Physics / Fizik

Permanent URI for this collectionhttps://hdl.handle.net/11147/6

Browse

Filters

2003 - 20064

Settings

Institution Author: search.filters.institutionAuthor.Göktaş, OktaySubject: search.filters.subject.Thin films

Search Results

Now showing 1 - 4 of 4
  • Conference Object
    Citation - WoS: 6
    Citation - Scopus: 9
    Sub-Bandgap Optical Absorption Spectroscopy of Hydrogenated Microcrystalline Silicon Thin Films Prepared Using Hot-Wire Cvd (cat-Cvd) Process
    (Elsevier Ltd., 2006) Göktaş, Oktay; Işık, Nebile; Okur, Salih; Güneş, Mehmet; Carius, Reinhard; Klomfaß, Josef; Finger, Friedhelm
    Hydrogenated microcrystalline silicon (μc-Si:H) thin films with different silane concentration (SC) have been prepared using the HW-CVD technique. Dual beam photoconductivity (DBP), photothermal deflection spectroscopy (PDS), and transmission measurements have been used to investigate the optical properties of the μc-Si:H films. Two different sub-bandgap absorption, α(hν), methods have been applied and analyzed to obtain a better insight into the electronic states involved. A good agreement has been obtained in the absorption spectrum obtained from the PDS and DBP measurements at energies above the bandgap. Differences between PDS and DBP spectra exist below the bandgap energy where DBP spectra always give lower α(hν) values and show a dependence on the SC. For some films, differences exist in the α(hν) spectra when the DBP measurements are carried out through the film and substrate side. In addition, for some films, there remains fringe pattern left on the spectrum after the calculation of the fringe-free absorption spectrum, which indicates structural inhomogeneities present throughout the film.
  • Conference Object
    Citation - WoS: 7
    Citation - Scopus: 10
    Sub-Bandgap Absorption Spectroscopy and Minority Carrier Transport Properties of Hydrogenated Microcrystalline Silicon Thin Films
    (National Institute of Optoelectronics, 2005) Güneş, Mehmet; Göktaş, Oktay; Okur, Salih; Işık, Nebile; Carius, Reinhard; Klomfaß, Josef; Finger, Friedhelm
    Hydrogenated microcrystalline silicon thin films have been prepared using HW-CVD and VHF-PECVD techniques with different silane concentrations. The steady-state photoconductivity, dual beam photoconductivity, photothermal deflection spectroscopy and steady-state photocarrier grating (SSPG) methods have been used to investigate the optical and electronic properties of the films. Two different sub-bandgap absorption methods have been applied and analyzed to obtain a better insight into the electronic states involved. For some films, differences existed in the optical absorption spectra when the measurements were carried out through the film side and through the substrate side. In addition, for some films, fringe patterns remained on the spectrum after the calculation of the fringe free absorption spectrum, which indicates that structural inhomogeneities were present throughout the film. Finally, minority carrier diffusion lengths deduced from the SSPG measurements were investigated as a function of the crystalline volume fraction (I c RS) obtained from Raman spectroscopy. The longest diffusion lengths and lowest sub-bandgap absorption coefficients were obtained for films deposited in the region of the transition to the amorphous growth.
  • Article
    Citation - WoS: 13
    Citation - Scopus: 14
    Electronic Transport Properties of Microcrystalline Silicon Thin Films Prepared by Vhf-Pecvd
    (Springer Verlag, 2004) Okur, Salih; Güneş, Mehmet; Göktaş, Oktay; Finger, Friedhelm; Carius, Reinhard
    Steady-state photocarrier grating (SSPG) and steady-state photoconductivity, σph, experiments have been carried out to investigate the electronic transport properties of undoped hydrogenated microcrystalline silicon (μc-Si: H) films prepared with very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). Material with different crystalline volume fractions was obtained by variation of the silane concentration (SC) in the process gas mixture. Pure amorphous silicon material was investigated for comparison. The ambipolar diffusion length, L amb, which is dominated by the minority carrier properties, is obtained both from the best fit to the experimental photocurrents ratio, β, versus grating period (Λ), and from the "Balberg plot" for the generation rates between 1019 and 1021 cm -3 s-1. Lamb increases from 86 nm with increasing SC and peaks around 200 nm for the SC = 5.6% and decreases again for higher SCs. Lamb values obtained from the intercept of the Balberg plot result in a small difference of around 5% for most of the samples. Minority carrier mobility-lifetime (μτ)-products are much lower than those of majority carriers, however, both majority and minority carrier μτ-products in microcrystalline silicon are higher than those of undoped hydrogenated amorphous silicon. The grating quality factor (γ 0) changes from 0.70 to 1.0 indicating almost negligible surface roughness present in the samples.
  • Conference Object
    Citation - WoS: 5
    Citation - Scopus: 5
    Photoconductivity Spectroscopy in Hydrogenated Microcrystalline Silicon Thin Films
    (Springer Verlag, 2003) Güneş, Mehmet; Akdaş, Deniz; Göktaş, Oktay; Carius, Reinhard; Klomfaß, Josef; Finger, Friedhelm
    Steady-state photoconductivity and sub-bandgap absorption measurements by the dual-beam photoconductivity (DBF) method were carried out on undoped hydrogenated microcrystalline silicon thin films prepared by VHF-PECVD and hot-wire chemical vapor deposition. The results are compared with those of the constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS). It is found that DBP, CPM, and PDS provide complementary data on the optoelectronic processes in microcrystalline silicon.