Preparation of boron and phosphorus-doped SiC :H films using electron cyclotron resonance chemical vapor deposition: Som
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Preparation of boron and phosphorus-doped SiC : H films using electron cyclotron resonance chemical vapor deposition: Some effects of microwave power S. F. Yoon, R. Ji, and J. Ahn School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Republic of Singapore (Received 18 October 1996; accepted 9 September 1998)
Hydrogenated silicon carbide films (SiC : H) were deposited using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) technique from a mixture of methane, silane, and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the microwave power on the deposition rate and optical band gap were investigated, and variations in the photo- and dark-conductivities and activation energy were studied in conjunction with film analysis using the Raman scattering technique. In the case of boron-doped samples, the conductivity increased rapidly to a maximum, followed by rapid reduction at high microwave powers. The ratio of the photo- to dark-conductivity ssphysd d peaked at microwave power of , 600 W. Under conditions of high microwave power, Raman scattering analysis showed evidence of the formation and increase in the silicon microcrystalline and diamond-like phases in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity. In the case of phosphorus-doped SiC : H samples, it was found that increase in the microwave power has the effect of enhancing the formation of the silicon microcrystalline phase in the films which occurred in correspondence to a rapid increase in the conductivity and reduction in the activation energy. The conductivity increase stabilized in samples deposited at microwave powers exceeding 500 W probably as a result of dopant saturation. Results from Raman scattering measurements also showed that phosphorus doping has the effect of enhancing the formation of the silicon microcrystals in the film whereas the presence of boron has the effect of preserving the amorphous structure.
I. INTRODUCTION
It is now known that hydrogenated silicon carbide (SiC : H) films possess the properties of both wide optical band gap and high conductivity.1 In recent years there have been widespread applications of SiC : H films, both amorphous and those containing microcrystalline phases, in devices such as light emitting diodes (LED’s), color displays, and solar cells. The majority of previous investigations into a-SiC : H films have concentrated on the use of the glow discharge plasma enhanced chemical vapor deposition (PECVD) technique using alkane sources such as CH4 , C2 H2 , and C2 H4 as C precursors and SiH4 as the silicon source.2– 4 Doping of the SiC : H films has been achieved using a variety of techniques such as the conventional PECVD5,6 and electron cyclotron resonance chemical vapor deposition7– 9 (ECR-CVD). The advantage of the ECR-CVD method is that it is capable of producing a highl
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