Surface modification of Si/Ge multi-layers by MeV Si ion bombardment

Abstract

We made 50 periodic nano-layers of Si/Ge superlattice films with Au layers deposited on both sides as metal contacts. Each layer is 7.3 nm thick. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT. The purpose of this study is to improve the figure of merit of layered structures used as thermoelectric generators. The multi-layer Si/Ge films were then bombarded by 5 MeV Si ions at five different fluences to form nano-cluster structures. Rutherford Backscattering Spectrometry (RBS) was used to determine the total film thickness and stoichiometry. The total thickness was found as 364 nm. To get the figure of merit before and after MeV bombardments, we have measured the cross plane thermal conductivity by 3 ω (3rd harmonic) method, cross plane Seebeck coefficient and electrical conductivity using Van der Pauw method. The electronic energy deposited due to ionization by the MeV Si beam in its track produces nano-scale structures. Micro-Raman spectra of the multilayered Si/Ge thin films were acquired using a surface sensitive LabRam spectrophotometer, equipped with a He–Ne laser with μ = 632.18 nm excitation wavelength to show nanoscale structure production effect on quantum well confinement by MeV Si on bombardment.