Scaling of Island Size Distributions in the Growth of Ni on GaAs(110)
- PDF / 1,842,868 Bytes
- 8 Pages / 414.72 x 648 pts Page_size
- 67 Downloads / 164 Views
ABSTRACT Island size distributions have been derived from scanning tunneling microscope (STM) images of Ni deposited on cleaved GaAs(110) at room temperature and above. For submonolayer coverages, this system forms 3-dimensional (3-D) reacted islands with the degree of reaction dependent upon the growth temperature. As has been found for other systems, the average island size (say) increases with temperature. The high temperature data (- 1500 C) shows two distinct island types, each with substantially different average size. The island size distributions have maxima at the smallest island sizes. For different coverages, plots of the area-normalized island size distributions versus the scaled variable s/sa,, show significant differences. However, above a cutoff value for s/s,,, the distributions can be renormalized to fall on a common curve. These characteristics and direct atomic-scale evidence are consistent with nucleation of islands via adatom-substrate exchange, but the temperature dependence of the total island density appears to be inconsistent with this being the only first-order rate process taking place.
INTRODUCTION The push toward device technologies requiring nanometer-scale contacts, buried metal interfaces, and hybrid electronic/magnetic devices may depend upon the successful growth of transition metals on semiconductors and vice-versa [1]. Ni/GaAs is particularly important because the presence of Ni has been shown to improve device reliability and process reproducibility for AuGeNi ohmic contacts [2]. In addition, lattice matching considerations and previous studies of Co/GaAs(110) and Fe/GaAs(110) suggest the possibility of growing metastable bcc Ni on GaAs(110) [3,4]. Our objective is to examine the island size distributions and the total number densities of islands to understand their implications for the kinetics of growth and compound formation. Previous photoemission results have shown that Ni reacts with GaAs(110) at room temperature with a NiAs component on the surface. Replacement reactions of Ni for As and Ni for Ga have been found, down to at least three layers below the surface
[5-7].
59
Mat. Res. Soc. Symp. Proc. Vol. 399 @1996 Materials Research Society
Figure 1: Simultaneously acquired STM images (I = lOpA) showing (a) empty states (Vt=p = -2V) and (b) filled states (Vtip = +2V). Arrows indicate two features that appear commonly in samples with low Ni coverage.
EXPERIMENT The experiments were performed in an ultra-high vacuum (UHV) chamber with a base pressure of 5 x 10-" torr. Samples consisted of (100) oriented n-type (Si doped, 2 x 1018 cm-3 ) and p-type (Zn doped, 2 x 1019 cm- 3 ) wafers, cleaved in vacuum to expose the GaAs(110) sample surface. Nickel was deposited by thermal evaporation from a tungsten filament. Coverages, island heights, volumes, and number densities were determined from STM images. Figure 1 shows dual-bias images of a small amount of Ni deposited at room temperature. The two features indicated in Fig. 1(a) probably result from different bonding configura
Data Loading...
