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8 Mar 2004

Volume 84, Issue 10, pp. 1623-1807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1798 (2004); http://dx.doi.org/10.1063/1.1664019 (3 pages)

Bartosz A. Grzybowski, Michal Radkowski, Christopher J. Campbell, Jessamine Ng Lee, and George M. Whitesides
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Reduction of positional errors in a four-point probe resistance measurement

D. C. Worledge

Appl. Phys. Lett. 84, 1695 (2004); http://dx.doi.org/10.1063/1.1655697 (3 pages) | Cited 4 times

Online Publication Date: 2 March 2004

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A method for reducing resistance errors due to inaccuracy in the positions of the probes in a collinear four-point probe resistance measurement of a thin film is presented. By using a linear combination of two measurements which differ by interchange of the I− and V− leads, positional errors can be eliminated to first order. Experimental data measured using microprobes show a substantial reduction in absolute error from 3.4% down to 0.01%–0.1%, and an improvement in precision by a factor of 2–4. The application of this technique to the current-in-plane tunneling method to measure electrical properties of unpatterned magnetic tunnel junction wafers is discussed. © 2004 American Institute of Physics.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.68.+m Photography, photographic instruments; xerography

Sensitivity of Pt/ZnO Schottky diode characteristics to hydrogen

Suku Kim, B. S. Kang, F. Ren, K. Ip, Y. W. Heo, D. P. Norton, and S. J. Pearton

Appl. Phys. Lett. 84, 1698 (2004); http://dx.doi.org/10.1063/1.1664012 (3 pages) | Cited 10 times

Online Publication Date: 2 March 2004

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Pt/ZnO Schottky diodes show changes in forward current of 0.3 mA at a forward bias of 0.5 V or alternatively a change of 50 mV bias at a fixed forward current of 8 mA when 5 ppm of H2 is introduced into a N2 ambient at 25 °C. The rectifying current–voltage (I–V) characteristic shows a nonreversible collapse to Ohmic behavior when as little as 50 ppm of H2 is present in the N2 ambient. At higher temperatures, the recovery is thermally activated with an activation energy of ∼ 0.25 eV. This suggests that introduction of hydrogen shallow donors into the ZnO is a contributor to the change in current of the diodes. © 2004 American Institute of Physics.
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85.30.Kk Junction diodes
72.80.Ey III-V and II-VI semiconductors
73.40.Ns Metal-nonmetal contacts

Correlation between photoelectric and optical absorption spectra of thermally evaporated pentacene films

Jiyoul Lee, S. S. Kim, Kibum Kim, Jae Hoon Kim, and Seongil Im

Appl. Phys. Lett. 84, 1701 (2004); http://dx.doi.org/10.1063/1.1668328 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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We have measured the spectral photoresponse of Al/pentacene Schottky junction photodiodes and optical absorption spectra of pentacene films thermally evaporated on glass. The photoelectric response exhibited the genuine highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition at 1.97 eV and interband absorption peaks at 2.3 and 2.5 eV. These peaks are also identified in the optical absorption spectra, but they are dominated by additional strong exciton peaks at 1.82 and 2.1 eV. By comparing these complementary measurements, we determine the HOMO–LUMO gap energy of 1.97 eV and the fundamental exciton binding energy of 0.15 eV for thin solid pentacene. © 2004 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.40.Fy Semiconductors

Bistable defect in mega-electron-volt proton implanted 4H silicon carbide

D. M. Martin, H. Kortegaard Nielsen, P. Lévêque, A. Hallén, G. Alfieri, and B. G. Svensson

Appl. Phys. Lett. 84, 1704 (2004); http://dx.doi.org/10.1063/1.1651656 (3 pages) | Cited 12 times

Online Publication Date: 2 March 2004

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Epitaxial 4H-SiC n-type layers implanted at room temperature with a low fluence of mega-electron-volt protons have been measured by deep level transient spectroscopy (DLTS). The proton fluence of 1×1012 cm−2 creates an estimated initial concentration of intrinsic point defects of about 1014 cm−3 of which about 10% remain after the implantation and gives rise to deep states in the upper part of the band gap. Here, we investigate the samples prior to high-temperature annealing and a very complex spectrum is revealed. In particular, a bistable defect M is discovered having two DLTS peaks, M1 and M3 at EC−0.42 and around EC−0.75 eV, respectively, in one configuration and one peak, M2 at EC−0.70 eV in the other configuration. The charge dependent thermal activation energies for the transformation between the bistable defect peaks are 0.90 and 1.40 eV. © 2004 American Institute of Physics.
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61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

On the superlinear increase in conductivity with dopant concentration in excitonic semiconductors

Brian A. Gregg, Si-Guang Chen, and Howard M. Branz

Appl. Phys. Lett. 84, 1707 (2004); http://dx.doi.org/10.1063/1.1668326 (3 pages) | Cited 11 times

Online Publication Date: 2 March 2004

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We show that the same factors that cause exciton formation in organic (excitonic) semiconductors, the low dielectric constant and the localized wave functions of the charge carriers, also control their doping processes. We compare doping in organic and inorganic semiconductors and show that the superlinear increase in conductivity with doping density should be a universal characteristic of excitonic semiconductors. The binding energy of the dopant electron to its conjugate cation in highly ordered perylene diimide films controls the free carrier density. The binding energy decreases with increasing dopant concentration because the neutral dopants increase the polarizability of the film. © 2004 American Institute of Physics.
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77.22.Ej Polarization and depolarization
72.80.Le Polymers; organic compounds (including organic semiconductors)
73.61.Ph Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)

Low-resistance Pt/Pd/Au ohmic contacts to p-type AlGaN

Han-Ki Kim, Tae-Yeon Seong, Ilesanmi Adesida, Chak Wah Tang, and Kei May Lau

Appl. Phys. Lett. 84, 1710 (2004); http://dx.doi.org/10.1063/1.1668331 (3 pages) | Cited 8 times

Online Publication Date: 2 March 2004

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We report on a Pt/Pd/Au metallization scheme for producing low-resistance ohmic contacts to moderately doped p-AlGaN:Mg (1.5×1017 cm−3). Annealed Pt/Pd/Au contact exhibits linear current–voltage characteristics, showing that a high-quality ohmic contact is formed. The Pt/Pd/Au contact exhibits a specific contact resistivity of 3.1×10−4 Ω cm2 when annealed at 600 °C for 1 min in a flowing N2 atmosphere. Using Auger electron spectroscopy and x-ray photoelectron spectroscopy, a preliminary explanation for ohmic contact formation is described. © 2004 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
79.20.Fv Electron impact: Auger emission

EL2-related metastable defects in semi-insulating GaAs

D. Kabiraj and Subhasis Ghosh

Appl. Phys. Lett. 84, 1713 (2004); http://dx.doi.org/10.1063/1.1667617 (3 pages) | Cited 7 times

Online Publication Date: 2 March 2004

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Thermally stimulated current spectroscopy, photoquenching, and photorecovery have been used to reveal the EL2-related metastable defect levels in semi-insulating GaAs. It has been found that one set of metastable levels is directly related to EL2 and the other set is indirectly related to EL2 defect through charge transfer. The origin of these EL2-related metastable levels has been discussed in the context of recently proposed three-center-complex model of EL2 in semi-insulating GaAs. © 2004 American Institute of Physics.
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71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.05.Ea III-V semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Surface depletion in doped SrTiO3 thin films

A. Ohtomo and H. Y. Hwang

Appl. Phys. Lett. 84, 1716 (2004); http://dx.doi.org/10.1063/1.1668329 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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Strong effects of surface depletion have been observed in metallic La-doped SrTiO3 thin films grown on SrTiO3 substrates by pulsed-laser deposition. The depletion layer grows with decreasing temperature due to the large temperature-dependent dielectric response of SrTiO3. When the depletion layer becomes comparable to or exceeds the thickness of the doped film, the Hall mobility shows significant enhancements as more of the electron distribution extends into the undoped substrate, in conceptual analogy to modulation doping in compound semiconductor heterostructures. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
73.61.Ng Insulators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Fg Pulsed laser ablation deposition
72.20.Ee Mobility edges; hopping transport
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