Positron annihilation in Si is a quantitaive, depth-sensitive technique for the detection of vacancylike defects or voids. A sensitivity of 5×1015 cm-3 for voidlike defects is easily achieved. The technique has been applied to a study of point-defect distributions in thin films of Si grown by molecular-beam epitaxy. A special procedure was developed to remove the influence of the native oxide on the positron measurement. 200-nm-thick films grown at temperatures between 475 and 560°C show no defects below the sensitivity limit and are indistinguishable from the bulk substrate. So are films grown at 220°C, provided a 2-min high-temperature anneal to a peak temperature of 500°C is executed every 30 nm during growth. If TRTA=450°C, part of the film contains vacancylike defects to a concentration of 1018 cm-3. These results correlate well with current-voltage characteristics of p-n junctions grown with different rapid thermal anneal (RTA) temperatures. Ion scattering, with a defect sensitivity of 1%, shows no difference between films grown with different TRTA. Recrystallization of amorphous films, deposited at room temperature and annealed in situ at 550°C, always leaves a significant defect concentration of 2×1018 cm-3; those defects are reduced but still present even after a 2-h 800°C furnace anneal.
ASJC Scopus subject areas
- Condensed Matter Physics