Thin SiGe virtual substrates for Ge heterostructures integration on silicon

Abstract

The possibility to reduce the thickness of the SiGe virtual substrate, required for the integration of Ge heterostructures on Si, without heavily affecting the crystal quality is becoming fundamental in several applications. In this work, we present 1 lm thick Si 1Àx Ge x buffers (with x > 0.7) having different designs which could be suitable for applications requiring a thin virtual substrate. The rationale is to reduce the lattice mismatch at the interface with the Si substrate by introducing composition steps and/or partial grading. The relatively low growth temperature (475 C) makes this approach appealing for complementary metal-oxide-semiconductor integration. For all the investigated designs, a reduction of the threading dislocation density compared to constant composition Si 1Àx Ge x layers was observed. The best buffer in terms of defects reduction was used as a virtual substrate for the deposition of a Ge/SiGe multiple quantum well structure. Room temperature optical absorption and photoluminescence analysis performed on nominally identical quantum wells grown on both a thick graded virtual substrate and the selected thin buffer demonstrates a comparable optical quality, confirming the effectiveness of the proposed approach.

Structural investigations of the α12Si–Ge superstructure

“…The r.m.s. amplitude of this waviness obtained by atomic force microscopy lies around 1 nm for two-step buffers with final Ge content similar to the used one (Cecchi et al, 2014). Typical lateral feature sizes correspond well to the lateral correlation lengths of $100 nm obtained in the XRR fits.…”

“…A double-step graded thin buffer, which guarantees an r.m.s. roughness below 1 nm and prevents wafer bending, has therefore been used (Cecchi et al, 2014). The whole structure including both the buffer and the magic motif was grown without interruption on RCAcleaned HF-dipped Si(001) substrates (p-type, 1-10 cm) by low-energy plasma-enhanced chemical vapor deposition (Isella et al, 2004).…”

Kirkendall void formation in reverse step graded Si1−xGex/Ge/Si(001) virtual substrates

“…A similar phenomenon was observed with linear step grading [31], where constant composition Si Ge 1 x x -layers with increasing Ge content were deposited directly onto Si(001). buffer layer via vacancy exchange, through the 60°misfit network at their interface, akin to the Kirkendall effect.…”

Ge quantum-well waveguide modulator at 1.3μm

“…Indeed, as demonstrated in several work, the buffer thickness on which the Ge/SiGe stacks are grown can be reduced without compromising the epitaxy quality and spoil the QCSE [17][18][19]. In order to assess the effect of the buffer thickness on the optical coupling efficiencies, we performed simulations based on eigenmode expansion method using both 360 nm and 150 nm thick buffer between silicon and Si 0.35 Ge 0.65 layer.…”