Near infra-red photoluminescence of Nd3+ in hydrogenated amorphous silicon sub-nitrides a-SiNx:H

Neodymium-doped hydrogenated amorphous silicon sub-nitrides a-SiNx:H thin films were deposited by rf-sputtering using a Si target partially covered by metallic Nd chips and Ar+N2+H2 sputtering gas. Characteristic Nd3+ near infra-red (NIR) photoluminescence (PL) was detected between 10 and 300 K with peaks at ∼935, ∼1090 and ∼1390 nm, corresponding to the intra-4f transitions 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2, respectively. Measurements using different excitation wavelengths indicate that the Nd3+ excitation occurs through the a-SiNx:H matrix. Varying the nitrogen content x from 0 to nearly 1.3 increases the matrix bandgap. The PL efficiency is maximum when the bandgap corresponds to twice the 4F3/2→4I9/2 transition, indicating a defect-related energy transfer mechanism. The temperature quenching can be as low as less than a factor 3 between 10 and 300 K for 2.8 eV gap samples. Thermal annealing can enhance the PL intensity by a factor 10. Neodymium concentrations above ∼3x1020 atoms/cm3 slightly reduce the PL intensity probably due to excess of inactive defect centers. Along with erbium-doped amorphous silicon alloys, a-SiNx:H can be used in the development of photonic devices in the future