Page - 87 - in Photovoltaic Materials and Electronic Devices

1306.62  cm−1  (0.162  eV)  can  be  associated  with  oxygen‐hydrogen  (O‐H)  bonds  in  the  thin  film,  such  as  the  formation  of  zinc  hydroxide  or  absorbed  water  or  stretching  modes  of  hydrogen  bonded  to  heavier  elements  like  zinc  [54].  The  large  broadening  of  this  absorption  peak  could  be  due  to  the  modification  or  damage  to  the  ZnO  as  a  result  of  exposure  to  hydrogen  in  the  plasma.    Figure  9.  Comparison  of  lower  energy  features  in  ε2  as  a  function  of  photon  energy  for  ZnO  with  (solid  line)  and  without  (dotted  line)  over‐deposition  of  a‐Si:H.  Parameters  describing  the  sample  without  and  with  over‐deposition  of  are  listed  in  Tables  4  and  5,  respectively.    3.3.2.  Chemical  Bonding  in  a‐Si:H  After  ZnO  deposition,  a  278  Å  thick  n‐layer  was  deposited  onto  a  ZnO/Ag  coated  substrate  with  deposition  conditions  given  in  Table  1.  The  n‐layer  optical  properties,  as  well  as  its  db  and  ds,  were  obtained  from  RTSE  analysis.  The  final  numerically  inverted  spectra  in  ε  for  the  n‐layer  were  fit  to  a  Cody‐Lorentz  oscillator  [71].  The  Cody‐Lorentz  oscillator  is  described  by:  Figure 9. Comparison of lower energy features in ε2 as a function of photon energyforZnOwith(solid line)andwithout (dottedline)over-depositionofa-Si:H. Parameters describing the sample without and with over-deposition of are listed in Tables4and5respectively. 3.3.2. ChemicalBondi g ina-Si:H After ZnO deposition, a 278 Å thick n-layer was deposited onto a ZnO/Ag coated substrate with deposition conditions given in Table 1. The n-layer optical properties, as well as its db and ds, were obtained from RTSE analysis. The final numerically inverted spectra in ε for the n-layer were fit to a Cody-Lorentz oscillator [71]. TheCody-Lorentzoscillator isdescribedby: ε2pEq“ $’&’% AE0ΓE` E2´E20 ˘2`Γ2E2 ` E´Eg ˘2` E´Eg ˘2`E2p EąEg 0 EďEg , (7) and ε1pEq“ 2piP 8ż 0 ξ ε2pξq ξ2´E2dξ (8) where A is the amplitude, Γ is the broadening, E0 is the resonance energy, Eg represents an absorption onset determined from a parabolic band constant dipole matrix element, and Ep + Eg represents the transition between Cody gap-like and Lorentz-like behavior. Analytical Kramers-Kronig transformation of ε2 yields ε1. Parameters describing ε for the n-layer at the deposition temperature T = 200 ˝C are A = 59˘2 eV,Γ= 2.12˘0.02 eV, E0 = 3.99˘0.01 eV, Eg = 1.58˘0.04 eV, and Ep =0.96˘0.09eV. 87