| Patterns regularly found in nature are always aesthetic experiences for us.Examples include spiral arrangements of distant nebulaes,ripples formed after a breeze puffed across the lake,six symmetric structure of snowflakes and atoms in crystals.Besides their aesthetic aspects,patterns change the ways of wave propagation and laid the foundations for modern electronic and optical devices providing functions not intrinsically available in the building blocks that form them.Patterns and Textures are the basis of the semiconductor devices,while the modulation of surface properties of functional materials is the key factor to the performances of devices.For example,carefully designed patterns fabricated on solar cells,light emitting diodes,and photodetectors can greatly increase the energy conversion efficiencies.Engineered defective sites on semiconductors offer the opportunities for the design of novel optoelectronic devices with functions that are not intrinsically available.In order to obtain devices with impressing properties and outstanding performances,it is essential to develop novel processing technology and to realize the control of semiconductor band structure engieering.Gallium arsenide(GaAs)and zinc oxide(ZnO)are typical optoelectronic semiconductors,which has been widely used in a wide variety of applications,such as solar cell,optoelectronic devices,etc.This paper was performed around the optical and mechanical methods for modification of semiconductor materials GaAs and ZnO,aiming at obtaining outstanding properties,such as near-infrared light promoted wettability recovery of superhydrophilic ZnO,photoresistless fabrication of periodic patterns on GaAs wafers by laser interference photochemical lithography,plasticity promoted band structure engineering achieved by arrayed indentation on GaAs wafers for the first time to obtain visible fluorescence emission,and so on.This dissertation is divided into six parts.The first chapter mainly introduced the research background and significance of our work,including the comparsion of the main micro-and nano-fabrication technologies,modulation methods of band structures of semiconductors(such as temperature,doping,quantum size effect,heterojunction,strain,UV irradiation,etc.),surface plasmons and research ideas and problems solved in this paper.In the second chapater,photoresistless fabrication of periodic patterns on GaAs wafers by laser interference photochemical lithography was reported.Detailed research contents are as follows.(1)A facile photochemical method based on laser interference etching for fabrication of two-dimensional(2D)gratings and quasi-hexagonal photonic patterns on GaAs wafers was reported.(2)The structures and periods of the patterns could be adjusted by changing the number of beams and by tuning the incident angles,respectively.The shape of interference patteren was determined by the number of beams,and the interference period was related to incident angle.(3)We found that the optical reflectivity of the etched samples was greatly reduced,especially for samples after three-beam interference etching with the minimum average reflectance of less than 2%,which could be easily adopted for fabricating anti-reflection layer of solar cells.(4)Photoluminescence(PL)study showed that slightly blue shifted PL peaks could be observed due to quantum confinement effect.In the third chapter,near-infrared(NIR)light promoted wettability recovery of superhydrophilic ZnO was investigated.Detailed research contents are as follows.(1)An intelligent near-infrared light controlled technology on dynamically tuning hydrophilic state of ZnO wafers after UV treatment was reported.The hydrophilic state could be reversibly controlled by the alternation of UV and NIR irradiation and the recovery time could be reduced to 30 min.(2)Nanoscratch technology was used for the first time to pattern ZnO wafers,enabling the transiton of surface wetting ability from hydrophilic(63.3°)to hydrophobic(124.5°).(3)The NIR light-controlled recovery mechanism were studied for the first time and selective actuation of vibrational overtone transitions of hydroxyl(OH)band and background absorption of water in the NIR region were considered as the main cause.(4)XPS analysis showed that the binding energy peaks of Zn 2p and O 1s exhibit a back and forth phenomenon when applied UV and NIR irradiation alternately.(5)Further experiments showed a detailed demonstration that oxygen content and humidity in air were crucial factors in determining the recovery process.Water molecules could hinder the recovery of oxygen vacancy,while an oxygen-rich environment could promote the recovery rate,supporting our model proposed above.In the forth chapter,nanomechanical properties of photoelectric semiconductors ZnO and GaAs based on nanoindentation and nanoscratch technologies were studied.Detailed research contents are as follows.(1)A continuous stiffness mode based on nanosuite was used to investigate nanomechanical properties(hardness and modulus)of ZnO and GaAs.(2)During the nanoindentation tests for ZnO,a pop-in phenomenon was found in the loading-displacement curve,which could be attributed to the dislocation nucleation.(3)The wear depth of ZnO and GaAs apparently increased linearly as the applied load was increased.In the fifth chapater,plasticity promoted band structure engineering achieved by arrayed indentation on GaAs wafers was investigated.Detailed research contents are as follows.(1)A new method for convenient fabrication of patterned GaAs decorated by photochemically synthesized Ag nanoplates was reported,and a visible PL phenomenon of indented GaAs was recorded for the first time.(2)It was confirmed that defect levels(artificially introduced or intrinsic)and light illumination were the determining factors for the growth of Ag nanoplates on GaAs.Ag cations could be selectively reduced by electrons from 1)indentation damage,2)intrinsic defect levels,and 3)conduction band,which results in different surface morphologies.(3)Our PL studies further showed that the band edge emission of p-GaAs would greatly blue shift to visible region after the patterning process,with strong white light emission that could be easily perceived by naked eyes.(4)Further study showed that patterned GaAs decorated with arrayed Ag nanoplates could serve as excellent SERS substrate,and this unique composite semiconductor/metal structure could be a candidate of hydrophobic material.In the last chapter,we summarized the conclusions and innovative points of this dissertation,and previewed the further studies.Innovations of this dissertation are as follows.(1)A photoresistless method based on laser interference photochemical etching for fabrication of 2D gratings and hexagonal photonic patterns on GaAs wafers was reported.The optical reflectivity of the etched samples was greatly reduced,with a minimum reflectance less than 2%.(2)We presented a novel method that enables dynamical wettability control of ZnO surface by alternative UV and NIR irradiation.The NIR promoted wettability recovery has been studied for the first time and the mechanism might be associated with vibrational overtone transitions of OH band.(3)We presented a new method for convenient fabrication of patterned GaAs decorated by photochemically synthesized Ag nanoplates,and a visible PL phenomenon of indented GaAs was recorded for the first time.We believed that both electronic band structure and structural geometry should be considered for the growth of Ag nanoplates. |
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