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1 Jul 2010

Volume 108, Issue 1, Articles (01xxxx)

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J. Appl. Phys. 108, 011101 (2010); http://dx.doi.org/10.1063/1.3457141 (19 pages)

Xunlin Qiu
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back to top Device Physics

Evaluating luminescence based voltage images of silicon solar cells

M. Glatthaar, J. Haunschild, R. Zeidler, M. Demant, J. Greulich, B. Michl, W. Warta, S. Rein, and R. Preu

J. Appl. Phys. 108, 014501 (2010); http://dx.doi.org/10.1063/1.3443438 (5 pages) | Cited 7 times

Online Publication Date: 2 July 2010

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In this paper we give a mathematical derivation of how luminescence images of silicon solar cells can be calibrated to local junction voltage. We compare two different models to extract spatially resolved physical cell parameters from voltage images. The first model is the terminal connected diode model, where each pixel is regarded as a diode with a certain dark saturation current, which is connected via a series resistance with the terminal. This model is frequently used to evaluate measurement data of several measurement techniques with respect to local series resistance. The second model is the interconnected diode model, where the diode on one pixel is connected with the neighbor diodes via a sheet resistance. For each model parameter at least one image is required for a coupled determination of the parameters. We elaborate how also the voltage calibration can be added as an unknown parameter into the models, and how the resulting system of equations can be solved analytically. Finally the application of the models and the different ways of voltage calibration are compared experimentally.
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88.40.jj Silicon solar cells
78.55.Ap Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects

Electronic structure variation during aging for Mg–Zr–O protective films in alternating current plasma display panel

Huiyan Wu, Jianfeng Wang, Zhongxiao Song, Kewei Xu, Yanhuai Li, and Chunliang Liu

J. Appl. Phys. 108, 014502 (2010); http://dx.doi.org/10.1063/1.3456493 (4 pages)

Online Publication Date: 2 July 2010

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The variation in both the discharge characteristic and microstructure during aging for Mg–Zr–O protective films was investigated. In the aging process, the firing voltage and the minimum sustain voltage were reduced by 18 V and 10 V, respectively. Meanwhile, the results of x-ray photoelectron spectroscopy (XPS) measurement revealed that the valence band edge of Mg–Zr–O protective films was slightly shifted to a low binding state and the density of states for valence bands was increased. The electronic structure variation related to the changes in crystal structure had an obvious influence on the improvement of discharge characteristic of Mg–Zr–O films.
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71.20.Ps Other inorganic compounds
68.55.-a Thin film structure and morphology
73.20.At Surface states, band structure, electron density of states
52.80.-s Electric discharges
52.75.-d Plasma devices

Synergistic effect on the efficiency of polymer light-emitting diodes upon blending of two green-emitting polymers

G. Bernardo, Q. Ferreira, G. Brotas, R. E. Di Paolo, A. Charas, and J. Morgado

J. Appl. Phys. 108, 014503 (2010); http://dx.doi.org/10.1063/1.3456997 (8 pages)

Online Publication Date: 2 July 2010

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Light-emitting diodes based on blends of the two green-emitting polymers, poly(9,9-dioctylfluorene-alt-benzothiadiazole), F8BT, and poly(9,9-dioctylfluorene-alt-bithiophene), F8T2, show efficiencies that lie in between those of the devices based on the neat polymers (with a maximum efficiency of approximately 4 cd/A for the devices with magnesium cathodes based on F8BT), except for the blend with 5% by weight of F8T2, which is more efficient than the device based on neat F8BT (a maximum efficiency of approximately 5 cd/A is obtained). In view of the lower photoluminescence efficiency of F8T2, we attribute this improvement to the improved hole transport brought about by F8T2, though is surprising that 5% by weight, is enough to significantly improve the charge balance within the emissive layer. A detailed photophysics study was carried out for the neat polymers and their blends and no clear evidence for energy transfer between the components was found. This unanticipated devices performance improvement points to the need of a deeper screening of available conjugated luminescent polymers.
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85.60.Jb Light-emitting devices

Anisotropy in structural and physical properties in tetrathiafulvalene derivatives-based zone-cast layers as seen by Raman spectroscopy, UV-visible spectroscopy, and field effect measurements

Sylwia Kotarba, Jaroslaw Jung, Aneta Kowalska, Tomasz Marszalek, Marcin Kozanecki, Pawel Miskiewicz, Marta Mas-Torrent, Concepció Rovira, Jaume Veciana, Josep Puigmarti-Luis, and Jacek Ulanski

J. Appl. Phys. 108, 014504 (2010); http://dx.doi.org/10.1063/1.3311554 (7 pages) | Cited 5 times

Online Publication Date: 7 July 2010

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We have studied anisotropy of thin layers of amphiphilic tetrathiafulvalene derivatives (TTF-4SCn, with n = 12, 18, and 22) obtained by zone-casting technique. All the films show optical anisotropy, as seen by polarized optical microscopy and polarized UV-visible spectroscopy. By using polarized Raman spectroscopy an angular dependence of intensity of different vibrational modes in respect to the zone-casting direction was determined. It was found that intensities of the modes related to central and ring C = C vibrations in the TTF core depend very strongly on the angle between the zone-cast direction and polarization plane of incident laser light. Comparison of the deduced orientation of the molecules in one of the films (TTF-4SC18) with its crystal structure shows that the polarized Raman spectroscopy can be useful for controlling orientation of molecules in thin films (e.g., for online monitoring). Organic field effect transistors (OFETs), with channels oriented in parallel and perpendicularly to the zone-casting direction, were built using the oriented TTF-4SCn films. In all cases a strong anisotropy of the charge carrier mobility (μ) was found; the best results were obtained for OFETs with TTF-4SC18, for which μ∥ = 0.25 cm2/V s, ON/OFF>105, and μ∥/μ⊥ ≈ 170.
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81.05.Fb Organic semiconductors
68.55.-a Thin film structure and morphology
73.50.Dn Low-field transport and mobility; piezoresistance
78.30.Jw Organic compounds, polymers
78.40.Me Organic compounds and polymers
78.66.Qn Polymers; organic compounds
85.30.Tv Field effect devices

High resolution on-chip thermometry using a microstrip-coupled transition edge sensor

D. J. Goldie, K. Rostem, and S. Withington

J. Appl. Phys. 108, 014505 (2010); http://dx.doi.org/10.1063/1.3429088 (5 pages)

Online Publication Date: 8 July 2010

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Our recent work demonstrated highly efficient coupling of broadband thermal photon radiation between the termination resistors of a superconducting microstrip transmission line measured using a transition edge sensor (TES). A simple modification of this scheme is presented that permits rapid thermometry of micron-scale objects at temperatures below 3 K. Broadband photon noise gives a limiting temperature sensitivity of 3.8 μK for a 1 s integration time for measurements at 0.5 K. In practice, phonon noise in the thermal link between the TES and the heat bath limits the achievable temperature resolution to about 30 μK for a typical TES with noise equivalent power of 2×10−17 W/math with the same integration time.
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07.20.Dt Thermometers
84.40.Az Waveguides, transmission lines, striplines
85.25.-j Superconducting devices

Interpretation of recombination at c-Si/SiNx interfaces by surface damage

Silke Steingrube, Pietro P. Altermatt, Daniel S. Steingrube, Jan Schmidt, and Rolf Brendel

J. Appl. Phys. 108, 014506 (2010); http://dx.doi.org/10.1063/1.3437643 (9 pages) | Cited 9 times

Online Publication Date: 8 July 2010

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The measured effective surface recombination velocity Seff at the interface between crystalline p-type silicon (p-Si) and amorphous silicon nitride (SiNx) layers increases with decreasing excess carrier density Δn<1015 cm−3 at dopant densities below 1017 cm−3. If such an interface is incorporated into Si solar cells, it causes their performance to deteriorate under low-injection conditions. With the present knowledge, this effect can neither be experimentally avoided nor fully understood. In this paper, Seff is theoretically reproduced in both p-type and n-type Si at all relevant Δn and all relevant dopant densities. The model incorporates a reduction in the Shockley–Read–Hall lifetime in the Si bulk near the interface, called the surface damage region (SDR). All of the parameters of the model are physically meaningful, and a parametrization is given for numerical device modeling. The model predicts that a ten-fold reduction in the density of defect states within the SDR is sufficient to weaken this undesirable effect to the extent that undiffused surfaces can be incorporated in Si solar cells. This may serve to simplify their fabrication procedures. We further discuss possible causes of the SDR and suggest implications for experiments.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
72.20.My Galvanomagnetic and other magnetotransport effects
81.05.Gc Amorphous semiconductors
61.66.Fn Inorganic compounds

Intrinsic detection efficiency of superconducting nanowire single-photon detectors with different thicknesses

M. Hofherr, D. Rall, K. Ilin, M. Siegel, A. Semenov, H.-W. Hübers, and N. A. Gippius

J. Appl. Phys. 108, 014507 (2010); http://dx.doi.org/10.1063/1.3437043 (9 pages) | Cited 10 times

Online Publication Date: 9 July 2010

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We evaluate experimentally the intrinsic detection efficiency (IDE) of superconducting NbN nanowire single-photon detectors in the range of wire thicknesses from 4 to 12 nm. The study is performed in the broad spectral interval between near-ultraviolet (wavelength 400 nm) and near-infrared (wavelength 2000 nm) light with plane waves at normal incidence. For visible light the IDE of the thinnest detectors reaches 70%. We use numerically computed absorptance of the nanowire-structures for the analysis of the experimental data. Variations in the detection efficiency with both the wire thickness and the wavelength evidence the red boundary of the hot-spot photon-detection mechanism. We explain the detection at larger wavelengths invoking thermal excitation of magnetic Pearl vortices over the potential barrier at the edges of the wire.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
42.82.-m Integrated optics
85.60.-q Optoelectronic devices

Investigation of the interface between silicon nitride passivations and AlGaN/AlN/GaN heterostructures by C(V) characterization of metal-insulator-semiconductor-heterostructure capacitors

M. Fagerlind, F. Allerstam, E. Ö. Sveinbjörnsson, N. Rorsman, A. Kakanakova-Georgieva, A. Lundskog, U. Forsberg, and E. Janzén

J. Appl. Phys. 108, 014508 (2010); http://dx.doi.org/10.1063/1.3428442 (6 pages) | Cited 6 times

Online Publication Date: 13 July 2010

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Capacitance-voltage [C(V)] measurements of metal-insulator-semiconductor-heterostructure capacitors are used to investigate the interface between silicon nitride passivation and AlGaN/AlN/GaN heterostructure material. AlGaN/AlN/GaN samples having different silicon nitride passivating layers, deposited using three different deposition techniques, are evaluated. Different interface state distributions result in large differences in the C(V) characteristics. A method to extract fixed charge as well as traps from the C(V) characteristics is presented. Rough estimates of the emission time constants of the traps can be extracted by careful analysis of the C(V) characteristics. The fixed charge is positive for all samples, with a density varying between 1.3×1012 and 7.1×1012 cm−2. For the traps, the peak density of interface states is varying between 16×1012 and 31×1012 cm−2 eV−1 for the three samples. It is concluded that, of the deposition methods investigated in this report, the low pressure chemical vapor deposited silicon nitride passivation shows the most promising results with regards to low densities of interface states.
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84.32.Tt Capacitors

Photogating effect as a defect probe in hydrogenated nanocrystalline silicon solar cells

Hongbo B. T. Li (李洪波), Ruud E. I. Schropp, and Francisco A. Rubinelli

J. Appl. Phys. 108, 014509 (2010); http://dx.doi.org/10.1063/1.3437393 (9 pages)

Online Publication Date: 13 July 2010

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The measurement of the spectrally resolved collection efficiency is of great importance in solar cell characterization. Under standard conditions the bias light is a solar simulator or a light source with a similar broadband irradiation spectrum. When a colored blue or red bias light is used instead, an enhanced collection efficiency effect, in the literature known as the photogating effect, can be observed under certain conditions. While most of the published reports on such effect were on solar cells with amorphous silicon based absorber layers, we have shown that the enhanced collection efficiency could be also present in thin film silicon solar cells where hydrogenated nanocrystalline silicon (nc-Si:H) is used as the absorber layer. In this article we present detailed experimental results and simulations aiming at a better understanding of this phenomenon. We show that the collection efficiency is strongly dependent on the intensity of bias light and the intensity of the monochromatic light. These experimental results are consistent with the computer predictions made by our code. We also show that the photogating effect is greatly enhanced when nanocrystalline silicon cells are built with an improperly doped p-layer or with a defective p/i interface region due to the reduced internal electric field present in such cells. The existence of this effect further proves that carrier transport in a nc-Si:H solar cell with an i-layer made close to the phase transition regime is influenced to a large extent by drift transport. The study of this effect is proposed as an alternative approach to gain a deeper understanding about the carrier transport scenarios in thin film solar cells, especially nanocrystalline silicon solar cells.
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88.40.J- Types of solar cells
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.43.Dq Amorphous semiconductors, metals, and alloys
81.05.Gc Amorphous semiconductors
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Surface current reduction in (211) oriented Cd0.46Zn0.04Te.50 crystals by Ar bombardment

L. F. Voss, P. R. Beck, A. M. Conway, R. T. Graff, R. J. Nikolic, A. J. Nelson, and S. A. Payne

J. Appl. Phys. 108, 014510 (2010); http://dx.doi.org/10.1063/1.3459859 (3 pages) | Cited 2 times

Online Publication Date: 14 July 2010

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Cd0.46Zn0.04Te.50 crystals have been exposed to high density Ar plasmas in order to modify the surface chemistry and control the surface conductivity. X-ray photoelectron spectroscopy reveals that this bombardment results in a modified surface atomic ratio, with Cd being preferentially removed compared to Te. In addition, the native oxide is removed and suppressed for an extended period of time. Current-voltage data is analyzed in order to determine the effect on surface leakage current after exposure. It is found that surface leakage current can be decreased by approximately 2.5 orders of magnitude following Ar+ bombardment.
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73.25.+i Surface conductivity and carrier phenomena
79.60.-i Photoemission and photoelectron spectra
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
72.80.Ey III-V and II-VI semiconductors

How to use a nanowire to measure vibrational frequencies: Device simulator results

A. P. Horsfield, Lianheng Tong, Yeong-Ah Soh, and P. A. Warburton

J. Appl. Phys. 108, 014511 (2010); http://dx.doi.org/10.1063/1.3459896 (9 pages)

Online Publication Date: 15 July 2010

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Here we present a theoretical investigation of double well nanowire device that will be studied experimentally over a range of temperatures. Our nanowires are made from InAs with three InP barriers between which lie two InAs quantum wells. These wells have associated with them sharp electronic states between which electrons can tunnel. In the absence of a bias, resonant transmission of electrons is possible; but on applying a bias the levels in neighboring wells acquire different energies, thereby frustrating transmission. If the offset in energy is matched by the frequency of a phonon within the device that couples to the electrons in the wells then there will be a rise in current. We present here the results of simple device simulator calculations, on the basis of which the dimensions of an optimized device are determined.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Temperature and electric field dependent mobility in poly(3-hexylthiophene) diodes

Michele Giulianini, Eric R. Waclawik, John M. Bell, and Nunzio Motta

J. Appl. Phys. 108, 014512 (2010); http://dx.doi.org/10.1063/1.3460111 (4 pages) | Cited 4 times

Online Publication Date: 15 July 2010

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Current-voltage (I-V) curves of poly(3-hexylthiophene) (P3HT) diodes have been collected to investigate the polymer hole-dominated charge transport. At room temperature and at low electric fields the I-V characteristic is purely Ohmic whereas at medium-high electric fields, experimental data shows that the hole transport is trap dominated in the space charge limited current (SCLC) regime. In this regime, it is possible to extract the I-V characteristic of the P3HT/Al junction showing the ideal Schottky diode behavior over five orders of magnitude. At high-applied electric fields, holes’ transport is found to be in the trap free SCLC regime. We have measured and modeled in this regime the holes’ mobility to evaluate its dependence from the electric field applied and the temperature of the device.
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85.30.Kk Junction diodes
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