magnetotransport in a magnetic-particle chain by Monte Carlo simulation. The influence of the correlations between magnetic particles on the system’s conductance is studied and an unusual tunneling magnetoresistance (TMR) effect is shown in the magnetic-particle chain. A large negative TMR at room temperature is obtained due to the strong magnetic interaction between particles. A separated hysteresis loop of TMR is observed at low temperature, and a large positive TMR peak appears at the coercive field. Both the theoretical calculation and the Monte Carlo simulation show an enhancement of TMR as the magnetic energy increases.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Mg Numerical simulation studies
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