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10 Sep 2007

Volume 91, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 91, 112501 (2007); http://dx.doi.org/10.1063/1.2780107 (3 pages)

Y. Liu, S. Gliga, R. Hertel, and C. M. Schneider
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Field-programmable rectification in rutile TiO2 crystals

John R. Jameson, Yoshiaki Fukuzumi, Zheng Wang, Peter Griffin, Koji Tsunoda, G. Ingmar Meijer, and Yoshio Nishi

Appl. Phys. Lett. 91, 112101 (2007); http://dx.doi.org/10.1063/1.2769961 (3 pages) | Cited 40 times

Online Publication Date: 10 September 2007

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The authors report “field-programmable rectification” in crystals of rutile TiO2. A “programming” voltage is applied between two Pt electrodes on the surface of a crystal. Afterwards, current can pass in the direction of the programming voltage, but not in the reverse direction. The polarity of the rectification can be reversed by applying a programming voltage of opposite sign. The effect was observed on the (110) and (100) surfaces, but not the (001) surface. The proposed mechanism is field-induced motion of oxygen vacancies, which pile up under the negative terminal, eliminating a Schottky barrier, but leaving one at the positive terminal intact.
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73.40.Ei Rectification
73.30.+y Surface double layers, Schottky barriers, and work functions

Lateral electron tunneling through single self-assembled InAs quantum dots coupled to superconducting nanogap electrodes

Kenji Shibata, Christo Buizert, Akira Oiwa, Kazuhiko Hirakawa, and Seigo Tarucha

Appl. Phys. Lett. 91, 112102 (2007); http://dx.doi.org/10.1063/1.2779970 (3 pages) | Cited 10 times

Online Publication Date: 10 September 2007

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The authors have fabricated superconductor-quantum dot-superconductor (SC-QD-SC) junctions by using SC aluminum electrodes with narrow gaps laterally contacting a single self-assembled InAs QD. The fabricated junctions exhibited clear Coulomb staircases and Coulomb oscillations at 40 mK. Furthermore, clear suppression in conductance was observed for the source-drain voltage, ∣VSD∣<2Δ/e, where Δ is the SC energy gap of Al. The absence of Josephson current that flows through QDs is due to the strong Coulomb interaction and non-negligible thermal fluctuation in our measurement system.
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73.63.Kv Quantum dots
74.50.+r Tunneling phenomena; Josephson effects
74.25.Jb Electronic structure (photoemission, etc.)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

X-ray photoemission spectroscopy determination of the InN/yttria stabilized cubic-zirconia valence band offset

P. D. C. King, T. D. Veal, S. A. Hatfield, P. H. Jefferson, C. F. McConville, C. E. Kendrick, C. H. Swartz, and S. M. Durbin

Appl. Phys. Lett. 91, 112103 (2007); http://dx.doi.org/10.1063/1.2783214 (3 pages) | Cited 6 times

Online Publication Date: 10 September 2007

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The valence band offset of wurtzite InN(0001)/yttria stabilized cubic-zirconia (YSZ)(111) heterojunctions is determined by x-ray photoemission spectroscopy to be 1.19±0.17 eV giving a conduction band offset of 3.06±0.20 eV. Consequently, a type-I heterojunction forms between InN and YSZ in the straddling arrangement. The low lattice mismatch and high band offsets suggest potential for use of YSZ as a gate dielectric in high-frequency InN-based electronic devices.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Direct-current control of radiation-induced differential magnetoresistance oscillations in two-dimensional electron systems

X. L. Lei

Appl. Phys. Lett. 91, 112104 (2007); http://dx.doi.org/10.1063/1.2783260 (3 pages) | Cited 10 times

Online Publication Date: 10 September 2007

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Magnetoresistance oscillations in two-dimensional electron systems driven simultaneously by a strong direct current and a microwave irradiation are analyzed within a unified microscopic scheme treating both excitations on an equal footing. The microwave-induced resistance oscillations are described by a parameter ϵω proportional to the radiation frequency, while the dc-induced resistance oscillations are governed by a parameter ϵj proportional to the current density. In the presence of both a microwave radiation and a strong dc, the combined parameter ϵω+ϵj is shown to control the main resistance oscillations, in agreement with the recent measurement [ Zhang et al., Phys. Rev. Lett. 98, 106804 (2007) ].
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72.20.My Galvanomagnetic and other magnetotransport effects
73.63.-b Electronic transport in nanoscale materials and structures

Effective work function modulation of TaN metal gate on HfO2 after postmetallization annealing

Youhei Sugimoto, Masanari Kajiwara, Keisuke Yamamoto, Yuusaku Suehiro, Dong Wang, and Hiroshi Nakashima

Appl. Phys. Lett. 91, 112105 (2007); http://dx.doi.org/10.1063/1.2783472 (3 pages) | Cited 12 times

Online Publication Date: 10 September 2007

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The effective work function (Φm,eff) of TaN on HfO2 after postmetallization annealing (PMA) was investigated using TaN/HfO2/SiO2/Si as a sample structure. We found that Φm,eff on HfO2 is stable at PMA temperatures of less than 600 °C and is 4.6 eV, which is approximately 0.2 eV higher than that on SiO2. In contrast, Φm,eff is modulated by PMA at temperatures greater than 750 °C. An analysis by x-ray photoelectron spectroscopy suggests that the increased Φm,eff is strongly related to Ta oxide formation near the TaN/HfO2 interface. The modulation of Φm,eff on HfO2 is discussed on the basis of intrinsic and extrinsic Fermi level pinning due to Ta–O bond formation at the TaN/HfO2 interface.
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73.30.+y Surface double layers, Schottky barriers, and work functions
77.55.-g Dielectric thin films
81.40.Gh Other heat and thermomechanical treatments
68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Prostate specific antigen detection using AlGaN/GaN high electron mobility transistors

B. S. Kang, H. T. Wang, T. P. Lele, Y. Tseng, F. Ren, S. J. Pearton, J. W. Johnson, P. Rajagopal, J. C. Roberts, E. L. Piner, and K. J. Linthicum

Appl. Phys. Lett. 91, 112106 (2007); http://dx.doi.org/10.1063/1.2772192 (3 pages) | Cited 19 times

Online Publication Date: 11 September 2007

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Antibody-functionalized Au-gated AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect prostate specific antigen (PSA). The PSA antibody was anchored to the gate area through the formation of carboxylate succinimdyl ester bonds with immobilized thioglycolic acid. The AlGaN/GaN HEMT drain-source current showed a rapid response of less than 5 s when target PSA in a buffer at clinical concentrations was added to the antibody-immobilized surface. The authors could detect a wide range of concentrations from 10 pg/ml to 1 μg/ml. The lowest detectable concentration was two orders of magnitude lower than the cutoff value of PSA measurements for clinical detection of prostate cancer. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN/GaN HEMTs for PSA screening.
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87.80.-y Biophysical techniques (research methods)
85.30.Tv Field effect devices
87.19.X- Diseases

Excellent passivation of highly doped p-type Si surfaces by the negative-charge-dielectric Al2O3

B. Hoex, J. Schmidt, R. Bock, P. P. Altermatt, M. C. M. van de Sanden, and W. M. M. Kessels

Appl. Phys. Lett. 91, 112107 (2007); http://dx.doi.org/10.1063/1.2784168 (3 pages) | Cited 53 times

Online Publication Date: 11 September 2007

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From lifetime measurements, including a direct experimental comparison with thermal SiO2, a-Si:H, and as-deposited a-SiNx:H, it is demonstrated that Al2O3 provides an excellent level of surface passivation on highly B-doped c-Si with doping concentrations around 1019 cm−3. The Al2O3 films, synthesized by plasma-assisted atomic layer deposition and with a high fixed negative charge density, limit the emitter saturation current density of B-diffused p+-emitters to ∼ 10 and ∼ 30 fA/cm2 on >100 and 54 Ω/sq sheet resistance p+-emitters, respectively. These results demonstrate that highly doped p-type Si surfaces can be passivated as effectively as highly doped n-type surfaces.
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81.65.Rv Passivation
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
61.72.S- Impurities in crystals
84.60.Jt Photoelectric conversion

Altering low-bias transport in zigzag-edge graphene nanostrips with edge chemistry

D. Gunlycke, J. Li, J. W. Mintmire, and C. T. White

Appl. Phys. Lett. 91, 112108 (2007); http://dx.doi.org/10.1063/1.2783196 (3 pages) | Cited 43 times

Online Publication Date: 12 September 2007

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Zigzag-edge graphene nanostrips could be terminated with a variety of atoms or functional groups. Presented local-density-functional calculations show that these different species have a significant impact on the electronic structure of these strips near the Fermi level. The terminations covered include hydrogen and oxygen atoms as well as hydroxyl and imine groups. Zigzag-edge nanostrips terminated with hydrogen atoms or hydroxyl groups exhibit spin polarization in equilibrium, while the nanostrips terminated with oxygen or imine groups are unpolarized, leading to much different low-bias transport properties.
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73.63.-b Electronic transport in nanoscale materials and structures
72.25.-b Spin polarized transport
71.20.Mq Elemental semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Boron-doped a-Si:H/c-Si interface passivation: Degradation mechanism

Stefaan De Wolf and Michio Kondo

Appl. Phys. Lett. 91, 112109 (2007); http://dx.doi.org/10.1063/1.2783972 (3 pages) | Cited 17 times

Online Publication Date: 12 September 2007

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The authors report that for a-Si:H/c-Si heterostructure solar cell fabrication the presence of a boron-doped a-Si:H(p+) overlayer may cause H2 effusion from a (few nanometers) thin underlying intrinsic a-Si:H(i) film at moderate temperatures. This phenomenon is in agreement with losses in the electronic passivation quality of c-Si/a-Si:H(i)/a-Si:H(p+) structures occurring during low temperature ( ⩽ 260 °C) postdeposition annealing. Consequently, it is argued that such passivation degradation is due to Si–H rupture in the a-Si:H(i) film, likely resulting in Si dangling bond defects, mediated by the presence of the doped layer.
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81.65.Rv Passivation
84.60.Jt Photoelectric conversion
61.72.Cc Kinetics of defect formation and annealing
71.55.Cn Elemental semiconductors

Donor/acceptor doping and electrical tailoring in ZnO quantum dots

Z. Z. Ye, Y. J. Zeng, Y. F. Lu, S. S. Lin, L. Sun, L. P. Zhu, and B. H. Zhao

Appl. Phys. Lett. 91, 112110 (2007); http://dx.doi.org/10.1063/1.2784198 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2007

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The authors report on donor/acceptor doping in ZnO quantum dots (QDs) grown by a metal-organic chemical vapor deposition method. The Ga donor and N acceptor, as identified by x-ray photoelectron spectroscopy (XPS), are introduced into ZnO QDs. They demonstrate, with a combination of valence band XPS and scanning tunneling microscopy, that the electrical properties as well as Fermi level of the ZnO QDs can be well tuned by the donor/acceptor doping. In addition, photoluminescence from the ZnO QDs with quantum confinement effect is observed.
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73.21.La Quantum dots
79.60.Jv Interfaces; heterostructures; nanostructures
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
73.63.Kv Quantum dots

Control of the electrode work function and active layer morphology via surface modification of indium tin oxide for high efficiency organic photovoltaics

Jong Soo Kim, Jong Hwan Park, Ji Hwang Lee, Jang Jo, Dong-Yu Kim, and Kilwon Cho

Appl. Phys. Lett. 91, 112111 (2007); http://dx.doi.org/10.1063/1.2778548 (3 pages) | Cited 51 times

Online Publication Date: 13 September 2007

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Indium tin oxide (ITO) substrates modified with self-assembled monolayers (SAMs) were used to control the anode work function and active layer morphology of organic solar cells based on poly(3-hexylthiophene)/[6:6]-phenyl-C61 butyric acid methyl ester heterojunctions. By using SAMs with the terminal groups –NH2, –CH3, and –CF3, the authors were able to control the hole injection barrier of the ITO closer to the highest occupied molecular orbital level of active layer and surface energy of the ITO substrate. A solar cell device with CF3 SAM treated ITO was found to exhibit high efficiency performance, about 3.15%.
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84.60.Jt Photoelectric conversion

Effective passivation of highly aluminum-doped p-type silicon surfaces using amorphous silicon

Robert Bock, Jan Schmidt, and Rolf Brendel

Appl. Phys. Lett. 91, 112112 (2007); http://dx.doi.org/10.1063/1.2784193 (3 pages) | Cited 10 times

Online Publication Date: 13 September 2007

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Highly aluminum-doped p-type emitters prepared by screen printing on crystalline silicon wafers are effectively passivated by plasma-enhanced chemical-vapor deposited amorphous silicon layers. Using the photoconductance decay technique, the authors measure emitter saturation current densities of 800±200 fA/cm2 for nonpassivated emitters and of 490±120 fA/cm2 for Al-p+ emitters passivated with a 20 nm thick amorphous silicon layer deposited at 225 °C. An additional annealing step at 300 °C for 10 min reduces the emitter saturation current density down to only 246±60 fA/cm2. The measured saturation current densities are the lowest values achieved so far for Al-doped p+ emitter.
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85.30.-z Semiconductor devices
85.40.Sz Deposition technology

Growth parameter-property phase diagram for pulsed laser deposited transparent oxide conductor anatase Nb:TiO2

S. X. Zhang, S. Dhar, W. Yu, H. Xu, S. B. Ogale, and T. Venkatesan

Appl. Phys. Lett. 91, 112113 (2007); http://dx.doi.org/10.1063/1.2785152 (3 pages) | Cited 24 times

Online Publication Date: 14 September 2007

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The authors performed a systematic study of the structural and electrical properties of Nb:TiO2 thin films by varying the substrate temperature (TS) and oxygen partial pressure (PO2). Niobium is found to incorporate easily and substitutionally into titanium lattice site as indicated by its low activation energy. By increasing TS, the carrier concentration (n) increases in the same way that niobium substitution fraction (s) increases, and the mobility increases as the structural quality is improved. With increasing PO2, n decreases dramatically though s does not change considerably. This may indicate that a large number of p-type native defects form, which “kill” the electrons produced by the Nb donors.
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68.55.-a Thin film structure and morphology
73.61.Ng Insulators
81.15.Fg Pulsed laser ablation deposition
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
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