Fabrications Of Sub-wavelength Structures And Their Modulations For Optoelectronic Materials

Optical sub-wavelength structures possess many novel optical and electrical properties,such as,sensing and imaging,which have significant and diverse applications into biology,optoelectronics and magnetoelectronics.2D photonic crystals,Bragg reflectors,1D metal structures,nanogap electrodes are widely used to modulate the optical properties,such as enhancing efficiency of photoluminescence,Laman effect and absorbing effect.There are already many efforts on the development of novel fabrication processes for nanomaterials and nanodevices.Currently,the sub-wavelength structures vertical to the wafer surfaces are typically fabricated by film growth method.Whilst,the sub-wavelength structures within the wafer surfaces are fabricated by the state-of-the-art electron-beam lithography?EBL?,focused ion beam?FIB?lithography and NIL and optical lithography?DUV,EUV,etc.?,which are extremely expensive in facilities and fabrications,and also low-efficient.It is significant to develop a reproducible,reliable,mass-production and cost-efficient way to fabricate sub-wavelength structures.In this thesis,we contribute several fabrications of sub-wavelength structures and study their modulation on optoelectronic materials.The thesis is divided into four parts as following:1.The fabrication of periodic sub-wavelength structure and its applications in the modulation of photoluminescence property of black phosphorus?BP?.Periodic sub-wavelength structures of Si₃N₄/SiO₂ were grown by plasma enhanced chemical vapor deposition?PECVD?method.BP based MIR surface-emitting laser was then made by coupled the Si₃N₄/SiO₂ structures with layered BP on silicon,in which the BP was used as active gain materials.The BP photoluminescence modulated by the embedded Si₃N₄/SiO₂ structures was studied.The prototype laser was optically pumped at 3794 nm and lasing is observed at³765nm.This work demonstrates a first BP based light emitting device,which should pave a pathway towards monolithic integration of Si-photonics in the MIR range.2.The fabrication of two dimensional?2D?periodic sub-wavelength structures and their modulations on the photoluminescence properties of Er-doped Ga₂O₃.2D periodic structures were firstly fabricated by using?111?oriented P-typed Si wafers via a self-assembly of PS microspheres,and then Er³⁺doped Ga₂O₃ films were grown on the structured wafers by pulsed laser deposition method.The cathodoluminescence of the Er³⁺doped Ga₂O₃ films were investigated to be influenced by different groove depth and grating period of the 2D sub-wavelength Si structure and the growth conditions,such as temperature,oxygen pressure and annealing.The experimental results show that the specimen grown under 450?substrate temperature,0.1 mbar O₂ pressure and 900?annealing exhibits the strongest green emission,and the periodic gratings of the 2D Si structure can obviously enhance the cathodoluminescence phenomenon of the Er³⁺doped Ga₂O₃films.In addition,theoretical calculation how the periodic Si structures influence on the cathodoluminescence of the Er³⁺doped Ga₂O₃ films was further carried out.3.The fabrication of GSBT and GST periodic sub-wavelength nanopatterns by laser direct writing technique and their modulation on the photoluminescence of near-infrared quantum dots.One-dimensional?1D?and two-dimensional?2D?periodic sub-wavelength nanopatterns on III-V GaAs substrates were fabricated by using phase change materials(Ge₂Sb₂Te₅?GST?and Ge₂Sb_1.5Bi_0.5Te₅?GSBT?).Minimum feature sizes of¹5 nm and 220 nm were achieved on the GSBT and GST,respectively.The 1D and2D sub-wavelength nanopatterns with 14 nm/220 nm feature size are successfully transferred to GaAs substrates and Au thin films.A²0 fold enhancement of photoluminescence was observed in the transferred sub-wavelength nanopattern of quantum dots embedded into Au films.4.The fabrication of Ti/SiO2 bilayer slit and its modulation application in nanogap electrodes.A sub-wavelength slit?⁵ nm?has been developed on Ti/SiO₂ bilayer film by laser direct writing?LDW?lithography technique,which is about 1/80 of wavelegth of the LDW system?405 nm laser and 0.9 NA objective?.Whilst,nanogap electrodes were also developed by laser induced thermal oxidization method,in which a 5 nm nanogap electrode with¹.6?10⁵ ON/OFF ratio was realized.The mass-production of nanogap electrodes array with⁵?10⁵ gaps was also achieved.The interaction between the focused laser and titanium film was theoretically studied.