| With the announcement of 10-nanometer chip fabrication process from Intel Corporation at 2016 Intel Developer Forum(IDF),the feature size of integrated circuit(IC)chip is gradually reduced and close to its physics limited.One of the possible solutions is combining novel photonic device with fashionable and mature microelectronic IC technology and then achieving Si-based optoelectronic and monolithic integration.So far,the most challenging work is to find an efficient and stable infrared light source.It is well known that bulk Si material is an indirect gap semiconductor.For bulk Si,it is hard to achieve high-efficiency infrared light emission.Developing a high-efficiency CMOS-compatible near-infrared light emitter with novel active ions is essential for the success of future optoelectronic integration.In this thesis,by use of size-tunable and high-density semiconductor quantum dots(QDs)as sensitizers,high-efficiency Si-based infrared light emission from rare earth ions(Er3+ions and Eu3+ions)and transition metal ions(Bismuth ions)has been achieved under condition of optical excitation or electrical pumping.To sum up,the main content of the dissertation is listed as follows1.Metal-oxide quantum dots(including ZnO,In2O3,and SnO2)doped amorphous SiO2 thin films were prepared by use of sol-gel and spin coating methods.Based on high-resolution TEM characterization,it was found that the average size of QDs gradually increased with the increasing annealing temperature and doping concentration of metal cations.According to FT-IR results,post-annealing treatment at the range of 900 to 1000℃ was an effective way to reduce non-radiative recombination centers in silica matrix,such as-OH groups.The formation of hexagonal phase’s ZnO QDs,cubic phase’s In2O3 QDs,and tetragonal rutile phase’s SnO2 QDs with uniform distribution was confirmed by the X-ray diffraction.And after annealing at 1000 ℃,we found only tetragonal rutile phase’s SnO2 QDs is chemically inactive with amorphous SiO2 host.A wide photoluminescence(PL)emission band was observed from QDs doped amorphous SiO2 host and could be attributed to surface defect states of QDs.Meanwhile,a size-dependent photoluminescence excitation(PLE)peak was found and could be ascribable to quantum confinement effect.To summarize,the density and average size of QDs could precisely controlled by preparation parameters.Both large absorption cross section and tunable emission wavelength indicated that metal-oxide QDs could be a promising high-performance sensitizer for near-infrared active ions.By use of SnO2 QDs with average size of 5.2nm as sensitizers,the related 613nm characteristic emission intensity from Eu3+ ions was enhanced by two orders of magnitude and also 1.54 μm characteristic emission intensity from Er3+ ions was obviously enhanced by more than three orders of magnitude.Selective PL and PLE measurements show that energy transfer process occured between SnO2 nanocrystals and Er3+ ions.Quantitative studies of PL decay lifetime and temperature-dependence PL demonstrateed that both high energy transfer efficiency(up to 63.4%)from SnO2 nanocrystals to Er3+ ions and the partial incorporation of Er3+ ions into SnO2 sites contribute to the PL enhancement.All these results had not only explained the greatly improving sensitization efficiency resulting from SnO2 nanocrystals but also indicated that the development of Er3+ ions and SnO2 nanocrystals co-doped silica thin film could be a promising high-performance near-infrared luminous using broadband UV pumping.2.Developing an electrically driven near-infrared light emitter is essential for the success of future monolithic optoelectronic integration.Over past two decades,a large variety of promising near-infrared luminescent materials,including Ge nanocrystals,impurities(Boron,Phosphorus)doped Si nanocrystals,Ⅳ binary alloy(SiGe,GeSn)films and III-V compound(InP,GaAs)materials,has been extensively investigated to achieve high-efficiency near-infrared emission.Among these different material systems,Erbium ions(Er3+)have been considered as the most promising candidate for near-infrared light emitter,since the unique 1.55 um emission coincides with the absorption minimum window of silica-based optical fibers and can be connected directly with the optical communication network.Although the obviously enhanced 1.54 μm characteristic emission have been demonstrated in our group under optical excitation conditions,until now no electrically driven Er3+-related laser has ever been reported.The major challenges for electrically driven Er3+ doped silica fiber are uncomfortably high driven voltages and ultralow electroluminescence(EL)emission efficiency,owing to the excellent insulation of silica host and intrinsic concentration quenching effect of Er3+,respectively.In this thesis,we designed and fabricated prototype infrared light-emitting devices containing Er3+ ions and size-tunable SnO2 QDs.The current-voltage curve of our device suggested the space charge limited current(SCLC)model.A strong near-infrared EL emission was experimentally observed with EL onset voltage below 10V.By use of SnO2 QDs with average size of 5nm as sensitizers,the near-infrared electroluminescence efficiency from Er3+ions was obviously enhanced by 30 times.We anticipated that our results would be a starting point for future researches on improving efficiency of Si-based on-chip light source.3.We demonstrated a CMOS-compatible method to fabricate amorphous SiO0.73 thin films doped with Bi ions.It exhibited greatly enhanced near-infrared characteristic emission originated from Bi ions by nearly 60 times via Si QDs size control.The optimal energy transfer efficiency(ETE)increased up to 92.1%by use of 4nm Si QDs as sensitizers.As a comparison with recent studies,by the similar calculation method,the ETE between Bi and Ho ions in oxyfluoride germanate glass was calculated as only 65.3%while that between Bi and Er ions in yttrium oxide was calculated as 70%.Besides,it is common knowledge that the product of emission cross-section and corresponding lifetime is a critical parameter to evaluate the optical amplification and laser media sin ce this product is proportional to amplification gain and inversely proportional to laser oscillation threshold.For Bi ions implanted amorphous SiO0.73 thin films,σem × τproduct was calculated as 4.2×10-23 cm2s,which was much larger than that in silicate glass(～7.0×10-24 cm2s)and Al-doped optical fibers(5.6×10-24 cm2s),which could be induced by high-efficient sensitization of Si NCs.We anticipated this Bi-doped near-infrared light emitter would be a new starting point for future research in boosting outputs of optical amplifiers.4.We introduced the fabrication process of novel liquid cells for in situ TEM and then reported in situ study of Fe3Pt-Fe2O3 core-shell nanoparticle growth by use of liquid cell transmission electron microscopy(TEM).By controlling the Fe to Pt ratio in the precursor solution,we achieved the growth of nanoparticles with the formation of an iron-platinum alloy core followed by an iron oxide shell in the electron beam-induced reactions.There is no substantial change in the growth kinetics of the iron oxide shell after the iron-platinum alloy core stopped growth.The core growth was arrested by depletion of the platinum precursor.Heteroepitaxy of Fe3Pt[101](core)‖α-Fe2O3[111](shell)was observed in most of the nanoparticles while polycrystalline iron oxide shell is developed eventually for strain relaxation.Our studies suggested that Pt atoms catalyze the reduction of iron ions to form the Fe3Pt alloy core and when Pt is depleted a direct precipitation of iron oxide results in the core-shell nanostructure formation. |
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