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15 May 2006

Volume 88, Issue 20, Articles (20xxxx)

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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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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 176 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 67 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 72 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 23 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

Systematic approach for analyzing reflectance-difference spectra: Application to silicon-dielectric interfaces

M. K. Brinkley, G. D. Powell, and D. E. Aspnes

Appl. Phys. Lett. 88, 202112 (2006); http://dx.doi.org/10.1063/1.2204844 (3 pages) | Cited 5 times

Online Publication Date: 19 May 2006

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We describe a combinatorial approach for analyzing reflectance-difference/reflectance-anisotropy (RD/RA) spectra that avoids the need to establish null orientations experimentally, suppresses experimental artifacts, signal averages, and allows RD/RA spectra to be assessed systematically for secondary contributions at principal angles different from that of the dominant contribution. Application to rapid-thermal-annealed oxidized and nitrided vicinal (111) Si-dielectric interfaces demonstrates the effectiveness of the procedure.
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78.20.-e Optical properties of bulk materials and thin films
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing

Heating in single-electron pumps driven by surface acoustic waves

Pawel Utko, Poul Erik Lindelof, and Kurt Gloos

Appl. Phys. Lett. 88, 202113 (2006); http://dx.doi.org/10.1063/1.2205169 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2006

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We use a practical thermometer based on the resistance of the two-dimensional electron gas to characterize single-electron devices driven by surface acoustic waves. At the typical microwave powers ( ∼ 10 dBm) required to observe the quantization of the acoustoelectric current in such structures, the electron-gas temperature increases from our base 1.8 K to 5–6 K. The power deposited by the surface acoustic wave itself can be clearly resolved. However, it is several times smaller than the overall rf heating, which occurs over a frequency range of few gigahertz.
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85.35.Gv Single electron devices
43.58.-e

Analysis of boron strain compensation in silicon-germanium alloys by Raman spectroscopy

Saurabh Chopra, Mehmet C. Ozturk, Veena Misra, Kris McGuire, and Laurie E. McNeil

Appl. Phys. Lett. 88, 202114 (2006); http://dx.doi.org/10.1063/1.2205752 (3 pages) | Cited 10 times

Online Publication Date: 19 May 2006

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The impact of heavy boron doping on the biaxial compressive strain in Si1−xGex layers grown on Si has been investigated using Raman spectroscopy and theoretical calculations. It is shown that one boron atom is sufficient to compensate the strain due to approximately 6.9 Ge atoms. This effect is appreciably large for boron concentrations as low as 1%, typical for applications, which employ heavily boron doped layers. Using strain compensation, the Ge content can be substantially increased without increasing the stored strain energy. This phenomenon can be useful in applications, which require low-resistivity p-type strained Si1−xGex layers with high Ge content.
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81.05.Hd Other semiconductors
78.30.Hv Other nonmetallic inorganics
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.S- Impurities in crystals
61.72.up Other materials
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