The growth process of germanium inverted quantum hut (IQH) structures embedded in silicon-germanium superlattice, has been investigated using anomalous x-ray scattering techniques. Although Si and Ge can form alloys in any molar ratio, it is well known  that Ge deposited on the Si (001) surface grows layer by layer for around three monolayers in a typical temperature range of 450?750C, which is used for molecular beam epitaxy (MBE) growth of such superlattice structures, as barriers to inter-diffusion are sufficiently high . The formation of quantum hut structures below the Ge wet layer with the apex pointing down towards the Si substrate occur  through an enigmatic inter-diffusion of Ge in the underlying Si lattice at lower growth temperature (~500C).We discuss here that these IQH structures form by the intermixing of germanium with previously deposited silicon producing an intriguing composition variation that keeps the out-of-plane lattice parameter of the alloy almost constant. We have identified a zero strain cubic structure, which extends towards the tip of these IQHs to accommodate large-scale inter-diffusion of germanium in silicon lattice. These self-assembled IQH structures exhibit strong photoluminescence (PL) around 0.8 eV with exciton-binding energy of 49 meV suggesting that photon induced carriers are predominantly captured at the tip of the IQH structures . 1. T. U. Schulli, J. Stangl, Z. Zhong, R. T. Lechner, M. Sztucki, T. H. Metzger, and G. Bauer, Phys. Rev. Lett. 90, 066105 (2003). 2. F. Liu and M. G. Lagally, Phys. Rev. Lett. 76, 3156 (1996). 3. H. H. Cheng,W. P. Huang, V. I. Mashanov, and G. Sun, J. Appl. Phys. 108, 044314 (2010). 4. M. Sharma, M. K. Sanyal, B. Satpati, O. H. Seeck and S. K. Ray, Phys. Rev. B 89, 205304 (2014).
Milan K. Sanyal is a senior Professor and former Director of Saha Institute of Nuclear Physics (SINP) – an autonomous institute in Department of Atomic Energy. He joined SINP in 1995 to initiate a research group in surface physics and before joining SINP he was a Scientific Officer in Bhabha Atomic Research Centre, Mumbai from 1977 and was a Research Associate in Brookhaven National Laboratory, USA from 1989 to1992. Prof. Sanyal is a fellow of all three academies of sciences in India, namely Indian National Science Academy, Indian Academy Sciences, The National Academy of Sciences, India. He is also a fellow of Asia-Pacific Academy of Materials and West Bengal Academy of Science and Technology, India. He has also received several awards including N.S. Satyamurthy Award, DAE Raja Ramanna Award, CNR Rao Prize Lecture in Advanced Materials and J.C. Bose fellowship. He was in the Council (2009-2012) of Indian National Science Academy and was President of both Indian Physical Society and Indian Physics Associations. At present Prof. Sanyal is Co-Chairman of India-Japan Science Council and Chairman of Research and Academic Advisory Council (RAAC) of the Institute of Nano Science and Technology, Mohali and member of several important national committees. Prof. Sanyal’s research interest are synchrotron x-ray and neutron scattering studies of surface and interfaces, Structure-property correlation in low-dimensional systems, Structure and morphology of solid and liquid interfaces and Charge ordering and electronic transport in nano-structured materials.