Synthesis of Highly Photosensitive a-SiC:H Films at High Deposition Rate by Plasma Decomposition of SiH 4 and C 2 H 2
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SYNTHESIS OF HIGHLY PHOTOSFNSITIVE a-SiC:H FILMS AT HIGH DEPOSITION RATE BY PLASMA DECOMPOSITION OF SiH. AND C2 H2 Y. NAKAYAMA, S. AKITA, K. WAKITA and T. KAWAMURA Electrical Engineering, College of Engineering, University of Osaka Prefecture, Mozu-Umemachi, Sakai, Osaka 591, Japan
ABSTRACT Highly photosensitive a-SiC:H films exhibiting nUT-product more than 6 2 10- cm /V at the band gap of 1.9 eV are prepared under the high deposition rate around 6pm/h by a plasma decomposition of SiH4 -C 2 H2 source mixture gas at higher rf power. It is also shown that the SiH4 -C 2 H2 gas system has a feature of the carbon incorporation into the films with the content nearly equal to that in the source mixture gas and hence is suitable for the high rate deposition process. This advantage and in addition the requirement of the higher rf power for obtaining the films with good electrical performance are discussed in terms of the dissociation reaction of the source gas and the secondary gas phase reactions in the plasma.
INTRODUCTION Recently, hydrogenated amorphous silicon carbide (a-SiC:H) with high photosensitivity comparable to hydrogenated amorphous silicon (a-Si:H) has been developed. The highly photosensitive a-SiC:H has wider band gap than the a-Si:H and offers many possibilities for solar cells, electrophotographic photoreceptors and heterostructure devices applications. However, the low deposition rate (
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Fig.7 Rf power dependence of the refractive index n, the V'B-value and the optical band gap Egopt.
x and the deposition rate DR.
H content under no change in x. The /F-value indicating the sharpness of the optical absorption edge is almost independent of the rf power and shows high value at 500•600W. It is also found that such film properties do not depend on the H2 flow rate ranging from 150 to 700sccm, and at the region less than 00sccm the film with mirror like surface is not obtained. In order to investigate the rf power dependence of the microscopic structure associated with Si-C bonds, we prepared samples with higher carbon content (x=0.3) at the rf power of 200 and 500 W. The IR absorption spectra ranging from 1000 to 600cm-' of these samples are shown in Fig. 8. The spectra can be decomposed to three Gaussian peaks P1, P2 and P 3 which are located near 780, 730 and 640cm-1 and assigned to the Si-C stretching modes [5] of C-Si(C3) and C-Si(C2Si) and the SiH waging mode, respectively. Though the intensity of P 3 for both samples is almost the same, the high power sample has stronger intensity of P, and P 2 than the other, indicating that the increase in the rf power is effective for making the Si-C network. It is also observed that NH(C) corresponding to the number of C-H bonds for the low power sample is more than that for the high power sample by a factor of 1.33. This result suggests that the C atoms which do not join in the Si-C network form the C-H bonds. It can be conclude that tR
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