QE and Suns-V-oc study on the epitaxial CSiTF solar cells

In order to clarify the major factors having confined the efficiencies of as-prepared crystalline silicon thin film (CSiTF) solar cells on the SSP (silicon sheets from powder) ribbons, QE (quantum efficiency) and Suns-V-oc study were performed on the epitaxial CSiTF solar cells fabricated on the SSP ribbons, the SSP ribbons after surface being zone melting recrystallized (ZMR) and single crystalline silicon (sc-Si) substrates. The results show that the epi-layers deposited on the SSP ribbons have rough surfaces, which not only increases the diffusion reflectance on the surfaces but also makes the anti-reflection coatings become structure-loosened, both of which would deteriorate the light trapping effect; in addition, the epi-layers deposited on the SSP ribbons possess poor crystallographic quality, so the heavy grain boundary (GB) recombination limits the diffusion length of the minority carriers in the epi-layers, which makes the as-prepared CSiTF solar cells suffer the worse spectra response at long-wavelength range. Nearly all the dark characteristic parameters of the CSiTF solar cells are far away from the ideal values. The performances of the CSiTF solar cells are especially affected by too high I-02 (the dark saturation current of space charge region) values and too low R-sh (parallel resistance) values. The higher 102 values are mainly caused by the heavy GB recombination resulting from the poor crystallographic qualities of the silicon active layers in the space charge regions, while the lower R-sh values are attributed to the electrical leakage at the un-passivated PN junction or solar cell edges after the solar cells are cut by the laser scriber.

Effect of incorporating nonlanthanoidal indium on optical properties of ferroelectric Bi4Ti3O12 thin films

Bi4Ti3O12 (BTO) and Bi3.25In0.75Ti3O12 (BTO:In) thin films were prepared on fused quartz and LaNiO3/Si (LNO) substrates by chemical solution deposition (CSD). Their microstructures, ferroelectric and optical properties were investigated by X-ray diffraction, scanning electron microscope, ferroelectric tester and UV-visible-NIR spectrophotometer, respectively. The optical band-gaps of the films were found to be 3.64 and 3.45 eV for the BTO and BTO:In films, respectively. Optical constants (refractive indexes and extinction coefficients) were determined from the optical transmittance spectra using the envelope method. Following the single electronic oscillator model, the single oscillator energy E-0, the dispersion energy E-d, the average interband oscillator wavelength lambda(0), the average oscillator strength S-0, the refractive index dispersion parameter (E-0/S-0), the chemical bonding quantity beta, and the long wavelength refractive index n(infinity) were obtained and analyzed. Both the refractive index and extinction coefficient of the BTO:In films are smaller than those of the BTO films. Furthermore, the refractive index dispersion parameter (E-0/S-0) increases and the chemical bonding quantity beta decreases in the BTO and BTO:In films compared with those of bulk. (C) 2007 Published by Elsevier B.V.

Deposition of p-type nc-SiC : H thin films with subtle carbon incorporation for applications in p-i-n solar cells

This paper presents a detailed study on the effects of carbon incorporation and substrate temperature on structural, optical, and electrical properties of p-type nanocrystalline amorphous silicon films. A p-nc-SiC: H thin film with optical gap of 1.92 eV and activation energy of 0.06 eV is obtained through optimizing the plasma parameters. By using this p-type window layer, single junction diphasic nc-SiC : H/a-Si : H solar cells have been successfully prepared with a V-oc of 0.94 eV.

Temperature dependence of the Raman-active modes in the nonpolar a-plane GaN film

Temperature dependences of the polarized Raman scattering spectra in the backscattering configuration of the nonpolar a-plane (or [11 (2) over bar0]-oriented) GaN thin film are analyzed in the range from 100 to 570 K. The nonpolar a-plane GaN film is grown on an r-plane [or (1 (1) over bar 02)-oriented] sapphire substrate by metal organic chemical vapor deposition. The spectral features of the Raman shifts, intensities, and linewidths of the active phonons modes A(1)(TO), E-1(TO), and E-2(high) are significantly revealed, and corresponding temperature coefficients are well deduced by the empirical relationships. With increasing the measurement temperature the Raman frequencies are substantially redshifted and the linewidths gradually broaden. The compressive-strain-free temperature for the nonpolar a-plane GaN film is found to be at about 400 K. Our studies will lead to a better understanding of the fundamental physical characteristics of the nonpolar GaN film. (c) 2007 American Institute of Physics.

Silicon thin films prepared in the transition region and their use in solar cells

Diphasic silicon films (nc-Si/a-Si:H) have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the nc-Si/a-Si:H has higher photoconductivity (sigma(ph)), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. The blue shift for the stretching mode and red shift for the wagging mode in the IR spectra also show the variation of the microstructure. By using this kind of film as intrinsic layer, a p-i-n junction solar cell was prepared with the initial efficiency of 8.51 % and a stabilized efficiency of 8.01% (AM 1.5, 100 mw/cm(2)) at room temperature. (c) 2006 Published by Elsevier B.V.

Magnetism and photoluminescence in manganese-gallium oxide nanowires with monoclinic and spinel structures

Manganese-gallium oxide nanowires were synthesized via in situ Mn doping during nanowire growth using a vapor phase evaporation method. The microstructure and composition of the products were characterized via transmission electron microscopy (TEM), field emission scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The field and temperature dependence of the magnetization reveal the obvious hysteresis loop and large magnitude of Curie-Weiss temperature. The photoluminescence of the manganese-gallium oxide nanowires were studied in a temperature range between 10 and 300 K. A broad green emission band was observed which is attributed to the T-4(1)-(6)A(1) transition in Mn2+ (3d(5)) ions. (c) 2005 Elsevier B.V. All rights reserved.

Structural and optical characterization of Zn1-xCdxO thin films deposited by dc reactive magnetron sputtering

Zn1-xCdxO crystal thin films with different compositions were prepared on silicon and sapphire substrates by the dc reactive magnetron sputtering technique. X-ray diffraction measurements show that the Zn1-xCdxO films are of completely (002)-preferred orientation for x less than or equal to 0.6. For x = 0.8, the Elm is a mixture of ZnO hexagonal wurtzite crystals and CdO cubic crystals. For pure CdO, it is highly (200) preferential-oriented. Photoluminescence spectrum measurement shows that the Zn1-xCdxO (x = 0.2) thin film has a redshift of 0.14 eV from that of ZnO reported previously.

Polarity determination for GaN thin films by electron energy-loss spectroscopy

The intensity of the N K edge in electron energy-loss spectra from a GaN thin film shows a pronounced difference when the orientation of the film approaches the (0002) and (000-2) Bragg reflections, along the polar direction. This experimental result can be interpreted by the effect associated with interference between the Bloch waves of the incident electron in the GaN crystal. The theoretical calculations indicate that, at the Bragg condition of g=0002 along the Ga-N bond direction, the thickness-averaged electron current density on the N atom plane is much higher than that at g=000 (2) over bar, with a maximum as the specimen thickness is about 0.4xi(0002) (the two-beam extinction distance). The delocalization effect on the experimental spectra is also discussed. (C) 2002 American Institute of Physics.

The PL "violet shift" of cerium dioxide on silicon

CeO2 thin film was fabricated by dual ion beam epitaxial technique. The phenomenon of PL violet shift at room temperature was observed, and the distance of shift was about 65 nm. After the analysis of crystal structure and valence in the compound were carried out by XRD and XPS technique, it was concluded that the PL shift was related with valence of cerium ion in the oxides. When the valence of cerium ion varied front tetravalence to trivalence, the PL peak position would move from blue region to violet region and the phenomenon of "violet shift" was observed.

Ultraviolet-blue electroluminescence from Gd3Ga5O12 : Ag

UV-blue light was obtained from a thin-film electroluminescence device using Gd3Ga5O12:Ag as a light-emitting layer, which was deposited by using electron-beam evaporation. The crystal composition and structure of Gd3Ga5O12:Ag were studied by x-ray powder diffraction, The Gd3Ga5O12:Ag has a photoluminescence emission which peaked at around 397 and 467 nm, which were attributed to the oxide vacancies and Ag+, respectively. The brightness of 32 cd/m(2) was obtained when an alternating voltage of 130 V at 1 kHz was applied. (C) 2000 American Institute of Physics. [S0003-6951(00)05031-2].

Raman study on residual strains in thin 3C-SiC epitaxial layers grown on Si(001)

Raman scattering measurement has been used to study the residual strains in the thin 3C-SiC/Si(001) epilayers with a variation of film thickness from 0.1 to 1.2 mu m. which were prepared by chemical vapor deposition (CVD)growth. Two methods have been exploited to figure our the residual strains and the exact LO bands. The final analyzing results show that residual strains exist in the 3C-SiC epilayers. The average stress is 1.3010 GPa, and the relative change of the lattice constant is 1.36 parts per thousand. Our measurements also show that 3C-SiC phonons are detectable even for the samples with film thickness in the range of 0.1 to 0.2 mu m. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Sputtering of ZnO buffer layer on Si for GaN blue light emitting materials

The preparation of high quality ZnO/Si substrates for the growth of GaN blue light emitting materials is considered. ZnO thin films have been deposited on Si(100) and Si(lll) substrates by conventional magnetron sputtering. Morphology, crystallinity and c-axis preferred orientation of ZnO thin films have been investigated by transmitting electron microscopy (TEM), X-ray diffraction (XRD) and X-ray rocking curve (XRC). It is proved that the ZnO thin films have perfect structure. The full-width-at-half-maximum (FWHM) of the ZnO(002) XRC of these films is about 1 degrees, while the minimum is 0.353 degrees. This result is better than the minimum FWHM (about 2 degrees) reported by other research groups. Moreover, comparison and discussion are given on film structure of ZnO/Si(100) and ZnO/Si(lll).

Microstructures of microcrystalline silicon thin films prepared by hot wire chemical vapor deposition

Undoped hydrogenated microcrystalline silicon (mu c-Si:H) thin films were prepared at low temperature by hot wire chemical vapor deposition (HWCVD). Microstructures of the mu c-Si:H films with different H-2/SiH4 ratios and deposition pressures have been characterized by infrared spectroscopy X-ray diffraction (XRD), Raman scattering, Fourier transform (FTIR), cross-sectional transmission electron microscopy (TEM) and small angle X-ray scattering (SAX). The crystallization of silicon thin film was enhanced by hydrogen dilution and deposition pressure. The TEM result shows the columnar growth of mu c-Si:H thin films. An initial microcrystalline Si layer on the glass substrate, instead of the amorphous layer commonly observed in plasma enhanced chemical vapor deposition (PECVD), was observed from TEM and backside incident Raman spectra. The SAXS data indicate an enhancement of the mass density of mu c-Si:H films by hydrogen dilution. Finally, combining the FTIR data with the SAXS experiment suggests that the Si--H bonds in mu c-Si:H and in polycrystalline Si thin films are located at the grain boundaries. (C) 2000 Elsevier Science S.A. All rights reserved.

Single dipole mode photonic crystal laser on InGaAsP/InP QW waveguide slab - art. no. 698436

Single point defect microcavity possesses only the degenerate dipole modes under certain photonic crystal structure parameters. By deforming lattice structure, the degeneracy of the dipole modes has been broken. Theoretical simulation shows the large splitting of 65nm between the splitted x-mode and y-mode, approximate to the luminescent gain spectrum, which benefits for the single mode lasing. Experimentally the single dipole mode lasing, y-mode, is achieved in the deformed microcavity.

Mode analysis of photonic crystal polarization beam splitter and its application in integrated circuits design - art. no. 698437

In this work, the guided modes of a photonic crystal polarization beam splitter (PC-PBS) are studied. We demonstrate that the transmission of a low-loss photonic crystal 120 degrees waveguide bend integrated with the PBS will be influenced if the PBS is multi-moded. We propose a single-moded PC-PBS structure by introducing deformed structures, and it shows twice the enhancement of the transmission. This device with remarkable improvement of performance is promising in the use of photonic crystal integrated circuits design.