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17 Nov 2008

Volume 93, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 93, 201101 (2008); http://dx.doi.org/10.1063/1.3025818 (3 pages)

W. Dai and C. M. Soukoulis
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Experimental determination of valence band offset at PbTe/CdTe(111) heterojunction interface by x-ray photoelectron spectroscopy

Jianxiao Si, Shuqiang Jin, Hanjie Zhang, Ping Zhu, Dongjiang Qiu, and Huizhen Wu

Appl. Phys. Lett. 93, 202101 (2008); http://dx.doi.org/10.1063/1.3028028 (3 pages) | Cited 6 times

Online Publication Date: 17 November 2008

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Lattice-matched PbTe/CdTe(111) heterojunction interfaces were studied using x-ray photoelectron spectroscopy. A type-I band alignment with a valence band offset of ΔEV = 0.135±0.05 eV and a conduction band offset of ΔEC = 1.145±0.05 eV is concluded. Within experimental error the determined valence band offset is in agreement with theoretical prediction by inclusion of spin-orbit interaction.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Advanced luminescence based effective series resistance imaging of silicon solar cells

H. Kampwerth, T. Trupke, J. W. Weber, and Y. Augarten

Appl. Phys. Lett. 93, 202102 (2008); http://dx.doi.org/10.1063/1.2982588 (3 pages) | Cited 19 times

Online Publication Date: 18 November 2008

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A technique for fast and spatially resolved measurement of the effective series resistance of silicon solar cells from luminescence images is introduced. Without compromising the speed of existing luminescence based series resistance imaging methods, this method offers significant advantages in that it is more robust against variations in local diode characteristics. Lateral variations in the series resistance of an industrial screen printed multicrystalline silicon solar cell obtained from this method show excellent correlation with a Corescan measurement and are also shown to be unaffected by lateral variations in the diode properties.
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84.60.Jt Photoelectric conversion

Low specific contact resistance of heavily phosphorus-doped diamond film

Hiromitsu Kato, Hitoshi Umezawa, Norio Tokuda, Daisuke Takeuchi, Hideyo Okushi, and Satoshi Yamasaki

Appl. Phys. Lett. 93, 202103 (2008); http://dx.doi.org/10.1063/1.3005639 (3 pages) | Cited 15 times

Online Publication Date: 18 November 2008

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Low resistive contacts were formed on heavily phosphorus-doped diamond (n+) films with phosphorus concentration of over ∼ 1020 cm−3 grown on (111) diamond substrates by microwave plasma enhanced chemical vapor deposition with precise control of growth conditions. The specific contact resistance was determined by characterizing the current-voltage relations by means of transfer length method. It was found that the resistance of Ti/n+ contact was significantly reduced down to the order of ∼ 10−3 Ω cm2 even at room temperature, which indicates that the barrier width would be narrow for tunneling through the barrier to take place by heavy phosphorus doping.
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73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling
61.72.up Other materials
73.40.Ns Metal-nonmetal contacts
81.05.U- Carbon/carbon-based materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Polarization-induced two-dimensional electron gases in ZnMgO/ZnO heterostructures

H. Tampo, H. Shibata, K. Maejima, A. Yamada, K. Matsubara, P. Fons, S. Kashiwaya, S. Niki, Y. Chiba, T. Wakamatsu, and H. Kanie

Appl. Phys. Lett. 93, 202104 (2008); http://dx.doi.org/10.1063/1.3028338 (3 pages) | Cited 19 times

Online Publication Date: 18 November 2008

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Both the formation mechanism and the origin of the two-dimensional electron gas (2DEG) in ZnMgO/ZnO heterostructures have been investigated. The 2DEG in the heterostructures was confirmed to originate from polarization-induced charge and was found to be dominant for transport at low temperatures as well as room temperature (RT) by transport measurements. The origin of 2DEG was concluded to be the surface of the ZnMgO layer based on both capacitance-voltage measurements and the dependence of the carrier concentration on the ZnMgO layer thickness. The largest sheet carrier concentration was 1.1×1013 cm−2 and the highest mobility for the heterostructure was obtained for a Mg composition of 0.61 at RT.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors

Alleviation of Fermi-level pinning effect on metal/germanium interface by insertion of an ultrathin aluminum oxide

Yi Zhou, Masaaki Ogawa, Xinhai Han, and Kang L. Wang

Appl. Phys. Lett. 93, 202105 (2008); http://dx.doi.org/10.1063/1.3028343 (3 pages) | Cited 36 times

Online Publication Date: 18 November 2008

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Due to the strong Fermi-level pinning close to the germanium (Ge) valence band edge, all metal/p-type Ge contacts show Ohmic characteristics, while metal/n-type Ge contacts exhibit rectifying behaviors. In this paper, we report a simple method to alleviate this Fermi-level pinning effect by inserting a thin layer of aluminum oxide (Al2O3), formed by oxidation of aluminum (Al), between the metal/Ge interface. The effective Schottky barrier heights of nickel (Ni)/n-type Ge, cobalt (Co)/n-type Ge, and iron (Fe)/n-type Ge decrease from 0.54, 0.62, and 0.61 eV to 0.39, 0.23, and 0.18 eV, respectively, with this thin layer of Al2O3. The tunneling oxide significantly suppresses the Fermi-level pinning, and yet does not restrict the current density. This method seems promising to realize low resistance metal contact to n-type Ge, which is essential to realize n-channel Ge complementary metal-oxide-semiconductor field-effect transistor with metal source and drain.
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73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ei Rectification
85.30.Tv Field effect devices
73.40.Gk Tunneling

Synthesis and transport property of AgSbTe2 as a promising thermoelectric compound

Heng Wang, Jing-Feng Li, Minmin Zou, and Tao Sui

Appl. Phys. Lett. 93, 202106 (2008); http://dx.doi.org/10.1063/1.3029774 (3 pages) | Cited 19 times

Online Publication Date: 18 November 2008

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Polycrystalline AgSbTe2 ternary compound materials with high phase purity were fabricated using a combined process of mechanical alloying and spark plasma sintering. It was found that stoichiometric AgSbTe2 is a promising composition for low-and-mediate temperature applications, whose ZT reaches 1.59 at 673 K, benefiting from its extremely low thermal conductivity (0.30 W/mK) in addition to its low electrical resistivity (<1.1×10−4 Ω m) and large positive Seebeck coefficient (260 μV/K). On the other hand, deviating from this formula would lead to unstable phase structures and higher thermal conductivity, which make the samples less attractive as thermoelectric materials or components of thermoelectric systems.
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72.20.Pa Thermoelectric and thermomagnetic effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Hd Other semiconductors
81.05.Mh Cermets, ceramic and refractory composites

Epitaxial growth of high mobility Cu2O thin films and application to p-channel thin film transistor

Kosuke Matsuzaki, Kenji Nomura, Hiroshi Yanagi, Toshio Kamiya, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 93, 202107 (2008); http://dx.doi.org/10.1063/1.3026539 (3 pages) | Cited 26 times

Online Publication Date: 20 November 2008

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Cu2O epitaxial films were grown for high mobility p-channel oxide thin-film transistors (TFTs). The use of a (110) MgO surface and fine tuning of a growth condition produced single phase epitaxial films with hole Hall mobilities ∼ 90 cm2 V−1 s−1 comparable to those of single crystals ( ∼ 100 cm2 V−1 s−1). TFTs using the epitaxial film channels exhibited p-channel operation although the field-effect mobilities and the on-to-off current ratio were not yet satisfactory ( ∼ 0.26 cm2 V−1 s−1 and ∼ 6, respectively).
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81.15.Fg Pulsed laser ablation deposition
68.55.ag Semiconductors
85.30.Tv Field effect devices

Valence band offset of the ZnO/AlN heterojunction determined by x-ray photoemission spectroscopy

T. D. Veal, P. D. C. King, S. A. Hatfield, L. R. Bailey, C. F. McConville, B. Martel, J. C. Moreno, E. Frayssinet, F. Semond, and J. Zúñiga-Pérez

Appl. Phys. Lett. 93, 202108 (2008); http://dx.doi.org/10.1063/1.3032911 (3 pages) | Cited 19 times

Online Publication Date: 20 November 2008

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The valence band offset of ZnO/AlN heterojunctions is determined by high resolution x-ray photoemission spectroscopy. The valence band of ZnO is found to be 0.43±0.17 eV below that of AlN. Together with the resulting conduction band offset of 3.29±0.20 eV, this indicates that a type-II (staggered) band line up exists at the ZnO/AlN heterojunction. Using the III-nitride band offsets and the transitivity rule, the valence band offsets for ZnO/GaN and ZnO/InN heterojunctions are derived as 1.37 and 1.95 eV, respectively, significantly higher than the previously determined values.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures

Selective-hydrogen sensing at room temperature with Pt-coated InN nanobelts

Wantae Lim, J. S. Wright, B. P. Gila, S. J. Pearton, F. Ren, Wei-Ta Lai, Li-Chyong Chen, Ming-Shien Hu, and Kuei-Hsien Chen

Appl. Phys. Lett. 93, 202109 (2008); http://dx.doi.org/10.1063/1.3033548 (3 pages) | Cited 8 times

Online Publication Date: 20 November 2008

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The hydrogen sensing characteristics of multiple InN nanobelts grown by metalorganic chemical vapor deposition were investigated. Pt-coated InN sensors could selectively detect hydrogen at the tens of ppm level at 25 °C, while uncoated InN showed no detectable change in current when exposed to hydrogen under the same conditions. Upon exposure to various concentrations of hydrogen (20–300 ppm) in N2 ambient, the relative resistance change increased from 1.2% at 20 ppm H2 to 4% at 300 ppm H2. Approximately 90% of the initial InN resistance was recovered within 2 min by exposing the nanobelts to air. Temperature-dependent measurements showed larger resistance change and faster response at high temperature compared to those at room temperature due to increase in catalytic dissociation rate of H2 as well as diffusion rate of atomic hydrogen into the Pt/InN interface. The Pt-coated InN nanobelt sensors were operated at low power levels ( ∼ 0.5 mW).
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Hc Catalytic methods
66.30.Ny Chemical interdiffusion; diffusion barriers
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

First-principles studies of water adsorption on graphene: The role of the substrate

Tim O. Wehling, Alexander I. Lichtenstein, and Mikhail I. Katsnelson

Appl. Phys. Lett. 93, 202110 (2008); http://dx.doi.org/10.1063/1.3033202 (3 pages) | Cited 50 times

Online Publication Date: 20 November 2008

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We investigate the electronic properties of graphene upon water adsorption and study the influence of the SiO2 substrate in this context using density functional calculations. Perfect suspended graphene is rather insensitive to H2O adsorbates, as doping requires highly oriented H2O clusters. For graphene on a defective SiO2 substrate, we find a strongly different behavior: H2O adsorbates can shift the substrate’s impurity bands and change their hybridization with the graphene bands. In this way, H2O can lead to doping of graphene for much lower adsorbate concentrations than for free hanged graphene. The effect depends strongly on the microscopic substrate properties.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.up Other materials
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