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5 Mar 2012

Volume 100, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 100, 101903 (2012); http://dx.doi.org/10.1063/1.3673327 (3 pages)

Michael Ian Lapsley, Anaram Shahravan, Qingzhen Hao, Bala Krishna Juluri, Stephen Giardinelli, Mengqian Lu, Yanhui Zhao, I-Kao Chiang, Themis Matsoukas, and Tony Jun Huang
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Evolution of structural and thermoelectric properties of indium-ion-implanted epitaxial GaAs

M. V. Warren, A. W. Wood, J. C. Canniff, F. Naab, C. Uher, and R. S. Goldman

Appl. Phys. Lett. 100, 102101 (2012); http://dx.doi.org/10.1063/1.3687912 (4 pages)

Online Publication Date: 5 March 2012

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We have examined the structural and thermoelectric properties of nanocomposites prepared by matrix-seeded growth, which consists of ion-beam-amorphization, followed by nanoscale recrystallization via annealing. We use a sputter-mask to increase the retained concentration of In+ ions in GaAs as a path towards the formation of nanoscale InAs crystals in an amorphous GaAs matrix. For the highest ion fluence, an enormous Seebeck coefficient of −12 mV/K is observed at 4 K. We discuss the temperature-dependence of the resistivity, Seebeck coefficient, and thermoelectric power factor in terms of the microstructure of the layers.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials

Emitter injection in terahertz quantum cascade lasers: Simulation of an open system

F. Wang, X. G. Guo, H. Li, and J. C. Cao

Appl. Phys. Lett. 100, 102102 (2012); http://dx.doi.org/10.1063/1.3692170 (4 pages)

Online Publication Date: 6 March 2012

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We investigate the carrier transport properties of a three-well terahertz quantum cascade laser which is considered as an open system by using self-consistent Bloch-Poisson equations. The simulation results show that a dynamic equilibrium is achieved, and the electric potential of each period slightly changes with time. Compared to other simulation methods with the cyclic boundary condition approximation, our open system modeling gives more reliable results on the current density-applied electric field and population inversion-applied electric field characteristics. Our modeling method can give more realistic results of working terahertz quantum cascade lasers without increasing the simulation complexity.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Ah General laser theory

Direct surface cyclotron resonance terahertz emission from a quantum cascade structure

François-Régis Jasnot, Louis-Anne de Vaulchier, Yves Guldner, Gérald Bastard, Angela Vasanelli, Christophe Manquest, Carlo Sirtori, Mattias Beck, and Jérôme Faist

Appl. Phys. Lett. 100, 102103 (2012); http://dx.doi.org/10.1063/1.3692572 (4 pages) | Cited 1 time

Online Publication Date: 6 March 2012

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A strong magnetic field applied along the growth direction of a semiconductor quantum well gives rise to a spectrum of discrete energy states, the Landau levels. By combining quantum engineering of a quantum cascade structure with a static magnetic field, we can selectively inject electrons into the excited Landau level of a quantum well and realize a tunable surface emitting device based on cyclotron emission. By applying the appropriate magnetic field between 0 and 12 T, we demonstrate emission from a single device over a wide range of frequencies (1-2 THz and 3-5 THz).
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71.70.Di Landau levels
78.67.De Quantum wells
76.40.+b Diamagnetic and cyclotron resonances

Tunnel field-effect transistor heterojunction band alignment by internal photoemission spectroscopy

Qin Zhang, Guangle Zhou, Huili G. Xing, Alan C. Seabaugh, Kun Xu, Hong Sio, Oleg A. Kirillov, Curt A. Richter, and N. V. Nguyen

Appl. Phys. Lett. 100, 102104 (2012); http://dx.doi.org/10.1063/1.3692589 (4 pages) | Cited 3 times

Online Publication Date: 6 March 2012

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The electron energy band alignment of a metal-oxide-semiconductor tunnel field-effect transistor heterojunction, W/Al2O3/InGaAs/InAs/InP, is determined by internal photoemission spectroscopy. At the oxide flat-band condition, the barrier height from the top of the InGaAs/InAs valence band and the top of the InP valence band to the bottom of the Al2O3 conduction band is determined to be 3.5 and 2.8 eV, respectively. The simulated energy band diagram of the heterostructure is shown to be consistent with the measured band alignments if an equivalent positive charge of 6.0 × 1012 cm−2 is present at the Al2O3/InGaAs. This interface charge is in agreement with previously reported capacitance-voltage measurements.
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85.30.Tv Field effect devices

The electronic and optical properties of Eu/Si-codoped anatase TiO2 photocatalyst

Yanming Lin, Zhenyi Jiang, Xiaoyun Hu, Xiaodong Zhang, and Jun Fan

Appl. Phys. Lett. 100, 102105 (2012); http://dx.doi.org/10.1063/1.3692750 (4 pages) | Cited 4 times

Online Publication Date: 6 March 2012

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The electronic and optical properties of Eu/Si-codoped anatase TiO2 are investigated using the density functional theory. The calculated results show that the synergistic effects of Eu/Si codoping can effectively extend the optical absorption edge, which can lead to higher visible-light photocatalytic activities than pure anatase TiO2. To verify the reliability of our calculated results, nanocrystalline Eu/Si-codoped TiO2 is prepared by a sol-gel-solvothermal method, and the experimental results also indicate that the codoping sample exhibits better absorption performance and higher photocatalytic activities than pure TiO2.
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78.40.Fy Semiconductors
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.16.-c Methods of micro- and nanofabrication and processing
82.50.-m Photochemistry
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.22.-f Electronic structure of nanoscale materials and related systems

Electron traps in amorphous In–Ga–Zn–O thin films studied by isothermal capacitance transient spectroscopy

Kazushi Hayashi, Aya Hino, Shinya Morita, Satoshi Yasuno, Hiroshi Okada, and Toshihiro Kugimiya

Appl. Phys. Lett. 100, 102106 (2012); http://dx.doi.org/10.1063/1.3691923 (4 pages) | Cited 2 times

Online Publication Date: 6 March 2012

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Electron traps in amorphous In–Ga–Zn–O (a-IGZO) thin films were studied using isothermal capacitance transient spectroscopy (ICTS). Broad peaks that shifted toward a longer elapsed time with an increase in the filling pulse width were detected from the ICTS spectra for metal-oxide-semiconductor diodes consisting of a Mo/SiO2/a-IGZO structure. The time constant of the peak position at 180 K was found to be from ∼1 m to ∼100 ms, corresponding to a range of energy level from ∼170 to ∼230 meV below the conduction band edge. The total trap density around the peak was estimated to be ∼1 × 1016 cm−3·eV−1. Further, according to the biasing voltage dependence of the ICTS signal, the density of the trap states increases by about three orders of magnitude near the interface between the a-IGZO and the gate dielectric layers. The electron transport in electronic devices using an a-IGZO could be influenced by the trap states detected in the present study.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.21.Ac Multilayers
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Jc Amorphous semiconductors; glasses
85.30.Kk Junction diodes

Temperature dependence of the indirect bandgap in ultrathin strained silicon on insulator layer

J. Munguía, J.-M. Bluet, O. Marty, G. Bremond, M. Mermoux, and D. Rouchon

Appl. Phys. Lett. 100, 102107 (2012); http://dx.doi.org/10.1063/1.3691955 (4 pages)

Online Publication Date: 6 March 2012

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Photoluminescence spectroscopy is applied on tensely strained silicon on insulator layer in order to evaluate the temperature dependence of the indirect energy bandgap. The strained silicon indirect bandgap follows a similar behaviour to bulk silicon at high temperature (from 80 K up to 300 K) which was described from the Varshni [Physica 34, 149 (1967)] and Bose-Einstein equations. Nevertheless, at low temperature (from 9 K to 80 K), an unusual blueshift of the bandgap is evidenced. The latter can be modelled considering band-tail states of density of states which are related to the strain fluctuation.
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71.20.Mq Elemental semiconductors
78.55.Ap Elemental semiconductors

Patterned oxide semiconductor by electrohydrodynamic jet printing for transparent thin film transistors

Sangkyu Lee, Jeonghyun Kim, Junghyun Choi, Hyunjung Park, Jaehwan Ha, Yongkwan Kim, John A. Rogers, and Ungyu Paik

Appl. Phys. Lett. 100, 102108 (2012); http://dx.doi.org/10.1063/1.3691177 (4 pages)

Online Publication Date: 8 March 2012

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This paper explores transport in transparent thin film transistors formed using a liquid precursor to indium zinc oxide, delivered to target substrates by electrohydrodynamic jet (e-jet) printing. Under optimized conditions, we observe field effect mobilities as high as 32 cm2V−1s−1, with on/off current ratios of 103 and threshold voltages of 2 V. These results provide evidence that material manipulated in fine-jet, electric field induced liquid flows can yield semiconductor devices without any adverse effects of residual charge or unintentional doping. E-jet printing methods provide levels of resolution (∼1.5 μm) that provide a path to printed transistors with small critical dimensions.
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85.30.Tv Field effect devices

Investigation of the direct band gaps in Ge1−xSnx alloys with strain control by photoreflectance spectroscopy

Hai Lin, Robert Chen, Weisheng Lu, Yijie Huo, Theodore I. Kamins, and James S. Harris

Appl. Phys. Lett. 100, 102109 (2012); http://dx.doi.org/10.1063/1.3692735 (4 pages) | Cited 4 times

Online Publication Date: 8 March 2012

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Unstrained and compressive-strained Ge1−xSnx alloys were grown on InGaAs buffer layers by molecular beam epitaxy. Photoreflectance at room temperature determines the direct bandgap energies of Ge1−xSnx alloys from the maxima of the light- and heavy-hole bands to the bottom of Γ valley. The lowest transition energies from photoreflectance are consistent with the energies derived from photoluminescence. The calculated bowing parameter is 2.42 ± 0.04 eV for the direct band gap of Ge1−xSnx alloys. The dilational and shear deformation potentials of the direct band gap are −11.04 ± 1.41 eV and −4.07 ± 0.91 eV, respectively. These basic material parameters are important in designing optoelectronic devices based on Ge1−xSnx alloys.
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71.20.Gj Other metals and alloys
78.55.Hx Other solid inorganic materials
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
78.66.Bz Metals and metallic alloys
73.61.At Metal and metallic alloys

The effects of organic material-treated SiO2 dielectric surfaces on the electrical characteristics of inorganic amorphous In-Ga-Zn-O thin film transistors

Mijeong Park, Jaeyoung Jang, Seonuk Park, Jiye Kim, Jiehyun Seong, Jiyoung Hwang, and Chan Eon Park

Appl. Phys. Lett. 100, 102110 (2012); http://dx.doi.org/10.1063/1.3691920 (4 pages)

Online Publication Date: 8 March 2012

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We investigated the influence of organic dielectric surfaces on the electrical characteristics of inorganic amorphous indium-gallium-zinc oxide (a-IGZO)-based thin film transistors (TFTs). To modify the dielectric surface, various self-assembled monolayers and polymer thin films with different functional groups were introduced. Electrical measurements of the a-IGZO TFTs using surface-modified gate dielectrics revealed that the threshold voltages shifted toward positive values as the surface functional groups attract more electrons in the a-IGZO thin films. These results indicate that the channel conductance and carrier density of a-IGZO TFTs could be tuned by simple modification of the dielectric surfaces with organic materials.
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85.30.Tv Field effect devices
73.40.-c Electronic transport in interface structures

Anomalous positive flatband voltage shifts in metal gate stacks containing rare-earth oxide capping layers

J. A. Caraveo-Frescas, M. N. Hedhili, H. Wang, U. Schwingenschlögl, and H. N. Alshareef

Appl. Phys. Lett. 100, 102111 (2012); http://dx.doi.org/10.1063/1.3692580 (4 pages)

Online Publication Date: 9 March 2012

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It is shown that the well-known negative flatband voltage (VFB) shift, induced by rare-earth oxide capping in metal gate stacks, can be completely reversed in the absence of the silicon overlayer. Using TaN metal gates and Gd2O3-doped dielectric, we measure a ∼350 mV negative shift with the Si overlayer present and a ∼110 mV positive shift with the Si overlayer removed. This effect is correlated to a positive change in the average electrostatic potential at the TaN/dielectric interface which originates from an interfacial dipole. The dipole is created by the replacement of interfacial oxygen atoms in the HfO2 lattice with nitrogen atoms from TaN.
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73.40.-c Electronic transport in interface structures
84.32.Tt Capacitors

Band gap control via tuning of inversion degree in CdIn2S4 spinel

Yohanna Seminovski, Pablo Palacios, Perla Wahnón, and Ricardo Grau-Crespo

Appl. Phys. Lett. 100, 102112 (2012); http://dx.doi.org/10.1063/1.3692780 (3 pages) | Cited 2 times

Online Publication Date: 9 March 2012

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Based on theoretical arguments, we propose a possible route for controlling the band-gap in the promising photovoltaic material CdIn2S4. Our ab initio calculations show that the experimental degree of inversion in this spinel (fraction of tetrahedral sites occupied by In) corresponds approximately to the equilibrium value given by the minimum of the theoretical inversion free energy at a typical synthesis temperature. Modification of this temperature, or of the cooling rate after synthesis, is then expected to change the inversion degree, which in turn sensitively tunes the electronic band-gap of the solid, as shown here by screened hybrid functional calculations.
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71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations
65.40.-b Thermal properties of crystalline solids

Lone conduction band in Cu2ZnSnSe4

Levent Gütay, Alex Redinger, Rabie Djemour, and Susanne Siebentritt

Appl. Phys. Lett. 100, 102113 (2012); http://dx.doi.org/10.1063/1.3691945 (4 pages) | Cited 3 times

Online Publication Date: 9 March 2012

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We present experimental proof for a narrow first conduction band in Cu2ZnSnSe4 semiconductor films as it has been predicted by theoretical calculations. The optical absorption characteristics of Cu2ZnSnSe4 thin films are analyzed by optical transmission spectroscopy. The experimental data show strong evidence for three absorption edges, as expected from theory, involving the valence band and two conduction bands, which are separated by a second band gap.
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71.20.Nr Semiconductor compounds
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics
78.40.Fy Semiconductors

Chemical and optical properties of carbon-doped TiO2: A density-functional study

Jibao Lu, Ying Dai, Meng Guo, Lin Yu, Kangrong Lai, and Baibiao Huang

Appl. Phys. Lett. 100, 102114 (2012); http://dx.doi.org/10.1063/1.3693525 (4 pages) | Cited 6 times

Online Publication Date: 9 March 2012

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The conflict of understandings on experimental results about chemical and optical properties of C-doped TiO2, which has been overlooked for a long time but is essential for studies of the basic properties of this material, is unraveled. It is shown that in anatase TiO2 the doped C and O atoms can easily couple with each other at typical synthesis conditions due to the large binding energy and small energy barrier, while in rutile phase, the coupling can hardly occur. The characteristics of the structures are elaborated in detail, which provides insights into the chemical, optical, and magnetic properties of C-doped TiO2.
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78.40.Ha Other nonmetallic inorganics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
71.20.Nr Semiconductor compounds
75.30.Cr Saturation moments and magnetic susceptibilities
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