Morphological Evolution in Highly Strained InSb/InAs(001)
- PDF / 1,009,025 Bytes
- 6 Pages / 414.9 x 635.4 pts Page_size
- 105 Downloads / 167 Views
103 Mat. Res. Soc. Symp. Proc. Vol. 618 ©2000 Materials Research Society
RESULTS AND DISCUSSION The morphological evolution of highly strained InSb films proceeds through several regimes as a function of thickness. The films initially nucleate isolated 3D islands even in the earliest stages of growth. The islands then coarsen and coalesce at slightly higher thicknesses, with some evidence of cooperative nucleation, or the sequential nucleation of islands and pits. Once the islands coalesce, the morphology evolves into long ridges aligned along the [110], however, those films are still discontinuous. At a thickness =100nm, the films finally become completely continuous and 2D growth proceeds via step flow of growth spirals present on the surface. Initial Island Nucleation For deposited thicknesses between 1 and 5 monolayers, the morphology of the InSb film consists of a low density of large isolated islands. Table 1 lists the density, dimensions, and nominal shape of features observed in these films. Figure lb shows an AFM micrograph of nominally 1 ML of InSb grown on the Sb-terminated surface. The surface has a low density (8xl08cm 2 ) of islands nominally 50 nm in diameter and 5nm tall that are located at surface steps. The underlying surface is the same as that of the Sb-terminated surface seen in Fig. 1. Therefore, it is unlikely that there is an appreciable wetting layer. It is curious to note that the RHEED pattern along the [110] azimuth at this thickness remains streaky. This is most likely due to the wide spacing of the islands. The fact that distinct 3D islands are observed even for thicknesses of 1 ML implies that no wetting layer was formed, and the film did not go through a pseudomorphic growth stage. This is in contrast with other material systems with similar magnitudes of strain such as InAs/GaAs (f=7.2%)[1] and GaSb/GaAs (f=7.8%)[4] which typically have wetting layers on the order of 1.5 ML. Even InSb/GaAs, which has a much higher misfit (f=14.6%), has been shown to have a wetting layer on the order of 1.5 ML. [4][5] It is likely, therefore, that the exposure of the InAs surface to Sb prior to growth resulted in a monolayer-thick layer of InSb. That is, once the InAs was exposed to Sb, the As on the surface was replaced by Sb resulting in a thin layer of InSb. Indeed, the morphology of the Sb terminated buffer layer is significantly Table 1: Island densities, dimensions, and nominal shape of InSb films grown on InAs, at various thicknesses. Thickness
Nominal shape
________(nm)
InAs/InAs
Terraces
Sb-terminated
Terraces and large
InAs I ML InSb
depressions Rounded
2 ML
Rectangular Rectangular Rectangular or Irregular Vacancy clusters Irregular islands
3 ML 7 ML
15 ML 31 ML 154 ML 310 ML
Density
Dimensions
Roughness
68 nm long terraces Large depressions4 x 07 cm"2 8 x 108 cm"2 3 x 109 cm"2 6 x 109 cm"2 Islands- 7101° cm2 Pits- 9 x 109 cm" 2
Terraces-156 nm long,
0.15 0.62
pits- 500 x 250 nm, -4 nm deep 50 nm diameter, 5 nm tall 90 x 40 nm, 7 nm tall 100 x 60 nm, 7.5 nm tall 176 x 8
Data Loading...
