Investigation of crystallographic changes across the Cr/a-Si interface by X-ray absorption spectroscopy

Abstract

X-ray Absorption Fine Structure spectroscopy (XAFS) has been employed to investigate the crystallographic changes that evolved across the Cr/a-Si interface as a function of annealing temperature. A stack of 400nm a-Si and50nm metallic Cr film is deposited onto a fused silica substrate by electron beam evaporation. Thesestacks are subjected to annealing temperature from 200°C to 700°C in nitrogen-rich atmosphere to facilitate the metal diffusion and subsequent phase formation across the interface. XAFS investigations were carried out in twoconfigurations to study the change in local chemistry of Cr indepth andtop layers of the stack simultaneously. XAFS analysis confirmed thatthe FSC stack annealed at 200°C has a dominant metallic Cr concentration along with a minority content of Cr2O3 andCr3Si. On increasing the annealing temperature, metallic Cr converted into Cr2O3 andCr3Si up to an intermediate temperature of 500°C and finally at 700°C it transformed to CrSi2. It is also confirmed from total reflection XAFSthatCr diffusion intoa-Si is the preferred phenomenon that takes place acrossthe Cr/a-Si interface. The diffusion of Cr and subsequent thermodynamic conditions required for the formation of different Cr phases are discussed to understand the factors that affect the Schottky properties of the Cr/a-Si interface.