Er And Defect Photoluminesence In Hydrogenated Amorphous Silicon

Er doped materials can emit light at 1.54μm due to an intra-4f transition from the excited state 4I13/2 to the ground state 4I15/2 in the Er3+ ion. Because this wavelength coincides with the minimum loss window of conventional silica-based optical fiber, many works are currently devoted to the study of Er doped materials. Photoluminescence (PL) of Er doped amorphous silicon (a-Si) was reported to have a high efficiency compared to that of Er doped crystalline Si. For the mechanism of the excitation of Er3+ ions in a-Si, it was proposed that photoexcited electrons which recombine on Si dangling bonds (DBs) transfer their energy nonradiatively to closely neighbored Er3+ ions. This process is called "defect-related Auger-excitation (DRAE)".We investigated the effect of N co-doping with Er in a-Si:H. All samples were prepared by rf magnetron sputtering method. The thermal quenching of Er PL tends to decrease with an increase in the N concentration in Er doped a-Si:H. But the intensity of Er PL also decreases. We examined the annealing effect on the Er PL intensity of Er doped a-SiN:H. The Er PL intensity was found to increase by annealing.In DRAE, it is thought that Si DBs play an important role in the excitation of Er3+ ions. In order to study a role of Si DBs in Er PL mechanism in a-Si:H, we prepared Er doped a-Si:H films with various density of Si DBs. The density of Si DBs was changed by three ways: (1) change of Ar-to-H2 gas ratio in the sputtering ambient, (2) light soaking and (3) annealing. The intensity of the Er PL tends to decrease with an increase in the density of Si DBs in the first two cases. In the case of annealing, the intensity of the Er PL first increases with a decrease in the density of Si DBs up to 250℃ and then continues to increase up to 350癈 even though the density of Si DBs increase. This increase in the Er PL intensity is probably caused by a change of the environment of Er3+ ions by annealing.We also studied a role of Si DBs in defect PL in Er doped a-Si:H. The density of Si DBs was changed by annealing. The intensity of the defect PL tends to decrease with an increase in the density of Si DBs. This decrease in the defect PL intensity is probably caused by the increase of the nonradiative tunneling transition with multiphonon emission because of the increase in the density of Si DBs.