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2 Jul 2007

Volume 91, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 91, 013501 (2007); http://dx.doi.org/10.1063/1.2753120 (3 pages)

J. Verd, A. Uranga, G. Abadal, J. Teva, F. Torres, F. Pérez-Murano, J. Fraxedas, J. Esteve, and N. Barniol
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Mg acceptor level in InN epilayers probed by photoluminescence

N. Khan, N. Nepal, A. Sedhain, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 91, 012101 (2007); http://dx.doi.org/10.1063/1.2753537 (3 pages) | Cited 10 times

Online Publication Date: 2 July 2007

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Mg-doped InN epilayers were grown on sapphire substrates by metal organic chemical vapor deposition. Effects of Mg concentration on the photoluminescence (PL) emission properties have been investigated. An emission line at ∼ 0.76 eV, which was absent in undoped InN epilayers and was about 60 meV below the band-to-band emission peak at ∼ 0.82 eV, was observed to be the dominant emission in Mg-doped InN epilayers. The PL spectral peak position and the temperature dependent emission intensity corroborated each other and suggested that the Mg acceptor level in InN is about 60 meV above the valance band maximum.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Optical quenching of NiO/Ni coated ZnO nanowires

Y. H. Park, Y. H. Shin, S. J. Noh, Yongmin Kim, S. S. Lee, C. G. Kim, K. S. An, and C. Y. Park

Appl. Phys. Lett. 91, 012102 (2007); http://dx.doi.org/10.1063/1.2753717 (3 pages) | Cited 10 times

Online Publication Date: 2 July 2007

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Low temperature photoluminescence (PL) measurements were carried out to investigate optical transition characteristics of ZnO nanowires, Ni nanodot, and NiO coated ZnO nanowires (NWs). PL emission spectra show emission peaks of distinctive bound exciton to neutral donor (D0X) and to acceptor (A0X) transition. The authors found that the optical quenching was drastic with increasing temperature and the activation energies are unusually small. The major PL emission peak for ZnO NW was switched from D0X to A0X for Ni–ZnO nanodot NWs. This is due to the reason that diffused hydrogen atoms into ZnO NWs during thermal annealing played as acceptors.
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78.67.Lt Quantum wires
78.55.Et II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
73.21.Hb Quantum wires
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

V/Al/V/Ag Ohmic contacts to n-AlGaN/GaN heterostructures with a thin GaN cap

M. A. Miller and S. E. Mohney

Appl. Phys. Lett. 91, 012103 (2007); http://dx.doi.org/10.1063/1.2753497 (3 pages) | Cited 8 times

Online Publication Date: 2 July 2007

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Silver is studied as a replacement for Au in V- and Ti-based Ohmic contacts to GaN-capped n-Al0.27Ga0.73N/GaN heterostructures for high electron mobility transistors. An optimized V/Al/V/Ag contact provided a low contact resistance of 0.27 Ω mm and specific contact resistance of 1.7×10−6 Ω cm2, and was much smoother than analogous Au-bearing metallizations. Transmission electron microscopy reveals a very limited reaction of the annealed metallization and semiconductor, leaving the Al0.27Ga0.73N layer intact. The majority of the Al0.27Ga0.73N interface is contacted by Ag-bearing phases. Silver has a lower work function than Au and facilitates the formation of a low-resistance Ohmic contact.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing

Heavy hole doping of epitaxial thin films of a wide gap p-type semiconductor, LaCuOSe, and analysis of the effective mass

Hidenori Hiramatsu, Kazushige Ueda, Hiromichi Ohta, Masahiro Hirano, Maiko Kikuchi, Hiroshi Yanagi, Toshio Kamiya, and Hideo Hosono

Appl. Phys. Lett. 91, 012104 (2007); http://dx.doi.org/10.1063/1.2753546 (3 pages) | Cited 24 times

Online Publication Date: 2 July 2007

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The high density hole doping (1.7×1021 cm−3) for a wide gap (Eg = ∼ 2.8 eV) p-type semiconductor was achieved on 40 nm thick Mg-doped LaCuOSe epitaxial films. These films exhibited distinct free carrier absorption, and the effective mass and momentum relaxation time were analyzed. Its small hole mobility [ ∼ 3.5 cm2/(V s)] compared to the electron mobilities of wide gap n-type semiconductors is attributed to a heavy effective mass of 1.6±0.2me. Regardless of the heavy hole doping, a band filling effect was not observed. These results are discussed with a rigid band model and an acceptor band model.
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61.72.up Other materials
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.20.Nr Semiconductor compounds
61.72.S- Impurities in crystals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Measurement of pressures in 10−10 Pa range from the damping speed of field emission current

B. Cho, T. Itagaki, T. Ishikawa, and C. Oshima

Appl. Phys. Lett. 91, 012105 (2007); http://dx.doi.org/10.1063/1.2753721 (3 pages) | Cited 4 times

Online Publication Date: 3 July 2007

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The damping behavior of field emission (FE) currents was monitored with W(111) tips under pressures down to 5×10−10 Pa. Semilogarithmic damping curves of FE currents were linear for 0.3 L hydrogen exposure in the thoroughly degassed extreme high vacuum (XHV) FE system. The slope of semilogarithmic damping curves was linearly proportional to the operation pressure, suggesting a method of measuring pressure in an XHV range. Electron stimulated desorption was not observed.
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79.70.+q Field emission, ionization, evaporation, and desorption

Effect of intrinsic stress from a nanoscale high-dielectric constant gate oxide on strain in a transistor channel

Hongtao Wang and Shriram Ramanathan

Appl. Phys. Lett. 91, 012106 (2007); http://dx.doi.org/10.1063/1.2753732 (3 pages) | Cited 1 time

Online Publication Date: 3 July 2007

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The author propose using a nanoscale gate dielectric directly as stressor to alter the strain field in a transistor channel. Using experimentally determined intrinsic stress generated from a gate dielectric, they analyze the strain field in a channel by finite element methods simulation. Analysis shows that the gate dielectric induced strain can be as large as 0.2% corresponding to ∼ 25% hole mobility enhancement. The results predict that performance improvement in semiconductor devices can be achieved by choosing proper dielectric film deposition conditions and optimizing geometric dimensions. The approach is compatible with other methods presently utilized for generating local strains as well as high-mobility semiconductor channel layers.
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85.30.Tv Field effect devices

Anisotropic low-temperature piezoresistance in (311)A GaAs two-dimensional holes

B. Habib, J. Shabani, E. P. De Poortere, M. Shayegan, and R. Winkler

Appl. Phys. Lett. 91, 012107 (2007); http://dx.doi.org/10.1063/1.2753735 (3 pages) | Cited 4 times

Online Publication Date: 3 July 2007

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The authors report low-temperature resistance measurements in a modulation-doped, (311)A GaAs two-dimensional hole system as a function of applied in-plane strain. The data reveal a strong but anisotropic piezoresistance whose magnitude depends on the density as well as the direction along which the resistance is measured. At a density of 1.6×1011 cm−2 and for a strain of about 2×10−4 applied along the [01math], e.g., the resistance measured along this direction changes by nearly a factor of 2, while the resistance change in the [math33] direction is less than 10% and has the opposite sign. The accurate energy band calculations indicate a pronounced and anisotropic deformation of the heavy-hole dispersion with strain, qualitatively consistent with the experimental data. The extremely anisotropic magnitude of the piezoresistance, however, lacks a quantitative explanation.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors

High efficiency InGaAs solar cells on Si by InP layer transfer

James M. Zahler, Katsuaki Tanabe, Corinne Ladous, Tom Pinnington, Frederick D. Newman, and Harry A. Atwater

Appl. Phys. Lett. 91, 012108 (2007); http://dx.doi.org/10.1063/1.2753751 (3 pages) | Cited 15 times

Online Publication Date: 3 July 2007

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InP/Si substrates were fabricated through wafer bonding and helium-induced exfoliation of InP, and InGaAs solar cells lattice matched to bulk InP were grown on these substrates using metal-organic chemical-vapor deposition. The photovoltaic characteristics of the InGaAs cells fabricated on the wafer-bonded InP/Si substrates were comparable to those synthesized on commercially available epiready InP substrates, thus providing a demonstration of wafer-bonded InP/Si substrates as an alternative to bulk InP substrates for solar cell applications.
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84.60.Jt Photoelectric conversion
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Low-temperature method for enhancing sputter-deposited HfO2 films with complete oxidization

Chih-Tsung Tsai, Ting-Chang Chang, Po-Tsun Liu, Po-Yu Yang, Yu-Chieh Kuo, Kon-Tsu Kin, Pei-Lin Chang, and Fon-Shan Huang

Appl. Phys. Lett. 91, 012109 (2007); http://dx.doi.org/10.1063/1.2753762 (3 pages) | Cited 11 times

Online Publication Date: 3 July 2007

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A low-temperature method, supercritical CO2 fluid (SCF) technology, is proposed to improve the dielectric properties of ultrathin hafnium oxide (HfO2) film at 150 °C without significant formation of parasitic oxide at the interface between HfO2 and Si substrate. In this research, the HfO2 films were deposited by dc sputter at room temperature and post-treated by SCF which is mixed with 5 vol % propyl alcohol and 5 vol % H2O. From high-resolution transmission electron microscopy image, the interfacial oxide of SCF-treated HfO2 film is only 5 Å thick. Additionally, the enhancements in the qualities of sputter-deposited HfO2 film after SCF process are exhibited by x-ray photoelectron spectroscopy and capacitance-voltage (C-V) measurement.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
79.60.Dp Adsorbed layers and thin films
81.65.Mq Oxidation

pH sensor using AlGaN/GaN high electron mobility transistors with Sc2O3 in the gate region

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

Appl. Phys. Lett. 91, 012110 (2007); http://dx.doi.org/10.1063/1.2754637 (3 pages) | Cited 12 times

Online Publication Date: 5 July 2007

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Ungated AlGaN/GaN high electron mobility transistors (HEMTs) exhibit large changes in current upon exposing the gate region to polar liquids. The polar nature of the electrolyte introduced leds to a change of surface charges, producing a change in surface potential at the semiconductor/liquid interface. The use of Sc2O3 gate dielectric produced superior results to either a native oxide or UV ozone-induced oxide in the gate region. The ungated HEMTs with Sc2O3 in the gate region exhibited a linear change in current between pH 3 and 10 of 37 μA/pH. The HEMT pH sensors show stable operation with a resolution of <0.1 pH over the entire pH range. The results indicate that the HEMTs may have application in monitoring pH solution changes between 7 and 8, the range of interest for testing human blood.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Enhancement of the room temperature luminescence of InAs quantum dots by GaSb capping

J. M. Ripalda, D. Alonso-Álvarez, B. Alén, A. G. Taboada, J. M. García, Y. González, and L. González

Appl. Phys. Lett. 91, 012111 (2007); http://dx.doi.org/10.1063/1.2753716 (3 pages) | Cited 15 times

Online Publication Date: 5 July 2007

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The authors have studied the use of antimony for the optimization of the InAs/GaAs(001) self-assembled quantum dot (QD) luminescence characteristics in the 1.3 μm spectral region. The best results have been obtained by capping InAs QDs with 2 ML of GaSb grown on top of a 3 ML GaAs barrier separating the InAs and the GaSb layers. This results in an order of magnitude enhancement of the room temperature luminescence intensity at 1.3 μm emission wavelength.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Negative capacitance in organic semiconductor devices: Bipolar injection and charge recombination mechanism

E. Ehrenfreund, C. Lungenschmied, G. Dennler, H. Neugebauer, and N. S. Sariciftci

Appl. Phys. Lett. 91, 012112 (2007); http://dx.doi.org/10.1063/1.2752024 (3 pages) | Cited 27 times

Online Publication Date: 6 July 2007

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The authors report negative capacitance at low frequencies in organic semiconductor based diodes and show that it appears only under bipolar injection conditions. They account quantitatively for this phenomenon by the recombination current due to electron-hole annihilation. Simple addition of the recombination current to the well established model of space charge limited current in the presence of traps yields excellent fits to the experimentally measured admittance data. The dependence of the extracted characteristic recombination time on the bias voltage is indicative of a recombination process which is mediated by localized traps.
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85.60.Jb Light-emitting devices

Ohmic contacts to n+-GaN capped AlGaN/AlN/GaN high electron mobility transistors

Liang Wang, Fitih M. Mohammed, Benedict Ofuonye, and Ilesanmi Adesida

Appl. Phys. Lett. 91, 012113 (2007); http://dx.doi.org/10.1063/1.2754371 (3 pages) | Cited 5 times

Online Publication Date: 6 July 2007

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Investigations of Ti/Al/Mo/Au Ohmic contact formation, premetallization plasma treatment effects, and interfacial reactions for n+-GaN capped AlGaN/AlN/GaN heterostructures are presented. Ti thickness played an important role in determining contact performance. Transmission electron microscopy studies confirmed that thick Ti layer was necessary to fully consume the GaN cap and the top of AlGaN to enable a higher tunneling current flow. A direct correlation of plasma treatment conditions with I-V linearity, current level, and contact performance was established. The plasma-affected region is believed to extend over 20 nm into the AlGaN and GaN.
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73.40.Ns Metal-nonmetal contacts
85.30.Tv Field effect devices
68.37.Lp Transmission electron microscopy (TEM)
52.77.-j Plasma applications
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