Electron and Hole Transient Currents in Hydrogenated Amorphous Silicon and Some Alloys Measured by the Photoconductive T
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Mat. Res. Soc. Symp. Proc. Vol. 507 © 1998 Materials Research Society
duration of 5ns and a wavelength of 530nm) creates electron-hole pairs very close to the top contact of the sample which is semitransparent. According to the polarity of the electric field applied across the sample (by an HP214B pulse generator) only one type of carrier drifts through the film towards the back contact. This carrier movement induces a current in the external circuit which is recorded on a IWATSU-8123 digitizing oscilloscope. The ASCII-coded data are sent to the computer over an IEEE-488 interface for further processing. An overview of the sample characteristics is given in Table I, with the addition of 'p' to the sample number if the sample is a p-i-n diode (if no 'p' is added the sample is a Schottky diode, and (p) means both types of diodes were available with exact the same deposition parmeters for the intrinsic layer), d is the sample thickness, [H] is the hydrogen content in atomic percent, rv and Rv are the gas flow ratios with rv = [CH 4 ]/([CH4]+[SiH 4]), Rv= [H2S]/[SiH4], x is the alloy atom fraction as in a-Si1 _xCx:H or a-Si 1 _xSx:H, and Eg is the optical gap calculated from optical absorption experiments. It can be observed that the optical gap widens upon alloying. Table I: An overview of the sample characteristics sample a-Si:H a-Si:C:H
a-Si:S:H
sample# 1 Clp C2(p) C3 C4(p) C6p S1 I S6p
d (in pm) 2.2 1.97 1.98 2.2 2.02 3.3 2.8 0.6
[H] (at. %) n.a. 14.7 22.2 21.1 29.3 n.a. n.a. n.a.
rv or Rv 0 0.118 0.2 0.3 0.4 0.30 0.044 5 x 10-6
x 0 0.013 0.033 0.043 0.088 < 0.1 0.015 0
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