Optical and electrical doping of silicon with holmium

Abstract

2 MeV holmium ions were implanted into Czochralski grown Si at a fluence of 5.5*10^14 Ho/cm^2. Some samples were co-implanted with oxygen to a concentration of (7±1)*10^19 cm^(-3). After recrystallization, strong Ho segregation to the surface is observed, which is fully suppressed by co-doping with O. After recrystallization, photoluminescence peaks are observed at 1.197, 1.96 and 2.06 lm, characteristic for the 5-I-6 --> 5-I-8 and 5-I-7 --> 5-I-8 transitions of Ho^(3+). The Ho^(3+) luminescence lifetime at 1.197 lm is 14 ms at 12 K. The luminescence intensity shows temperature quenching with an activation energy of 11 meV, both with and without O co-doping. The observed PL quenching cannot be explained by free carrier Auger quenching, but instead must be due to energy backtransfer or electron hole pair dissociation. Spreading resistance measurements indicate that Ho exhibits donor behavior, and that in the presence of O the free carrier concentration is enhanced by more than two orders of magnitude. In the O co-doped sample 20% of the Ho^(3+) was electrically active at room temperature.