We have used high resolution X-ray diffraction photoluminescence (PL) and secondary ion mass spectrometry to study the structural and optical properties of different Si/Si1-xGex quantum well (QW) structures grown using an advanced chemical vapor deposition (CVD) reactor. To understand the stability of the QW designs, and correlate the structural as well as the optical properties with the interlayer diffusion of these structures, we have subjected the different QWs to post-processing temperatures ranging from 600 degreesC to 1000 degreesC for I h each. The investigated samples include single, symmetric and different asymmetric double QW structures. The main finding of this study is that postgrowth thermal stability of this CVD grown QW is different from MBE grown samples. In addition, the design of the QW being single or double QW structure is clearly observed to affect the interlayer diffusion and hence, stability.