Study On The Measurement Methods Of Threading Dislocations In Semiconductor Material Heteroepitaxy And Their Applications

With the development of silicon-based optoelectronic integration,heteroepitaxial growth of ?-? materials on silicon substrate has attracted great attention due to the wide application of ?-? materials in optoelectronic devices,especially in light-emitting devices.When studying the quality of silicon-based ?-? materials,it is very important to accurately characterize the threading dislocation density,which can provide a basis for the improvement of heteroepitaxial growth technology and boost the realization of high-quality heteroepitaxial growth.Electron channel contrast imaging(ECCI),transmission electron microscopy(TEM),wet chemical etching and atomic force microscopy(AFM)are the main methods to characterize dislocations.This paper mainly studies the measurement accuracy and error sources of the above four dislocation characterization methods,especially the experimental study of ECCI test method,and obtains the optimal test conditions when using ECCI to measure GaAs/Si heteroepitaxial wafers.At the same time,through comprehensive analysis,the optimization scheme to improve the measurement accuracy is proposed.The main research work and achievements of this paper are as follows:(1)The working voltage of ECCI is determined by comparing the image contrast obtained under 10 kV,15 kV and 20 kV;By adjusting the tilt angle and rotation angle of the sample stage,the center cursor of the scanning electron microscope is aligned with the Kikuchi line corresponding to the intersection center of g(220),g(400),g(220)and g(400)of the GaAs epitaxial layer respectively,and the corresponding electron channel pattern(ECP)mode at the maximum contrast is determined;By fixing the working voltage and ECP mode and adjusting the tilt angle of the sample stage,the tilt angle of the sample stage with the best contrast is determined.Finally,the test condition of maximum contrast for ECCI in measuring GaAs/Si heteroepitaxial wafers is obtained:tilt the sample stage to Bragg angle(1.43°)at 15 kV,at the same time,aim the center cursor of SEM at the intersection of Kikuchi line corresponding to g(400)and g(220).(2)According to the experimental measurement,the characteristics of four dislocation characterization techniques,ECCI,TEM,EPD and AFM,are compared,and their measurement accuracy and application scenarios are analyzed.Some testing methods are proposed,such as surface ECCI testing at very shallow depth,combination of plane ECCI and section ECCI,combination of plane ECCI and section TEM,etc.(3)The characterization of GaAs/Si grooved mesa samples was completed,and the basic conditions of the mesa epitaxial growth samples were obtained according to XRD,PL,ECCI and AFM measurements.It is observed that the penetration dislocation density increases at first and then keeps stable on the mesa dimension from 10 ?m to 500 ?m.The dislocation density of 10 ?m mesa dimension(6.7×10⁷ cm^-2)was about 27%lower than that of 50 ?m mesa dimension(9.2×10⁷ cm^-2).This work lays a foundation for the subsequent improvement and optimization of the heteroepitaxial process by investigating the correlation between the threading dislocation density and the mesa dimension.