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31 Mar 2003

Volume 82, Issue 13, pp. 1999-2184

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Appl. Phys. Lett. 82, 2094 (2003); http://dx.doi.org/10.1063/1.1563813 (3 pages)

Y. J. Lee, J. von Boehm, M. Pesola, and R. M. Nieminen
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Determination of the charge carrier compensation mechanism in Te-doped GaAs by scanning tunneling microscopy

J. Gebauer, E. R. Weber, N. D. Jäger, K. Urban, and Ph. Ebert

Appl. Phys. Lett. 82, 2059 (2003); http://dx.doi.org/10.1063/1.1563835 (3 pages) | Cited 10 times

Online Publication Date: 25 March 2003

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We identified the charge carrier compensation mechanism in Te-doped GaAs with atomically resolved scanning tunneling microscopy. Three types of defects were found: tellurium donors (TeAs), Ga vacancies (VGa), and Ga vacancy–donor complexes (VGa–TeAs). We show quantitatively that the compensation in Te-doped bulk GaAs is exclusively caused by vacancy–donor complexes in contrast to Si-doped GaAs. This is explained with the Fermi-level effect as the universal mechanism leading to Ga vacancy formation in n-doped GaAs, and a Coulomb interaction leading to the formation of the complexes. The quantification of the carrier compensation yields a −3e charge state of VGa in bulk GaAs. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.72.J- Point defects and defect clusters
61.72.Yx Interaction between different crystal defects; gettering effect

Investigation of trap processes in polycrystalline silicon thin film transistors by ac measurement

Feng Yan, Piero Migliorato, and Tatsuya Shimoda

Appl. Phys. Lett. 82, 2062 (2003); http://dx.doi.org/10.1063/1.1564635 (3 pages) | Cited 3 times

Online Publication Date: 25 March 2003

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We report a method for characterizing trap generation–recombination processes in polycrystalline silicon thin film transistors. A small ac voltage was superimposed on a dc gate voltage and the ac current was measured at the source. A theoretical model was developed, whereby n-channel thin film transistors were analyzed. A resonant peak in the imaginary part of the ac current and a corresponding step in the real part were found at frequency of 147 Hz. Our data indicate that the ac response is dominated by a single trap level. By combining the ac current measurement with a low frequency capacitance measurement, we have determined the trap energy, capture cross section, and trap density to be, respectively, 0.91 eV above the valence band, 3.1×10−21 cm2, and 5.7×1015 cm−3. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
71.55.Cn Elemental semiconductors
85.30.De Semiconductor-device characterization, design, and modeling
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Thermoelectric properties of Al1−xInxN and Al1−y−zGayInzN prepared by radio-frequency sputtering: Toward a thermoelectric power device

Shigeo Yamaguchi, Yasuo Iwamura, and Atsushi Yamamoto

Appl. Phys. Lett. 82, 2065 (2003); http://dx.doi.org/10.1063/1.1560560 (3 pages) | Cited 23 times

Online Publication Date: 25 March 2003

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With the aim of fabricating a thermoelectric power device using III-nitride semiconductors, we recently studied thermoelectric properties of Al1−xInxN and Al1−y−zGayInzN prepared by rf sputtering. For Al0.35In0.65N with 0.63-μm thickness, the maximum power factor was 3.63×10−4 W/mK2. For Al0.26Ga0.44In0.30N, the maximum power factor was 5.58×10−5 W/mK2. © 2003 American Institute of Physics.
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73.50.Lw Thermoelectric effects
81.15.Cd Deposition by sputtering
85.80.Fi Thermoelectric devices
73.61.Ey III-V semiconductors

Function principle of a relaxation oscillator based on a bistable quantum Hall device

G. Nachtwei, N. G. Kalugin, B. E. Sağol, Ch. Stellmach, and G. Hein

Appl. Phys. Lett. 82, 2068 (2003); http://dx.doi.org/10.1063/1.1563729 (3 pages) | Cited 8 times

Online Publication Date: 25 March 2003

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We present a simple relaxation oscillator based on a quantum Hall device with Corbino geometry near the breakdown of the quantum Hall effect. In the hysteresis region of the breakdown, the quantum Hall device exhibits bistable behavior. If a resistance is connected in series and a capacitor in parallel to the quantum Hall device, the bistable switching leads to subsequent charging and discharging of the capacitor, detectable as relaxation oscillations. We explain the observed oscillations by solving Kirchhoff’s equations and obtain a good quantitative description of the experiment. From this, we deduce some dynamical parameters of the Corbino device and discuss the performance limits of the oscillator. © 2003 American Institute of Physics.
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84.30.Ng Oscillators, pulse generators, and function generators
73.43.Qt Magnetoresistance
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)

Valence-band structure of self-assembled InAs quantum dots studied by capacitance spectroscopy

C. Bock, K. H. Schmidt, U. Kunze, S. Malzer, and G. H. Döhler

Appl. Phys. Lett. 82, 2071 (2003); http://dx.doi.org/10.1063/1.1564288 (3 pages) | Cited 10 times

Online Publication Date: 25 March 2003

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Hole transport into self-assembled InAs quantum dots (QDs) embedded in a GaAs/AlAs matrix was studied by capacitance spectroscopy. From the differential capacitance, a Coulomb blockade energy of EC0h ≈ 22 meV for holes in the ground state was extracted. When the front barrier between the dot layer and the Schottky contact is precisely reduced by selective wet chemical etching, the QD ground state signal shifts to lower gate voltages according to a simple leverage law. From the linear fit of the voltage shift versus the front barrier thickness the hole binding energy of E0h ≈ 194 meV was determined. © 2003 American Institute of Physics.
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73.21.La Quantum dots
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling

Cathodoluminescence and Hall-effect measurements in sulfur-doped chemical-vapor-deposited diamond

Kazushi Nakazawa, Minoru Tachiki, Hiroshi Kawarada, Aki Kawamura, Kenji Horiuchi, and Takefumi Ishikura

Appl. Phys. Lett. 82, 2074 (2003); http://dx.doi.org/10.1063/1.1563829 (3 pages) | Cited 14 times

Online Publication Date: 25 March 2003

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Dominant n-type conductivity in sulfur-doped chemical-vapor-deposited diamond is observed by Hall-effect measurement. The activation energy is estimated at 0.5–0.75 eV above 600 K. Below 600 K, the carrier concentration deviates from the activation energy, and Hall mobility decreases in comparison with that above 600 K. It is considered that hopping conduction takes place. By cathodoluminescence measurement, free-exciton recombination radiation is observed in spite of a very high sulfur doping level of 2.5% during deposition, where boron is not detected by secondary ion mass spectroscopy. Therefore, the n-type conductivity of sulfur-doped diamond is caused by a sulfur-related mechanism. © 2003 American Institute of Physics.
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73.61.Cw Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
78.60.Hk Cathodoluminescence, ionoluminescence
73.50.Dn Low-field transport and mobility; piezoresistance
71.35.-y Excitons and related phenomena
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.S- Impurities in crystals

Origin of high-temperature ferromagnetism in (Ga,Mn)N layers grown on 4H–SiC(0001) by reactive molecular-beam epitaxy

S. Dhar, O. Brandt, A. Trampert, L. Däweritz, K. J. Friedland, K. H. Ploog, J. Keller, B. Beschoten, and G. Güntherodt

Appl. Phys. Lett. 82, 2077 (2003); http://dx.doi.org/10.1063/1.1564292 (3 pages) | Cited 116 times

Online Publication Date: 25 March 2003

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We report on the growth, structural as well as magnetic characterization of (Ga,Mn)N epitaxial layers grown directly on 4H–SiC(0001) by reactive molecular-beam epitaxy. We focus on two layers grown under identical conditions except for the Mn/Ga flux ratio. Structural characterization reveals that the sample with the lower Mn content is a uniform alloy, while in the layer with the higher Mn content, Mn-rich clusters are found to be embedded in the (Ga,Mn)N alloy matrix. Although the magnetic behavior of both the samples is similar at low temperatures, showing antiferromagnetic characteristics with a spin-glass transition, the sample with higher Mn content additionally exhibits ferromagnetic properties at and above room temperature. This ferromagnetism most likely originates from the Mn-rich clusters in this sample. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.50.Lk Spin glasses and other random magnets
81.05.Ea III-V semiconductors
75.40.-s Critical-point effects, specific heats, short-range order
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors

Electron tunneling from channel to gate

Peter J. Price

Appl. Phys. Lett. 82, 2080 (2003); http://dx.doi.org/10.1063/1.1564633 (2 pages) | Cited 2 times

Online Publication Date: 25 March 2003

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A general treatment based on the Gamow formulation of tunneling escape through an enclosing barrier is developed for analysis of the escape of electrons from the conducting channel of a field effect transistor through the barrier layer into the gate. The result gives the tunneling rate calculated from computed wave functions of the quantum levels, without requiring these to correspond to quasiclassical motion in the channel region, but rather for the general case including the ground state. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
73.40.Gk Tunneling
73.20.-r Electron states at surfaces and interfaces

Effect of Be++O+ coimplantation on Be acceptors in GaN

Yoshitaka Nakano, Tetsu Kachi, and Takashi Jimbo

Appl. Phys. Lett. 82, 2082 (2003); http://dx.doi.org/10.1063/1.1564641 (3 pages) | Cited 3 times

Online Publication Date: 25 March 2003

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P-type regions were produced in undoped GaN films by Be+ and Be++O+ implantation and subsequent annealing at temperatures between 1000 and 1050 °C. From thermal admittance spectroscopic measurements, the activation energy of the Be acceptor level was found to decrease from ∼240 to ∼163 meV by the implantation of additional O atoms, which is in reasonable agreement with the improvement in p-type doping characteristics determined by room-temperature Hall-effect measurements. These results indicate that Be++O+ coimplantation reduces the depth of the Be acceptor level based on a site-competition effect. Therefore, these acceptor levels are most probably attributable to Be atoms at interstitial and Ga-lattice sites. © 2003 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
71.55.Eq III-V semiconductors
61.80.Jh Ion radiation effects
61.72.J- Point defects and defect clusters

The Franz–Keldysh effect in shocked GaN:Mg

H. Y. Peng, M. D. McCluskey, Y. M. Gupta, M. Kneissl, and N. M. Johnson

Appl. Phys. Lett. 82, 2085 (2003); http://dx.doi.org/10.1063/1.1563837 (3 pages) | Cited 5 times

Online Publication Date: 25 March 2003

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The band gap of uniaxially strained semi-insulating GaN:Mg has been examined using time-resolved optical transmission measurements in shock-wave experiments. For longitudinal stresses between 2.9 and 4.6 GPa, the absorption edge broadened significantly. Such a broadening is consistent with the presence of large piezoelectric fields (Franz–Keldysh effect) generated due to shock compression. For stresses greater than 4.6 GPa, however, the absorption edge remained relatively sharp. The sharp absorption onset suggests the presence of free charge carriers that screen the piezoelectric field, thereby suppressing the Franz–Keldysh effect. These observations indicate that electrical breakdown occurs at a field of 1 MV/cm. One possible mechanism that could result in free carriers is the dissociation of Mg–H complexes under the very high piezoelectric fields. © 2003 American Institute of Physics.
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71.20.Nr Semiconductor compounds
81.05.Ea III-V semiconductors
62.50.-p High-pressure effects in solids and liquids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics
77.65.-j Piezoelectricity and electromechanical effects
77.22.Jp Dielectric breakdown and space-charge effects

Valence band alignment with a small spike at the CuI/CuInS2 interface

I. Konovalov and R. Szargan

Appl. Phys. Lett. 82, 2088 (2003); http://dx.doi.org/10.1063/1.1564634 (3 pages) | Cited 10 times

Online Publication Date: 25 March 2003

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From the point of view of the “doping pinning rule,” application of p-type buffer layer materials for CuInS2 solar cells may lead to record levels of cell efficiency due to an optimal band offset at the interface. Under simplified simulation conditions, an increase in efficiency of up to about 18% was predicted. Evaluation of the valence band offset between CuI and single crystalline CuInS2 by photoelectron spectroscopy displays a spike height of (0.1±0.2) eV, optimal for solar cell applications. The positions of the valence band edge were determined by assuming a parabolic distribution of the density of states. © 2003 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
84.60.Jt Photoelectric conversion
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures

Cu(In1−xGax)Se2 growth studies by in situ spectroscopic light scattering

R. Scheer, A. Neisser, K. Sakurai, P. Fons, and S. Niki

Appl. Phys. Lett. 82, 2091 (2003); http://dx.doi.org/10.1063/1.1563309 (3 pages) | Cited 11 times

Online Publication Date: 25 March 2003

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The growth of polycrystalline Cu(In1−xGax)Se2 thin films using a three-stage deposition process has been investigated by in situ diffuse spectroscopic light scattering in the wavelength range of 400–800 nm. Differences in the time dynamics of the intensity at different wavelengths can be explained by the development of surface roughness at different length scales. Of specific interest is the development of roughness around the stoichiometric points of film formation. It is shown that on-line monitoring of the spectroscopic light scattering can be used for process control and for adjustment of the final film roughness. © 2003 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth
78.66.Li Other semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Hd Other semiconductors

Comparison of oxygen-chain models for late thermal double donors in silicon

Y. J. Lee, J. von Boehm, M. Pesola, and R. M. Nieminen

Appl. Phys. Lett. 82, 2094 (2003); http://dx.doi.org/10.1063/1.1563813 (3 pages) | Cited 1 time

Online Publication Date: 25 March 2003

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The electronic and atomic structures of the oxygen chains assigned to late thermal double donors (TDDs) in silicon are studied using accurate total-energy calculations. We find that the ring-type O-chain model is best suited for TDDs and better than the di-Y-lid-type O-chain model. The ring-type O chains have slightly alternating C2v–C1h symmetry consistent with the recent high-field electron paramagnetic resonance experiments. The spin densities of the double-donor states are located outside the region of the O atoms, which makes the hyperfine interaction of an unpaired donor electron with the 17O nuclear spins very weak. © 2003 American Institute of Physics.
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71.55.Cn Elemental semiconductors
71.70.Jp Nuclear states and interactions
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