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19 Apr 2004

Volume 84, Issue 16, pp. 2971-3207

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3139 (2004); http://dx.doi.org/10.1063/1.1710717 (3 pages)

Slava V. Rotkin and Karl Hess
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Phosphorescence of aluminum tris(quinoline-8-olate)

M. Cölle and C. Gärditz

Appl. Phys. Lett. 84, 3160 (2004); http://dx.doi.org/10.1063/1.1711185 (3 pages) | Cited 29 times

Online Publication Date: 13 April 2004

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Phosphorescence from an aluminum tris(quinoline-8-olate) (Alq3)-based organic light-emitting diode was observed by measuring the delayed electroluminescence at low temperatures. The spectra as well as the transient intensities were investigated. Vibronic progressions of the phosphorescence (T1→S0 transition) were resolved and the triplet energy of Alq3 was measured to be 2.05±0.1 eV. The lifetimes of the triplet state were determined from the delayed fluorescence as well as from the phosphorescence decay to be 8.1±0.5, 7.0±0.5, and 5.6±0.5 ms at 30, 50, and 80 K, respectively. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

Anomalous hot-carrier-induced degradation of offset gated polycrystalline silicon thin-film transistors

A. Hatzopoulos, C. A. Dimitriadis, G. Pananakakis, G. Ghibaudo, and G. Kamarinos

Appl. Phys. Lett. 84, 3163 (2004); http://dx.doi.org/10.1063/1.1707222 (3 pages)

Online Publication Date: 13 April 2004

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Hot-carrier effects in offset gated n-channel polycrystalline silicon thin-film transistors of channel length L = 10 μm and intrinsic offset lengths ΔL = 0.5 and 1 μm are investigated. The gate- and drain-bias conditions for maximum device degradation were determined from substrate current measurements. The experimental data show that hot-carrier stress provokes an anomalous threshold voltage and on-state current degradation, exhibiting a “staircase-like” degradation with stress time. These results lead to the conclusion that, at the initial stages of stress, a small offset region from the drain end is damaged due to charging of the grain boundaries. As the stress proceeds further and the grain boundary traps are filled with electrons generated by impact ionization, the damage is transferred to the neighboring offset region, resulting in a staircase-like degradation of the device parameters with stress time. © 2004 American Institute of Physics.
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81.05.Cy Elemental semiconductors
85.30.Tv Field effect devices
61.72.Mm Grain and twin boundaries
73.50.Fq High-field and nonlinear effects

Remote collection and measurement of photogenerated carriers swept by surface acoustic waves in GaN

T. Palacios, F. Calle, and J. Grajal

Appl. Phys. Lett. 84, 3166 (2004); http://dx.doi.org/10.1063/1.1711172 (3 pages) | Cited 9 times

Online Publication Date: 13 April 2004

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The interaction of surface acoustic waves and photogenerated carriers in GaN has been used for the fabrication of a remote ultraviolet detector where the carrier collector electrode is far away from the illuminated region. In this device, the recombination of the photogenerated carriers at the region where they are created is prevented by the potential fields associated with the acoustic wave, and the carriers are swept by the acoustic wave to the collector electrode. This effect is strongly dependent on the frequency and power of the acoustic waves and therefore of the input radio frequency signal. New optoelectronic devices based on the combination of the acoustic and electronic properties of the semiconductors can be envisaged. © 2004 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
68.35.Iv Acoustical properties
43.35.Pt Surface waves in solids and liquids
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Diagnostics of doping integrity in n+/p/n+ transistor-channel structure by scanning nonlinear dielectric microscopy

Takashi Matsukawa, Chiaki Yasumuro, Meishoku Masahara, Hisao Tanoue, and Seigo Kanemaru

Appl. Phys. Lett. 84, 3169 (2004); http://dx.doi.org/10.1063/1.1707224 (3 pages) | Cited 5 times

Online Publication Date: 13 April 2004

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Scanning nonlinear dielectric microscopy was used to diagnose doping integrity in a transistor channel. The carrier state at various points in a pn junction was defined as n-type, p-type, or depletion through nonlinear capacitance (dC/dV) profiling and pinpoint capacitance–voltage analysis. Carrier state analysis was applied to the n+/p/n+ transistor channel of structures with different process parameters. An increase in the n+ activation temperature from 800 to 950 °C caused shrinkage in channel length of the p-type region. Decreasing the substrate acceptor concentration from 1018 to 1017 cm−3 caused depletion of the entire channel when the gate length was less than 200 nm. © 2004 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.37.-d Microscopy of surfaces, interfaces, and thin films
71.55.Cn Elemental semiconductors
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Extension of Coulomb blockade region by quantum confinement in the ultrasmall silicon dot in a single-hole transistor at room temperature

Masumi Saitoh and Toshiro Hiramoto

Appl. Phys. Lett. 84, 3172 (2004); http://dx.doi.org/10.1063/1.1710709 (3 pages) | Cited 26 times

Online Publication Date: 13 April 2004

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First room-temperature (RT) observation of extended Coulomb blockade (CB) region due to quantum confinement in the ultrasmall silicon dot in a single-hole transistor (SHT) is described. We fabricate single-dot SHTs in the form of metal-oxide-semiconductor field-effect transistors with an extremely constricted channel. Both large CB oscillation with the peak-to-valley current ratio (PVCR) of 40.4 and clear negative differential conductance (NDC) with the PVCR of 11.8 (highest ever reported) are observed at RT in the fabricated device. The observed NDC is attributable to the resonant tunneling due to the large quantum level spacing in the ultrasmall dot whose size is estimated to be about 2 nm. © 2004 American Institute of Physics.
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85.35.Gv Single electron devices
85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Band alignment at the i-ZnO/CdS interface in Cu(In,Ga)(S,Se)2 thin-film solar cells

L. Weinhardt, C. Heske, E. Umbach, T. P. Niesen, S. Visbeck, and F. Karg

Appl. Phys. Lett. 84, 3175 (2004); http://dx.doi.org/10.1063/1.1704877 (3 pages) | Cited 14 times

Online Publication Date: 13 April 2004

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The interface between the i-ZnO layer and the CdS buffer in Cu(In,Ga)(S,Se)2 thin-film solar cells from the Shell Solar baseline process has been investigated using ultraviolet- and x-ray photoelectron spectroscopy and inverse photoemission. Combining both techniques, a direct determination of the conduction and valence band offsets at the interface is possible. Different from existing models, we find a flat conduction band alignment (i.e., a conduction band offset of 0.10±0.15 eV), ∼ 0.5 eV above the Fermi level, and a valence band offset of 0.96±0.15 eV. © 2004 American Institute of Physics.
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84.60.Jt Photoelectric conversion
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Nr Semiconductor compounds
78.70.-g Interactions of particles and radiation with matter

Coulomb oscillations based on band-to-band tunneling in a degenerately doped silicon metal-oxide-semiconductor field-effect transistor

Kyung Rok Kim, Dae Hwan Kim, Jong Duk Lee, and Byung-Gook Park

Appl. Phys. Lett. 84, 3178 (2004); http://dx.doi.org/10.1063/1.1707217 (3 pages) | Cited 1 time

Online Publication Date: 13 April 2004

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We report Coulomb oscillations based on band-to-band tunneling through a valence band in silicon metal-oxide-semiconductor field-effect transistors. Degenerately p+-doped channel and n+-doped source/drain enables band-to-band tunneling, which can play a major role in the transport between the channel and source/drain. The formation of tunnel barriers and a quantum dot in a single-electron transistor structure originates from two p+–n+ tunnel junctions and a p+-doped channel with mesoscopic dimension, respectively. Coulomb-blockade oscillations with multiple peaks were clearly observed at liquid nitrogen temperature. Using the electrical and thermal characterization of the quantum dot, single-electron charging effect based on band-to-band tunneling is confirmed. © 2004 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.63.Kv Quantum dots
85.30.Tv Field effect devices
71.20.Mq Elemental semiconductors
85.35.Gv Single electron devices
61.72.uf Ge and Si

Enhanced efficiency of plastic photovoltaic devices by blending with ionic solid electrolytes

Fang-Chung Chen, Qianfei Xu, and Yang Yang

Appl. Phys. Lett. 84, 3181 (2004); http://dx.doi.org/10.1063/1.1710712 (3 pages) | Cited 15 times

Online Publication Date: 13 April 2004

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One of the major technology bottlenecks of polymer photovoltaic cells is the low photoinduced current, due to the low carrier mobility and short exciton migration distance. In this letter we demonstrated that the electric current for polymer PV cells can be significantly enhanced by adding a small amount of ionic solid electrolyte. Heterojunction polymer photovoltaic devices, consisting of poly[2-methoxy-5-(2′-ethyl-hexyoxy)-1,4-phenylene vinylene] (MEH-PPV) C60 and/or methanofullerene([6,6]-phenyl C61-butyric acid methyl ester) (PCBM) as the active materials, were fabricated. It has been found that the power efficiency of the organic was enhanced by blending ionic solid electrolyte, such as polyethylene oxide into the active layer. It is believed that the optimized polymer morphology, the improved electrical conductivity, and the in situ photodoping of MEH-PPV contribute to this enhancement of photovoltaic efficiency. © 2004 American Institute of Physics.
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84.60.Jt Photoelectric conversion
72.80.Le Polymers; organic compounds (including organic semiconductors)
85.60.-q Optoelectronic devices
72.20.Fr Low-field transport and mobility; piezoresistance
82.45.Gj Electrolytes
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Bias-induced threshold voltages shifts in thin-film organic transistors

H. L. Gomes, P. Stallinga, F. Dinelli, M. Murgia, F. Biscarini, D. M. de Leeuw, T. Muck, J. Geurts, L. W. Molenkamp, and V. Wagner

Appl. Phys. Lett. 84, 3184 (2004); http://dx.doi.org/10.1063/1.1713035 (3 pages) | Cited 83 times

Online Publication Date: 13 April 2004

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An investigation into the stability of metal-insulator-semiconductor (MIS) transistors based on α-sexithiophene is reported. In particular, the kinetics of the threshold voltage shift upon application of a gate bias has been determined. The kinetics follow stretched-hyperbola-type behavior, in agreement with the formalism developed to explain metastability in amorphous-silicon thin-film transistors. Using this model, quantification of device stability is possible. Temperature-dependent measurements show that there are two processes involved in the threshold voltage shift, one occurring at T ≈ 220 K and the other at T ≈ 300 K. The latter process is found to be sample dependent. This suggests a relation between device stability and processing parameters. © 2004 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
85.30.Tv Field effect devices
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