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14 Mar 2005

Volume 86, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 86, 113104 (2005); http://dx.doi.org/10.1063/1.1883725 (3 pages)

S. Bhattacharyya, C. Sinturel, J. P. Salvetat, and M.-L. Saboungi
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Effect of hydrogen peroxide treatment on the characteristics of Pt Schottky contact on n-type ZnO

Sang-Ho Kim, Han-Ki Kim, and Tae-Yeon Seong

Appl. Phys. Lett. 86, 112101 (2005); http://dx.doi.org/10.1063/1.1862772 (3 pages) | Cited 60 times

Online Publication Date: 7 March 2005

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We report on the formation of good Pt Schottky contacts on the Zn-terminated n-type ZnO (0001) surfaces ( ∼ 2×1017 cm−3) using surface treatment with a hydrogen peroxide solution. The Pt contacts on organic solvent-cleaned ZnO (0001) show leaky behavior with a high leakage current of ∼ −0.05 A under −5 V reverse bias voltage, whereas the hydrogen peroxide-treated contacts show Schottky behavior with very low leakage current of ∼ −6.5×10−8 A under −5 V reverse bias voltage. Schottky barrier heights estimated from current-voltage and capacitance-voltage characteristics are 0.89 and 0.93 eV, respectively. Room-temperature photoluminescence results show that the hydrogen peroxide treatment is fairly effective in removing deep-level defects near the ZnO surface region. In addition, the preliminary deep-level transient spectroscopy result is also presented.
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81.05.Dz II-VI semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Cf Surface cleaning, etching, patterning
73.40.Ns Metal-nonmetal contacts
71.55.Gs II-VI semiconductors
78.68.+m Optical properties of surfaces
78.55.Et II-VI semiconductors

Ab initio computation of the mean inner Coulomb potential of amorphous carbon structures

M. Schowalter, J. T. Titantah, D. Lamoen, and P. Kruse

Appl. Phys. Lett. 86, 112102 (2005); http://dx.doi.org/10.1063/1.1885171 (3 pages) | Cited 5 times

Online Publication Date: 7 March 2005

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The mean inner Coulomb potential (MIP) of amorphous carbon structures was computed for slabs with mass densities between ρ = 2.0 g/cm3 and ρ = 3.5 g/cm3 by the full potential linearized augmented plane-wave (FLAPW) method. The amorphous carbon structures consisting of 64 carbon atoms were generated by a classical metropolis Monte Carlo procedure using the Tersoff potential for carbon. The MIP shows a linear dependence on the mass density. Values of the MIP of the amorphous carbon structures are compared with experimental values and with computed values for the MIP of graphite and diamond.
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61.43.Bn Structural modeling: serial-addition models, computer simulation
61.43.Er Other amorphous solids
68.35.B- Structure of clean surfaces (and surface reconstruction)

Hydrogen sensing properties of a Pt‐oxide‐Al0.24Ga0.76As high-electron-mobility transistor

Chin-Chuan Cheng, Yan-Ying Tsai, Kun-Wei Lin, Huey-Ing Chen, and Wen-Chau Liu

Appl. Phys. Lett. 86, 112103 (2005); http://dx.doi.org/10.1063/1.1883721 (3 pages) | Cited 6 times

Online Publication Date: 7 March 2005

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The interesting hydrogen sensing performances of a Pt-oxide-AlGaAs (MOS) high electron mobility transistor (HEMT) are studied and demonstrated. The effects of hydrogen adsorption on device performances such as the threshold voltage shift ΔVth, drain saturation current variation ΔIDS, and transient response are presented. ΔVth and ΔIDS decreased with increasing operating temperature. This suggests that, at higher temperature, less hydrogen atoms diffuse through the Pt bulk and reach the interface between the Pt metal and oxide layer resulting from the relatively faster formation rate of hydroxyl on the Pt surface. The response curves of the studied Pt-AlGaAs MOS HEMT show various profiles at different temperatures. The influences of hydrogen concentration and temperature on the interface sites occupied by adsorbed atoms are also studied.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices
82.80.-d Chemical analysis and related physical methods of analysis

Charge transport and recombination in bulk heterojunction solar cells studied by the photoinduced charge extraction in linearly increasing voltage technique

A. J. Mozer, N. S. Sariciftci, L. Lutsen, D. Vanderzande, R. Österbacka, M. Westerling, and G. Juška

Appl. Phys. Lett. 86, 112104 (2005); http://dx.doi.org/10.1063/1.1882753 (3 pages) | Cited 51 times

Online Publication Date: 8 March 2005

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Charge carrier mobility and recombination in a bulk heterojunction solar cell based on the mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)-C61 (PCBM) has been studied using the novel technique of photoinduced charge carrier extraction in a linearly increasing voltage (Photo-CELIV). In this technique, charge carriers are photogenerated by a short laser flash, and extracted under a reverse bias voltage ramp after an adjustable delay time (tdel). The Photo-CELIV mobility at room temperature is found to be μ = 2×10−4 cm2 V−1 s−1, which is almost independent on charge carrier density, but slightly dependent on tdel. Furthermore, determination of charge carrier lifetime and demonstration of an electric field dependent mobility is presented.
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84.60.Jt Photoelectric conversion

pH measurements with single ZnO nanorods integrated with a microchannel

B. S. Kang, F. Ren, Y. W. Heo, L. C. Tien, D. P. Norton, and S. J. Pearton

Appl. Phys. Lett. 86, 112105 (2005); http://dx.doi.org/10.1063/1.1883330 (3 pages) | Cited 60 times

Online Publication Date: 8 March 2005

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Single ZnO nanorods with Ohmic contacts at either end exhibit large changes in current upon exposing the surface region to polar liquids introduced through an integrated microchannel. The polar nature of the electrolyte introduced led to a change of surface charges on the nanorod, producing a change in surface potential at the semiconductor∕liquid interface. The nanorods exhibit a linear change in conductance between pH 2 and 12 of 8.5 nS/pH in the dark and 20 nS/pH when illuminated with ultraviolet (365 nm) light. The nanorods show stable operation with a resolution of ∼ 0.1 pH over the entire pH range. The results indicate that ZnO nanorods may have applications in integrated chemical, gas, and fluid monitoring sensors.
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82.47.Rs Electrochemical sensors
82.45.Gj Electrolytes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.40.Mr Semiconductor-electrolyte contacts
73.40.Ns Metal-nonmetal contacts
73.25.+i Surface conductivity and carrier phenomena
72.40.+w Photoconduction and photovoltaic effects

Integration of a gate electrode into carbon nanotube devices for scanning tunneling microscopy

J. Kong, B. J. LeRoy, S. G. Lemay, and C. Dekker

Appl. Phys. Lett. 86, 112106 (2005); http://dx.doi.org/10.1063/1.1883301 (3 pages) | Cited 5 times

Online Publication Date: 8 March 2005

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We have developed a fabrication process for incorporating a gate electrode into suspended single-walled carbon nanotube structures for scanning tunneling spectroscopy studies. The nanotubes are synthesized by chemical vapor deposition directly on a metal surface. The high temperature (800 °C) involved in the growth process poses challenging issues such as surface roughness and integrity of the structure which are addressed in this work. We demonstrate the effectiveness of the gate on the freestanding part of the nanotubes by performing tunneling spectroscopy that reveals Coulomb blockade diamonds. Our approach enables combined scanning tunneling microscopy and gated electron transport investigations of carbon nanotubes.
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85.35.Kt Nanotube devices
81.07.De Nanotubes
73.63.Fg Nanotubes
73.23.Hk Coulomb blockade; single-electron tunneling
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Hydrogenation∕deuteration of the Si–SiO2 interface: Atomic-scale mechanisms and limitations

L. Tsetseris and S. T. Pantelides

Appl. Phys. Lett. 86, 112107 (2005); http://dx.doi.org/10.1063/1.1883710 (3 pages) | Cited 3 times

Online Publication Date: 8 March 2005

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The mechanisms responsible for exchange of hydrogen with deuterium at the Si–SiO2 interfaces are analyzed through first-principles calculations. The associated reaction barrier is found to be 1.94 eV, in agreement with experiments of Cheng et al. [IEEE Electron. Device Lett. 22, 203 (2001) ; Cheng et al.J. Appl. Phys. 90, 6536 (2001) ] that studied the kinetics of the phenomenon through electrical measurements. The substitution of hydrogen by deuterium can be limited by another possible process, the breakup of the D2 molecule to a pair of Si–D bonds, which has a similar barrier.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Tr Kinetic isotope effects including muonium
82.30.Nr Association, addition, insertion, cluster formation

Electrical characteristics of GaN implanted with Si+ at elevated temperatures

Y. Irokawa, O. Fujishima, T. Kachi, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 86, 112108 (2005); http://dx.doi.org/10.1063/1.1884744 (3 pages) | Cited 4 times

Online Publication Date: 9 March 2005

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Si+ implantation at multiple ion energies (30–360 keV) into GaN for n-type doping was carried out at substrate temperatures from 27 to 700 °C, followed by annealing at 1150–1400 °C for 5 min. At total doses of 2.0×1014 cm−2 (corresponding to an approximately uniform Si concentration of ∼ 4×1018 cm−3), the use of elevated implant temperature does not produce improved electrical characteristics. For anneal temperatures below ∼ 1300 °C, the resulting sheet resistance of the GaN implanted at 700 °C was approximately a factor of 2 higher than for room-temperature implantation, mainly through a lower sheet carrier density. At the higher annealing temperatures (>1300 °C), elevated implant temperature produced similar sheet resistances to implantation carried out at room temperature. For annealing at 1300 °C, the lowest sheet resistances (<700 Ω/◻) and highest activation efficiencies ( ∼ 65%) were obtained for implant temperatures <400 °C. The most plausible explanation is that at these doses, SiGa (i.e., donor state) site occupation is not a strong function of the initial amount of damage created by the implantation.
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73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.Cc Kinetics of defect formation and annealing
61.72.S- Impurities in crystals

Electrical spin injection in multiwall carbon nanotubes with transparent ferromagnetic contacts

S. Sahoo, T. Kontos, C. Schönenberger, and C. Sürgers

Appl. Phys. Lett. 86, 112109 (2005); http://dx.doi.org/10.1063/1.1882761 (3 pages) | Cited 35 times

Online Publication Date: 9 March 2005

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We report on electrical spin injection measurements on multiwall carbon nanotubes (MWNTs). We use a ferromagnetic alloy Pd1−xNix with x ≈ 0.7 which allows us to obtain devices with resistances as low as 5.6 kΩ at 300 K. The yield of device resistances below 100 kΩ, at 300 K, is around 50%. We measure at 2 K a hysteretic magneto-resistance due to the magnetization reversal of the ferromagnetic leads. The relative difference between the resistance in the antiparallel (AP) orientation and the parallel (P) orientation is about 2%.
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75.50.Cc Other ferromagnetic metals and alloys
72.25.Ba Spin polarized transport in metals
72.25.Mk Spin transport through interfaces
75.60.Jk Magnetization reversal mechanisms
75.47.Np Metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Surface recombination velocity of silicon wafers by photoluminescence

D. Baek, S. Rouvimov, B. Kim, T.-C. Jo, and D. K. Schroder

Appl. Phys. Lett. 86, 112110 (2005); http://dx.doi.org/10.1063/1.1884258 (3 pages) | Cited 4 times

Online Publication Date: 9 March 2005

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Photoluminescence (PL) and optical reflection measurements, obtained in the two-wavelength SiPHER PL instrument, are used to determine the surface recombination velocity of silicon wafers. Local measurements and contour maps are possible allowing surface recombination maps to be displayed. This instrument also allows doping and trap density measurements. Surface recombination velocities from 10 to 106 cm/s can be measured on low or high resistivity polished and epitaxial wafers.
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73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
73.25.+i Surface conductivity and carrier phenomena
78.55.Ap Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si

Controlled growth of Zn-polar ZnO epitaxial film by nitridation of sapphire substrate

Z. X. Mei, X. L. Du, Y. Wang, M. J. Ying, Z. Q. Zeng, H. Zheng, J. F. Jia, Q. K. Xue, and Z. Zhang

Appl. Phys. Lett. 86, 112111 (2005); http://dx.doi.org/10.1063/1.1884266 (3 pages) | Cited 25 times

Online Publication Date: 9 March 2005

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Surface nitridation is used to eliminate O-polar inversion domains and control the growth of single-domain Zn-polar ZnO film on sapphire (0001) substrate by rf-plasma-assisted molecular-beam epitaxy. It is found that the nitridation temperature is crucial for achieving quality AlN buffer layers and ZnO films with cation polarity, as demonstrated by ex situ transmission electron microscopy. Under optimal growth conditions, a 4×4 surface reconstruction was observed, which is confirmed to be a characteristic surface structure of the Zn-polar films, and can be used as a fingerprint to optimize the ZnO growth.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.37.Lp Transmission electron microscopy (TEM)

On the formation and stability of p-type conductivity in nitrogen-doped zinc oxide

Teresa M. Barnes, Kyle Olson, and Colin A. Wolden

Appl. Phys. Lett. 86, 112112 (2005); http://dx.doi.org/10.1063/1.1884747 (3 pages) | Cited 78 times

Online Publication Date: 10 March 2005

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The behavior of nitrogen in ZnO thin films grown by high-vacuum plasma-assisted chemical vapor deposition is examined. Highly oriented (002) films doped with 0–2 at. % N were characterized by x-ray photoelectron spectroscopy, x-ray diffraction (XRD), Seebeck, and Hall measurements. XRD measurements revealed that the zinc oxide lattice constant decreased systematically with nitrogen doping. The as-deposited films were p-type at high doping levels, as confirmed by both Seebeck and Hall measurements. However, it was observed that hole conduction decreased and films reverted to n-type conductivity in a period of several days. This change was accompanied by a simultaneous increase in the lattice constant. The transient electrical behavior may be explained by compensation caused either by hydrogen donors or through defect formation processes common to analogous II-VI semiconductors.
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81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
68.55.A- Nucleation and growth
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Lw Thermoelectric effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
61.72.uj III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Band gaps of the dilute quaternary alloys GaNxAs1−x−yBiy and Ga1−yInyNxAs1−x

S. Tixier, S. E. Webster, E. C. Young, T. Tiedje, S. Francoeur, A. Mascarenhas, P. Wei, and F. Schiettekatte

Appl. Phys. Lett. 86, 112113 (2005); http://dx.doi.org/10.1063/1.1886254 (3 pages) | Cited 7 times

Online Publication Date: 11 March 2005

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We report strong band gap photoluminescence at room temperature in dilute quaternary GaNxAs1−x−yBiy alloys (x<1.6%,y<2.6%) grown by molecular beam epitaxy. The band gap of the alloy can be approximated by the band gap of GaAs minus the reduction in gap associated with the effects of N and Bi alloying individually. A one-parameter method for fitting the composition dependence of the band gaps of dilute quaternary semiconductor alloys is proposed which is in excellent agreement with data for Ga1−yInyNxAs1−x.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Ultrapure C60 field-effect transistors and the effects of oxygen exposure

A. Tapponnier, I. Biaggio, and P. Günter

Appl. Phys. Lett. 86, 112114 (2005); http://dx.doi.org/10.1063/1.1883327 (3 pages) | Cited 30 times

Online Publication Date: 11 March 2005

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We report on electrical measurements of C60-based field-effect transistors (FETs) that were fabricated and characterized in an ultrahigh vacuum, and on how their properties are affected by progressive exposure to impurity gases. The in situ experiments demonstrated that oxygen-free devices have unipolar n-type characteristics with an electron field-effect mobility of up to 0.08 cm2/V s immediately after fabrication, and up to 0.5 cm2/V s after an annealing treatment in a high vacuum. Upon oxygen exposure, the effective electron mobility dramatically decreases in a way that depends on the diffusion time of oxygen into the C60 thin film. It is shown that contact with oxygen can lead to C60-FETs with ambipolar characteristics. The real-time measurement of the degradation of the devices subjected to oxygen allows us to derive the diffusion rate for oxygen molecules in C60 thin films, yielding a diffusion constant D = 4×10−12 cm2/s.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices
73.61.Wp Fullerenes and related materials
66.30.J- Diffusion of impurities
81.40.Gh Other heat and thermomechanical treatments
73.50.Dn Low-field transport and mobility; piezoresistance

Scanning probe investigation of surface charge and surface potential of GaN-based heterostructures

B. J. Rodriguez, W.-C. Yang, R. J. Nemanich, and A. Gruverman

Appl. Phys. Lett. 86, 112115 (2005); http://dx.doi.org/10.1063/1.1869535 (3 pages) | Cited 11 times

Online Publication Date: 11 March 2005

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Scanning Kelvin probe microscopy (SKPM) and electrostatic force microscopy (EFM) have been employed to measure the surface potentials and the surface charge densities of the Ga- and the N-face of a GaN lateral polarity heterostructure (LPH). The surface was subjected to an HCl surface treatment to address the role of adsorbed charge on polarization screening. It has been found that while the Ga-face surface appears to be unaffected by the surface treatment, the N-face surface exhibited an increase in adsorbed screening charge density (1.6±0.5×1010 cm−2), and a reduction of 0.3±0.1 V in the surface potential difference between the N- and Ga-face surfaces.
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81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.-b Surface treatments
68.43.Mn Adsorption kinetics
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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