The Theoretical Study Of Dislocation Core Structures In Semiconductor Silicon And Zns

The function of the material is determined by its structure.The structure of silicon and ZnS determines that they have certain conductivity,but their conductivities are not strong,but as the temperature increases,the conductivity of them will enhance,so they has the properties of a semiconductor.They are main used to make semiconductor devices,high temperature materials,communication materials,electronic and optoelectronic devices,etc.,and are widely used in aerospace,medical and other industries.Although the two-dimensional materials have attracted much attention in recent years,and it has a broad application advancement,it cannot completely replace the status of traditional three-dimensional materials.In practical applications,the environment in which silicon and ZnS materials are located cannot remain unchanged,and in different environments,the problem of conversion between brittle and ductile of silicon materials and the plasticity problem of inorganic semiconductor zinc sulfide have been the focus of research.Since silicon and sphalerite ZnS are the diamond-structured crystal containing two sets of face-centered cubic lattices,there are two different types of slip systems on the{111}plane,namely glide-set and shuffle-set.In this work,the improved Peierls model is used to study the dislocation core structure in silicon and zinc sulfide.The main works are as follow:(1)The partial dislocations in semiconductor siliconConsidering the high temperature conditions observed in experiments,the glide layer dislocations of silicon dominate the plastic deformation.Then,at the temperature of brittleness and toughness transformation,there is still such a problem,whether dislocations can switch from one plane set to the other,and how does this process go on,that is also a problem which has been around for many years.In the past few decades,researchers have proposed many possible solutions to explain the properties of dislocations in silicon and their role in brittle-to-ductile transition,and to compare and discuss with reliable experimental and theoretical results.Under these given knowledges,it is still difficult to draw clear conclusions on this issue,and further research is needed to better understand the relationship between atomic-scale dislocation structures and their mobility.Under the current technical conditions,there is no way to observe the movement of dislocations on the atomic scale,and theoretical prediction has always been a common mothed.The Peierls model is the most ideal model for studying dislocation structures.It is good for dislocations with wide dislocation width,but the width of the partial dislocation in silicon is very narrow,and the discreteness cannot be ignored.Therefore,it is necessary to use a fully discrete Peierls model that is more in line with the actual material.In previous research work,we found that the two core reconstruction structures of the 90°partial dislocations in silicon can be obtained from theoretical predictions,based on which,we can predicted another core reconstruction structure of the 30°partial dislocation in silicon theoretically,and obtained a partial kink of 30°partial dislocation according to the new core reconstruction structure,thereby finding the minimum energy path for kink motion.It is expected that the path can be studied from atomic simulation in the future.(2)The screw dislocation in semiconductor siliconMost experimental and theoretical studies on diamond cubic materials refer to silicon as a model.At high temperature,that is,in the ductile region,most studies tend to the decomposed screw dislocations(two 30°partial dislocations)and decomposed 60°dislocations(a 30°partial dislocation and a 90°partial dislocation)determine the plasticity of the silicon,while the 30°partial dislocation is not so easy to move compared to the 90°partial dislocation,so it is believed that the plasticity of silicon is mainly determined by the 30°partial dislocation at high temperature.However,at low temperature,that is,in the brittle region,the effects of dislocations are less clear.In fact,deformation experiments performed under pressure confinement,or in scratch tests show that the dislocations do not decompose at low temperature,and dislocations are found in many directions,such as 30°dislocations,screw dislocations,and 60°dislocations,and there are even 41°dislocations that have not been studied.Whether these dislocations are located in the glide-set or the shuffle-set is not sure,although it is generally believed that these belong to shuffle-set dislocations.In order to understand the roles of glide-set and shuffle-set dislocations in the plastic deformation process,it is most important to study the mobility of these dislocations.From a geometric point of view,the dislocation of the shuffle-set is easier to move than that on the glide-set,because it only needs to destroy one covalent bond during the movement,and the glide-set needs to destroy three.Moreover,this conclusion is also confirmed by calculating the Peierls stress,in which the Peierls stress of the decomposed glide-set dislocation is about one order of magnitude larger than that of the undissociated shuffle-set dislocation.However,in the recent study of Peierls stresses on undissociated dislocations,the range of conclusions reached has exceeded the error range.The reason may be that it is not explicitly stated whether the undissociated dislocations are planar or non-planar dislocation.In order to solve this problem,based on the previously studied non-planar screw dislocations of cubic centered structures,using the formula of the interaction energy in unit length between dislocations to derive the four-fold dislocation equation with arbitrary angle between the slip planes,and obtained the dislocation structure and the related stress field and the displacement field.(3)Dislocation in the sphalerite ZnSInorganic semiconductors are generally brittle,but recently Oshima et al.found that zinc sphalerite-structured semiconductor zinc sulfide has extraordinary plasticity under completely dark conditions.They performed a room temperature deformation test of zinc sulfide(ZnS)under different light conditions and found that the zinc sulfide crystals immediately broke when deformed under light irradiation.On the contrary,it was found that zinc sulfide crystals can be plastically deformed in complete darkness until the deformation strain e_t=45%.In addition,the optical band gap of the deformed zinc sulfide crystal is significantly reduced.These results indicate that dislocations in zinc sulfide become mobile in complete darkness,and that doubling of dislocations affects the optical band gap across the crystal,indicating that the inorganic semiconductor is not necessarily brittle in nature.In the study by Oshima et al.,the effect of the deformation on the optical band gap was measured by uniformly deforming the zinc sulfide crystal.It is concluded that the stacking fault itself does not result in a reduction in the optical band gap of the deformed zinc sulfide,while partial dislocations can have a greatly reduced band gap around the dislocation core.While the current calculations do not explicitly deal with the actual dislocation core structure,this particular electronic structure of the partially dislocation core may have a strong influence on the band gap and color of the deformed zinc sulfide specimens,especially with rising dislocation density.