Microvoids in a-Si:H and a-SiGe:H alloys

Photoinduced Dehydrogenation of Defects in Undopeda-Si:H Using Positron Annihilation Spectroscopy

“…The results show little process condition dependency in the S parameter of the film, agreeing with Muramatsu et al who also noted no appreciable change in S on light soaking [22]. In sharp contrast is the very noticeable change in the W parameter on light soaking shown in Fig.…”

“…The two samples studied in this work, both giving similar results, were 1 mm intrinsic a-Si:H homogeneous films grown by pure silane ͑SiH 4 ͒ PECVD (plasma enhanced chemical vapor deposition) at a deposition rate of 1.5 nm͞s [17] on quartz, at rf power 40 W, and substrate temperature 0031-9007͞00͞84(4)͞769(4)$15.00 330 ± C. The ratio of photoconductivity to dark conductivity of the film was about 5 orders, indicating material of solar cell quality. The light soaking illumination intensity was 100 mW cm 22 . The Staebler-Wronski effect was observed in the electrical measurements.…”

“…Despite many PAS studies using both positron beams [21,22,25,26] and conventional sources [23,[27][28][29], there is as yet no general consensus on the positron trapping sites in a-Si:H. Much of the uncertainty apparently arises from the variations in film preparation techniques [21,25]. However, evidence exists for four possible positron trapping states, namely, (i) coordination defects ͑1n͒ (ii) divacancylike defects ͑2n͒ (iii) vacancylike agglomerates comprising of ϳ5 missing atoms ͑5n͒, and (iv) large 10-20 Å diameter microvoids in which some positrons exist as bound Ps (MV).…”

“…The assertion that PECVD grown films contain 2n-type defects comes from positron lifetime studies [22,24], where the observed 310 to 350 ps component is identified with the 325 ps lifetime of divacancies in c-Si [30]. A number of studies also find a short lifetime component (190-256 ps) from some films [23,27,28].…”

Structural properties of a-Si films and their effect on aluminum induced crystallization

“…Excessive residual hydrogen in PECVD grown a-Si is known to cause micro-voids upon subsequent heat treatments. 12,13 The hydrogen content in the respective films are discussed below. The AIC kinetics also differed between the two sample sets; the necessary annealing time for initial nucleation as well as the completion of crystallization for P-9 was significantly shorter than that for P-29.…”