Positive secondary Ion emission from Si1 xGex bombarded by O2 +

The positive secondary ion yields of B+ (dopant), Si+ and Ge+ were measured for Si1 xGex (0 x 1) sputtered by 5.5 keV 16O2 + and 18O2 +. It is found that the useful yields of Ge+ and B+ suddenly drop by one order of magnitude by varying the elemental composition x from 0.9 to 1 (pure Ge). In order to clarify the role of oxygen located near surface regions, we determined the depth profiles of 18O by nuclear resonant reaction analysis (NRA: 18O(p,a)15N) and medium energy ion scattering (MEIS) spectrometry. Based on the useful yields of B+, Si+ and Ge+ dependent on x together with the elemental depth profiles determined by NRA and MEIS, we propose a probable surface structure formed by 5.5 keV O2 + irradiation