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16 Apr 2001

Volume 78, Issue 16, pp. 2267-2404

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Passivation of oxygen-related donors in microcrystalline silicon by low temperature deposition

Y. Nasuno, M. Kondo, and A. Matsuda

Appl. Phys. Lett. 78, 2330 (2001); http://dx.doi.org/10.1063/1.1364657 (3 pages) | Cited 43 times

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Low-temperature processing for high-performance solar cells based on hydrogenated microcrystalline silicon (μc-Si:H) has been developed using a conventional rf plasma-enhanced chemical vapor deposition (PECVD) technique at an excitation frequency of 13.56 MHz under a high deposition pressure condition. Among pin type solar cells, it is found that deposition temperature of i-layer at 140 °C is effective particularly for improving open circuit voltage (Voc), surprisingly without deteriorating short circuit current or fill factor. Carrier density of undoped μc-Si abruptly decreases for deposition temperatures lower than 180 °C, and the improvement of Voc is ascribed to a decrease of shunt leakage current arising from the oxygen-related donors. This implies that oxygen-related donors can be passivated at low deposition temperatures and that hydrogen plays an important role for the passivation. We propose a simple model for the hydrogen passivation of oxygen related donors. We apply this passivation technique to solar cells, and consequently a conversion efficiency of 8.9% (Voc=0.51 V, Jsc=25 mA/cm−1, FF=0.70) has been obtained in spite of an oxygen concentration of 2×1019 cm−3 in combination with device optimization such as a p-layer. Effect of deposition temperature of i-layer upon other solar cell parameter, short circuit current, and fill factor is also discussed. © 2001 American Institute of Physics.
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73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Rv Passivation
52.77.Dq Plasma-based ion implantation and deposition
84.60.Jt Photoelectric conversion

Room-temperature excitons in wide-gap layered-oxysulfide semiconductor: LaCuOS

K. Ueda, S. Inoue, H. Hosono, N. Sarukura, and M. Hirano

Appl. Phys. Lett. 78, 2333 (2001); http://dx.doi.org/10.1063/1.1364656 (3 pages) | Cited 54 times

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Sharp optical absorption and emission peaks near the band gap (Eg ≈ 3.1 eV) were observed in LaCuOS polycrystalline thin films at room temperature. The absorption peak was able to be detected at temperatures as high as 490 K, and its intensity remarkably increased with decreasing temperature. The spectral position of the absorption peak and its temperature dependence almost agreed with those of the emission peak. It was concluded that the sharp absorption and emission peaks originate from excitons. On the basis of semiquantitative consideration about the excitons, it is suggested that the electronic-structure characteristic of the layered-crystal structure of LaCuOS is responsible for the stability of the excitons. The observation of the exciton absorption and emission at room temperature revealed that LaCuOS is a promising material for optoelectronic applications such as light-emitting devices. © 2001 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.40.Ha Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

Formation of a SiO2/SiC structure at 203 °C by use of perchloric acid

Hikaru Kobayashi, Takeaki Sakurai, Masayoshi Nishiyama, and Yasushiro Nishioka

Appl. Phys. Lett. 78, 2336 (2001); http://dx.doi.org/10.1063/1.1364510 (3 pages) | Cited 3 times

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A chemical method for the low-temperature formation of a SiO2/SiC structure is developed using perchloric acid (HClO4). The thickness of the SiO2 layer increases linearly with the time of the immersion of 6H-SiC(0001) in the HClO4 solution at 203 °C, indicating the reaction-limited process. The immersion in 20 h results in the formation of an 80-nm-thick SiO2 layer. The SiO2 layer contains little carbon and suboxide species, but includes chlorine (Cl) species with the atomic concentration of 0.2%, leading to a high leakage current density. Heat treatment at 900 °C removes the Cl species, and the leakage current density becomes negligibly low. © 2001 American Institute of Physics.
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81.65.Mq Oxidation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing

Origin of electric field enhancement in field emission from amorphous carbon thin films

J. D. Carey, R. D. Forrest, and S. R. P. Silva

Appl. Phys. Lett. 78, 2339 (2001); http://dx.doi.org/10.1063/1.1366369 (3 pages) | Cited 44 times

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The observation of electron emission from amorphous carbon thin films at low applied electric fields is explained in terms of an enhancement of the field brought about by dielectric inhomogeneities within the film. These inhomogeneities originate from the differences between conductive, spatially localized sp2 C clusters surrounded by a more insulating sp3 matrix. By a more complete understanding of the concentration and distribution of the clusters, a generic model for field emission from amorphous carbon thin films can be developed. Extensions of this model to explain the emission properties of carbon nanotubes and carbon nanocomposite materials are also presented. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption

Highly conductive epitaxial CdO thin films prepared by pulsed laser deposition

M. Yan, M. Lane, C. R. Kannewurf, and R. P. H. Chang

Appl. Phys. Lett. 78, 2342 (2001); http://dx.doi.org/10.1063/1.1365410 (3 pages) | Cited 84 times

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Epitaxial growth of both pure and doped CdO thin films has been achieved on MgO (111) substrates using pulsed laser deposition. A maximum conductivity of 42 000 S/cm with mobility of 609 cm2/V s is achieved when the CdO epitaxial film is doped with 2.5% Sn. The pure CdO epitaxial film has a band gap of 2.4 eV. The band gap increases with doping and reaches a maximum of 2.87 eV when the doping level is 6.2%. Both grain boundary scattering and ionized impurity scattering are found to contribute to the mobility of CdO films. © 2001 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
68.55.-a Thin film structure and morphology
71.20.Nr Semiconductor compounds
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Surface morphology evolution in highly mismatched Sb-graded buffer layers on GaAs

Eric B. Chen, David C. Paine, Parvez N. Uppal, Kirby Nichols, and John S. Ahearn

Appl. Phys. Lett. 78, 2345 (2001); http://dx.doi.org/10.1063/1.1366361 (3 pages) | Cited 2 times

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Ternary GaAs1−ySby and quaternary Al0.5Ga0.5As1−ySby compositionally step-graded buffer structures graded to a 4.6% mismatch on GaAs were evaluated by transmission electron microscopy. Cross-sectional bright field imaging (g = 004) revealed the presence of compositional modulations parallel to the (001) interface with a period of 1–2 nm that were used to establish the morphology of the growth surface during buffer layer deposition. Analysis of the Sb-graded ternary structures shows that the growth surface remained planar with a maximum peak-to-valley height of 4.4±0.6 nm located near the topmost layer. A threading dislocation density of 108–109 cm−2 was measured in both types of buffer layers and an improvement in peak-to-valley amplitude (2.3±0.5 nm vs 4.4±0.6 nm) was observed in the Al-containing quaternary alloys. © 2001 American Institute of Physics.
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61.72.Lk Linear defects: dislocations, disclinations
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
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