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14 Jan 2008

Volume 92, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 92, 022509 (2008); http://dx.doi.org/10.1063/1.2807274 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, and Youn-Seok Choi
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Bandgap and effective mass of epitaxial cadmium oxide

P. H. Jefferson, S. A. Hatfield, T. D. Veal, P. D. C. King, C. F. McConville, J. Zúñiga–Pérez, and V. Muñoz–Sanjosé

Appl. Phys. Lett. 92, 022101 (2008); http://dx.doi.org/10.1063/1.2833269 (3 pages) | Cited 33 times

Online Publication Date: 14 January 2008

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The bandgap and band-edge effective mass of single crystal cadmium oxide, epitaxially grown by metal-organic vapor-phase epitaxy, are determined from infrared reflectivity, ultraviolet/visible absorption, and Hall effect measurements. Analysis and simulation of the optical data, including effects of band nonparabolicity, Moss-Burstein band filling and bandgap renormalization, reveal room temperature bandgap and band-edge effective mass values of 2.16±0.02 eV and 0.21±0.01m0 respectively.
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71.20.Nr Semiconductor compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
78.66.Li Other semiconductors
73.61.Le Other inorganic semiconductors
78.30.Hv Other nonmetallic inorganics
78.40.Fy Semiconductors

Spin-orbit splitting of a hydrogenic donor impurity in GaAs/GaAlAs quantum wells

Shu-Shen Li and Jian-Bai Xia

Appl. Phys. Lett. 92, 022102 (2008); http://dx.doi.org/10.1063/1.2833692 (3 pages) | Cited 20 times

Online Publication Date: 14 January 2008

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The electronic states of a hydrogenic donor impurity in GaAs/GaAlAs quantum wells are investigated theoretically in the framework of effective-mass envelope function theory, including the effect of Rashba spin-orbit coupling. The splits of electron energy levels are calculated. The results show that (1) the split energy of the excited state is larger than that of the ground state; (2) the split energy peak appears as the GaAs well width increases from zero; and (3) the maximum split energy reaches about 1.6 meV. Our results are useful for the application of Rashba spin-orbit coupling to photoelectric devices.
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73.21.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.55.Eq III-V semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Electron transport of nanotube-based gas sensors: An ab initio study

Arta Sadrzadeh, Amir A. Farajian, and Boris I. Yakobson

Appl. Phys. Lett. 92, 022103 (2008); http://dx.doi.org/10.1063/1.2829609 (3 pages) | Cited 5 times

Online Publication Date: 14 January 2008

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The effect of physisorption of NO2 gas molecules on quantum transport properties of semiconducting carbon nanotubes is studied using ab initio calculations and Green function formalism. The results show that the conductance change is mainly due to the electric dipole moment of NO2. It is also shown that upon exposure of nanotube to different concentrations of gas, the common feature is the shift in conductance toward lower energies. This suggests that physisorption of NO2 will result in a decrease (increase) in conductance of p-type (n-type) nanotubes with Fermi energies close to the edge of valence and conduction band.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.Fk Electrochemical methods

Interface studies of ZnO nanowire transistors using low-frequency noise and temperature-dependent I-V measurements

Sanghyun Ju, Sunkook Kim, Saeed Mohammadi, David B. Janes, Young-Geun Ha, Antonio Facchetti, and Tobin J. Marks

Appl. Phys. Lett. 92, 022104 (2008); http://dx.doi.org/10.1063/1.2830005 (3 pages) | Cited 12 times

Online Publication Date: 14 January 2008

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Single ZnO nanowire (NW) transistors fabricated with self-assembled nanodielectric (SAND) and SiO2 gate insulators were characterized by low-frequency noise and variable temperature current-voltage (I-V) measurements. According to the gate dependence of the noise amplitude, the extracted Hooge’s constants (αH) are ∼ 3.3×10−2 for SAND-based devices and ∼ 3.5×10−1 for SiO2-based devices. Temperature-dependent I-V studies show that the hysteresis of the transfer curves and the threshold voltage shifts of SAND-based devices are significantly smaller than those of SiO2-based devices. These results demonstrate the improved SAND/ZnO NW interface quality (lower interface-trap states and defects) in comparison to those fabricated with SiO2.
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85.35.-p Nanoelectronic devices
85.30.-z Semiconductor devices

Piezoelectric nanogenerator using CdS nanowires

Yi-Feng Lin, Jinhui Song, Yong Ding, Shih-Yuan Lu, and Zhong Lin Wang

Appl. Phys. Lett. 92, 022105 (2008); http://dx.doi.org/10.1063/1.2831901 (3 pages) | Cited 49 times

Online Publication Date: 14 January 2008

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Vertically grown cadmium sulfide (CdS) nanowire (NW) arrays were prepared using two different processes: hydrothermal and physical vapor deposition (PVD). The NWs obtained from the hydrothermal process were composed of alternating hexagonal wurtzite (WZ) and cubic zinc blende (ZB) phases with growth direction along WZ ⟨0001⟩ and ZB [111]. The NWs produced by PVD process are single crystalline WZ phase with growth direction along ⟨0001⟩. These vertically grown CdS NW arrays have been used to converting mechanical energy into electricity following a developed procedure [ Z. L. Wang and J. Song Science 312, 242 (2006) ]. The basic principle of the CdS NW nanogenerator relies on the coupled piezoelectric and semiconducting properties of CdS, and the data fully support the mechanism previously proposed for ZnO NW nanogenerators and nanopiezotronics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.35.-p Nanoelectronic devices

Ohmic contact formation on n-type Ge

R. R. Lieten, S. Degroote, M. Kuijk, and G. Borghs

Appl. Phys. Lett. 92, 022106 (2008); http://dx.doi.org/10.1063/1.2831918 (3 pages) | Cited 34 times

Online Publication Date: 14 January 2008

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Severe Fermi level pinning at the interface between n-Ge and a metal leads to the formation of a Schottky barrier, almost independent on the metal work function. Therefore, it seems impossible to form metal Ohmic contacts on moderately, n-type doped Ge layers. For p-type Ge, the Fermi level pinning works opposite: all metal contacts show Ohmic behavior. This fixed behavior can be altered by the introduction of a thin Ge3N4 layer. Ge3N4 seems effective in reducing Fermi level pinning and, therefore, allows the formation of Ohmic contacts on n-type Ge and a rectifying contact on p-type Ge.
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73.40.Ns Metal-nonmetal contacts
73.40.Ei Rectification
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states

Violet luminescence in phosphorus-doped ZnO epitaxial films

A. Allenic, X. Q. Pan, Y. Che, Z. D. Hu, and B. Liu

Appl. Phys. Lett. 92, 022107 (2008); http://dx.doi.org/10.1063/1.2834696 (3 pages) | Cited 16 times

Online Publication Date: 15 January 2008

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A violet luminescence band at 3.1099 eV was observed at 12.5 K in phosphorus-doped ZnO epitaxial films deposited by O2 plasma-assisted pulsed laser ablation. The band results from a transition between a shallow donor and a deep acceptor induced by phosphorus doping. The activation energy of the acceptor varies with the phosphorus concentration [P] and is 0.34 eV when [P] is 1.7×1019 cm−3. Under oxygen-rich conditions, the dominant acceptor in P2O5-doped ZnO may be the zinc vacancy, in agreement with recent first-principles calculations.
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78.66.Hf II-VI semiconductors
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Characterization of AlN metal-semiconductor-metal diodes in the spectral range of 44–360 nm: Photoemission assessments

A. BenMoussa, J. F. Hochedez, R. Dahal, J. Li, J. Y. Lin, H. X. Jiang, A. Soltani, J.-C. De Jaeger, U. Kroth, and M. Richter

Appl. Phys. Lett. 92, 022108 (2008); http://dx.doi.org/10.1063/1.2834701 (3 pages) | Cited 11 times

Online Publication Date: 15 January 2008

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The absolute responsivity of a metal-semiconductor-metal (MSM) photodiode based on high quality AlN material has been tested from the vacuum ultraviolet (vuv) to the near UV wavelength range (44–360 nm). The metal finger Schottky contacts have been processed to 2 μm in width with spacing between the contacts of 4 μm. In the vuv wavelength region, the measurement methodology is described in order to distinguish the contribution of the photoemission current from the internal diode signal. In the wavelength range of interest, AlN MSM is sensitive and stable under brief vuv irradiation. The MSM shows a 200/360 nm rejection ratio of more than four orders of magnitude and demonstrates the advantages of wide band gap material based detectors in terms of high rejection ratio and high output signal for vuv solar observation missions.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Electronic structure of GeO2-passivated interfaces of (100)Ge with Al2O3 and HfO2

V. V. Afanas’ev, A. Stesmans, A. Delabie, F. Bellenger, M. Houssa, and M. Meuris

Appl. Phys. Lett. 92, 022109 (2008); http://dx.doi.org/10.1063/1.2831668 (3 pages) | Cited 27 times

Online Publication Date: 15 January 2008

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Analysis of internal photoemission and photoconductivity in Ge/thermal germanium oxide/high-dielectric constant oxide (HfO2,Al2O3) structures reveals that the bandgap of the germanium oxide interlayer is significantly lower (4.3±0.2 eV) than that of stiochiometric GeO2 (5.4–5.9 eV). As a result, the conduction and valence band offsets at the interface appear to be insufficient to block electron and hole injection leading to significant charge trapping in the GeOx/high-κ oxide stack. Formation of a hydroxyl-rich Ge oxide phase is suggested to be responsible for the modification of the oxide properties.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
73.40.Ns Metal-nonmetal contacts
77.22.Ch Permittivity (dielectric function)

Unipolar resistive switching characteristics of ZnO thin films for nonvolatile memory applications

Wen-Yuan Chang, Yen-Chao Lai, Tai-Bor Wu, Sea-Fue Wang, Frederick Chen, and Ming-Jinn Tsai

Appl. Phys. Lett. 92, 022110 (2008); http://dx.doi.org/10.1063/1.2834852 (3 pages) | Cited 77 times

Online Publication Date: 16 January 2008

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Highly (002)-oriented and columnar-grained ZnO thin films were prepared by radio frequency magnetron sputtering at room temperature. The Pt/ZnO/Pt devices exhibit reversible and steady bistable resistance switching behaviors with a narrow dispersion of the resistance states and switching voltage. Only a low forming electric field was required to induce the resistive switching characteristics. The resistance ratios of high resistance state to low resistance state were in the range of 3–4 orders of magnitude within 100 cycles of test. It was also found that the conduction mechanisms dominating the low and high resistance states are Ohmic behavior and Poole-Frenkel emission, respectively.
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73.40.Sx Metal-semiconductor-metal structures
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
85.30.De Semiconductor-device characterization, design, and modeling

Electron counting at room temperature in an avalanche bipolar transistor

Marc Lany, Giovanni Boero, and Radivoje Popovic

Appl. Phys. Lett. 92, 022111 (2008); http://dx.doi.org/10.1063/1.2830015 (3 pages)

Online Publication Date: 18 January 2008

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We report on real-time detection of single electrons inside a n-p-n bipolar junction transistor at room temperature. Single electrons injected through the base-emitter junction trigger with a high probability the avalanche breakdown of the strongly reverse-biased collector-base junction. The breakdown, rapidly stopped by an avalanche quenching circuit, produces a voltage pulse at the collector which corresponds to the detection of a single electron. Pulse rates corresponding to currents down to the attoampere range are measured with an integration time of about 10 s.
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85.30.Pq Bipolar transistors
85.30.Kk Junction diodes

Modeling of nitrogen profile effects on direct tunneling probability in ultrathin nitrided oxides

Po-Tsun Liu, Chen-Shuo Huang, D. Y. Lee, P. S. Lim, S. W. Lin, C. C. Chen, H. J. Tao, and Y. J. Mii

Appl. Phys. Lett. 92, 022112 (2008); http://dx.doi.org/10.1063/1.2835706 (3 pages)

Online Publication Date: 18 January 2008

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The dependence of the gate tunneling current (Jg) on nitrogen profile (N profile) within an ultrathin silicon oxynitride film is reported. It was found that gate tunneling current is dependent on N profile, even with equal oxide thickness and nitrogen dosage. Gate tunneling current increased with steeper N profile, and it had higher sensitivity for p-type metal-oxide-semiconductor field-effect transistor (MOSFET) than n-type MOSFET. A direct tunneling model based on Wentzel-Kramers-Brillouin approximation has been proposed. The model described the influence of N profiles on gate tunneling current through local change of dielectric constant, band bending, and effective mass. Also, it reasonably explained the different Jg sensitivity in n-/p-MOSFETs, a phenomenon that has not been addressed in earlier publications.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Gk Tunneling
77.22.Ch Permittivity (dielectric function)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
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