Influence of Si interdiffusion on carbon-induced growth of Ge quantum dots: a strategy for tuning island density

Abstract

We have studied the epitaxial growth of self-assembled Ge quantum dots when a submonolayer of carbon is deposited on a Ge wetting layer (WL) prior to the growth of the dots. Using atomic-force microscopy combined with optical techniques like Raman and ellipsometry, we performed a systematic study of the role played by thermally activated Si interdiffusion on dot density, composition and morphology, by changing only the growth temperature T(WL) of the WL. Strikingly, we observe that higher dot densities and a narrower size distribution are achieved by increasing the deposition temperature T(WL), i.e. by enhancing Si interdiffusion from the substrate. We suggest a two-stage growth procedure for fine tuning of dot topography (density, shape and size) useful for possible optoelectronic applications.

Density control on self-assembling of Ge islands using carbon-alloyed strained SiGe layers

“…The peak at 301.3 cm −1 is ascribed to the Ge-Ge phonon mode of the Ge QDs and its spectral position is indicative of a very high Ge content of x Ͼ 0.90 and almost complete strain relaxation ͑⑀ ʈ Ϸ −0.005͒. 15 We point out that for the buffer layer with highest Ge concentration we expected its Ge-Ge mode to be observable in Raman spectra as well at ϳ305 cm −1 . In fact, its contribution to the Ge-Ge phonon peak of the dots can be spectrally deconvoluted by fitting this peak with two Lorentzians, as illustrated by the dotted curves in Fig.…”

“…This scenario is consistent with our recent work addressing the influence of Si interdiffusion when the carbon-induced QDs are grown on pure Ge wetting layers deposited at different temperatures. 15 Again the dot density increases with increasing deposition temperature of the wetting layer, i.e., with higher Si content of the surface onto which the dots nucleate.…”

“…14,15 In this Letter we present a different route for manipulating Ge island self-assembling based on the combination of epitaxial growth on strained SiGe buffer layers and carbon predeposition. Inspired by our recent results on the influence of Si interdiffusion and the Ge-C repulsive interaction on the resulting Ge dot topography 15 we make use of the effect that a submonolayer deposition of C has on the Ge adatom diffusion. Our results point to a reduction by two orders of magnitude of dot density with increasing Ge content in the buffer layer.…”

Raman scattering of capped and uncapped carbon‐induced Ge dots under hydrostatic pressure

“…This surface modification allows for the control of shape and density ( ) of islands in the next growth step, when 6 Å ∼ of Ge are deposited at 500 °C. The resulting topography consists of dome-shaped dots 10-15 nm high [10]. For the capped sample, a 10 nm thick Si layer was subsequently grown at low temperature (300 °C) in order to avoid silicon intermixing and to preserve the island shape.…”

“…The carbon-induced Ge dots under investigation are Ge rich (>90%) dome-shaped islands [10,11], whose enhanced aspect-ratio leads to an efficient relaxation of the strain originating at the island/substrate interface due to the lattice mismatch between Ge and Si (∼4%). Raman scattering spectroscopy gives information on the average Ge content and mean strain of the islands.…”