In this work we present the study of fabrication, Ge incorporation, structure and electronic properties of nano-structured Ge y Si 1-y :H films with y>0.5 prepared by low frequency (LF) PECVD. Ge y Si 1-y :H films were deposited by LF PECVD at a frequency f= 110 kHz from SiH 4 +GeH 4 +H 2 gas mixture. SiH 4 and GeH 4 flows were varied to fabricate the films in wide range of 0 = 24.0±0.7 nm, dispersion ∆D=11.0±0.2 nm and fill factor FF=0.313, Ge content y=0. . These films showed also the lowest values of Urbach energy E U =0.030 eV and low defect absorption α D = 5xl0 2 cm -1 (at photon energy hν = 1.04 eV) indicating on low density of localized states in mobility gap. Doped films have been also fabricated and studied. Finally we shall discuss application of the above films in photovoltaic devices.
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 <H>, standard height deviation Rq, lateral correlation length Lc, area distribution function F(s), mean grain area <s>, diameter distribution function F(d), and mean grain diameter <d>. The roughness <H> 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 <H>, 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.
We report on a systematic study of growth rate, surface morphology, hydrogen and oxygen incorporation, optical and electrical properties in Ge:H and Ge Y Si 1-Y :H, Y> 0.85 films, deposited in a capacitive reactor by low frequency PE CVD. Silane and germane were used as feed gases diluted by hydrogen. Hydrogen dilution is characterized by R= Q H2 /[Q SiH4 +Q GeH4 ], where Q H2 , Q SiH4 , and Q GeH4 are gas flows of hydrogen, silane and germane, respectively. The flow was varied in the range of R=20 to 80. Composition of the films was characterized by SIMS profiling. We did not observed a significant change of the deposition rate V d in Ge Y Si 1-Y :H films over the range of R, while for Ge:H films V d was significantly reduced for R>50. AFM characterization of the surface morphology demonstrated that at R=50 average height (R) reached a maximum in both Ge:H and Ge Y Si 1-Y :H films, while average diameter (R) had a minimum in Ge Y Si 1-Y :H films and maximum in Ge:H films. Both Ge:H and Ge Y Si 1-Y :H films demonstrated a change of E 04 in the studied range of R, and a minimum clearly appeared in ∆E at R=50-60 suggesting significant reduction in weak bonds of these films. The activation energy of conductivity E a slightly increases with R in Ge:H films and shows no definitive trend in Ge Y Si 1-Y :H: films. Both FTIR and SIMS data show a general trend of decreasing hydrogen and oxygen content with R. These two types of films showed different behavior and correlations between surface morphology and optical and electrical properties.
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