Fabrication And Optical Properties Of Silicon Oxide Films Embedded With Erbium Silicates

Si-based optoelectronics is one of the most important research fields in the development of information technology.There has been an urgent requirement for an efficient Si-based light source which is compatible with the ultra-large-scale-integration(ULSI)technology.Bulk silicon is an indirect-bandgap semiconductor and is therefore very inefficient as a light emitter,so various approaches have been proposed to solve this problem during the last decades.Among these approaches,Er-doped Si-based materials have been attracting a lot of attention due to the 1540 nm light emission from Er ions which corresponds to a minimum in the loss spectrum of silica fibers.However,the excitation cross section of Er ions is very small and the Er concentrations in most Si-based hosts are highly limited.Therefore,how to realize efficient luminescence of Er ions is the key problem and the combination of Er silicates and sensitizers is an important route towards efficient luminescence of Er.In this dissertation,the polymorphic transformation,the luminescent properties,the crystal structures,and the sensitized photoluminescence(PL)of Er silicates are systematically investigated.The primary innovative results are summarized as follows:(1)Er silicate films with different polymorphs have been successfully fabricated and the influence of the Er:Si ratio of the film,the annealing temperature and the annealing atmosphere on the crystallization and polymorphic transformation of Er silicates has been discovered.The crystallization temperature of Er silicates in Si oxide films highly doped with Er is near 1000 ℃.When the Er:Si ratio in the film is close to 1:1,the polymorphic transformation process from low temperature to high temperature is from y-Er2Si2O7 to a-Er2Si2O7,then to β-Er2Si2O7.When the Er:Si ratio is close to 2:1,the polymorphic transformation process from low temperature to high temperature is from X1-Er2SiO5 to α-Er2Si2O7,then to β-Er2Si2O7.However,the deviation of the film chemical compositons from the stoichiometry of Er silicates and the annealing in oxygen atmosphere will both restrain the transformation of Er silicates from low temperature polymorph to high temperature polymorph and decreases the sizes of Er silicate grains.(2)Different Er silicate polymorphs lead to different luminescent properties.A correlation has been established between the crystallographic data of different polymorphs and the luminescent properties,including PL peak positions,light emission efficiency,PL lifetime and temperature quenching effect.y-Er2Si2O7 shows the highest PL efficiency and the longest PL lifetime followed by α-Er2Si2O7 and β-Er2Si2O7,and X1-Er2SiO5 shows the shortest PL lifetime.In addition.y-Er2Si2O7 also shows much less thermal quenching than α-Er2Si2O7.Through calculation,the ratio among the Er lifetime-density products(LDP)of these polymoiphs,which represent the capability of light amplification at 1540 nm,is 3.1:1.5:1.3:1.2.The stronger photoluminescence(PL)intensity,longer PL lifetime,and less PL thermal quenching of y-Er2Si2O7 are attributed to the larger density of optically active Er ions,the larger Er-Er average distance and the higher symmetry,and the stronger Er-O bonding,respectively.(3)Si oxide films co-embedded with amorphous Si(a-Si)clusters and Er silicates have been successfully fabricated and the formation of Si nanocrystals has been found to be limited by the crystallization of Er silicates.When the annealing temperature is low,a large number of Si nanocrystals are formed in the film.However,when the annealing temperature rises to the crystallization temperature of Er silicates,the Si nanocrystals are found to have disappeared and Er silicates start to crystallize,forming an amorphous Si(a-Si)clusters-embedded Er silicate film.If we prolong the annealing time,still no Si nanocrystals can form in the a-Si clusters because the existence of the surrounded crystalline Er silicate shell will greatly increase the nucleation barrier for Si nanocrystals.(4)The sensitized PL of Er silicates in Si-rich Er silicate films is attributed to an energy-transfer process mediated by a-Si clusters and luminescent centers(LCs).After annealing,sensitized PL of Er silicates has been achieved in a-Si-embedded Er silicate films and the main sensitizers are a-Si clusters and LCs.In order to improve the sensitized PL from Er silicates,an innovative two-step annealing process is utilized to optimize the structure,the crystal quality,the polymorph composition,and the concentration of sensitizers of the Si-rich Er silicate films at the same time.The best sensitized PL intensity is achieved in the film annealed at 1000 ℃ for 30 min followed by 1100 ℃ for 30 min.