Host Isotope Effect on the Local Vibration Modes of VH2 and VOH2 Defects in Isotopically Enriched 28Si, 29Si and 30Si Single Crystals

Local vibrational modes of a vacancy with two hydrogen atoms (VH2) and of a vacancy with one oxygen and two-hydrogen atoms (VOH2) in silicon have been investigated using isotopically enriched 28Si, 29Si, and 30Si single crystals. Infrared absorption spectroscopy revealed shifts in the Si–H stretch frequencies of the two defects when the mass of the silicon host atoms was changed. The observed stretch frequencies can for each defect be accounted for with a simple vibrational model based on two coupled Morse oscillators. The anharmonic contribution to the local vibrational mode frequencies of these two defects is evaluated.