Optical Properties of Amorphous Films of an a-Si1−x Gex:H Solid Solution with Different Concentrations of Hydrogen

Abstract

The IR absorption spectra of hydrogenated amorphous films of an a-Si 0.60 Ge 0.40 :H solid solution that were obtained by plasmachemical deposition at different partial pressures of hydrogen P H 2 have been investigated.The oscillator strengths Γ that depend substantially on P H 2 have been determined. It is shown that hydrogen is contained in the films mainly in the GeH and SiH forms. Using integral absorptions I w , the concentrations of hydrogen were determined. The highest value of P H 2 is observed at Γ = 0.51, P = 4.16, N H = 9.7⋅10 21 cm -3 , and C H = 23.7 at.%. It has been established that the oscillator strengths depend on the hydrogen concentration: they decrease on hydrogen effusion and increase with the hydrogen concentration. It is shown that the hydrogen concentration in the films of the a-Si 0.60 Ge 0.40 :H solid solution can be controlled by changing its pressure.

Effect of heat treatments on the properties of hydrogenated amorphous silicon for PV and PVT applications

“…Besides the presence of the dihydrides, also polysilane chains (SiH 2 ) n , n P 2, do exist in the annealed layers, as it could be concluded from the analysis (not shown here) of the bending mode peak of the annealed layers by deconvolution. The bending mode was in fact seen to contain the peak at 853 cm À1 , usually assigned to the chain (SiH 2 ) n , n P 2, (Brodsky et al, 1977;Langford et al, 1992;Amato et al, 1991;Nadzhafov and Isakov, 2005;Lucovsky et al, 1979;Touir et al, 1999;Daouahi et al, 2000;Tsai and Fritzsche, 1979), beside the one at 887 cm À1 typical of the SiH 2 dihydride (Brodsky et al, 1977;Langford et al, 1992;Amato et al, 1991;Nadzhafov and Isakov, 2005;Lucovsky et al, 1979;Touir et al, 1999;Daouahi et al, 2000;Tsai and Fritzsche, 1979). The simultaneous decrease of the LSM 1994 cm À1 peak, assigned to isolated SiH monohydrides (Manfredotti et al, 1994;Von Keudell and Abelson, 1998;Lucovsky et al, 1979;Touir et al, 1999), would also suggest that previously isolated SiH bonds may have undergone clustering with formation of (SiH) n groups.…”

“…Several values for the A's of the stretching mode to be included in Eqs. (2) and (3) have appeared in the literature (Brodsky et al, 1977;Amato et al, 1991;Langford et al, 1992;Smets et al, 2003;Nadzhafov and Isakov, 2005). The most accepted values are those of Amato et al (1991) and Langford et al (1992) who determined them through calibration of the FTIR data versus hydrogen concentrations measured by ERDA and NRA (nuclear-reaction analysis), respectively.…”

“…They are generally isolated network sites and are associated with H bonded at isolated dangling bonds and vacancies (Brodsky et al, 1977;Langford et al, 1992;Amato et al, 1991;Manfredotti et al, 1994;Von Keudell and Abelson, 1998;Lucovsky et al, 1979;Touir et al, 1999;Jackson and Tsai, 1992;Daouahi et al, 2000). The vibration mode at the high wavenumber of 2094 cm À1 (HSM) is instead due to the SiH 2 dihydrides and polysilane chains (SiH 2 ) n , n P 2 (Brodsky et al, 1977;Langford et al, 1992;Amato et al, 1991;Manfredotti et al, 1994;Nadzhafov and Isakov, 2005;Von Keudell and Abelson, 1998;Lucovsky et al, 1979;Touir et al, 1999;Daouahi et al, 2000). The increase of the HSM 2094 cm À1 peak in the annealed samples can be due to the thermal activation of H atoms that have occupied interstitial sites, i.e.…”

On the formation of blisters in annealed hydrogenated a-Si layers

“…To this aim, the relative H concentration, C H = N H / N Si with N Si the atomic density of Si (5 × 10 22 cm −3 ), was calculated from deconvoluted IR spectra in the stretching mode range as described in the ‘Methods’ section. Several values for the A of the stretching mode to be included in Equations 2 and 3 have appeared in the literature [1,22-25]. It should be mentioned that a local oscillator strength (modified by local field effects and screening by the a-Si matrix) involved in the stretching vibrations leads to different A values which are not directly proportional to the hydrogen concentration.…”

“…Similar results can be obtained by using the proportionality A constant of Brodsky et at. [22] scaled down by a factor of 2 as it was implicitly suggested by them as they wrote that their results are overestimated by a factor of 2 [22,25]. Among the others, Smets et al suggested instead to use A 2000 = A 2100 = 9.1 × 10 19 cm −2 [1].…”