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23 Aug 2010

Volume 97, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 97, 081901 (2010); http://dx.doi.org/10.1063/1.3457448 (3 pages)

Zhaofeng Li, Rongkuo Zhao, Thomas Koschny, Maria Kafesaki, Kamil Boratay Alici, Evrim Colak, Humeyra Caglayan, Ekmel Ozbay, and C. M. Soukoulis
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Influence of electron-electron scattering on transport characteristics in monolayer graphene

X. Li, E. A. Barry, J. M. Zavada, M. Buongiorno Nardelli, and K. W. Kim

Appl. Phys. Lett. 97, 082101 (2010); http://dx.doi.org/10.1063/1.3483612 (3 pages) | Cited 6 times

Online Publication Date: 23 August 2010

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The influence of electron-electron scattering on the distribution function and transport characteristics of intrinsic monolayer graphene is investigated via an ensemble Monte Carlo simulation. Due to the linear dispersion relation in the vicinity of the Dirac points, it is found that pair-wise collisions in graphene do not conserve the ensemble average velocity in contrast to conventional semiconductors with parabolic energy bands. Numerical results indicate that electron-electron scattering can lead to a decrease in the low field mobility by more than a factor of 2 for moderate electron densities. The corresponding degradation in the saturation velocity is more modest at around 15%. At high densities, the impact gradually diminishes due to increased degeneracy.
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72.80.Vp Electronic transport in graphene
72.20.Fr Low-field transport and mobility; piezoresistance
73.22.Pr Electronic structure of graphene

High temperature electrical conduction in nanoscale hafnia films under varying oxygen partial pressure

Changhyun Ko, Michael Shandalov, Paul C. McIntyre, and Shriram Ramanathan

Appl. Phys. Lett. 97, 082102 (2010); http://dx.doi.org/10.1063/1.3482940 (3 pages) | Cited 3 times

Online Publication Date: 23 August 2010

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Point defect equilibration in nanocrystalline hafnium oxide thin films in the monoclinic (m-HfO2) phase was studied by electrochemical measurements performed under varying temperature and oxygen partial pressure (PO2) on films of 35–63 nm thickness on single crystal MgO and Al2O3 substrates. The conductance varied as (PO2)n, where n is the in the range ∼ +1/11 to ∼ +1/14, at high PO2. The increasing conductance with PO2 suggests that the electronic conduction in the HfO2 films is p-type and oxygen interstitials or hafnium vacancies, rather than oxygen vacancies, could be dominant charged point defects in nanocrystalline, undoped m-HfO2 films.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.D- High-permittivity gate dielectric films
73.63.Bd Nanocrystalline materials
61.72.jd Vacancies

Tuning single GaAs quantum dots in resonance with a rubidium vapor

N. Akopian, U. Perinetti, L. Wang, A. Rastelli, O. G. Schmidt, and V. Zwiller

Appl. Phys. Lett. 97, 082103 (2010); http://dx.doi.org/10.1063/1.3478232 (3 pages) | Cited 4 times

Online Publication Date: 23 August 2010

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We study single GaAs quantum dots with optical transitions that can be brought into resonance with the widely used D2 transitions of rubidium atoms. We achieve resonance by Zeeman or Stark shifting the quantum dot levels. We discuss an energy stabilization scheme based on the absorption of quantum dot photoluminescence in a rubidium vapor. This offers a scalable means to counteract slow spectral diffusion in quantum dots.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects
78.20.Ls Magneto-optical effects

Interface-controlled layer exchange in metal-induced crystallization of germanium thin films

Shu Hu (胡澍), Ann F. Marshall, and Paul C. McIntyre

Appl. Phys. Lett. 97, 082104 (2010); http://dx.doi.org/10.1063/1.3480600 (3 pages) | Cited 7 times

Online Publication Date: 24 August 2010

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Low-temperature synthesis of polycrystalline germanium (poly-Ge) thin films is of great interest in thin-film photovoltaic and electronics applications. We demonstrate metal (Al)-induced crystallization to form poly-Ge thin films on both glass and polymer substrates at temperatures as low as 200 °C. An interfacial diffusion control layer, intentionally interposed between the Al and the underlying amorphous Ge (a-Ge) layer, is found to achieve layer exchange while suppressing uncontrolled Ge crystallization within the bilayer samples. Germanium thin films with micron-size grains and (111)-preferred orientation are prepared by controlled Ge nucleation and Ge lateral overgrowth of Al during a-Ge crystallization.
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68.55.ag Semiconductors
64.70.dg Crystallization of specific substances
64.60.Q- Nucleation

A nanoscale Ti/GaAs metal-semiconductor hybrid sensor for room temperature light detection

A. K. M. Newaz, W.-J. Chang, K. D. Wallace, L. C. Edge, S. A. Wickline, R. Bashir, A. M. Gilbertson, L. F. Cohen, and S. A. Solin

Appl. Phys. Lett. 97, 082105 (2010); http://dx.doi.org/10.1063/1.3480611 (3 pages) | Cited 1 time

Online Publication Date: 24 August 2010

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We report an individually addressable Ti/GaAs metal-semiconductor hybrid optical nanosensor with positive photoresistance and a sensitivity that increases as the device dimensions shrink. The underlying physics relates to the crossover from ballistic to diffusive transport of the photoinduced carriers and the geometric enhancement of the effect associated with a Schottky-barrier-coupled parallel metal shunt layer. For a 250 nm device under 633 nm illumination we observe a specific detectivity of D∗ = 5.06×1011 cm √Hz/W with a dynamic response of 40 dB.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.30.+y Surface double layers, Schottky barriers, and work functions

Gate controlled magnetoresistance in a silicon metal-oxide-semiconductor field-effect-transistor

C. Ciccarelli, B. G. Park, S. Ogawa, A. J. Ferguson, and J. Wunderlich

Appl. Phys. Lett. 97, 082106 (2010); http://dx.doi.org/10.1063/1.3475771 (3 pages) | Cited 4 times

Online Publication Date: 25 August 2010

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We present a study of the magnetoresistance (MR) of a Si metal-oxide-semiconductor field-effect-transistor (MOSFET) at the break-down regime when a magnetic field is applied perpendicular to the plane of the device. We have identified two different regimes where we observe a large and gate-voltage dependent MR. We suggest two different mechanisms which can explain the observed high MR. Moreover, we have studied how the MR of the MOSFET scales with the dimensions of the channel for gate voltages below the threshold. We observed a decrease in the MR by two orders of magnitude by reducing the dimensions of the channel from 50×280 μm2 to 5×5 μm2.
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85.30.Tv Field effect devices

Microwave induced zero-conductance state in a Corbino geometry two-dimensional electron gas with capacitive contacts

A. A. Bykov, I. V. Marchishin, A. V. Goran, and D. V. Dmitriev

Appl. Phys. Lett. 97, 082107 (2010); http://dx.doi.org/10.1063/1.3483765 (3 pages) | Cited 1 time

Online Publication Date: 26 August 2010

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Microwave induced photoconductivity of a two-dimensional electron gas in selectively doped GaAs/AlAs heterostructures has been studied using the Corbino geometry with capacitive contacts at a temperature T = 1.6 K and magnetic field B up to 0.5 T. Zero-conductance states have been observed in the samples under study subject to microwave radiation, similarly to the samples with Ohmic contacts. It has been shown that Ohmic contacts do not play a significant role for observation of zero-conductance states induced by microwave radiation.
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81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.40.+w Photoconduction and photovoltaic effects
72.20.My Galvanomagnetic and other magnetotransport effects
61.82.Fk Semiconductors

Extremely low surface recombination velocities on crystalline silicon wafers realized by catalytic chemical vapor deposited SiNx/a-Si stacked passivation layers

Koichi Koyama, Keisuke Ohdaira, and Hideki Matsumura

Appl. Phys. Lett. 97, 082108 (2010); http://dx.doi.org/10.1063/1.3483853 (3 pages) | Cited 7 times

Online Publication Date: 26 August 2010

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Catalytic chemical vapor deposition (Cat-CVD), also called hot-wire CVD, yields silicon-nitride/amorphous-silicon (SiNx/a-Si) stacked layers with remarkably low surface recombination velocities (SRVs) of lower than 1.5 cm/s for n-type crystalline Si (c-Si) wafers, and lower than 9.0 cm/s for p-type wafers. The temperature throughout the formation of stacked layers is lower than 250 °C. The usage of a-Si films significantly enhances the effective carrier lifetime of c-Si wafers, and SiNx films are also essential for reducing SRVs to such low levels.
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73.25.+i Surface conductivity and carrier phenomena
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.Rv Passivation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Cy Elemental semiconductors
68.55.ag Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

The effect of deposition power on the electrical properties of Al-doped zinc oxide thin films

B. S. Chun, H. C. Wu, M. Abid, I. C. Chu, S. Serrano-Guisan, I. V. Shvets, and Daniel. S. Choi

Appl. Phys. Lett. 97, 082109 (2010); http://dx.doi.org/10.1063/1.3483232 (3 pages) | Cited 8 times

Online Publication Date: 27 August 2010

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We investigated the effect on the electronic properties of aluminum (Al)-zinc oxide (ZnO) films by modulating the radio frequency sputtering power. Our experimental results show that increasing the sputtering power increases the Al doping concentration, decreases the resistivity, and also shifts the Zn 2p and O 1s to higher binding energy states. Our local-density approximation (LDA) and LDA+U calculations show that the shift in higher binding energy and resistivity decrease are due to an enhancement of the O 2p–Zn 3d coupling and the modification of the Zn 4s–O 2p interaction in ZnO induced by Al doping.
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73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
81.15.Cd Deposition by sputtering
81.05.Dz II-VI semiconductors
71.20.Nr Semiconductor compounds

Density of trap states measured by photon probe into ZnO based thin-film transistors

Kimoon Lee, Gunwoo Ko, Gun Hwan Lee, Gi bok Han, Myung M. Sung, Tae Woo Ha, Jae Hoon Kim, and Seongil Im

Appl. Phys. Lett. 97, 082110 (2010); http://dx.doi.org/10.1063/1.3483763 (3 pages) | Cited 6 times

Online Publication Date: 27 August 2010

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We report on photo-excited trap-charge-collection spectroscopy, contrived to measure the density of deep-level traps near channel/dielectric interface in a working ZnO based thin-film transistor as a function of photon probe energy. Free charges trapped at a certain energy level are liberated by the correspondingly energetic photons and then electrically collected at the source/drain electrodes. During this photo-electric process, the threshold voltage of TFT shifts and its magnitude provides the density-of-state information of charge traps. In the present work, we directly characterized the density-of-state of ZnO based thin-film transistors with polymer-oxide double dielectrics after evaluating their gate stabilities.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ga II-VI semiconductors
71.55.Gs II-VI semiconductors

Electroluminescence from ZnO nanoflowers/GaN thin film p-n heterojunction

Jaehui Ahn, Michael A. Mastro, Jennifer Hite, Charles R. Eddy, Jr., and Jihyun Kim

Appl. Phys. Lett. 97, 082111 (2010); http://dx.doi.org/10.1063/1.3481415 (3 pages) | Cited 4 times

Online Publication Date: 27 August 2010

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Dielectrophoretic force was employed to position ZnO nanoflowers on a p-type GaN thin film prepatterned with Ti/Al/Ni/Au n-type and Ni/Au p-type contact metallizations. Analytical and finite element calculations were employed to determine the optimal alternating current frequency to attract the randomly dispersed ZnO nanoflowers to the n-type contact located on but isolated from the p-GaN thin film. The n-type ZnO nanoflower/p-type GaN thin film heterojunction displayed rectifying current-voltage behavior characteristic of a pristine p-n junction diode and emitted violet light under forward bias above 4.7–5.5 V.
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85.30.Kk Junction diodes
82.45.-h Electrochemistry and electrophoresis
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Mobility and saturation velocity in graphene on SiO2

Vincent E. Dorgan, Myung-Ho Bae, and Eric Pop

Appl. Phys. Lett. 97, 082112 (2010); http://dx.doi.org/10.1063/1.3483130 (3 pages) | Cited 20 times

Online Publication Date: 27 August 2010

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We examine mobility and saturation velocity in graphene on SiO2 above room temperature (300–500 K) and at high fields ( ∼ 1 V/μm). Data are analyzed with practical models including gated carriers, thermal generation, “puddle” charge, and Joule heating. Both mobility and saturation velocity decrease with rising temperature above 300 K, and with rising carrier density above 2×1012 cm−2. Saturation velocity is >3×107 cm/s at low carrier density, and remains greater than in Si up to 1.2×1013 cm−2. Transport appears primarily limited by the SiO2 substrate but results suggest intrinsic graphene saturation velocity could be more than twice that observed here.
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61.48.Gh Structure of graphene
81.05.ue Graphene
72.80.Vp Electronic transport in graphene
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