Quantitative investigation of the influence of carbon surfactant on Ge surface diffusion and island nucleation on Si(100)

Abstract

We investigated the surface diffusion and island nucleation of Ge on Si(100) in presence of a submonolayer coverage of carbon as surfactant by using scanning Auger microscopy and atomic force microscopy. Ge stripes have been deposited and lithographically etched on a Si substrate and used as sources for the surface diffusion of Ge promoted by annealing at 600, 650, and 700 °C. The diffusion coefficient has been determined by fitting the postannealing coverage profiles measured by Auger microscopy with a one-dimensional continuous model. The carbon coverage has been spatially modulated on a single sample, allowing the measurement of the diffusion coefficient as a function of the C thickness at 600 °C. We show that the reduction in the diffusion coefficient while increasing the surfactant coverage is described by a linear dependence of the diffusion activation energy on the C coverage. This dependence is discussed in terms of the chemical interactions among Si, C, and Ge, of the surface roughness and the local strain field induced by the C surfactant. Spontaneous nucleation of SiGe islands coexists with the continuous surface diffusion of Ge. The transition of the island nucleation as a function of the carbon coverage is observed to be continuous from the Stranski-Krastanov mode to the Volmer-Weber regime. We propose a consistent scenario correlating diffusion and nucleation parameters within a diffusion limited growth regime and show the existence of a threshold for C coverage below which no effect is observed

Monitoring the kinetic evolution of self-assembled SiGe islands grown by Ge surface thermal diffusion from a local source

“…(1) it demonstrate that the gross features of our experimental results can be described based on the kinetics of the diffusion alone, and (2) it allows to quantify the scaling dependence of the island density in the random diffusion area on the diffusion length, as discussed in the next paragraph. Figure 3(f) shows the linear scaling behavior exhibited by n 0 when plotted as a function of 1/Dτ (D is the diffusion coefficient and τ is the annealing time), where Dτ is derived by √ the diffusion length (L = 2 Dτ ) from the diffusion profiles measured at each annealing temperature [32]. This confirms quantitatively the diffusive origin of the decreasing gradient of the island density at higher temperatures.…”

Delayed plastic relaxation limit in SiGe islands grown by Ge diffusion from a local source

“…1(a)). SAM analysis 15 shows that the Ge content of the over-layer is approximately constant within the nucleation region (x < 20 lm) and its average value decreases from $0.8 at 600 C to $0.64 at 700 C. This temperature dependence reflects the thermally activated nature of the Si incorporation. When our results are compared to typical MBE data, where Ge concentration values of the wetting layer greater than 0.86 have been found even at 700 C, 26 it is evident that the thermal diffusion from a local source results in an enhanced intermixing within the OL, whose origin will be discussed in details later.…”

“…[15][16][17] Briefly, Ge stripes (width % 5 lm, thickness % 150 nm) are obtained by a lithographic patterning of pure Ge thin films, deposed by Low Energy Plasma Enhanced Chemical Vapour Deposition (LEPECVD), 24 and are annealed by Joule heating flowing a DC current through the Si(100) substrate. For the cases investigated here, the samples were annealed at 600 C for 15 min and at 700 C for 6 min.…”

“…For this purpose, we have fabricated Ge stripes and annealed them in ultra-high vacuum (UHV) at different temperatures inducing Ge diffusion and islands self-assembly. As reported in previous works, [15][16][17] this methodology has provided a unique approach for the investigation of the factors governing the growth process. From our previous results, 17 we concluded that the island growth evolves in a diffusion-limited regime and it is mainly driven by the short-range interactions between the growing islands and the diffusing Ge atoms.…”

Suppression of segregation of the phosphorus δ-doping layer in germanium by incorporation of carbon

“…It has been known that carbon is the dominant residual impurity on the surface of Ge substrates after chemical cleaning and preannealing in vacuum. 25) We use such residual carbon impurities to investigate the effect of carbon insertion, as shown schematically at the top left side of Fig. 1.…”