Preparation of Compositionally GradientThin Films by Ion-Beam Evaporation, страница 3

FIGURE 2. Substrate position (r) dependence of the composition of the thin film that is prepared by an ion-beam irradiation on Si and Ge plates

However, in Figure 2, the substrate position (r’), where the ratio of Si and Ge atoms was one to one, was close to the substrate edge as –58 mm. If such a position is near r=0 mm, the Si content in the compositionally gradient Si-Ge thin film can change from 0 to 100 at. % on the substrate. Then, to control the amount of ablation plasma emitted from the Si and Ge plates, the position (x) of the target was moved from 0 to 10 mm, as could be seen in Figure 1. With increasing in x from 0 to 10 mm, the center of ion beam, which indicated the highest E, was irradiated from the boundary of the Si and Ge plates to the Si plate [6]. Furthermore, the result of Figure 2 was obtained under the condition of x=0 mm.

Table II shows r’ and a of the compositionally gradient Si-Ge thin films that are prepared in x ranging from 0 to 10 mm. The substrate position having the Si content of 50 at. % was found to approach to r = 0 mm with increasing in x from 0 to 10 mm. Additionally, at x=5 and 10 mm, the Si content in the compositionally gradient Si-Ge thin films was clarified to change from 0 to 100 at. % on the substrates. Moreover, a of the thin films synthesized at x=5 and 10 mm was 1.5 and 3.0 at. %/mm, respectively.

From the above results, with increasing in x from 0 to 10 mm, although a of the thin films gradually increased from 0.8 to 3.0 at. %/mm, the Si content in the compositionally gradient Si-Ge thin films could change from 0 to 100 at. % on the substrates. Therefore, since the development of new phases seems to be fully achieved without mask control by the IBE method, the present results can indicate a new possibility for the preparation of compositionally gradient thin films.

CONCLUSIONS

From these experimental results, we have obtained the following conclusions:

·  Without mask control, the compositionally gradient Si-Ge thin films are synthesized by an ion-beam irradiation on Si and Ge plates. One of the compositionally gradient Si-Ge thin films has low value as a=0.8 at. %/mm.

·  With increasing in x from 0 to 10 mm, a of the compositionally gradient Si-Ge thin films increases from 0.8 to 3.0 at. %/mm.

·  The Si content in the compositionally gradient Si-Ge thin films with a=1.5 and 3.0 at. %/mm changes from 0 to 100 at. % on the substrates.

ACKNOWLEDGEMENTs

This work was partly supported by the 21^st COE Program of Ministry of Education, Culture, Sports, Science and Technology, Japan.

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