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Sub-gap Photoconductivity in Germanium-silicon Films Deposited by Low Frequency Plasma

Published online by Cambridge University Press:  01 February 2011

Andrey Kosarev  and
Francisco Avila
Andrey Kosarev
Affiliation:
[email protected]@gmail.com, Institute National for Astrophysics, OPtics and Electronics, Electronics, L.E.Erro No.1, col. Tonatzintla, Puebla, Puebla, 72840, Mexico, 52 222 26631000/1409, 52 222 2470517
Francisco Avila
Affiliation:
[email protected], Institute National for Astrophysics, Optics and Electronics, Electronics, Puebla, Puebla, Mexico
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Abstract

(GexSi1-x:H) films are of much interest for many device applications because of narrow band gap and compatibility with films deposited by plasma. However, electronic properties of GexSi1-x:H films for high Ge content x > 0.5 have been studied less than those of Si films. In this work, we present a study of sub-gap photoconductivity (σpc) in GexSi1-x:H films for x = 1 and x = 0.97 deposited by low frequency plasma enhanced chemical vapor deposition (LF PECVD) with both various H-dilution (RH) during growth (non-doped films) and boron (B) incorporation in the films. Spectra of sub-gap photoconductivity σpc(hν) were measured in the photon energy range of hν = 0.6 to 1.8 eV. σpc(hν) spectra were normalized to constant intensity. For hν < Eg two regions in σpc(hν) can be distinguished: “A”, where σpc is related to transitions between tail and extended states, and “B”, where photoconductivity is due to defect states. σpc(hν) in ”A” region showed exponential behavior that could be described by some characteristic energy EUPC similar to Urbach energy EU in spectral dependence of optical absorption. EUPC > EU was observed in all the films studied. This together with higher relative values (i.e. normalized by the maximum value at hν = Eg) for photoconductivity comparing with those for α means that mobility-lifetime product (μτ) depends on photon energy μτ = f(hν) that was determined from α(hν)and σpc(hν). μτ(hν) increases by factor of 20 to 40 depending on the sample with reducing hν from 1.1 to 0.7 eV. In some samples, this dependence was monotonous, while in others demonstrated maxima related to both interference and density of states. Effects of both RH and boron incorporation have been found and are discussed.

Keywords

photoconductivityplasma depositionGe
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1245: Symposium A – Amorphous and Polycrystalline Thin-Film Silicon Science and Technology-2010 , 2010 , 1245-A17-04
Copyright
Copyright © Materials Research Society 2010

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