Ge/SiGe multiple quantum well fabrication by reduced-pressure chemical vapor deposition

Abstract

In this paper we deposit structures comprising a stack of 10 periods made of 15-nm-thick Ge multiple quantum wells (MQWs) enclosed in a 15-nmthick Si 0.2 Ge 0.8 barrier on SiGe virtual substrates (VSs) featuring different Ge content in the 85%-100% range to investigate the influence of heteroepitaxial strain on Si 0.2 Ge 0.8 and Ge growth. With increasing Ge concentration of the VS, the growth rate of Si 0.2 Ge 0.8 in the MQWs increases. Si incorporation into the Si 0.2 Ge 0.8 layer also becomes slightly higher. However, almost no influence of the growth rate is observed for Ge growth in the MQWs. We argue that increased tensile strain promotes the Si reaction at the surface. In the case of Si 0.2 Ge 0.8 growth on Ge, we observe a smeared interface due to Ge segregation during the growth. Furthermore, we observe that the interface width increases with increasing Ge concentration of the VS. We attribute this observation to the increased segregation of Ge driven by increased strain energy accumulated in the Si 0.2 Ge 0.8 layers. We also observe that the MQW layer "filters out" threading dislocations formed in the VS.

Non-isothermal phase-field modelling with thermocapillary convection: Laser-written in-plane SiGe heterostructures for photonic applications

“…The phasefield gradient ∇ has the highest value at the bottom of the molten zone, which increases the effect of phase segregation according to Eq. (16). Therefore, the most Si-rich region in the under-cladding occurs at the bottom, as shown in Figure 3 The phase-field modelling provides good agreement when compared to the experimental observations of the scan-speed-dependent Ge redistribution.…”

“…The Si0.5Ge0.5 epilayers were epitaxiallygrown on (100) silicon substrates by reduced pressure chemical vapour deposition (RPCVD). 16 As a thermal source, we used a continuous wave (CW) laser operating at 532 nm and an experimental setup schematically shown in Supplementary Figure S2. The laser beam with a power of 3 W was focused to a spot with a diameter of 5 µm on the surface of the Si0.…”

“…41,42 To understand the effect of the thermocapillary convection on the distribution of composition within the molten zone, Navier-Stokes equations were solved concurrently with Eqs. (16) and (24). To reduce the simulation volume and computational cost, we chose a beam spot size of 2 µm and a scan range of 10 µm, which are smaller in size compared to the experimental parameters.…”

“…The convection-diffusion-segregation equation in Eq. (16), which is coupled to the Navier-Stokes and heat transport equations, was solved in a segregated way using a parallel sparse direct solver (PARDISO). Time discretization was done using the backwards differentiation formula (BDF).…”

“…Generally, phase segregation is an undesired phenomenon even for epitaxial growth of vertical heterostructures in semiconductor alloy epilayers. This is particularly true for SiGe alloys, 16 which have a large miscibility gap between the liquidus and solidus curves in the equilibrium phase diagram.…”