Time-resolved photoluminescence in a-SiNx:H〈Nd〉 planar waveguides: evidence for stimulated emission

Abstract

Abstract We performed lifetime measurements on the 1128 nmNd3+ emission from a neodymium-doped amorphous hydrogenated silicon sub-nitride (a SiNx:H〈Nd〉) planar waveguide. The 1.5 μm thick sample was prepared by reactive rf-sputtering. Lifetime measurements were performed exciting with a multiline Ar+ laser. The sample temperature was varied between 25 and 300 K, and the excitation power between 0.2 and 8 kW/cm2. In all measurement conditions the luminescence decay can be expressed by two exponentials. The fast decay has a lifetime between 40 and 60 μs and the slow decay has a lifetime between 1 and 3 ms. The excitation photon energy is not resonant with any of the Nd3+ transitions, consequently the excitation energy must be transferred from the host nitride to the Nd3+ ions. The fast lifetime is almost independent of the temperature, indicating that it is related to the excitation transfer process. As the temperature increases the probability of carrier recombination through processes that do not excite Nd3+ ions increases. The slow lifetime is associated with the intrinsic Nd3+ lifetime. It is shorter at low temperatures and high excitation rates. At 26 K, it decreases by a factor 2 when the excitation power goes from 2 to 8 kW/cm2. The lifetime decrease with the excitation power is associated with the onset of stimulated emission from the Nd3+ ions.