Periodic Arrangement of Ge Islands on SI(111)
- PDF / 3,944,849 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 18 Downloads / 213 Views
1 Mat. Res. Soc. Symp. Proc. Vol. 317. ©1994 Materials Research Society
RESULTS AND DISCUSSION
Mesh Pattern In reflection high-energy electron diffraction (RHEED) patterns, 7x7 spots from the original
Si(l11) surface remain even after the Ge deposition at RT. This is because the 7x7
reconstruction is preserved at the a-Ge/Si interface [4]. When the surface was annealed at
about 200'C, diffuse integral-order streaks appeared in the RHEED pattern, indicating a-Ge
layers had begun to crystallize. The critical thickness for the relaxed island formation t, was
4 monolayers (6.5 A) [5,6]. RHEED patterns from the 7A-Ge sample grown using 400'C
annealing still included 7x7 spots as well as transmission diffraction spots created in relaxed
Ge islands. Ge islands were formed before the interface 7x7 reconstruction was completely destroyed. Annealing at higher temperatures caused the 7x7 reconstruction to be transformed into 5x5 reconstruction.
FIG.1. AFM image of 10-A-thick Ge layers deposited on Si( 11) at room temperature and annealed at 450"C for 10 min. The scanning area is 9000 x 9000
Figure 1 shows an AFM image of the 10•- nm. Ge/Si(1 11) surfaces grown using 450"C, 10-min annealing. This figure clearly shows that Ge islands are arranged in a mesh pattern. Planar view TEM images also showed that Ge islands with moir6 fringes are arranged in such a mesh pattern. Their typical size' and height are 30 and 5 nm. These images indicate that a-Ge layers do not crystallize uniformly, but that there are defined positions where they easily crystallize. We next examined the conditions needed to obtain this mesh pattern. We investigated the thickness, temperature, and misorientation dependences of island patterns. Figures 2(a)-2(c) show AFM images of 7-, 12-, and 30-A-thick Ge layers, respectively. The annealing was done at 400"C for 10 min. The 12A-Ge/Si(1 11) surface shows the clearest pattern. The mesh pattern does not look clear at smaller thicknesses because island size varies. On the other hand, because the island density increases as thickness increases, the pattern is disguised in Fig. 2(c).
(a)
(b)()
FIG. 2. AFM images of Ge layers deposited on Si(I 11) at room temperature and annealed at 400*C for 10 min.
The Ge thicknesses are (a)7 A,(b)12 A,and (c)30 A.The scanning area is 4000 x 4000 nm.
42
(a) (b) (C) FIG.3. AFM images of 10-A-thick Ge layers deposited on Si(l 11) at room temperature and annealed at (a) 200C, (b) 450TC, and (c) 550C. The annealing time was 10 min and the scanning area is 4000 x 4000 nm. Figures 3(a)-3(c) show AFM images of Ge island patterns grown at 200, 450, and 550°C, respectively. The Ge thickness and annealing time were 10 A and 10 min. The sample grown at 450"C shows the clearest mesh pattern. Figure 3(a) also shows the mesh pattern, but the islands are much smaller than those in Fig. 3(b). This is probably because the a-Ge films were not perfectly crystallized. On the other hand, the Ge islands in Fig. 3(c) are larger than those in Fig. 3(b) and the pattern is blurred. This is
Data Loading...
