**3.1.3 Microscopic structure**

In figures 5 (a) and (b), the FWHM of the Si-H and Si-H2 stretching mode peaks in the FTIR spectra are platted against the density of Si-H and Si-H2, respectively. The films were prepared at the VHF input power of 2 or 10 W using the each electrode configuration i.e., triode or diode system as indicated in the figure. The substrate temperature is 250 oC in every case. While the scattered relation is observed in the Si-H bond case, one can see the good correlation between the Si-H2 bond densities and their FWHMs. Moreover, while

Fabrication of the Hydrogenated

deteriorates photosensitivity.

diode deposition system (*d*ms = 0 cm).

**3.2.1 Spin density** 

**3.2 Stabilities of the triode-deposited a-Si:H films** 

**3.1.4 Conductivity** 

Amorphous Silicon Films Exhibiting High Stability Against Light Soaking 309

the FWHM values of the S-H peaks are more or less in the same range, the narrower FWHMs of the Si-H2 peaks are observed in the triode-deposited films. Furthermore, when the electrode configuration is the same (triode or diode), the films prepared at the lower

The conductivities of the a-Si:H films fabricated using the triode system are measured. Figure 6 shows the dark and photoconductivities of the films. The photoconductivity was measured under the illumination of 100 mW/cm2 white light. The observed darkconductivities are of the order of 10-11 S/cm. The deposition rate of the triode system is typically less than 1 Å/s, which may cause unfavorable impurity incorporations during the film growth, causing the reduction of photosensitivity due to the increase of darkconductivity. The dark-conductivity of the triode-deposited a-Si:H is, however, in the range equivalent to that observed in the diode-deposited film grown at 7.3 Å/s, and the photoconductivities of those films are of the order of 10-5 S/cm. The result indicates that the triode-deposited a-Si:H films do not contain substantial number of impurities which

Fig. 6. The dark and photoconductivities of the a-Si:H films prepared either by a triode or a

Degradation of the film prepare by the triode system is checked by measuring the change of neutral spin density by light soaking. Figure 7 shows the result [Shimizu et al., 2008]. All the films were prepared at 250 oC, and as a comparison, the results of the diode-deposited films are also shown. The spin density is plotted against Si-H2 bond density. The initial defect densities are almost the same throughout the samples (≈ 2×1015 cm-3). On the other hand,

VHF input power exhibit narrower FWHMs of the Si-H2 peaks.

Fig. 4. Si-H and Si-H2 bond densities in the a-Si:H films fabricated under the various conditions. Open and closed circle: VHF = 2 W, with a single mesh (2 W, SM), open and closed square: VHF = 10 W, with a single mesh (10 W, SM), open and closed triangle: VHF = 10 W, with double mesh (10 W, DM). As a comparison, those of the conventionally prepared films without the mesh are also shown (diode, *d*ms = 0 cm). [Shimizu et al., 2007]

Fig. 5. FWHM of the Si-H and Si-H2 stretching mode peaks in the FTIR spectra platted against the density of Si-H and Si-H2, respectively. The films were prepared at the VHF input power of 2 or 10 W using the each electrode configuration (triode or diode) as indicated.

the FWHM values of the S-H peaks are more or less in the same range, the narrower FWHMs of the Si-H2 peaks are observed in the triode-deposited films. Furthermore, when the electrode configuration is the same (triode or diode), the films prepared at the lower VHF input power exhibit narrower FWHMs of the Si-H2 peaks.
