Published online by Cambridge University Press: 17 March 2011
P type Czochralski (Cz) and float-zone (FZ) grown silicon wafers were investigated with doping levels of 5×1014 and 2×1015 cm−3, respectively. Hydrogen ions are implanted at a dose of 2×1016 cm−2, at energies in the range 20 to 250 keV and are accumulated at depth Rp in the range 0.2 to 2.4 μm. After implantation the wafers are annealed between 350 and 600°C 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 Rp, hydrogen concentration achieves 1021 cm−3. I-V and C-V curves confirm the formation of a N-type layer in which the donor concentration is about 5×1017 cm−3. When the samples are annealed at temperatures higher than 550°C 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 1016 cm−2 gives rise to the formation of shallow donors.