Defects dynamics in P+ implanted 6H-SiC, studied by AFM and positron annihilation
|Grzegorz P. Karwasz 1,3, Riccardo Rurali 2, Giovanni Consolati 4, Philippe Godignon 2|
1. Dipartimento di Fisica, Universita' di Trento, via Sommarive, 14, Trento 38050, Italy
6H-SiC 0.6 mm thick monocrystals from Cree Inc. have been implanted by phosphorus ions with 1014cm-2 dose at 280 keV energy. TRIM modelling yields the P+ ions profile of 200 nm FWHM centred at about 380 nm. Samples were studied by positron annihilation technique, using a depth resolved, variable energy (0.1-25 keV) slow positron beam at Trento University. Doppler-broadening of the 511 keV annihilation line, indicating annihilation with low-momentum electrons was monitored. Positron-diffusion numerical packet VEPFIT was used to analyse data. For un-implanted samples present results agree well with data of Ohshima et al. (1998) - a slow fall of the annihilation S-parameter from the surface (0.493) to the bulk (0.465) value, indicating a long (190 nm) diffusion length, i.e. absence of positron-trapping defects. This result is also confirmed by positron-lifetime measurements performed at Politecnico di Milano, yielding essentially a lifetime of 148 ps. Ohshima et al. implanted samples with at a lower fluence - 1013 cm-2 and lower energy (200 keV) P+ ions; their "as-implanted" samples show a similar dependence as our - with a wide flat region of slightly risen defectiveness (S-value of 0.497). However, in order to reproduce reasonably well the depth of the damaged layer, one has to assume presence of strong (10 kV/cm) electric fields in the implanted region. Otherwise, VEPFIT program would, as an artefact, indicate the implanted depth down to as much as 1100 nm. With annealing, S-curves show a rising maximum, moving towards surface - probably, in as-implanted samples the defects are decorated by P+ ions and do not trap positrons in effective way. After the highest temperature annealing (1400C for Oshima, 1550C for us), our results differ from those of Ohshima et al. In their samples, SiC recovers totally and no defects at any depth are seen by positrons; in our samples a highly defected region (S=0.524) still extends for the first 50 nm depth.
Presentation: oral at E-MRS Fall Meeting 2003, Symposium A, by Grzegorz P. Karwasz
See On-line Journal of E-MRS Fall Meeting 2003
Submitted: 2003-05-08 11:40 Revised: 2009-06-08 12:55