Study On The Growth Mechanism And Nucleation Theory Of InP Nanostructures

Ⅲ-Ⅴ semiconductor nanostructures has been the focus of attention in nanotechnology field over the past 20 years,due to its superior properties and potential applications in the field of basic science and optical electronics.In particular,the one-dimensional nanowires have been extensively studied in photonic devices including solar cells,light-emitting diodes,lasers,transistors,and photodetectors.Despite the great success of nanowires in both research and application,many challenges still exist in terms of synthesis,assembly,fabrication and the ability to form complex nanostructures.It has been demonstrated that nanostructures with twoand three-dimensional(2D and 3D)shapes can provide possible solutions.The different shapes of these nanostructures can improve the material properties and device functionality.Therefore,the study of the fabrication process and growth mechanism of nanostructures is of great significance for future research and application.This paper mainly studies the growth mechanism of nanostructures.For nanostructure(NS)growth,it takes place from thermodynamic dominant nucleation stage to kinetic dominant equilibrium crystal state(ECS).Although the NS morphology evolution is predictive under thermodynamic approach,this process has never been explored by kinetics.It has always been unclear about how the diffusion-induced growth works during the initially unstable nucleation stage.For better understanding of these correlated mechanisms,highly uniform arrays of wurtzite(WZ)InP NSs of ring-like and membrane geometries,grown by self-catalyzed selective area epitaxy(SAE)were utilized for theoretical analysis.The main achievements are listed as follows.(1).The initial process of nanostructure growth is the nucleation stage controlled by thermodynamics.Therefore,in order to further analyze and study the role of thermodynamics and kinetics in the growth process of nanostructures,we first studied the nucleation process of ring-like InP nanostructures.The thermodynamic model of nanostructures nucleation is established,and the critical radius of nucleation and the nucleation barrier at the corner of nanometer ring are calculated.It is found that the nucleation barrier at the corner is smaller than the plane,so the particle nucleation at the corner is preferred,which also explains the phenomenon that the inner ring rotation compared to the outer ring.It also gives us a better understanding of the growth mechanisms of nanostructures.(2).Through the analysis of membrane-and prism-nanostructures found in the shape of the growth process evolution,if only by thermodynamic factors explain the nanostructure growth process is not enough profound,the driving force of the growth process of nanostructure is the result of thermodynamics and kinetic mechanism work together,their interaction in the process of the whole shape evolution.The concept of "uniform diffusion effect" for the sidewall growth of nanostructures in different directions is proposed.Therefore,the previous explanation of shape evolution due to minimum energy cost could also be understood in kinetic way.Based on the above analysis,a kinetic model for the growth of nanostructures was established under the restriction of thermodynamic approach,and the growth rates of nanostructures in both transverse and longitudinal directions were calculated.A general time-dependent growth model of self-catalyzed NS in arbitrary shape is obtained under the restriction of thermodynamic approach.Finally,the formation mechanism of trenches on nanomembrane top facets is analyzed.