Optical activation of erbium doped porous silicon by hydrogen plasma treatment

Er3+-doped porous silicon (Er:PS) shows strong room temperature emissions at similar to 1.54 mu m. However, its spectrum is usually much broader than that of Er-doped crystalline silicon (full-width at half maximum - FWHM - is similar to 10 nm). It is probably because Er ions are located in amorphous phases. We report in this paper that strong and very sharp Er3+ 1.54 mu m emissions are obtained, when Er:PS samples are treated in a hydrogen plasma. Porous silicon layers are formed by anodic etching and then doped with Er3+ ions in an ErCl3/ethanol solution by an electrochemical method, and then treated in a hydrogen plasma at similar to 1000 degrees C from 0.5 min to 90 min for the optical activation. Several sharp peaks are observed at 20K, of which the strongest peak is located at 1.538 mu m with an FWHM less than 1 nm. This value is comparable to that obtained from Er3+-doped crystalline silicon formed by means of molecular beam epitaxy (MBE) or ion implantation. Comparisons are made among hydrogen plasma, argon plasma, H-2 flow and vacuum for the post-dope annealing atmosphere. Fourier-transform infrared (FT-IR) absorption and secondary ions mass spectrometry (SIMS) measurements are also carried out. We conclude that preferential etching of amorphous surface layers, and termination of dangling bonds of silicon nanocrystallites with hydrogen atoms and formation of Er-H complexes may be responsible for the strong and sharp Er3+-related luminescence.