The dynamics of photoexcited carriers in microcrystalline silicon

Abstract

Dependences of the diffusion coefficient and the lifetime of photoexcited carriers in undoped microcrystalline silicon ( μc-Si) on the volume fraction and the grain size were observed by a transient grating method and the dynamics of photexcited carriers is discussed. Under the condition of a constant grain size, the lifetime decreases with the increase of the volume fraction but the diffusion coefficient increases with the increase of the volume fraction for any fraction larger than 0.2. The dependence of the lifetime was explained well by a carrier recombination at grain boundary regions. The dependences of the diffusion coefficient and the dark conductivity were interpreted by a percolation process.

Opto-Electronic Properties of μc-Si Grown from SiF4 and H2 by PECVD

“…5 is a plot of the dark conductivity against the Raman FWHM. Although the FWHM lies in a small range from 10 to 13 cm1, indicating almost identical grain sizes of -60 A, the dark conductivity at room temperature ranges from 10-2 to 10-8 S-cm-1, the latter value being close to that of a-Si:H. The highest value that we obtain, 1.1 x 10-2 S.cm-1 , is comparable to the highest value of _10-2 Scm-1 [15] observed in films grown from SiH 4 . This result suggests that the conductivity is not determined by bulk properties.…”

“…As for the conductivity of undoped glow discharge deposited jic-Si, Mishima et al [14] have reported that it is determined by the volume fraction of crystalline material, and Komura et al [15] interpreted the conductivity by a percolation process. Konuma et al [16] have shown that the conductivity increases with crystallite size.…”

Electrical and optical properties of µc-SiH films

“…99 ~o Hz + 1 ~o Sill4) have been grown. At higher concentration of hydrogen the deposition rate also decreases (Vamier et al 1984) helping in increasing the crystallite size in the film (Kamuro et al 1984). The films have been analyzed by x-ray diffraction and TEM for their microcrystallinity.…”

Characteristics of the low energy photoluminescence in μc-Si films

“…One finds that the peak energy redshifts by about 170 meV from 15 to 180 K. According to the carrier thermalization model, the PL peak energy reflects the carrier distribution dominated by multiple trapping processes, and the PL peak energy shift follows E peak (T) ϪE peak (0)ϭϪE D , where E D ϭkT ln( 0 r ) is the demarcation energy. Using a reasonable value of the recombination lifetime, r Ϸ10 Ϫ6 s for c-Si, 11 one obtains E D (180 K) ϪE D (15 K)Ϸ180 meV. Figure 2͑b͒ plots the total PL intensity I PL (T) versus temperature for samples with X c ϭ81%, 83%, and 89%.…”

“…1͑b͒. Using the recombination lifetime r Ϸ10 Ϫ6 s, 11 one obtains the characteristic temperature of the exponential tail states, T 0 , equal to 283, 275, and 240 K. The value is about two times smaller than that of 500 K in a-Si:H. Again, it is in agreement with the narrower PL bandwidth in c-Si than in a-Si:H. Figure 3͑a͒ shows the PL energy spectra as a function of excitation intensity of sample T529. The data were obtained by using 632.8 nm laser excitation at 15 K. One can see that the PL peak shifts to high energy as the excitation intensity increases.…”