Fabrication of Homogeneous Ultra-Thin Sige-on-Insulator Layer for Thermoelectric Applications

SiGe nanostructures has attracted much attention in recent years in order to realize high-efficient thermoelectric devices due to carrier confinement effect and alloying effect [1,2]. For this purpose, in the present study, we fabricated a compositionally-homogeneous thin SGOI (SiGe on insulator) substrate by simple sputtering and physical evaporation techniques and characterized its crystallographic properties and thermal conductivity. A 30-nm-thick Si layer was sputtered on a thermally-oxidized Si wafer (SiO2 thickness: 103 nm), followed by the deposition of a thin Ge film with a thickness of 30 nm, at room temperature. Afterwards, Si-Ge diffusion was carried out by a rapid thermal annealing process at 880oC for 10 and 120 min. The prepared SGOI substrates were characterized by means of XRD, SEM, EPMA, Raman spectroscopy, XPS, and AFM, which showed the formation of a compositionally-homogeneous poly-crystalline Si1-xGex layer with x=0.45 (thickness: 60 nm). The thermal conductivity was determined by a picosecond time-domain thermoreflectance (TDTR) method at room temperature and shown in the figure, as a function of annealing time. For a reference, the measured values of our as-deposited Ge/Si layer and a commercial single-crystalline SGOI substrate (x=0.5) are also plotted. It is found that our poly-crystalline SGOI layer has lower thermal conductivity of 0.87 W/mK, compared with that of a single-crystalline SGOI 1.43 W/mK. [1] H. Kim, I. Kim, H.-J. Choi, and W. Kim, Appl. Phys. Lett., 96 (2010) 233106. [2] R. Basu, S. Bhattacharya, R. Bhatt, M. Roy, S. Ahmad, A. Singh, M. Navaneethan, Y. Hayakawa, D. K. Aswal, and S. K. Gupta, J. Mater. Chem. A, 2 (2014) 6922. Figure 1