Fabrication And Optical Properties Of Long Luminescence Lifetime Erbium Silicates

Silicon-based integrated optoelectronics requires high gain optical amplifiers and compact light sources in the telecom wavelength range.Bulk silicon is very inefficient in emitting light due to the nature of indirect-bandgap semiconductor.The erbium-containing materials are promising candidates because of the ability to emit at 1.5?m via the intra-4f transition.Er-doped materials cannot produce sufficient gain for chip-scale integration due to the low erbium concentration in hosts limited by solid solubility and segregation.Crystalline Er compounds such as erbium silicate with periodical arrangement of erbium ions have a much higher erbium concentration up to 10²² cm^-3.And researchers also have found that nearly all erbium ions in Er silicate are optically active.Therefore,Er compounds are expected to potentially realize Si-based light sources and optical amplifiers.So far,the existing Er compounds suffer from short lifetime and poor sensitized luminescence,which hinder the lager-scale application in silicon-based integrated optoelectronics.This dissertation focuses on the improving luminescent lifetime and sensitized luminescence of erbium silicate.The influence of microstructure on lifetime and the creation of efficient energy transfer between sensitizers and erbium silicate are systematically investigated.The main innovative results in this dissertation are summarized as following:?1?We have developed a reduced Er-Er interaction strategy for pursuing long lifetime and high efficiency luminescence in Er compounds.Annealing temperature,atmosphere and Er/Si ratio dependence of the optical properties from Er silicate nanowires embedded in silicon oxide films have been investigated.The record long lifetime?-Er₂Si₂O₇ of 844?s is achieved through simultaneously reducing defect density and Er³⁺-Er³⁺interaction.The low defect density in the?-Er₂Si₂O₇ nanowires is mainly attributed to following aspects:no hydroxyl groups contamination,effective surface passivation and saturation of oxygen vacancies.The interaction of Er-Er ions is confined by the alteration of phonon density of states effects in the?-Er₂Si₂O₇nanowires.More significantly,the strong up-conversion emissions in the?-Er₂Si₂O₇nanowires also reduce effectively due to the nanoconfinement effect.?2?Er silicate/porous silicon?PS?composites with effective sensitized erbium emission at 1.53?m have been synthesized on the PS framework.The influence of anodization current density,anodization time and Si wafer type on sensitized luminescence has been analyzed.Based on spectra and microstructure characterizations,we confirm that Si nanocrystals act as sensitizer of erbium ions that locate in erbium silicate and host.The sensitized erbium luminescence may be further improved by coating PS more uniformly.The temperature dependence of photoluminescence intensity and lifetime is investigated,which concludes a phonon-mediated energy transfer process.?3?We obtain the efficient sensitized luminescence of Er chloride silicate?ECS?nanocrystal via interparticle energy transfer for the first time,where the ECS nanocrystals were formed at the vicinity of Si nanocrystals in oxide host.Our experimental results have proven that 10%Er/Si ratio sample has the optimum sensitized emission due to the fine distribution of two type nanocrystals and strong Si nanocrystal luminescence.The pump power dependence of Si and ECS nanocrystal illustrates that the proportion of nanocrystals which can participate the energy transfer process shall be further increased for better sensitized erbium emission.?4?We have investigated the evolution of film's microstructure and optical properties when the annealing temperature increases.Results have shown that the Er-rich clusters at the vicinity of Si nanocrystals need 1100? annealing temperature or higher to crystallize.The sensitized luminescence is affected by Si nanocrystals'luminescence and the energy transfer efficiency?ETE?.The Si nanocrystals'luminescence increases with annealing temperature up to 1100?.However,when we continue to increase the annealing temperature,the luminescence redshifts and the luminescence intensity declines rapidly.The sample annealed at 900? has higher ETE due to the closer distance between Si nanocrystals and Er³⁺,which most Er ions located in amorphous matrix.With higher annealing temperature,the ECS nearby Si nanocrystals gradually crystallize so that the particles'distance becomes closer to enhance the ETE.Given these two factors,the sample annealed at 1100? has the most excellent sensitized emission.