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19 Dec 2005

Volume 87, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 87, 252501 (2005); http://dx.doi.org/10.1063/1.2149972 (3 pages)

R. Katoh, T. Hihara, D. L. Peng, and K. Sumiyama
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Reflection high energy electron diffraction observation of surface mass transport at the two- to three-dimensional growth transition of InAs on GaAs(001)

F. Patella, F. Arciprete, M. Fanfoni, V. Sessi, A. Balzarotti, and E. Placidi

Appl. Phys. Lett. 87, 252101 (2005); http://dx.doi.org/10.1063/1.2147731 (3 pages) | Cited 12 times

Online Publication Date: 12 December 2005

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We have followed by reflection high-energy electron diffraction the nucleation of InAs quantum dots on GaAs(001), grown by molecular-beam epitaxy with growth interruptions. Surface mass transport gives rise, at the critical InAs thickness, to a huge nucleation of three-dimensional islands within 0.2 monolayers (ML). Such surface mass diffusion has been evidenced by observing the transition of the reflection high-energy electron diffraction pattern from two- to three-dimensional during the growth interruption after the deposition of 1.59 ML of InAs. It is suggested that the process is driven by the As2 adsorption-desorption process and by the lowering of the In binding energy due to compressive strain. The last condition is met first in the region surrounding dots at step edges where nucleation predominantly occurs.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Fx Diffusion; interface formation
68.65.Hb Quantum dots (patterned in quantum wells)
68.43.Mn Adsorption kinetics
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Photoluminescence study of Sb-doped p-type ZnO films by molecular-beam epitaxy

F. X. Xiu, Z. Yang, L. J. Mandalapu, D. T. Zhao, and J. L. Liu

Appl. Phys. Lett. 87, 252102 (2005); http://dx.doi.org/10.1063/1.2146208 (3 pages) | Cited 88 times

Online Publication Date: 12 December 2005

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We investigated photoluminescence (PL) from reliable and reproducible Sb-doped p-type ZnO films grown on n-Si (100) by molecular-beam epitaxy. Well-resolved PL spectra were obtained from completely dopant-activated samples with hole concentrations above 1.0×1018 cm−3. From free electron to acceptor transitions, acceptor binding energy of 0.14 eV is determined, which is in good agreement with analytical results of the temperature-dependent PL measurements. Another broad peak at 3.050 eV, which shifts to lower energy at higher temperatures, indicates the formation of deep acceptor level bands related to Zn vacancies, which are created by Sb doping.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
71.55.Gs II-VI semiconductors
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Structure investigation of low-temperature-grown GaAsSb, a material for photoconductive terahertz antennas

J. Sigmund, C. Sydlo, H. L. Hartnagel, N. Benker, H. Fuess, F. Rutz, T. Kleine-Ostmann, and M. Koch

Appl. Phys. Lett. 87, 252103 (2005); http://dx.doi.org/10.1063/1.2149977 (3 pages) | Cited 20 times

Online Publication Date: 13 December 2005

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The formation of precipitates after an annealing process in low-temperature-grown GaAs0.6Sb0.4 is observed. We use high-resolution transmission electron microscopy for a detailed structure investigation and demonstrate the functionality of the material, which has a band gap of 0.86 eV, for ultrafast optical switches. The average diameter of the clusters is 5.7 nm in the bulk region, while larger clusters are observed near the interface to a 1.3% lattice mismatched Al0.77In0.23As buffer layer. After an annealing treatment, the sheet resistance is increased by five orders of magnitude to 1.7×108 Ω/sq, which is sufficiently high to enable Auston switch operation. We report terahertz (THz) emission from the material measured in a THz time-domain spectroscopy setup. THz generation is demonstrated by using a six interdigital finger metal-semiconductor-metal structure at the feed-point of a log-periodic antenna.
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84.40.Ba Antennas: theory, components and accessories
85.60.-q Optoelectronic devices
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Surface passivation of III-V compound semiconductors using atomic-layer-deposition-grown Al2O3

M. L. Huang, Y. C. Chang, C. H. Chang, Y. J. Lee, P. Chang, J. Kwo, T. B. Wu, and M. Hong

Appl. Phys. Lett. 87, 252104 (2005); http://dx.doi.org/10.1063/1.2146060 (3 pages) | Cited 134 times

Online Publication Date: 13 December 2005

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Al2O3 was deposited on In0.15Ga0.85As/GaAs using atomic-layer deposition (ALD). Without any surface preparation or postthermal treatment, excellent electrical properties of Al2O3/InGaAs/GaAs heterostructures were obtained, in terms of low electrical leakage current density (10−8 to 10−9 A/cm2) and low interfacial density of states (Dit) in the range of 1012 cm−2 eV−1. The interfacial reaction and structural properties studied by high-resolution x-ray photoelectron spectroscopy (HRXPS) and high-resolution transmission electron microscopy (HRTEM). The depth profile of HRXPS, using synchrotron radiation beam and low-energy Ar+ sputtering, exhibited no residual arsenic oxides at interface. The removal of the arsenic oxides from Al2O3/InGaAs heterostructures during the ALD process ensures the Fermi-level unpinning, which was observed in the capacitance-voltage measurements. The HRTEM shows sharp transition from amorphous oxide to single crystalline semiconductor.
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81.65.Rv Passivation
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states
68.35.Ct Interface structure and roughness
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.37.Lp Transmission electron microscopy (TEM)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

High carrier mobility in low band gap polymer-based field-effect transistors

Miaoxiang Chen, Xavier Crispin, Erik Perzon, Mats R. Andersson, Tönu Pullerits, Mattias Andersson, Olle Inganäs, and Magnus Berggren

Appl. Phys. Lett. 87, 252105 (2005); http://dx.doi.org/10.1063/1.2142289 (3 pages) | Cited 20 times

Online Publication Date: 12 December 2005

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A conjugated polymer with a low band gap of 1.21 eV, i.e., absorbing infrared light, is demonstrated as active material in field-effect transistors (FETs). The material consists of alternating fluorene units and low band gap segments with electron donor-acceptor-donor units composed of two electron-donating thiophene rings attached on both sides of a thiadiazolo-quinoxaline electron-acceptor group. The polymer is solution-processable and air-stable; the resulting FETs exhibit typical p-channel characteristics and field-effect mobility of 0.03 cm2 V−1 s−1.
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85.30.Tv Field effect devices

p-type behavior in In–N codoped ZnO thin films

L. L. Chen, J. G. Lu, Z. Z. Ye, Y. M. Lin, B. H. Zhao, Y. M. Ye, J. S. Li, and L. P. Zhu

Appl. Phys. Lett. 87, 252106 (2005); http://dx.doi.org/10.1063/1.2146309 (3 pages) | Cited 51 times

Online Publication Date: 13 December 2005

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p-type ZnO thin films have been realized by the In–N codoping method. Secondary ion mass spectroscopy revealed that the nitrogen incorporation was enhanced by the presence of indium in ZnO. The as-grown In–N codoped ZnO film shows acceptable p-type behavior at room temperature with high film quality. A conversion from p-type conduction to n type in a range of temperature was confirmed by Hall effect measurement. The lowest reliable room-temperature resistivity was found to be 3.12 Ω cm with a carrier concentration of 2.04×1018 cm−3 and a Hall mobility of 0.979 cm2 V−1 S−1. The p-type behavior is stable.
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73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Effect of Cl2/Ar dry etching on p-GaN with Ni/Au metallization characterization

Kuang-Po Hsueh, Hung-Tsao Hsu, Che-Ming Wang, Shou-Chian Huang, Yue-Ming Hsin, and Jinn-Kong Sheu

Appl. Phys. Lett. 87, 252107 (2005); http://dx.doi.org/10.1063/1.2149156 (3 pages) | Cited 10 times

Online Publication Date: 14 December 2005

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This work investigates the effect of Cl2/Ar dry etching on p-GaN. The root-mean-square (rms) surface roughness is measured, and the depth display (Bearing analysis) is monitored. The current-voltage characteristics of etched p-GaN with Ni (20 nm)/Au (20 nm) metallization are studied. Experimental results indicate that the etching rate does not increase significantly with the Cl2 flow rate at a constant power or chamber pressure. The Bearing ratio data exhibit a much stronger variation with etch conditions, the rms displays the same trend but to a lesser extent.
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81.65.Cf Surface cleaning, etching, patterning
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Noise-voltage mapping by a quantum-Hall electrometer

Y. Kawano and T. Okamoto

Appl. Phys. Lett. 87, 252108 (2005); http://dx.doi.org/10.1063/1.2149221 (3 pages) | Cited 6 times

Online Publication Date: 14 December 2005

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We have developed a scanning type of noise sensor system, which utilizes the detection of local voltage fluctuations with a quantum Hall effect (QHE) electrometer. This technique has enabled us to produce the first image of a noise-voltage distribution in a QHE sample. The experimental data clearly reveal that a large amount of noise occurs in the lower magnetic field region of a QHE plateau of Landau-level-filling factor 2 and that it is concentrated in a high-potential edge region of the Hall bar sample. These findings can be reasonably explained as originating from unstable electron transfer taking place when the nonequilibrium edge state equilibrates with the bulk state. These results identify our sensor system as a unique probe of nonequilibrium edge states in QHE systems.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.43.-f Quantum Hall effects

12.5 nm base pseudomorphic heterojunction bipolar transistors achieving fT = 710 GHz and fMAX = 340 GHz

Walid Hafez, William Snodgrass, and Milton Feng

Appl. Phys. Lett. 87, 252109 (2005); http://dx.doi.org/10.1063/1.2149510 (3 pages) | Cited 13 times

Online Publication Date: 14 December 2005

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The pseudomorphic collector structure is known to allow enhanced collector transport, facilitating higher current cutoff frequencies at lower current densities and junction temperatures compared to traditional single heterojunction structures. The performance of a 0.25×3 μm2 pseudomorphic heteojunction bipolar transistors achieves peak fT of 710 GHz (fMAX = 340 GHz) at a collector current density of 20 mA/μm2. The same device achieves a fT/fMAX of 540/407 GHz at a reduced current density of 7.5 mA/μm2. The epitaxial structure employs a 12.5 nm strained InGaAs base and 55 nm InGaAs collector, and exhibits a β of 115 and breakdown voltage of BVCEO = 1.75 V.
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85.30.Pq Bipolar transistors

Electronegativity model for barrier formation at metal/organic interfaces

J. X. Tang, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 87, 252110 (2005); http://dx.doi.org/10.1063/1.2149178 (3 pages) | Cited 11 times

Online Publication Date: 15 December 2005

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An electronegativity model is proposed to characterize the variation of charge injection barrier heights at metal/organic interfaces. In contrast to the traditionally used metal work function, barrier heights at interfaces are shown to be linearly dependent on metal electronegativity for a wide range of organic materials. The physical basis for the better suitability of electronegativity than work function to describe barrier heights is discussed. While barrier formation is caused by charge transfer between metals and organic semiconductors, the variation of the barrier height is related to the electronegativity difference of metals. The applicability of the electronegativity model to compound or alloy electrodes, such as indium tin oxide having no defined electronegativity, is also exemplified.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Carrier relaxation dynamics in annealed and hydrogenated (GaIn)(NAs)/GaAs quantum wells

K. Hantke, J. D. Heber, S. Chatterjee, P. J. Klar, K. Volz, W. Stolz, W. W. Rühle, A. Polimeni, and M. Capizzi

Appl. Phys. Lett. 87, 252111 (2005); http://dx.doi.org/10.1063/1.2149154 (3 pages) | Cited 8 times

Online Publication Date: 15 December 2005

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We measured time-resolved photoluminescence on as-grown, annealed, as well as annealed and hydrogenated (Ga0.7In0.3)(N0.006As0.994)/GaAs quantum-well structures. The postgrowth treatment changes not only the photoluminescence decay time but also the intensity of photoluminescence directly after excitation. This initial luminescence intensity is determined by a competition between relaxation of electrons into nitrogen related potential fluctuations in the conduction band and their capture by deep traps. In contrast, the decay of the photoluminescence is mainly determined by the competition between radiative and nonradiative recombination, which are both influenced by localization. Annealing decreases localization effects and nonradiative recombination. Hydrogenation also reduces localization effects but increases nonradiative recombination.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.De Quantum wells
73.21.Fg Quantum wells
73.63.Hs Quantum wells
71.55.Eq III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Switch-on overshoot transient decay mechanism in polycrystalline silicon thin-film transistors

G. J. Papaioannou, M. Exarchos, D. N. Kouvatsos, and A. T. Voutsas

Appl. Phys. Lett. 87, 252112 (2005); http://dx.doi.org/10.1063/1.2138806 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2005

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The present work investigates the switch-on transient decay in polycrystalline thin-film transistors. The decay is found to follow the stretched exponential relaxation model independently of the polycrystalline film properties and the device bias conditions or operating temperature. The temperature dependence of the stretched exponential relaxation allows for the determination of the decay time and, furthermore, the process activation energy.
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85.30.Tv Field effect devices

Electrical activation of the Fe2+/3+ trap in Fe-implanted InP

B. Fraboni, A. Gasparotto, T. Cesca, A. Verna, G. Impellizzeri, and F. Priolo

Appl. Phys. Lett. 87, 252113 (2005); http://dx.doi.org/10.1063/1.2150281 (3 pages) | Cited 5 times

Online Publication Date: 16 December 2005

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We have studied the electrical activation of the Fe2+/3+ trap in Fe-implanted InP by means of capacitance-voltage and deep level transient spectroscopy analyses. Five deep traps have been identified and we have characterized the concentration and depth distribution of the Fe2+/3+ deep trap, located at EC–0.66 eV. The InP substrate background doping, i.e., the Fermi-level position, plays a crucial role in the Fe activation process by setting an upper limit to the amount of Fe centers electrically activated as deep acceptor traps.
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71.55.Eq III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Phonon-induced breakdown of negative bend resistance in an asymmetric Si/SiGe cross junction

U. Wieser, S. A. Poenariu, U. Kunze, and T. Hackbarth

Appl. Phys. Lett. 87, 252114 (2005); http://dx.doi.org/10.1063/1.2150268 (3 pages) | Cited 2 times

Online Publication Date: 16 December 2005

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An asymmetric nanoscale cross junction is fabricated from a high-mobility Si/SiGe heterostructure. At T = 4.2 K, the four-terminal current-voltage characteristics reveal a polarity-dependent breakdown of the negative bend resistance. The breakdown is accompanied by negative differential conductance found in the two-terminal current-voltage characteristics of the orthogonal current leads. We attribute this behavior to phonon emission by hot electrons. From gate-voltage-dependent measurements, we determine a phonon threshold of 19 meV.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
63.20.-e Phonons in crystal lattices

Spin dynamics in dilute nitride semiconductors at room temperature

L. Lombez, P.-F. Braun, H. Carrère, B. Urbaszek, P. Renucci, T. Amand, X. Marie, J. C. Harmand, and V. K. Kalevich

Appl. Phys. Lett. 87, 252115 (2005); http://dx.doi.org/10.1063/1.2150252 (3 pages) | Cited 18 times

Online Publication Date: 16 December 2005

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We report optical studies in undoped GaAsN epilayers and InGaAsN quantum wells, which show that a strong electron spin polarization can persist at room temperature. This is a direct consequence of the long spin relaxation time of electrons in dilute nitride materials. Introducing less than 1% of nitrogen in the binary (GaAs) or ternary (InGaAs) alloy increases the electron spin relaxation time at T = 300 K by a factor greater than 20 in as-grown material before annealing. A drastic drop in the electron spin relaxation time is observed for annealed samples.
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72.25.Dc Spin polarized transport in semiconductors
78.66.Fd III-V semiconductors
78.67.De Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing

The Meyer-Neldel compensation law for electrical conductivity in olivine

Xiaoping Wu and Yong-Fei Zheng

Appl. Phys. Lett. 87, 252116 (2005); http://dx.doi.org/10.1063/1.2150270 (3 pages) | Cited 3 times

Online Publication Date: 16 December 2005

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The electrical conductivity in olivine is found to obey the compensation law or the Meyer-Neldel rule; that is, a linear correlation exists between the logarithm of prefactor and activation energy. It is shown that the electrical conductivities due to different conduction mechanisms or conducting species converge to a constant at a characteristic temperature, resulting in the Meyer-Neldel rule. A number of experimental diffusion data in olivine also test the validity of the suggestion through the Nernst-Einstein equation.
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72.80.Jc Other crystalline inorganic semiconductors

Temperature-dependent exciton dynamics in a ZnO thin film

Fang-Yi Jen, Yen-Cheng Lu, Cheng-Yen Chen, Hsiang-Chen Wang, C. C. Yang, Bao-ping Zhang, and Yusaburo Segawa

Appl. Phys. Lett. 87, 252117 (2005); http://dx.doi.org/10.1063/1.2150277 (3 pages) | Cited 24 times

Online Publication Date: 16 December 2005

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We measured the temperature-dependent photoluminescence (PL) decay time of the mixed system of free exciton (FX) and donor-bound exciton (Dmath) in a ZnO thin film. From the measured cw PL spectra, we also calibrated the individual spectral widths and integrated PL intensities of FX and Dmath by fitting the spectra with four Lorentzian functions. The radiative lifetime of the mixed system was then calibrated based on the thermal quenching rate of the total integrated PL intensity of the system. With the system radiative lifetime data, FX radiative lifetimes were estimated by using a theoretical relation between the lifetime and the spectral width. From the results of FX radiative lifetime, we calibrated the Dmath radiative lifetimes by considering the emission intensity ratio between FX and Dmath. The results support our model that the Dmath radiative behavior is similar to that of FX when the thermal energy is smaller than the donor binding energy.
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71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.40.Gh Other heat and thermomechanical treatments

“EL2” revisited: Observation of metastable and stable energy levels of EL2 in semi-insulating GaAs

D. Kabiraj and Subhasis Ghosh

Appl. Phys. Lett. 87, 252118 (2005); http://dx.doi.org/10.1063/1.2150579 (3 pages) | Cited 3 times

Online Publication Date: 16 December 2005

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By using a combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in light of the recently proposed models for EL2 in GaAs.
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71.55.Eq III-V semiconductors

Effects of heavy boron doping on the valence band offset at the Si1−xGex/Si interface and Si1−xGex band gap

Jing Liu and Mehmet C. Ozturk

Appl. Phys. Lett. 87, 252119 (2005); http://dx.doi.org/10.1063/1.2149295 (3 pages) | Cited 3 times

Online Publication Date: 16 December 2005

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Heavily boron-doped Si1−xGex alloys are currently used in recessed source/drain regions of nanoscale metal oxide silicon field effect transistors. Small boron atoms can partially compensate the Si1−xGex strain and change its band gap, which can influence key device parameters such as the junction contact resistance. In this work, the depletion region capacitance of SiGe/Si heterojunction diodes was measured to determine the valence band offset and the Si1−xGex band gap. The results show that boron doping can have a significant impact on the Si1−xGex band gap and values between those of relaxed and fully strained Si1−xGex alloys can be obtained.
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73.20.At Surface states, band structure, electron density of states
61.72.uf Ge and Si
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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