Confined states in parabolic cylinder quantum dots

Observation of optical gain in silicon nanocrystals (Si-nc) is critically dependent on a very delicate balance among the Si-nc gain cross-sections, the optical mode losses and confinement factors of the waveguide structures, the Si-nc concentration and the strongly competing fast non-radiative Auger processes. Here we report on optical gain measurements by variable stripe length (VSL) method on a set of silicon nanocrystals formed by thermal annealing at 1250°C of SiOx films with different silicon contents prepared by plasma-enhanced chemical vapour deposition. Time-resolved VSL has revealed fast component in the recombination dynamics under gain conditions. Fast lifetime narrowing and superlinear emission has been unambiguously observed. To explain our experimental results we propose a four levels recombination model. Within a phenomenological rate equations description including Auger processes and amplified spontaneous emission we obtained a satisfactory agreement with time-resolved experiments and explained the strong competition between stimulated emission and fast non-radiative Auger processes.