On Silicon Amorphisation During Different Mass Ions Implantation

Abstract

Amorphisation of silico single crystals during different mass 80 keV ions bombardment (B⁺, C⁺, Ne⁺, Ar, Sb⁺) has been studied by means of three independent techniques, (a) IR absorption at I,8 μ wavelength (divacancy absorption), (b) IR reflection near a fundamental absorption edge, and (c) electron microscopy and fast electron diffraction. Irradiation was carried out at room temperature. From the analysis of data obtained it can be concluded that two types of disordered regions arise during ion bombardment, (a) amorphous regions (A.R.) and (b) disordered, but still processing crystalline structure regions; which we call the crystalline disordered regions (CDR). In CDR the defect concentration is so high that divacancies do not appear. The defect concentration in CDR gradually increases with the increasing of irradiation dose. When; the defect concentration achieves some critical value CDR transforms sharply to an amorphous state. Such amorphisation mechanism prevails for light ions. For heavy ions (Sb⁺) amorphisation arises mainly from a one-step AR formation. The proposed model of amorphisation gives the qualitative explanation of dose dependence of refractive index for different ions.