Absorption Strengths of Si-H Vibrational Modes in Hydrogenated Silicon
- PDF / 432,114 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 67 Downloads / 198 Views
AI
(1)
with I = Sw•I0(w)dw.
(2)
Here, ca(ow) is the IR absorption coefficient at the frequency w. A precisely known value of A allows the determination of the hydrogen concentration via fairly simple, non-destructive IR absorption measurements. Moreover, data of A for the Si-H stretching modes at 2000 and 2100 cm" 1 are of importance for the microstructure factor [1]. This latter quantity is widely used for the characterization of a-Si:H microstructure and quality. It is of interest, furthermore, if the A values of the two Si-H stretching absorptions at 2000 and 2100 cm" are equal or differ. This information may contribute to a better understanding of the nature of the Si-H stretching mode splitting which is still a matter of discussion [2]. While the Si-H stretching mode doublet has been attributed by Lucovsky et al. [3] to a difference in frequency of Si-H vibrators in SiH (monohydride) and SiH 2 (dihydride) bonding configurations, the doublet was associated by Cardona [4] and Wagner and Beyer [5] to a difference in the stretching frequency of Si-H groups incorporated in the bulk material or located at internal surfaces, respectively. Since the first measurements of the absorption strength of the Si-H stretching mode by Freeman and Paul [6] and of the Si-H wagging mode by Fang et al. [7], considerable work on this subject has been published, the most recent comprehensive publications by Langford et al. [8] and by Manfredotti et al. [9]. While the A value of the Si-H wagging mode at 640 cm-1 was generally considered as sample independent and constant [7,10], work in particular by Shanks et al. [10] suggested that A of the Si-H stretching modes, in particular A2100 of the 601
Mat. Res. Soc. Symp. Proc. Vol. 507 ©1998 Materials Research Society
2100 cm- 1 mode is sample dependent and that A 00 and A 2 differ considerably. Langford et al. [8], on the other hand, suggested that all A vmues for a-9%NH are essentially sample independent and found A2100 to exceed A200 by a factor of 2.4. Manfredotti et al. [9] reported 2.8. Most previous work on Twas based on the comparison between infrared A 0/Aa0 absorption data and data on the hydrogen density obtained by measurements like nuclear reaction or hydrogen effusion. However, information about a sample dependence of the A values can also be obtained from IR absorption measurements alone by studying ratios of absorption strength values. Thus errors arising from the independent measurement of hydrogen density can be eliminated. Aim of the present paper is to discuss the constancy of the ratios of A values and thus of A for various IR absorption peaks on the basis of a large set of experimental data of hydrogenated amorphous and microcrystalline Si films and hydrogenimplanted crystalline Si. Using hydrogen effusion to determine the hydrogen density, we also derive absolute values of A for our set of samples. EXPERIMENT
Amorphous Si:H films were prepared by rf plasma deposition in two capacitively coupled glow discharge reactors. Typical deposition conditions for the fi
Data Loading...
