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17 Jun 2002

Volume 80, Issue 24, pp. 4483-4665

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Effect of Ga content on defect states in CuIn1−xGaxSe2 photovoltaic devices

J. T. Heath, J. D. Cohen, W. N. Shafarman, D. X. Liao, and A. A. Rockett

Appl. Phys. Lett. 80, 4540 (2002); http://dx.doi.org/10.1063/1.1485301 (3 pages) | Cited 29 times

Online Publication Date: 10 June 2002

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Defects in the band gap of CuIn1−xGaxSe2 have been characterized using transient photocapacitance spectroscopy. The measured spectra clearly show response from a band of defects centered around 0.8 eV from the valence band edge as well as an exponential distribution of band tail states. Despite Ga contents ranging from Ga/(In+Ga) = 0.0 to 0.8, the defect bandwidth and its position relative to the valence band remain constant. This defect band may act as an important recombination center, contributing to the decrease in device efficiency with increasing Ga content. © 2002 American Institute of Physics.
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71.55.Ht Other nonmetals
81.05.Hd Other semiconductors
84.60.Jt Photoelectric conversion
71.20.Nr Semiconductor compounds
72.40.+w Photoconduction and photovoltaic effects
61.66.Bi Elemental solids
61.66.Dk Alloys

Theoretical valence band offsets of semiconductor heterojunctions

Kyurhee Shim and Herschel Rabitz

Appl. Phys. Lett. 80, 4543 (2002); http://dx.doi.org/10.1063/1.1483904 (3 pages) | Cited 2 times

Online Publication Date: 10 June 2002

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A theoretical model is presented to predict the valence band offsets of heterojunction semiconductors. The total valence band offsets are split into bulk and interfacial contributions. The bulk contributions are based on the tight binding approach while the localized effects at the interface are described by the bond exchange and the elastic energy due to the strained layer. We calculate the valence band offsets for various types of heterojunctions and compare that with experimental data and the results of other theoretical calculations. Our results are in good agreement with experimental data for most of the systems explored. This suggests that the present model is generic and contains the dominant physical factors operative at the interface to make it applicable to various heterojunctions. © 2002 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Anti-domain-free GaP, grown in atomically flat (001) Si sub-μm-sized openings

B. J. Ohlsson, J.-O. Malm, A. Gustafsson, and L. Samuelson

Appl. Phys. Lett. 80, 4546 (2002); http://dx.doi.org/10.1063/1.1485311 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2002

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We demonstrate a method for growth of GaP nanocrystals on Si(001), developed to avoid defects related to antiphase domain boundaries in the proximity of the GaP/Si interface. The technique is based on sub-μm-sized selective-area epitaxy of GaP on atomically flat Si in masked openings. We have used field-emission scanning electron microscopy together with transmission electron microscopy to illustrate the method with examples of monocrystalline GaP nanocrystals. The optical properties of the nanocrystals were investigated by low-temperature cathodoluminescence. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.60.Hk Cathodoluminescence, ionoluminescence
81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials

Electroreflectance of the AlGaN/GaN heterostructure and two-dimensional electron gas

S. R. Kurtz, A. A. Allerman, D. D. Koleske, and G. M. Peake

Appl. Phys. Lett. 80, 4549 (2002); http://dx.doi.org/10.1063/1.1487447 (3 pages) | Cited 13 times

Online Publication Date: 10 June 2002

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A contacted electroreflectance technique was used to characterize the electronic properties of AlGaN/GaN heterostructures and field-effect transistors. By studying variations in the electroreflectance with applied electric field, spectral features associated with the AlGaN barrier, the two-dimensional electron gas at the interface, and bulk GaN were observed. The AlGaN barrier displayed Franz–Keldysh oscillations which provided estimates of barrier-layer composition and electric field. The electron gas Fermi energy was determined from analysis of the broad two-dimensional electron gas feature. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states

Decrease in the leakage current density of Si-based metal–oxide–semiconductor diodes by cyanide treatment

Akira Asano, Asuha, Osamu Maida, Yoshihiro Todokoro, and Hikaru Kobayashi

Appl. Phys. Lett. 80, 4552 (2002); http://dx.doi.org/10.1063/1.1484249 (3 pages) | Cited 23 times

Online Publication Date: 10 June 2002

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Crown-ether cyanide treatment, which includes the immersion of Si in KCN solutions containing 18-crown-6 molecules, is found to greatly decrease the leakage current density of Si-based metal–oxide–semiconductor (MOS) diodes. The decrease by one order of magnitude for the single crystalline Si-based MOS diodes is attributable to the elimination of Si/SiO2 interface states by reaction with cyanide ions and formation of Si–CN bonds. The reduction in the leakage current density by two orders of magnitude is caused for polycrystalline Si-based MOS diodes, and this decrease is attributed to the passivation of trap states in poly-Si as well as the interface states. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.Kk Junction diodes
73.20.At Surface states, band structure, electron density of states
73.61.Cw Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Characteristics of MgO/GaN gate-controlled metal–oxide– semiconductor diodes

Jihyun Kim, R. Mehandru, B. Luo, F. Ren, B. P. Gila, A. H. Onstine, C. R. Abernathy, S. J. Pearton, and Y. Irokawa

Appl. Phys. Lett. 80, 4555 (2002); http://dx.doi.org/10.1063/1.1487903 (3 pages) | Cited 56 times

Online Publication Date: 10 June 2002

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Gate-controlled n+p metal–oxide–semiconductor diodes were fabricated in p-GaN using MgO as a gate dielectric and Si+ implantation to create the n+ regions. This structure overcomes the low minority carrier generation rate in GaN and allowed observation of clear inversion behavior in the dark at room temperature. By contrast, diodes without the n+ regions to act as an external source of minority carriers did not show inversion even at measurement temperatures of 300 °C. The gated diodes showed the expected shape of the current–voltage characteristics, with clear regions corresponding to depletion and inversion under the gate. The MgO was deposited prior to the Si implantation and was stable during the activation annealing for the Si-implanted n+ regions. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.uj III-V and II-VI semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing

A study of subbands in AlGaN/GaN high-electron-mobility transistor structures using low-temperature photoluminescence spectroscopy

C. Y. Fang, C. F. Lin, Edward Yi Chang, and M. S. Feng

Appl. Phys. Lett. 80, 4558 (2002); http://dx.doi.org/10.1063/1.1485310 (3 pages) | Cited 8 times

Online Publication Date: 10 June 2002

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Al0.15Ga0.85N/GaN high-electron-mobility transistor (HEMT) structures with various δ-doping concentrations and spacer thicknesses grown on sapphire by metalorganic chemical-vapor deposition are investigated. The Hall mobility is as high as 1333 cm2/V s at room temperature and 6330 cm2/V s at 77 K. Two-dimensional electron gas (2DEG) phenomena, which have not been clearly resolved in the literature, are observed by photoluminescence (PL) spectra at low temperature in this study. The PL spectra peaks of the interband transitions from 2DEG subbands to the valence band are in the range from 3.486 to 3.312 eV. The effects of the strain caused by different Al fractions of the top layer, and that of the spacer thickness on the 2DEG phenomena are discussed. Redshifts due to temperature variations for various HEMT structures are observed in 2DEG subbands and in the band-edge emission, which is believed to be evidence of interband transitions from 2DEG subbands to valence bands. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.20.At Surface states, band structure, electron density of states
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Ferromagnetic properties of Zn1−xMnxO epitaxial thin films

S. W. Jung, S.-J. An, Gyu-Chul Yi, C. U. Jung, Sung-Ik Lee, and Sunglae Cho

Appl. Phys. Lett. 80, 4561 (2002); http://dx.doi.org/10.1063/1.1487927 (3 pages) | Cited 266 times

Online Publication Date: 10 June 2002

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We report on ferromagnetic characteristics of Zn1−xMnxO (x = 0.1 and 0.3) thin films grown on Al2O3(00⋅1) substrates using laser molecular-beam epitaxy. By increasing the Mn content, the films exhibited increases in both the c-axis lattice constant and fundamental band gap energy. The Curie temperature obtained from temperature-dependent magnetization curves was 45 K for the film with x = 0.3, depending on the Mn composition in the films. The remanent magnetization and coercive field of Zn0.9Mn0.1O at 5 K were 0.9 emu/g and 300 Oe, respectively. For Zn0.7Mn0.3O, the remanent magnetization at 5 K increased to 3.4 emu/g. © 2002 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Discrete surface state related to nitrogen-vacancy defect on plasma-treated GaN surfaces

Tamotsu Hashizume and Ryusuke Nakasaki

Appl. Phys. Lett. 80, 4564 (2002); http://dx.doi.org/10.1063/1.1485309 (3 pages) | Cited 23 times

Online Publication Date: 10 June 2002

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Detailed studies on the defect-related surface states of plasma-exposed n-GaN surfaces were carried out. An anomalous flat portion appeared in the metal–insulator–semiconductor capacitance–voltage characteristics for the sample exposed to H2 plasma, corresponding to a localized peak at EC−0.5 eV in the surface state density distribution. Atomic-force microscope and x-ray photoemission studies revealed the formation of Ga droplets on H2-plasma-treated GaN surfaces, caused by the desorption of nitrogen atoms in the form of NHx. These results suggested that a nitrogen-vacancy-related state near the conduction-band edge was introduced on the H2-plasma-treated GaN surface. No such effects took place on the N2-plasma-treated GaN surfaces. © 2002 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Dv Composition, segregation; defects and impurities
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
61.72.J- Point defects and defect clusters

Detection of single charges and their generation-recombination dynamics in Si nanowires at room temperature

Akira Fujiwara, Kenji Yamazaki, and Yasuo Takahashi

Appl. Phys. Lett. 80, 4567 (2002); http://dx.doi.org/10.1063/1.1487451 (3 pages) | Cited 12 times

Online Publication Date: 10 June 2002

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Detection of single electrons and single holes is demonstrated at room temperature in Si nanowire transistors using an electron-hole (e–h) system. Photogenerated carriers are stored in a quantum dot electrically formed in a Si wire by a front gate. The stored charges affect the current of the other type of carriers that flow along the bottom of the Si wire. The linear photoresponce of single-charge generation is observed. It is revealed that the recombination occurs by a bimolecular process, suggesting that it is due to the e–h interband transition. These results open up the possibility of developing single-photon devices with this system. © 2002 American Institute of Physics.
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73.63.Nm Quantum wires
73.21.Hb Quantum wires
73.63.Bd Nanocrystalline materials
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.22.-f Electronic structure of nanoscale materials and related systems
85.35.Gv Single electron devices

Defect-related density of states in low-band gap InxGa1−xAs/InAsyP1−y double heterostructures grown on InP substrates

T. H. Gfroerer, L. P. Priestley, F. E. Weindruch, and M. W. Wanlass

Appl. Phys. Lett. 80, 4570 (2002); http://dx.doi.org/10.1063/1.1487449 (3 pages) | Cited 8 times

Online Publication Date: 10 June 2002

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We have measured the excitation-dependent radiative efficiency in a set of lattice-matched InxGa1−xAs/InAsyP1−y double heterostructures incrementally lattice mismatched to InP substrates. We find that the overall rate of defect-related recombination shows little change from the lattice-matched case. However, the excitation-dependent transition between defect-related and radiative recombination changes dramatically with mismatch. While a simple defect recombination model assuming defect levels concentrated near the middle of the band gap fits well for the lattice-matched material, the model does not fit the shape of the efficiency curve for the mismatched structures. We show that the addition of band edge exponential tails to the defect-related density of states gives a much better theoretical fit. © 2002 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.20.At Surface states, band structure, electron density of states
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
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