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15 Aug 2007

Volume 102, Issue 4, Articles (04xxxx)

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N-polar GaN/AlGaN/GaN high electron mobility transistors

Siddharth Rajan, Alessandro Chini, Man Hoi Wong, James S. Speck, and Umesh K. Mishra

J. Appl. Phys. 102, 044501 (2007); http://dx.doi.org/10.1063/1.2769950 (6 pages) | Cited 52 times

Online Publication Date: 17 August 2007

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We describe the development of N-polar GaN-based high electron mobility transistors grown by N2 plasma-assisted molecular beam epitaxy on C-face SiC substrates. High mobility AlGaN/GaN modulation-doped two-dimensional electron gas channels were grown, and transistors with excellent dc and small-signal performance were fabricated on these wafers. Large-signal dispersion was observed, and the trap states responsible for this were identified, and layer designs to remove the dispersive effects of these traps were demonstrated. Finally, an AlGaN-cap layer was used to reduce gate leakage in these devices, and a low-dispersion high breakdown voltage device was achieved. This detailed study of dispersion and leakage in N-polar GaN-based transistors establishes a technological base for further development of field effect devices based on N-polar III-nitrides.
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85.30.Tv Field effect devices

The effect of diffusion-limited lifetime on implied current voltage curves based on photoluminescence data

M. D. Abbott, R. A. Bardos, T. Trupke, K. C. Fisher, and E. Pink

J. Appl. Phys. 102, 044502 (2007); http://dx.doi.org/10.1063/1.2756529 (7 pages) | Cited 3 times

Online Publication Date: 17 August 2007

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Quasi-steady-state photoconductance measurements and Suns-photoluminescence are useful techniques in predicting the electrical terminal characteristics of partially finished solar cells in contactless mode even prior to the junction formation. In both techniques, a measured average minority carrier density in the bulk is correlated with the carrier density at the edge of the junction and thereby with an implied voltage. This paper discusses experimental artifacts in such experiments that can be caused by the diffusion-limited effective minority carrier lifetime. Here these effects are discussed theoretically and demonstrated experimentally in relation to the Suns-photoluminescence technique only, because the range of implied voltages that is affected is generally not accessible via photoconductance measurements. A simple technique is proposed to correct the curves and increase the range of voltages measured accurately by the Suns-photoluminescence technique. It is concluded that the influence of diffusion-limited lifetime must be considered when interpreting Suns-photoluminescence curves, particularly in samples with a surface that is passivated by a shunted junction.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
84.60.Jt Photoelectric conversion

Influence of source-drain electric field on mobility and charge transport in organic field-effect transistors

B. H. Hamadani, C. A. Richter, D. J. Gundlach, R. J. Kline, I. McCulloch, and M. Heeney

J. Appl. Phys. 102, 044503 (2007); http://dx.doi.org/10.1063/1.2769782 (7 pages) | Cited 15 times

Online Publication Date: 21 August 2007

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We report on a strong field-dependent mobility in organic field-effect transistors fabricated by using poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT-C14) as the active polymer layer. Charge transport and mobilities in devices annealed in the mesophase show a more pronounced dependence on channel length as compared with as-cast devices. Analysis reveals that the contact effects in both sets of devices are negligible from room temperature down to ≈ 100 K. We show that this field dependence is consistent with a Poole-Frenkel model of mobility. Finally, the nonlinear transport data for short channel devices are modeled consistently in the Poole-Frenkel framework over a broad temperature range.
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85.30.Tv Field effect devices

Eight logic states of tunneling magnetoelectroresistance in multiferroic tunnel junctions

F. Yang, M. H. Tang, Z. Ye, Y. C. Zhou, X. J. Zheng, J. X. Tang, J. J. Zhang, and J. He

J. Appl. Phys. 102, 044504 (2007); http://dx.doi.org/10.1063/1.2768075 (5 pages) | Cited 20 times

Online Publication Date: 22 August 2007

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We propose a theoretical model based on the concept of multiferroic tunnel junction. The model is capable of producing eight different logic states by combining the spin-filter effect and the screening of polarization charges between two electrodes through a general spintronic tunneling. The dependence of the conductance ratio with very large magnitude on electric polarization, exchange splitting, barrier width, and bias voltage is investigated. The result may provide some insights into the realization of octal data storage (namely, the eight different logic states are used as octal code), which could lead to the tremendous increase of memory storage density.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity
72.25.-b Spin polarized transport

Effect of growth temperature on defect states of GaAsSbN intrinsic layer in GaAs/GaAsSbN/GaAs photodiode for 1.3 μm application

S. Wicaksono, S. F. Yoon, W. K. Loke, K. H. Tan, K. L. Lew, M. Zegaoui, J. P. Vilcot, D. Decoster, and J. Chazelas

J. Appl. Phys. 102, 044505 (2007); http://dx.doi.org/10.1063/1.2769801 (7 pages) | Cited 18 times

Online Publication Date: 23 August 2007

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A GaAsSbN layer closely lattice matched to GaAs was used as an intrinsic layer (i layer) in a GaAs/GaAsSbN/GaAs p-i-n photodiode with response up to 1.3 μm. Deep level transient spectroscopy measurement on the GaAs/GaAsSbN/GaAs reveals two types of hole traps (HTs) in the GaAsSbN i layer; (i) HT1: a shallow N-related defect state (Ea ∼ 0.10–0.12 eV) and (ii) HT2: an AsGa point defect-related midgap defect state with Ea ∼ 0.42–0.43 eV. Reduction in growth temperature from 480 to 420 °C reduces the HT2 trap concentration from 4×1015 to 1×1015 cm−3, while increases the HT1 trap concentration from 1×1014 to 7×1014 cm−3. Reduction in the HT2 trap concentration following growth temperature reduction was attributed to the suppression of AsGa point defect formation. Evidence of possible change of the AsGa midgap state to a shallow level defect due to the formation of (AsGa–NAs) pairs was also suggested to have increased the HT1 trap concentration and reduced the HT2 trap concentration. An ∼ 4 dBm improvement in photoresponse under 1.3 μm laser excitation and approximately eight times reduction in dark current at −8 V reverse bias were attributed to the reduction in the overall trap concentration and mainly the reduction of the AsGa-related midgap trap concentration in the sample grown at 420 °C.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Theoretical analysis of breakdown probabilities and jitter in single-photon avalanche diodes

S. L. Tan, D. S. Ong, and H. K. Yow

J. Appl. Phys. 102, 044506 (2007); http://dx.doi.org/10.1063/1.2772531 (7 pages) | Cited 4 times

Online Publication Date: 24 August 2007

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A simple random ionization path length model is used to investigate the breakdown probabilities and jitter in single photon avalanche diodes (SPADs) with submicron multiplication widths. The simulation results show that increasing the multiplication width may not necessarily increase the breakdown probability relative to the breakdown voltage, as the effect of dead space becomes more dominant in thinner multiplication regions at realistic ionization threshold energies for GaAs. On the other hand, reducing the multiplication width results in smaller breakdown time and jitter, despite the increased dead space. The effect of dead space in degrading breakdown time and jitter is relatively weak and further compensated by the stronger influence of large feedback ionization at high fields. Thus, SPAD designs that can minimize the dark count rate may potentially benefit from enhanced breakdown probability, breakdown time, and jitter by reducing the thickness of the multiplication region.
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85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling

Thermal stability of molecularly functionalized mesoporous silica thin films

A. P. Singh, D. D. Gandhi, R. Moore, and G. Ramanath

J. Appl. Phys. 102, 044507 (2007); http://dx.doi.org/10.1063/1.2771042 (4 pages) | Cited 1 time

Online Publication Date: 27 August 2007

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We report the stability of ordered mesoporous silica (MPS) thin films functionalized with mercaptan- and cyanide-terminated organosilanes upon annealing at temperatures up to 500 °C in vacuum, nitrogen, and air. Electron spectroscopy analyses indicate that the molecules are attached to the surfaces of the films as well as the pores inside the films. The cyanide-functionalized MPS films are stable up to 500 °C in vacuum, N2, and air ambient. In contrast, mercaptan-functionalized MPS films are stable only up to 400 °C in vacuum due to the higher reactivity of mercaptan with oxygen. Our results provide insights into effects of temperature and gas environments on the properties of molecularly functionalized porous dielectrics, and would be important considerations for developing new options for interlayer electrical isolation of nanodevice wiring.
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68.60.Dv Thermal stability; thermal effects
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.43.Gt Powders, porous materials
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
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