Donor behaviour of implanted hydrogen ions in silicon wafers
Résumé
P type Czochralski (Cz) and float-zone (FZ) grown silicon wafers were investigated with doping levels of 5x10(14) and 2x10(15) cm(-3), respectively. Hydrogen ions are implanted at a dose of 2x10(16) cm(-2), at energies in the range 20 to 250 keV and are accumulated at depth R-p in the range 0.2 to 2.4 mum. After implantation the wafers are annealed between 350 and 600 degreesC for 30 min, under argon flow. It is found that a graduated n-p junction is formed, and after metallization a photovoltaic device is obtained, which works like a solar cell. SIMS analysis shows that, around R-p, hydrogen concentration achieves 10(21) cm(-3). I-V and C-V curves confirm the formation of a N-type layer in which the donor concentration is about 5x10(17) cm(-3). When the samples are annealed at temperatures higher than 550degreesC the counter-doping vanishes. The observed behaviour of hydrogen is irrespective of oxygen concentrations in the wafers as it occurs in Cz (oxygen rich) like in FZ (oxygen poor) wafers. If the wafers are ion implanted with helium at the same dose and energy no junction appears. It is concluded that the agglomeration of hydrogen in silicon after ion implantation at a dose exceeding 10(16) cm(-2) gives rise to the formation of shallow donors.