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13 Sep 1999

Volume 75, Issue 11, pp. 1491-1646

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Performance and stability of Si:H p–i–n solar cells with i layers prepared at the thickness-dependent amorphous-to-microcrystalline phase boundary

Randy J. Koval, Joohyun Koh, Z. Lu, L. Jiao, R. W. Collins, and C. R. Wronski

Appl. Phys. Lett. 75, 1553 (1999); http://dx.doi.org/10.1063/1.124752 (3 pages) | Cited 19 times

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Systematic studies have been carried out on the transition from the amorphous to the microcrystalline phase in intrinsic Si:H as a function of the accumulated film thickness and the effect of this transition on p–i–n solar cell performance [J. Koh, Y. Lee, H. Fujiwara, C. R. Wronski, and R. W. Collins, Appl. Phys. Lett. 73, 1526 (1998)]. Guided by a deposition phase diagram obtained from real-time spectroscopic ellipsometry, cell structures having i layers deposited with different H2-dilution levels and thicknesses were investigated. For these structures, the fill factors are controlled by the bulk i layers. From the systematic changes in the fill factors, specifically their initial and degraded steady-state values and their degradation kinetics, the effects of the transition from the amorphous to the microcrystalline phase within the Si:H layers are identified, and insights are obtained into the properties of these structurally graded materials. © 1999 American Institute of Physics.
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84.60.Jt Photoelectric conversion
64.70.K- Solid-solid transitions
73.61.Jc Amorphous semiconductors; glasses

Reversible gas doping of bulk α-hexathiophene

J. H. Schön, Ch. Kloc, and B. Batlogg

Appl. Phys. Lett. 75, 1556 (1999); http://dx.doi.org/10.1063/1.124753 (3 pages) | Cited 3 times

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The sensitivity of the electrical properties of α-hexathiophene single crystals to exposure to air, oxygen, helium, and nitrogen is investigated by space charge limited current spectroscopy. Whereas no changes are seen in helium and nitrogen atmosphere, the acceptor concentration and trap density increase in air or oxygen. Nevertheless, stable equilibrium concentrations, much lower than in thin films, are reached after a few days of exposure and remain unchanged for many months. Therefore, the observed thin film device instabilities and their degradation have to be ascribed to grain boundary-enhanced or interface effects. The present results indicate that air-stable electronic devices can be prepared from oligothiophenes. © 1999 American Institute of Physics.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
72.20.Ht High-field and nonlinear effects
71.55.Ht Other nonmetals
61.72.up Other materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

InGaAs heteroepitaxy on GaAs compliant substrates: X-ray diffraction evidence of enhanced relaxation and improved structural quality

P. D. Moran, D. M. Hansen, R. J. Matyi, J. G. Cederberg, L. J. Mawst, and T. F. Kuech

Appl. Phys. Lett. 75, 1559 (1999); http://dx.doi.org/10.1063/1.124754 (3 pages) | Cited 16 times

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In0.44Ga0.56As (3% mismatch) films 3 μm thick were grown simultaneously on a conventional GaAs substrate, glass-bonded GaAs compliant substrates employing glasses of different viscosity, and a twist-bonded GaAs compliant substrate. High-resolution triple-crystal x-ray diffraction measurements of the breadth of the strain distribution in the films and atomic force microscopy measurements of the film’s surface morphology were performed. The films grown on the glass-bonded compliant substrates exhibited a strain distribution whose breadth was narrowed by almost a factor of 2 and a surface roughness that decreased by a factor of 4 compared to the film simultaneously grown on the conventional substrate. These improvements in the film’s structural quality were observed to be independent of the viscosity of the glass-bonding media over the range of viscosity investigated and were not observed to occur for the film grown on the twist-bonded substrate. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Ea III-V semiconductors

Attenuated total reflection Fourier transform infrared spectroscopy study of the adsorption of organic contaminants on a hydrogen-terminated Si(111) surface in air

Shen Ye, Taro Ichihara, and Kohei Uosaki

Appl. Phys. Lett. 75, 1562 (1999); http://dx.doi.org/10.1063/1.124755 (3 pages) | Cited 21 times

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The adsorption of organic contaminants on a hydrogen-terminated Si(111) surface was investigated using attenuated total reflection Fourier transform infrared spectroscopy. When the hydrogen-terminated Si(111) surface was exposed to dry air, the sharp Si–H monohydride peak became weaker and a broad component became visible in the lower wave-number region. Furthermore, a number of bands within the C–H stretching region were observed. The intensity of the sharp Si–H band was recovered to a certain extent and those of the broad component and the C–H bands decreased after the sample was rinsed in hexane. These results suggest that the contamination by organic adsorbates is not accompanied by a chemical bond formation. © 1999 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
81.65.Cf Surface cleaning, etching, patterning
78.30.Am Elemental semiconductors and insulators
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

The Bloch–Grüneisen mobility of two-dimensional electron gas in AlGaN/GaN heterostructures

N. A. Zakhleniuk, C. R. Bennett, M. Babiker, and B. K. Ridley

Appl. Phys. Lett. 75, 1565 (1999); http://dx.doi.org/10.1063/1.124756 (3 pages) | Cited 9 times

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We present calculations of the Bloch–Grüneisen electron mobility in zincblende (ZB) and wurtzite (WZ) AlGaN/GaN quantum-well heterostructures. Within the Boltzmann equation approach, we derive an expression for the momentum relaxation time which explicitly takes into account the Pauli principle restrictions, and show that these are comparable in importance to a screening effect at temperatures up to 150 K provided that the electron density is high. This is of particular importance for GaN-based quantum wells for which very high electron densities initiated by the strain-induced and spontaneous polarization fields have been recently reported. Dependences of the mobility on the lattice temperature and the electron density for both ZB and WZ GaN are presented, and it is shown that the WZ mobility is higher than the ZB mobility. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Shallow p-type SiGeC layers synthesized by ion implantation of Ge, C, and B in Si

H. Kurata, K. Suzuki, T. Futatsugi, and N. Yokoyama

Appl. Phys. Lett. 75, 1568 (1999); http://dx.doi.org/10.1063/1.124757 (3 pages) | Cited 2 times

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We investigated the characteristics of p-type SiGeC layers for possible application to source/drain regions of sub-100 nm metal–oxide–semiconductor field-effect transistors. We synthesized the SiGeC layer by the high-dose ion implantation of Ge and C into Si substrate and subsequent annealing. We succeeded in fabricating shallow p+/n junctions by the incorporation of C, of which the peak concentration is more than 1%. B diffusion in this layer was significantly suppressed, and the depth profile of B was reproduced with a process simulation in which a diffusion coefficient much lower than the reported value was assumed. This should be attributed to decreased Si interstitials. We examined the sheet resistance and contact resistance of the SiGeC layer, and found that the increase in resistance is tolerable as compared with a SiGe layer. This is because the carrier deactivation by the incorporation of C was not serious, which was confirmed by the spreading resistance measurement. The junction leakage in the p+/n diode was reduced with the increase in the concentration of C. Hence, SiGeC is a promising material for use in shallow and low resistance p+/n junctions. © 1999 American Institute of Physics.
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61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing
85.30.Tv Field effect devices
85.30.Kk Junction diodes

Boron-related minority-carrier trapping centers in p-type silicon

Daniel Macdonald, Mark Kerr, and Andrés Cuevas

Appl. Phys. Lett. 75, 1571 (1999); http://dx.doi.org/10.1063/1.124758 (3 pages) | Cited 19 times

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Photoconductivity-based measurements of recombination lifetimes in multicrystalline silicon are often hampered by carrier trapping effects, which cause a characteristically large relative increase in the photoconductance. Single-crystal p-type float-zone wafers of varying resistivities were cross contaminated with multicrystalline wafers that exhibited such trapping. A proportion of the impurities present in the multicrystalline samples was found to effuse into the float-zone wafers, where they act as both recombination centers and trapping centers. By the application of a simple theoretical model, the trap density in the float-zone samples was determined, and found to be directly proportional to the boron-dopant concentration. These results suggest that the trapping centers are caused by boron-impurity pairs. © 1999 American Institute of Physics.
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71.55.Cn Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
72.80.Cw Elemental semiconductors

Fluorescence scanning near-field optical microscopy of conjugated polymer blends

R. Stevenson, M. Granström, and D. Richards

Appl. Phys. Lett. 75, 1574 (1999); http://dx.doi.org/10.1063/1.124783 (3 pages) | Cited 14 times

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Fluorescence scanning near-field optical microscopy with a spatial resolution of ∼ 150 nm is used to investigate blends of conjugated polymers in a poly(methylmethacrylate), PMMA, matrix. These blends, which phase segregate on a length scale of several hundred nanometers, have a high degree of correlation between their fluorescence and topographic images, as illustrated by measurements taken from a sample of 5% by weight of poly(2-methoxy-5-(2′,6′-dimethyloctyloxy)-pphenylenevinylene), OC1C10” PPV, in PMMA. In a blend containing both poly(2,5-dihexyloxyp-phenylenevinylene), CN-PPV, and poly(2-dimethyloctylsilyl-p-phenylenevinylene), DMOS-PPV, spectroscopic contrast was used to identify material both on the surface and buried within a thin transparent film. © 1999 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
78.66.Qn Polymers; organic compounds
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
78.55.Kz Solid organic materials
07.79.Fc Near-field scanning optical microscopes
64.75.-g Phase equilibria

Surface plasmon-enhanced photoluminescence from a single quantum well

N. E. Hecker, R. A. Höpfel, N. Sawaki, T. Maier, and G. Strasser

Appl. Phys. Lett. 75, 1577 (1999); http://dx.doi.org/10.1063/1.124759 (3 pages) | Cited 33 times

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We have dramatically enhanced the photoluminescence intensity emitted from a single quantum well (typically by factors of 3–6) by covering the sample surface with a thin semitransparent metallic film. Using a photolithographically prepared gold grating, we show that this enhancement is due to the excitation of surface plasmons on the metal. By selectively turning off the surface plasmon excitation via sample or light polarization rotation, the enhancement can be suppressed. © 1999 American Institute of Physics.
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78.66.-w Optical properties of specific thin films
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.40.Ns Metal-nonmetal contacts
78.55.-m Photoluminescence, properties and materials

Effects of deep levels on transconductance dispersion in AlGaAs/InGaAs pseudomorphic high electron mobility transistor

Kyoung Jin Choi, Jong-Lam Lee, and Hyung Mo Yoo

Appl. Phys. Lett. 75, 1580 (1999); http://dx.doi.org/10.1063/1.124760 (3 pages) | Cited 7 times

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The effects of deep levels on the transconductance dispersion in an AlGaAs/InGaAs pseudomorphic high electron mobility transistor was interpreted using capacitance deep level transient spectroscopy (DLTS). Transconductance was decreased by 10% in the frequency range of 10 Hz–10 kHz at the negative gate bias, but it was increased at the positive one. In the DLTS spectra, two hole trap-like signals corresponding to surface states were only observed at the negative pulse bias, whereas the DX-center with the activation energy of 0.42±0.01 eV were observed at the positive one. The activation energy agrees well with that obtained from the temperature dependence of the positive transconductance dispersion, 0.39±0.03 eV. These provide evidence that the positive and negative transconductance dispersions are due to the DX center and surface states, respectively. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
71.55.Eq III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Electroabsorption and retardation due to intersubband transitions in coupled quantum wells

R. Kapon, N. Cohen, A. Sa’ar, V. Thierry-Mieg, and R. Planel

Appl. Phys. Lett. 75, 1583 (1999); http://dx.doi.org/10.1063/1.124761 (3 pages) | Cited 1 time

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Electro-optical modulation due to intersubband transitions in a coupled quantum well structure is experimentally studied. By using an appropriate set of cross/parallel polarizer-analyzer measurements, we were able to resolve the contribution of electroabsorption and electroretardation to the overall modulation of the infrared light. Fitting the experimental results to a simple model that allows the quantum properties of the structure to vary with the applied electric field revealed that the most significant contribution to the modulation comes from linewidth broadening of the optical transition. We attribute this effect to a larger degree of localization of the envelope states near the interfaces that give rise to a faster dephasing time due to elastic scattering. © 1999 American Institute of Physics.
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78.20.Jq Electro-optical effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.-w Optical properties of specific thin films
78.30.-j Infrared and Raman spectra

A surfactant-mediated relaxed Si0.5Ge0.5 graded layer with a very low threading dislocation density and smooth surface

J. L. Liu, C. D. Moore, G. D. U’Ren, Y. H. Luo, Y. Lu, G. Jin, S. G. Thomas, M. S. Goorsky, and K. L. Wang

Appl. Phys. Lett. 75, 1586 (1999); http://dx.doi.org/10.1063/1.124762 (3 pages) | Cited 37 times

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A method to grow a relaxed Si0.5Ge0.5 graded layer with a very smooth surface and a very low threading dislocation density using solid-source molecular-beam epitaxy is reported. This method included the use of Sb as a surfactant for the growth of a 2 μm compositionally graded SiGe buffer with the Ge concentration linearly graded from 0% to 50% followed by a 0.3 μm constant Si0.5Ge0.5 layer. The substrate temperature was kept at 510 °C during the growth. Both Raman scattering and x-ray diffraction were used to determine the Ge mole fraction and the degree of strain relaxation. Both x-ray reflectivity and atomic force microscopy measurements show a surface root mean square roughness of only 20 Å. The threading dislocation density was determined to be as low as 1.5×104 cm−2 as obtained by the Schimmel etch method. This study shows that the use of a Sb surfactant and low temperature growth is an effective method to fabricate high-quality graded buffer layers. © 1999 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
68.60.Bs Mechanical and acoustical properties
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