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21 Sep 1992

Volume 61, Issue 12, pp. 1369-1473

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Effect of microvoids on initial and light‐degraded efficiencies of hydrogenated amorphous silicon alloy solar cells

S. Guha, J. Yang, Scott J. Jones, Yan Chen, and D. L. Williamson

Appl. Phys. Lett. 61, 1444 (1992); http://dx.doi.org/10.1063/1.107564 (3 pages) | Cited 38 times

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Using a combination of infrared absorption and small‐angle x‐ray scattering on hydrogenated amorphous silicon alloy films and efficiency measurements of solar cells with intrinsic layers prepared under nominally identical conditions to those for the deposition of the films, we observe a correlation between microstructure in the films and solar cell performance. With increasing microvoid density, both the initial and light‐degraded performance of solar cells are found to deteriorate.
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84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Luminescence cycling and defect density measurements in porous silicon: Evidence for hydride based model

S. M. Prokes, W. E. Carlos, and V. M. Bermudez

Appl. Phys. Lett. 61, 1447 (1992); http://dx.doi.org/10.1063/1.107565 (3 pages) | Cited 74 times

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Changes in dangling bond densities in porous silicon were measured and results indicate a relatively low dangling bond density (roughly 3×1016 bonds/cm3) in as‐prepared samples, which increases by a factor of 6–7 upon quenching of the photoluminescence (PL). The electron spin resonance (ESR) data suggest the presence of significant disorder in the as‐prepared 1 Ω cm porous silicon samples, which may correlate with an enhanced PL intensity. The results of heat cycling and HF dipping experiments suggest that a continuous decrease in particle size does not result in a continuous PL blue shift, as would be expected in the quantum confinement model. These results will be discussed in terms of a hydride/polysilane luminescence mechanism.
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78.55.Hx Other solid inorganic materials
81.40.Tv Optical and dielectric properties related to treatment conditions

Temperature‐dependence of the growth orientation of atomic layer growth MgO

Ron Huang and Adrian H. Kitai

Appl. Phys. Lett. 61, 1450 (1992); http://dx.doi.org/10.1063/1.107514 (3 pages) | Cited 24 times

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High‐quality MgO thin films deposited on Si(111) substrates by atomic layer growth (ALG) are formed by a hydrolysis surface reaction of Mg(C2H5)2 and H2O. The growth orientation of MgO changes from (111) to (100), when the temperature of the silicon substrate changes from 600 to 900 °C. The growth orientation difference of MgO grown by ALG is rationalized in terms of the surface diffusion coefficients on MgO.
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68.55.-a Thin film structure and morphology

Growth studies on Si0.8Ge0.2 channel two‐dimensional hole gases

D. W. Smith, C. J. Emeleus, R. A. Kubiak, E. H. C. Parker, and T. E. Whall

Appl. Phys. Lett. 61, 1453 (1992); http://dx.doi.org/10.1063/1.107515 (3 pages) | Cited 13 times

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We report a study of the influences of MBE conditions on the low‐temperature mobilities of Si/Si0.8Ge0.2 2DHG structures. A significant dependence of 2DHG mobility on growth temperature is observed with the maximum mobility of 3640 cm2 V−1 s−1 at 5.4 K being achieved at the relatively high‐growth temperature of 640 °C. This dependence is associated with a reduction in interface charge density. Studies on lower mobility samples show that Cu contamination can be reduced both by growth interruptions and by modifications to the Ge source; this reduction produces improvements in the low‐temperature mobilities. We suggest that interface charge deriving from residual metal contamination is currently limiting the 4‐K mobility.  
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73.50.Dn Low-field transport and mobility; piezoresistance
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Hydrodynamic analysis of submicrometer n+nn+ diodes for microwave generators

V. Gruzhinskis, E. Starikov, P. Shiktorov, L. Reggiani, M. Saraniti, and L. Varani

Appl. Phys. Lett. 61, 1456 (1992); http://dx.doi.org/10.1063/1.107516 (3 pages) | Cited 11 times

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We present a theoretical investigation on the electrical behavior of submicrometer n+nn+ diode microwave generators. To this end we adopt a mixed scheme which uses space‐homogeneous and stationary Monte Carlo simulations to provide the input parameters for a hydrodynamic analysis of the diode performances. Comparison between GaAs and InP made devices working at 400 K give similar results by predicting generation frequencies up to 700 GHz for an active region length of 0.2 μm.
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85.30.De Semiconductor-device characterization, design, and modeling
72.20.Ht High-field and nonlinear effects
72.30.+q High-frequency effects; plasma effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Preparation of YbBa2Cu3O7−x films on Si(100) substrates using SrTiO3 buffer layers

Hiroshi Ishiwara, Naoki Tsuji, Hiroyuki Mori, and Hiroshi Nohira

Appl. Phys. Lett. 61, 1459 (1992); http://dx.doi.org/10.1063/1.107517 (3 pages) | Cited 14 times

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We report that superconducting YbBa2Cu3O7−x films are formed on Si(100) substrates using SrTiO3 films as buffer layers. SrTiO3 buffer layers are prepared on Si using a focused electron beam evaporation method, while YbBa2Cu3O7−x films are prepared using a dc arc discharge evaporation method. It has been shown that the SrTiO3 thin film is effective to transmit the crystalline information of a Si(100) substrate to the YbBa2Cu3O7−x film and to block the diffusion of Si atoms into the film. The highest Tc (zero) of the film was 73 K.  
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74.70.-b Superconducting materials other than cuprates
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Rectifying current‐voltage characteristics in YBa2Cu3O7−x/NdGaO3/ n‐SrTiO3 diodes

H. Takauchi, A. Yoshida, H. Tamura, T. Imamura, and S. Hasuo

Appl. Phys. Lett. 61, 1462 (1992); http://dx.doi.org/10.1063/1.107518 (3 pages) | Cited 4 times

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Rectifying current‐voltage characteristics were analyzed for YBa2Cu3O7−x/NdGaO3/n‐SrTiO3 diodes made by depositing NdGaO3 barriers and YBa2Cu3O7−x films on Nb‐doped SrTiO3 substrates using KrF excimer laser ablation. The diode capacitance measured at 10 kHz indicated that the relative permittivity of the NdGaO3 barrier was 13 at 10 K. Diodes exhibited rectifying current‐voltage characteristics where they conducted better for positive voltages on the n‐SrTiO3 than for negative voltages. The current density of the diode having a 5‐nm‐thick NdGaO3 barrier biased around 1 V on the n‐type SrTiO3 was 0.2 A/cm2 at 30 K. This current density is at least six orders of magnitude higher than that obtained for diodes with YBa2Cu3O7−x electrodes directly placed on n‐SrTiO3 substrates.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
74.70.-b Superconducting materials other than cuprates
73.40.Ei Rectification

Observation of superstructures on the surfaces of sputtered YBa2Cu3O7−x thin films by low‐energy electron diffraction

H. Behner, W. Rauch, and E. Gornik

Appl. Phys. Lett. 61, 1465 (1992); http://dx.doi.org/10.1063/1.107519 (3 pages) | Cited 3 times

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The surface structures of sputtered c‐axis‐oriented YBa2Cu3O7−x (YBCO) thin films were studied by means of low‐energy diffraction (LEED). The in situ analysis, without exposing the films to air, showed the formation of superstructures of the YBCO (001) 2×2 and YBCO (001) 4×1 type. Air‐exposed surfaces showed no LEED pattern but could be transformed into the YBCO (001) 2×2 structure by annealing at 500 °C. The observed superstructures are interpreted as being due to oxygen loss of the YBCO surface region, causing an oxygen vacancy ordering in the basal CuO planes.
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74.70.-b Superconducting materials other than cuprates
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Co/Ni multilayers with perpendicular magnetic anisotropy: Kerr effect and thermomagnetic writing

F. J. A. den Broeder, H. W. van Kesteren, W. Hoving, and W. B. Zeper

Appl. Phys. Lett. 61, 1468 (1992); http://dx.doi.org/10.1063/1.107520 (3 pages) | Cited 5 times

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Perpendicular magnetic anisotropy has recently been predicted and confirmed for a Co1/Ni2 multilayer [G. H. O. Daalderop, P. J. Kelly, and F. J. A. den Broeder, Phys. Rev. Lett. 68, 682 (1992)]. This letter reports on some magneto‐optical properties of this new multilayer. Its polar Kerr effect appeared to be considerably larger than for a Co1/Pd2 multilayer and comparable to a Co1/Pt2 multilayer. For certain vapor deposition conditions, the perpendicular magneto‐optic hysteresis loop of a 120 Å Co1/Ni2 layer showed 100% remanence with a coercivity as high as 140 kA/m. Thermomagnetic writing was possible despite the high Curie temperature.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Distribution of trap levels in field stimulated exoelectron emission

Masahito Tagawa, Koji Tsuzuki, Mikio Mori, Nobuo Ohmae, and Masataka Umeno

Appl. Phys. Lett. 61, 1471 (1992); http://dx.doi.org/10.1063/1.107521 (3 pages) | Cited 1 time

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Trap levels of exoelectrons in high purity aluminum were estimated from the emission properties of field stimulated exoelectrons. The trap level of exoelectron in 99.9999% pure aluminum was found at about 0.2 eV higher than the Fermi level of aluminum and those in less pure aluminum were distributed in a higher energy region. The observed distribution of exoelectron trap levels agrees with the trap level determined by photostimulated exoelectron emission and also explains the glow curves of field stimulated exoelectron emissions from aluminum specimens of different purities.  
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79.75.+g Exoelectron emission
79.70.+q Field emission, ionization, evaporation, and desorption
73.20.Hb Impurity and defect levels; energy states of adsorbed species
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