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15 May 2006

Volume 88, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 203101 (2006); http://dx.doi.org/10.1063/1.2203932 (3 pages)

Andrea Ponzoni, Elisabetta Comini, Giorgio Sberveglieri, Jun Zhou, Shao Zhi Deng, Ning Sheng Xu, Yong Ding, and Zhong Lin Wang
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Synthesis and ethanol sensing properties of indium-doped tin oxide nanowires

X. Y. Xue, Y. J. Chen, Y. G. Liu, S. L. Shi, Y. G. Wang, and T. H. Wang

Appl. Phys. Lett. 88, 201907 (2006); http://dx.doi.org/10.1063/1.2203941 (3 pages) | Cited 37 times

Online Publication Date: 16 May 2006

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Indium-doped tin oxide (ITO) nanowires are synthesized in mass production via thermal evaporation of In2O3, SnO, and graphite mixture powders. The transverse sizes of these nanowires range from 70 to 150 nm, and the lengths are up to several tens of micrometers. The three elements In, Sn, and O uniformly distribute over the whole nanowire, respectively. The atomic concentration of In is about 5%. The gas sensors realized from these ITO nanowires are very sensitive to ethanol gas, and the sensitivity is about 40 against 200 ppm ethanol at the work temperature of 400 °C. Both the response and recovery time are shorter than 2 s. These results suggest that ITO nanowires are good candidates for fabricating gas sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
81.16.-c Methods of micro- and nanofabrication and processing

Cooperative atomic motions and core rearrangement in dislocation cross slip

Srinivas Pendurti, Sukky Jun, In-Ho Lee, and Vish Prasad

Appl. Phys. Lett. 88, 201908 (2006); http://dx.doi.org/10.1063/1.2204449 (3 pages) | Cited 4 times

Online Publication Date: 16 May 2006

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Atomistic study of cross slip of a screw dislocation in copper is presented using the action-optimization numerical technique which seeks the most probable dynamic pathway on the potential-energy surface of the atomic system during the cross-slip process. The observed mechanism reveals features of both competing mechanisms postulated in literature, i.e., the Fleischer mechanism and the Friedel-Escaig mechanism. Due to cooperative atomic motions and complex core rearrangement during the process, the activation energies of the current cross-slip mechanism are around 0.5 eV less than the lowest ever reported in corresponding studies using atomistic numerical techniques.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
82.20.Kh Potential energy surfaces for chemical reactions
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Laser-induced microexplosion confined in a bulk of silica: Formation of nanovoids

Saulius Juodkazis, Hiroaki Misawa, Tomohiro Hashimoto, Eugene G. Gamaly, and Barry Luther-Davies

Appl. Phys. Lett. 88, 201909 (2006); http://dx.doi.org/10.1063/1.2204847 (3 pages) | Cited 17 times

Online Publication Date: 16 May 2006

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We report on the nanovoid formation inside synthetic silica, viosil, by single femtosecond pulses of 30–100 nJ energy, 800 nm wavelength, and 180 fs duration. It is demonstrated that the void is formed as a result of shock and rarefaction waves at pulse power much lower than the threshold of self-focusing. The shock-compressed region around the nanovoid is demonstrated to have higher chemical reactivity. This was used to reveal the extent of the shock-compressed region by wet etching. Application potential of nanostructuring of dielectrics is discussed.
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82.33.Vx Reactions in flames, combustion, and explosions
61.72.Qq Microscopic defects (voids, inclusions, etc.)
42.62.-b Laser applications
78.47.-p Spectroscopy of solid state dynamics
62.50.-p High-pressure effects in solids and liquids
81.65.Cf Surface cleaning, etching, patterning

Suppression of heterogeneous bubble nucleation by upstream subcooled liquid flow

J. Li and G. P. Peterson

Appl. Phys. Lett. 88, 201910 (2006); http://dx.doi.org/10.1063/1.2205148 (3 pages) | Cited 2 times

Online Publication Date: 16 May 2006

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The threshold levels for quasi-steady-state bubble nucleation on a smooth platinum surface located in a microchannel, both with and without liquid flow, are explored. The measured threshold for motionless liquid compares well with the theoretical value as calculated from the classical kinetics of nucleation. The measured threshold for the case of flow in the microchannel exceeds the measured value for motionless liquid and even exceeds the theoretical value. The observed phenomena suggest that in the absence of impurities, classical theory can accurately predict the heterogeneous nucleation. In addition, subcooled fluids were found to suppress bubble nucleation.
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47.55.db Drop and bubble formation
47.55.dr Interactions with surfaces
47.60.-i Flow phenomena in quasi-one-dimensional systems
64.60.Q- Nucleation

Initial growth stage of a highly mismatched strontium film on a hydrogen-terminated silicon (111) surface

Hidehito Asaoka, Tatsuya Yamazaki, and Shin-ichi Shamoto

Appl. Phys. Lett. 88, 201911 (2006); http://dx.doi.org/10.1063/1.2205160 (3 pages) | Cited 2 times

Online Publication Date: 16 May 2006

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We report the formation of an atomically abrupt interface without strain in a strontium film using a hydrogen buffer layer on silicon, in spite of large lattice mismatch such as 12%. The onset of the initial growth stage of strontium film with its bulk lattice constant occurs with one atomic layer deposition. The interfacial monoatomic layer of hydrogen together with the first one atomic layer of strontium acts as an effective buffer layer. Our results provide microscopic evidence of heteroepitaxial growth of the strain-free film with the atomically abrupt interface in a highly mismatched system.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness

Blue luminescent isolated Alq3 molecules in a solid-state matrix

M. M. Levichkova, J. J. Assa, H. Fröb, and K. Leo

Appl. Phys. Lett. 88, 201912 (2006); http://dx.doi.org/10.1063/1.2203966 (3 pages) | Cited 11 times

Online Publication Date: 17 May 2006

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Thin vacuum deposited films of aluminum tris(8-hydroxyquinolinate) (Alq3) embedded in SiO2 matrix at concentrations corresponding to a single-molecule distribution are investigated. The spectral properties of the films are studied by luminescence spectroscopy. It is established that the dilution of Alq3 in the matrix leads to blueshift of the luminescence maximum up to 0.28 eV compared to pure Alq3 layers. In contrast to the recently reported facial isomer of Alq3 in the crystalline δ phase, we conclude from our spectral data the observation of facial isomer molecules.
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78.66.Qn Polymers; organic compounds
78.66.Li Other semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth
82.80.-d Chemical analysis and related physical methods of analysis

Reduced buckling in one dimension versus two dimensions of a compressively strained film on a compliant substrate

R. L. Peterson, K. D. Hobart, F. J. Kub, H. Yin, and J. C. Sturm

Appl. Phys. Lett. 88, 201913 (2006); http://dx.doi.org/10.1063/1.2204456 (3 pages) | Cited 6 times

Online Publication Date: 17 May 2006

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Compliant substrates are useful for manipulating the strain state of thin films. However the compliant layer may permit undesirable roughening (buckling) of a compressively strained film. In this work, we quantitatively compare two-dimensional and one-dimensional buckling in thin silicon-germanium films under biaxial and uniaxial compressive stresses, respectively. For the same strain level, films with one-dimensional stress and thus one-dimensional buckling exhibit slower buckling and lower final steady state buckling amplitude, which makes them technologically advantageous compared to biaxially strained films, which exhibit two-dimensional buckling. The results are explained through modeling.
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68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.55.-a Thin film structure and morphology
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Investigations of the characteristics of strain-free oxidation on InAlAs epilayer lattice matched to indium phosphide

Premchander Perumal, Jong Min Kim, Yong Tak Lee, and Sang Sub Kim

Appl. Phys. Lett. 88, 201914 (2006); http://dx.doi.org/10.1063/1.2204654 (3 pages) | Cited 1 time

Online Publication Date: 17 May 2006

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High resolution x-ray diffraction and transmission electron microscopy (TEM) were used to study the strain behavior in InAlAs oxides grown on In0.52Al0.48As epilayer lattice matched to InP (100) substrates by wet thermal oxidation technique. The relaxed strain morphology has been observed between the InAlAs oxides and lattice matched InAlAs epilayer to InP substrates with the optimization of process temperature, rate of oxidation, and time. Almost strain-free InAlAs oxide layer with high crystallographic quality was obtained on InAlAs epilayer, which is similar to that of lattice matched InAlAs epilayer grown on InP substrate.
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81.65.Mq Oxidation
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)

Radiation-induced differential optical absorption of metal nanoparticles

Oleg Plaksin, Yoshihiko Takeda, Hiroshi Amekura, and Naoki Kishimoto

Appl. Phys. Lett. 88, 201915 (2006); http://dx.doi.org/10.1063/1.2205161 (3 pages) | Cited 4 times

Online Publication Date: 17 May 2006

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A method of measuring the temperature of metal nanoparticles under ion bombardment is proposed. Optical absorption in the range of the surface plasmon resonance of metal nanoparticles was measured during implantation of 3 MeV Cu2+ ions into silica glass to derive a difference in optical absorption between beam on and off regimes. The radiation-induced differential (RD) spectra were similar to the spectra of thermomodulation (TM) and quite different from the spectra of nonlinear optical response measured by the pump-probe method. Increasing amplitude of RD and TM spectra was assigned to an increase of lattice temperature of Cu nanoparticles.
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78.40.Kc Metals, semimetals, and alloys
78.47.-p Spectroscopy of solid state dynamics
61.72.up Other materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Red phosphorescence in Sr4Al14O25: Cr3+,Eu2+,Dy3+ through persistent energy transfer

Ruixia Zhong, Jiahua Zhang, Xia Zhang, Shaozhe Lu, and Xiao-jun Wang

Appl. Phys. Lett. 88, 201916 (2006); http://dx.doi.org/10.1063/1.2205167 (3 pages) | Cited 16 times

Online Publication Date: 17 May 2006

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Cr3+, Eu2+, and Dy3+ codoped Sr4Al14O25 has been synthesized by solid-state reaction. Long persistent phosphorescence in red of Cr3+ and in blue of Eu2+ has been observed in this system with persistence times of over 2 h for the red and 10 h for the blue. Red phosphorescence is performed through persistent energy transfer from Eu2+ to Cr3+, converting the blue to the red. Concentration effect is analyzed based on energy transfer. The calculated results are in good agreement with the experimental data. The different decay patterns of the red and blue phosphorescence are measured and discussed.
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78.55.Hx Other solid inorganic materials

Lifetime study of N impurity states in GaAs1−xNx (x = 0.1%) under hydrostatic pressure

W. J. Wang, X. D. Yang, B. S. Ma, Z. Sun, F. H. Su, K. Ding, Z. Y. Xu, G. H. Li, Y. Zhang, A. Mascarenhas, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 88, 201917 (2006); http://dx.doi.org/10.1063/1.2205729 (3 pages) | Cited 1 time

Online Publication Date: 17 May 2006

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The lifetimes of a series of N-related photoluminescence lines (A2–A6) in GaAs1−xNx (x = 0.1%) were studied under hydrostatic pressures at ∼ 30 K. The lifetimes of A5 and A6 were found to increase rapidly with increasing pressure: from 2.1 ns at 0 GPa to more than 20 ns at 0.92 GPa for A5 and from 3.2 ns at 0.63 GPa to 10.8 ns at 0.92 GPa for A6. The lifetime is found to be closely correlated with the binding energy of the N impurity states, which is shown either in the pressure dependence for a given emission line or in the lifetime variation from A2 to A6.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors

Diffusion of zinc vacancies and interstitials in zinc oxide

Paul Erhart and Karsten Albe

Appl. Phys. Lett. 88, 201918 (2006); http://dx.doi.org/10.1063/1.2206559 (3 pages) | Cited 50 times

Online Publication Date: 18 May 2006

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The self-diffusion coefficient of zinc in ZnO is derived as a function of the chemical potential and Fermi level from first-principles calculations. Density functional calculations in combination with the climbing image-nudged elastic band method are used in order to determine migration barriers for vacancy, interstitial, and interstitialcy jumps. Zinc interstitials preferentially diffuse to second nearest neighbor positions. They become mobile at temperatures as low as 90–130 K and therefore allow for rapid defect annealing. Under predominantly oxygen-rich and n-type conditions self-diffusion occurs via a vacancy mechanism.
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66.30.Lw Diffusion of other defects
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
65.40.G- Other thermodynamical quantities

Neutron diffraction investigation of hysteresis reduction and increase in linearity in the stress-strain response of superelastic NiTi

C. R. Rathod, B. Clausen, M. A. M. Bourke, and R. Vaidyanathan

Appl. Phys. Lett. 88, 201919 (2006); http://dx.doi.org/10.1063/1.2204650 (3 pages) | Cited 11 times

Online Publication Date: 18 May 2006

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In situ neutron diffraction measurements during loading have been performed on plastically deformed superelastic NiTi samples. The measurements observed retained B19′ phase in the unloaded state as a result of the plastic deformation in otherwise completely B2 phase samples. A reversible stress-induced B2–B19′ transformation on application and removal of stress occurred in the presence of this retained B19′ phase. The amount and orientation of this retained B19′ phase changed with cycling. Such direct atomic scale observations in the bulk are used here for the first time to qualitatively elucidate the macroscopic stress-strain response in plastically deformed superelastic NiTi.
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81.05.Bx Metals, semimetals, and alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.30.Kf Martensitic transformations

High strength hexagonal structured dendritic phase reinforced Zr–Ti–Ni bulk alloy with enhanced ductility

S. Scudino, J. Das, M. Stoica, K. B. Kim, M. Kusy, and J. Eckert

Appl. Phys. Lett. 88, 201920 (2006); http://dx.doi.org/10.1063/1.2206695 (3 pages) | Cited 21 times

Online Publication Date: 18 May 2006

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A Zr74.9Ti10.5Ni14.6 nanostructure-dendrite composite was prepared by copper mold casting. X-ray diffraction, and scanning and transmission electron microscopies, reveal a microstructure comprising ultrafine-scale dendrites with hexagonal structure and a two-phase interdendritic matrix, consisting of nanocrystalline hexagonal and tetragonal phases. Room temperature compression tests show evident yielding and 6% plastic strain together with work hardening up to 1622 MPa. These results indicate that composite materials based on hexagonal phases might be an alternative to composites containing body-centered cubic phase reinforcements.
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61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.40.Lm Deformation, plasticity, and creep
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
62.20.F- Deformation and plasticity
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Electron emission mechanism of diamond characterized using combined x-ray photoelectron spectroscopy/ultraviolet photoelectron spectroscopy/field emission spectroscopy system

Hisato Yamaguchi, Takatoshi Yamada, Masato Kudo, Yuji Takakuwa, and Ken Okano

Appl. Phys. Lett. 88, 202101 (2006); http://dx.doi.org/10.1063/1.2200229 (3 pages) | Cited 9 times

Online Publication Date: 15 May 2006

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Clarification on electron emission mechanism of diamond is one essential approach to realize the clear vision of vacuum nanoelectronics. Electric field of less than 5 V/μm is enough to extract electrons from diamond, whereas field of one to two orders of magnitude higher is needed to extract electrons from conventional metal emitter tips. Diamond has various advantages as an electron emitter in addition to the low-threshold voltage, such as negative electron affinity and high thermal conductivity. The difficulty in clarification of electron emission mechanism is the factor preventing diamond from being used in a practical way. In this study, combined spectroscopy of x-ray photoelectron spectroscopy/ultraviolet photoelectron spectroscopy/field emission spectroscopy was performed to characterize the electron emission mechanism of diamond. The results indicated the first successful observation of applied voltage dependence on the origin of field-emitted electrons.
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79.70.+q Field emission, ionization, evaporation, and desorption
79.60.Bm Clean metal, semiconductor, and insulator surfaces
72.80.Cw Elemental semiconductors

Electrical observations of filamentary conductions for the resistive memory switching in NiO films

D. C. Kim, S. Seo, S. E. Ahn, D.-S. Suh, M. J. Lee, B.-H. Park, I. K. Yoo, I. G. Baek, H.-J. Kim, E. K. Yim, J. E. Lee, S. O. Park, H. S. Kim, U-In Chung, J. T. Moon, et al.

Appl. Phys. Lett. 88, 202102 (2006); http://dx.doi.org/10.1063/1.2204649 (3 pages) | Cited 178 times

Online Publication Date: 15 May 2006

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Experimental results on the bistable resistive memory switching in submicron sized NiO memory cells are presented. By using a current-bias method, intermediate resistance states and anomalous resistance fluctuations between resistance states are observed during the resistive transition from high resistance state to low resistance state. They are interpreted to be associated with filamentary conducting paths with their formation and rupture for the memory switching origin in NiO. The experimental results are discussed on the basis of filamentary conductions in consideration of local Joule heating effect.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Fabrication of metallic air bridges using multiple-dose electron beam lithography

E. Girgis, J. Liu, and M. L. Benkhedar

Appl. Phys. Lett. 88, 202103 (2006); http://dx.doi.org/10.1063/1.2204833 (3 pages) | Cited 6 times

Online Publication Date: 15 May 2006

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The techniques of fabricating metallic air bridges using different resists in a one-step electron beam lithography are presented. The exposure process employed a single-layer polymethyl methacrylate (PMMA) or photoresists with either different doses in the span and feet areas or with varying acceleration voltage of the electron beam. The process using photoresists with different doses has produced air bridges more stable than what the PMMA method using various acceleration voltages would achieve. Using this method, air bridges up to 12 μm long have been fabricated. The length and height of these metallic air bridges vary with the photoresist thickness.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.Nd Micro- and nanolithography

Determination of acceptor concentration in GaN from photoluminescence

M. A. Reshchikov

Appl. Phys. Lett. 88, 202104 (2006); http://dx.doi.org/10.1063/1.2204835 (3 pages) | Cited 5 times

Online Publication Date: 15 May 2006

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The concentration of the acceptor responsible for the yellow luminescence (YL) band at about 2.2 eV in GaN is determined from photoluminescence. The YL band intensity increases linearly with excitation power density and partially saturates above some critical value. The dependence is quantitatively described within a phenomenological model accounting for recombination statistics in GaN layer and saturation of acceptors with photogenerated holes. The incomplete saturation of the YL intensity at high excitation intensities is explained by gradual saturation of acceptors at different distances from the sample surface. The identity of deep and shallow acceptors in GaN is discussed.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Electroluminescence from ZnO nanowires in n-ZnO film/ZnO nanowire array/p-GaN film heterojunction light-emitting diodes

Min-Chang Jeong, Byeong-Yun Oh, Moon-Ho Ham, and Jae-Min Myoung

Appl. Phys. Lett. 88, 202105 (2006); http://dx.doi.org/10.1063/1.2204655 (3 pages) | Cited 68 times

Online Publication Date: 16 May 2006

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ZnO nanowire-array-embedded n-ZnO/p-GaN heterojunction light-emitting diodes were fabricated by growing Mg-doped p-GaN films, ZnO nanowire arrays, and polycrystalline n-ZnO films consecutively. Electroluminescence emission having the wavelength of 386 nm was observed under forward bias in the heterojunction diodes and the UV-violet light was emerged from the ZnO nanowires. The heterojunction diode was thermal treated in hydrogen ambient to increase the electron injection rate from the n-ZnO films into the ZnO nanowires. High concentration of electrons supplied from the n-ZnO films activated the radiative recombination in the ZnO nanowires, i.e., increased the light-emitting efficiency of the heterojunction diode.
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78.67.Lt Quantum wires
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.40.Gh Other heat and thermomechanical treatments
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

n-type AlN layer by Si ion implantation

Masakazu Kanechika and Tetsu Kachi

Appl. Phys. Lett. 88, 202106 (2006); http://dx.doi.org/10.1063/1.2204656 (2 pages) | Cited 1 time

Online Publication Date: 16 May 2006

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n-type AlN layer was obtained by Si ion implantation and the subsequent activation annealing. Si ions were implanted to an unintentionally doped AlN layer grown on a sapphire substrate at an acceleration energy of 90 keV with a dose of 5×1015 cm−2. The activation annealing was performed at 1400 °C for 10 min in a nitrogen ambient. We characterized it by Hall-effect measurements in a temperature range from 373 to 873 K. These revealed that the carrier type exhibited n type, the carrier concentration at 373 K was approximately 8.8×1015 cm−3, and that the Hall mobility at 373 K was as high as 20 cm2 V−1 s−1. The donor ionization energy was 294 meV. The Hall mobility varied as T−1.1 (T is the absolute temperature) above 523 K.
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61.72.uj III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Photoluminescence property of InGaN single quantum well with embedded AlGaN δ layer

Jongwoon Park and Yoichi Kawakami

Appl. Phys. Lett. 88, 202107 (2006); http://dx.doi.org/10.1063/1.2205731 (3 pages) | Cited 34 times

Online Publication Date: 16 May 2006

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We investigate the photoluminescence (PL) properties of a thick InGaN single quantum well (SQW) in which an AlGaN δ layer is embedded. The δ layer offers an extra degree of freedom which may be employed to tune the emission wavelength. One of the most salient features of such a QW structure is that the long-wavelength tuning is feasible with lower indium composition. The δ layer also increases the wave function overlap between holes and electrons, shortening the PL lifetime. All the measurement results are consistent with the numerical predictions. The QW structure could be of great importance in the design of long-wavelength lasers.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors

Structural, electrical, and optical properties of p-type ZnO thin films with Ag dopant

Hong Seong Kang, Byung Du Ahn, Jong Hoon Kim, Gun Hee Kim, Sung Hoon Lim, Hyun Woo Chang, and Sang Yeol Lee

Appl. Phys. Lett. 88, 202108 (2006); http://dx.doi.org/10.1063/1.2203952 (3 pages) | Cited 73 times

Online Publication Date: 17 May 2006

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p-type ZnO films have been fabricated on a (0001) Al2O3 substrate, using Ag2O as a silver dopant by pulsed laser deposition. The structural property of those films is systematically characterized by observing the shift of (0002) peak to investigate the substitution of Ag+ for Zn+. Narrow deposition temperature for Ag-doped p-type ZnO films has been obtained in the range of 200–250 °C with the hole concentration of 4.9×1016–6.0×1017 cm−3. A neutral acceptor bound exciton has been clearly observed by photoluminescence emitted at 3.317 eV in Ag-doped p-type ZnO thin films.
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78.55.Et II-VI semiconductors
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
71.35.-y Excitons and related phenomena
68.55.-a Thin film structure and morphology

Optical monitoring of nonequilibrium carrier lifetime in freestanding GaN by time-resolved four-wave mixing and photoluminescence techniques

T. Malinauskas, K. Jarašiūnas, S. Miasojedovas, S. Juršėnas, B. Beaumont, and P. Gibart

Appl. Phys. Lett. 88, 202109 (2006); http://dx.doi.org/10.1063/1.2204651 (3 pages) | Cited 24 times

Online Publication Date: 18 May 2006

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Optical monitoring of nonequilibrium carrier dynamics was performed in freestanding GaN. Four-wave mixing kinetics directly provided carrier lifetime of 5.4 ns in the layer, while complementary measurements by photoluminescence technique revealed the fast transients with subnanosecond decay time. Numerical modeling of photoluminescence decay taking into account the carrier spatial-temporal dynamics allowed us to attribute an origin of the fast photoluminescence transients to carrier diffusion to the bulk and to reabsorption of the backward emission. The studies demonstrated carrier diffusion limited applicability of the time-resolved photoluminescence technique for carrier lifetime measurements in a high quality thick III-nitride layers.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Carrier concentration dependence of acceptor activation energy in p-type ZnO

O. Lopatiuk-Tirpak, W. V. Schoenfeld, L. Chernyak, F. X. Xiu, J. L. Liu, S. Jang, F. Ren, S. J. Pearton, A. Osinsky, and P. Chow

Appl. Phys. Lett. 88, 202110 (2006); http://dx.doi.org/10.1063/1.2206700 (3 pages) | Cited 20 times

Online Publication Date: 18 May 2006

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The characteristics of an acceptor level in Sb-doped, p-type ZnO were studied using cathodoluminescence (CL) spectroscopy as a function of hole concentration. Variable-temperature CL measurements allowed us to estimate the activation energy of an Sb-related acceptor from temperature-induced decay of CL intensity. The values of activation energy of about 212±28, 175±20, 158±22, and 135±15 meV were obtained for samples with carrier concentrations of 1.3×1017, 6.0×1017, 8.2×1017, and 1.3×1018 cm−3, respectively. The involvement of acceptor levels is supported by the temperature-dependent hole concentration measurements. The possible origins of the strong temperature dependence are discussed.
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71.55.Gs II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
72.80.Ey III-V and II-VI semiconductors

Model to explain the anisotropic phenomenon of effective mobility of organic field-effect transistors

Liwei Shang, Congshun Wang, and Ming Liu

Appl. Phys. Lett. 88, 202111 (2006); http://dx.doi.org/10.1063/1.2203959 (3 pages) | Cited 2 times

Online Publication Date: 19 May 2006

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Recent research has revealed that the overall effective mobility of organic field-effect transistors depends on the anisotropy film. To account for this behavior, a modified model is proposed based on the previous grain boundary trap model. In this model, the degeneration factor, which is related to the maximal misorientation angle of grains, is introduced to describe the difference between aligned and nonaligned organic films. More explicit definitions of effective grain length and grain boundary are given concerning this anisotropic phenomenon. The simulation results are consistent with experimental data for aligned pentacene and copper phthalocyanine (CuPc).
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
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