Studies Of High-resolution Electron Microscopy Methods And Its Applications In Semiconductors

High-resolution transmission electron microscopy?HRTEM?is one of the most effective methods for the characterization of crystal structures,especially of defect structures,at atomic resolution.Due to the influences of imaging aberrations of the electron optic systems and specimen thickness,HRTEM images may not reflect the crystal structures correctly.Therefore,it is essential to carry out the image contrast analysis and image processing if reliable structural information is to be obtained.In the last two decades,the presence and applications of spherical-aberration?C_s?correction techniques have led to a great improvement of HRTEM image resolution and have provided the researchers more experimental approaches.However,it is still hard to give a good explanation for the C_s-corrected HRTEM images under the present imaging theories,so it is necessary to make investigations on the related imaging theories and image processing methods.This dissertation can be divided into two parts: the first part shows the applications of HRTEM and deconvolution processing methods on the determination of defect structures in GaN films;the second part shows the research of non-linear imaging in the formation of S-corrected HRTEM images.Detials are as follows:1.The atomic configurations of different kinds of defects in GaN epitaxial film were investigated using a 200 k V transmission electron microscope with a point resolution about 0.2 nm.The image deconvolution processing was utilized to transform the [2???0] high-resolution images that do not directly reflect examined crystal structures to structure maps.Then the quality and resolution of the restored structure maps were furtherly improved via reflection amplitude correction.Although the interatomic distance of atoms Ga and N in the dumbbell is just 0.113 nm,which is far beyond the point resolution of the microscope we used,different kinds of atoms still can be recognized based on the image contrast analysis method.On the basis of these investigations,the structures,polarities and formation mechanisms of different kinds of defects were successfully determined,include stacking faults,partial,perfect and dissociated dislocations;several kinds of atomic configurations were determined from the experimental images for the first time.2.The non-linear imaging component in diffractogram?the Fourier transform of image intensity?was investigated through the transmission cross-coefficient?TCC?theory and the pseudo-weak phase object approximation?PWPOA?theory.By obtaining the exit wave function through PWPOA theory,the analytical expressions of linear?I₁????and non-linear?I₂????imaging components in diffractogram were derived based on TCC theory.The influences of specimen thickness and imaging parameters on I₁???and I₂???were analyzed.It is found that I₁???and I₂???is an odd and even function of C_s and ?f_eff,respectively.Based on these investigations,a method for separating I₁???and I₂???in C_S-corrected images was proposed and the influences of I₂???on the diffractogram and deconvolution processing were analysed.