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  • 1
    Electronic Resource
    Electronic Resource
    Plasma-enhanced chemical-vapor-deposited oxide for low surface recombination velocity and high effective lifetime in silicon (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2856-2859 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that plasma-enhanced chemical-vapor deposition (PECVD) of thin SiO2 on Si wafers followed by rapid thermal annealing (RTA) can result in very high effective carrier lifetime ((approximately-greater-than)5 ms) and extremely low surface recombination velocity (≤2 cm/s). Thin SiO2 (∼100 A(ring)) layers were prepared by direct PECVD at 250 °C and RTA was performed at 350 °C in forming gas. Detailed metal-oxide-semiconductor analysis and model calculations showed that such a low recombination velocity is the result of moderately high positive oxide charge (5×1011–1×1012 cm−2 ) and relatively low midgap interface-state density (5×1010–1×1011 cm−2 eV−1). RTA was found to be superior to furnace annealing, and a forming gas ambient was better than a nitrogen ambient for achieving a very low surface recombination velocity. Some degradation in the surface recombination velocity or effective lifetime was observed. It is found that a PECVD SiN cap on top of the thin SiO2 not only suppressed this degradation but also enhanced the effective lifetime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354638
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  • 2
    Electronic Resource
    Electronic Resource
    Re-evaluation of the derivatives of the half order Fermi integrals (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7030-7034 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Fermi integrals of half orders are important in the simulation of semiconductor transport processes. Several of these integrals (−1/2, 1/2, 3/2, 5/2) have been recently retabulated since the 1938 study by McDougall and Stoner [Phil. Trans. Roy. Soc. A 237, 67 (1938)], but the derivatives were not re-evaluated. The original integral values were calculated without the aid of high speed computers by using approximate series evaluation and tabulations of exponentials and zeta functions. In addition, a discrepancy was found in the literature since the original study in 1938. The second derivative of F1/2 has been mistakenly represented as being proportional to a Fermi integral of another order. This article tabulates the half order Fermi integrals from −1/2 to 5/2 over the reduced energy range −5 to 20 in 0.25 increments. The first two derivatives of F−1/2 are also calculated by numerical integration and tabulated to aid in interpolation. It is shown that the second derivative of F1/2 is not proportional to another Fermi integral. A suitable interpolation scheme is proposed to calculate the values of the Fermi integrals of various order to high accuracy over the total reduced energy range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352420
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  • 3
    Electronic Resource
    Electronic Resource
    The effects of CdCl2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 881-889 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl2 dip followed by a 400 °C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl2-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature (J-V-T) analysis revealed that the CdCl2 treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl2 treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7×10−7 A/cm2 to 2.6×10−9 A/cm2 and, (c) an increase in cell Voc from 385 to 720 mV. The CdCl2 also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl2-treated structures indicate that the CdCl2 treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl2-treated devices at Ev + 0.64 eV which is attributed to the formation of VCd-related defects during the annealing process after the CdCl2 dip. J-V-T analysis demonstrated that this trap is the probable source of dominant recombination in the CdCl2-treated cells. An inverse correlation was found between the density of the Ev + 0.64 eV trap and cell Voc, suggesting that the heat treatment with CdCl2 may eventually limit the CdTe/CdS cell performance unless the formation of this defect complex is controlled or eliminated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349652
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of ZnO varistor degradation using lifetime positron-annihilation spectroscopy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 8380-8386 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron-annihilation spectroscopy (PAS) was used in the lifetime mode to study changes in the grain-boundary defect equilibrium associated with dc-bias-induced degradation of a ZnO varistor. The PAS lifetime spectra were collected while the sample was under an applied bias ranging from 100 V ( ∼ 400 V/cm) to 500 V ( ∼ 2000 V/cm). The current through the sample was continuously monitored. The simple trapping model was used to interpret the lifetime PAS results and to obtain an estimate for the positron-capture rate. The experimental results show that an increase in the bias voltage results in a decrease in the positron-trap density and an increase in the positron lifetime associated with the dominant positron trap. These results are explained on the basis of a decrease in the concentration of negatively charged zinc vacancies at the grain boundary. The PAS results support the ion-migration model for degradation, which suggests that the bias-induced migration of positively charged zinc interstitials to the grain boundary reduces the concentration of negatively charged zinc vacancies at the boundary. This results in a reduction in the barrier height (degradation) and is consistent with the PAS data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347402
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of rapid thermal anneal on refractive index and hydrogen content of plasma-enhanced chemical vapor deposited silicon nitride films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5384-5388 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The objective of this paper is to understand and quantify the effects of rapid thermal anneal (RTA) on refractive index, thickness, and hydrogen content of plasma-enhanced, chemical vapor-deposited (PECVD) silicon nitride films. It is shown that RTA is more effective than identical furnace anneal. A threshold in as-deposited refractive index value is found, above which the index of a silicon nitride film increases, while the thickness and bonded hydrogen content decreases as result of the RTA. In addition, the magnitude of increase in the index is proportional to the as-deposited index value. The threshold index value increases with the increase in silicon nitride deposition temperature. A direct correlation is found between the annealing-induced increase in refractive index and the corresponding decrease in total bonded hydrogen concentration in the PECVD silicon nitride films. Finally, it is shown that the release of bonded hydrogen from the film can passivate defects in the underlying silicon substrate and increase the performance of silicon devices such as solar cells. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363480
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  • 6
    Electronic Resource
    Electronic Resource
    Modeling and characterization of interface state parameters and surface recombination velocity at plasma enhanced chemical vapor deposited SiO2–Si interface (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2048-2054 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effective surface recombination velocity (Seff) at plasma enhanced chemical vapor deposited (PECVD) SiO2/Si interface as a function of surface band bending under illumination was obtained by combining the photoconductive voltage decay measurements with indium tin oxide gate bias voltage, metal-oxide-semiconductor-capacitance voltage, measurements and theoretical calculations. The capture cross sections for electrons and holes are obtained for the first time for the PECVD SiO2/Si interface state. Theoretical calculations of Seff based on the interface parameters, including interface state density and cross sections for electron and hole, were performed to see the effects of the positive oxide charge density (Qox) on Seff. It is found that roughly a 10 times larger value of Qox compared to the midgap interface state density is required to reduce Seff below 10 cm/s for 5 Ω cm (100) p-type Si. These results prove the potential of PECVD SiO2 for effective passivation of Si surfaces for devices like solar cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356307
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison of covariance linear predictive modeling to the modulation function method for use in deep level transient spectroscopy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4560-4569 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article provides a quantitative understanding of the merits and disadvantages of various methods of analyzing the deep level transient spectroscopy (DLTS) transients and spectrums. The modulation function method is compared to the covariance method of linear predictive modeling (CMLPM) transient analysis technique, and conventional DLTS spectrum methods. It is found that for high signal to noise ratio transients (high trap concentration), the modulation function method is superior to all other methods. As the signal to noise ratio decreases, CMLPM resolves closely spaced defect levels better than any other method examined. For very low signal to noise ratios, the effects of noise can only be overcome by the inherent averaging present in the more conventional DLTS spectrum analyses. The proper choice of modulation functions is also discussed, and a modified modulation function is proposed for higher resolution of closely spaced traps. Finally, DLTS transients from an electron irradiated sample containing five traps, are analyzed by conventional DLTS spectrum methods, the modulation function method and CMLPM to experimentally support the theoretical predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355950
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  • 8
    Electronic Resource
    Electronic Resource
    Correlations between CdTe/CdS/SnO2/glass solar cell performance and the interface/surface properties (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2151-2153 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Surface and interface properties of CdTe/CdS/SnO2/glass heterojunction solar cells are studied by means of x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and optical reflectance (OR) techniques. First, n-type CdS layer was grown by solution growth technique on the SnO2 coated glass substrate and then the p-type CdTe was deposited on CdS by metal-organic chemical-vapor deposition. Despite many other efficiency limiting mechanisms in CdTe solar cells, this article shows that surfaces and interfaces play an important role in determining the cell efficiency. In an attempt to correlate the surface and interface properties to the cell performance, a series of CdTe/CdS solar cells with different conversion efficiencies were fabricated and analyzed. It was found that high efficiency cells possess Te-rich CdTe surface along with smooth interfaces, as revealed by XPS, SIMS, and OR measurements, while low efficiency cells display near stoichiometric or Cd-rich CdTe surface and abrupt interfaces. The impact and role of interface/surface properties on CdTe solar cell performance are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361041
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  • 9
    Electronic Resource
    Electronic Resource
    Efficient combination of surface and bulk passivation schemes of high-efficiency multicrystalline silicon solar cells (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3457-3461 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conventional and electromagnetically casted multicrystalline silicon solar cells are fabricated following different passivation schemes. Thin layers (∼100 A(ring)) of thermal dry and plasma-enhanced chemical-vapor-deposition (PECVD) SiO2 are implemented for surface oxide passivation of multicrystalline silicon solar cells and compared. It is found that growing thin layers of thermal dry oxide results in efficient surface passivation. However, for thin PECVD SiO2 layers it is necessary to perform low-temperature forming gas anneal, postdeposition, in order to observe the surface passivation effect. In addition, hydrogen plasma passivation has been optimized for achieving deep penetration of atomic hydrogen in the material ((approximately-greater-than)30 μm) and as a consequence very effective bulk passivation of multicrystalline silicon solar cells. By combining front and back thermal dry SiO2 passivation with hydrogen remote plasma treatment, a cell efficiency of 17% (independently confirmed) on 4 cm2 area and 180 μm thickness is realized without any Al gettering. On the other hand, the cell efficiencies obtained using thin layers of PECVD SiO2 are found to be very comparable to the efficiency of the cells fabricated with thermal dry SiO2 layers provided that PECVD Si3N4/SiO2 are used as a double-layer antireflection coating. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359977
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  • 10
    Electronic Resource
    Electronic Resource
    Concentration-dependent near and above band edge absorption in doped InP and its effect on solar cell modeling (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2666-2670 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absorption coefficients for n- and p-type InP are reported for the first time in the energy range of 1.3–3.0 eV in this paper. In order to obtain absorption coefficients in the higher energy range of 1.8–3.0 eV, extremely thin (∼0.2 μm) InP samples were fabricated and bonded to glass substrates. For measurements in the lower energy range of 1.3–1.6 eV, samples with thickness in the range of 0.5–0.9 μm were found to be optimum. For energies below 1.6 eV, the absorption coefficients are a strong function of the doping concentration. However, in the energy range of 1.8–3.0 eV there is little doping dependence and the measured absorption coefficients follow the theoretical calculations. In the case of n-type samples, absorption coefficients decrease with increasing doping concentration and the absorption edge moves to higher energy due to the Burstein–Moss effect. For p-type samples, the absorption edge shifts to lower energies due to transitions between band tails. Model calculations show that the use of accurate doping-dependent absorption coefficients reported in this paper, as opposed to the commonly used absorption coefficients of undoped InP, can result in significant improvement in the predicted internal quantum efficiency and device parameters of InP solar cells. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360128
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