AFM Morphology Study of Si 1-Y Ge Y :H Films Deposited by LF PE CVD from Silane- Germane with Different Dilution
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A18.5.1
AFM Morphology Study of Si1-Y GeY:H Films Deposited by LF PE CVD from SilaneGermane with Different Dilution L. Sanchez1, A.Kosarev1, A.Torres1, T.Felter2, A.Ilinskij3 1 Institute National for Astrophysics, Optics and Electronics, Puebla 7200, México 2 Lawrence Livermore National Laboratory, Livermore, CA 94550,USA 3 Benemerita Universidad Autonoma de Puebla, Puebla, 7200, México ABSTRACT The morphology of Si1-Y GeY:H films in the range of Y=0.23 to 0.9 has been studied by AFM. The films were deposited by Low Frequency (LF) PE CVD at substrate temperature Ts=300 C and discharge frequency f=110 kHz from silane+germane mixture with and without, Ar and H2 dilution. The films were deposited on silicon and glass substrates. AFM images were taken and analyzed for 2x2 µm2 area. All the images demonstrated “grain” like structure, which was characterized by the height distribution function F(H) average roughness , standard height deviation Rq, lateral correlation length Lc, area distribution function F(s), mean grain area , diameter distribution function F(d), and mean grain diameter . The roughness of the films monotonically increases with Y for all dilutions, but more significantly in the films deposited without dilution. Lc continuously grows with Y in the films deposited without dilution, while more complex behavior of Lc(Y) is observed in the films deposited with H- or Ar dilution. The sharpness of F(H) characterized by curtosis γ depends on dilution, and the sharpest F(H) are for the films deposited with Ar ( γ=5.30,Y=0.23) and without dilution (γ=4.3, Y=0.45). Isothermal annealing caused an increase of , Lc in the films deposited with H- and Ar dilutions, while in the films prepared without dilution the behavior was more complex, depending on the substrates. After the annealing a significant sharpening of the height distributions, F(H), was observed in the films deposited with H dilution or without dilution. INTRODUCTION Plasma deposited films have a broad range of applications due to the versatile character of the materials and their compatibility with standard silicon technology. Among them silicongermanium alloy Si1-YGeY:H, is a promising material with an optical gap less than amorphous silicon films. As a low-bandgap material it can be used in multi-junction solar cells [1,2], photodetectors [3,4], and un-cooled micro-bolometers [5-7]. Despite implementation in devices, Si1YGeY:H films have been significantly less studied than plasma deposited silicon films. Reviews of earlier works can be found in ref. [8,9]. Si1-YGeY:H films deposited in low frequency (LF) plasma were reported in ref. [10] and more systematically in ref. [11]. In the latter a significant effect of feed gas dilution on electronic properties has been observed. Study of surface morphology, i.e. roughness is an important part of structural characterization. Surface roughness of low temperature PECVD a-Si:H films has been studied by Dalakos et al. [12], who studied roughness evolution during growth. Evolution of roughness in a-SiNx: films has
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