HRXRD Characterization of MBE Epitaxial Materials and Related Nanostructures
Examensarbete för masterexamen
For high performance semiconductor electronics and optoelectronics, the quality of the materials used for device fabrication is critical to the device performance. Therefore, material characterization is an essential step in a device fabrication process. X-ray diffraction (XRD) is a powerful nondestructive technique for characterizing crystalline materials, e.g semiconductor materials. It provides information on structures, phases, preferred crystal orientations, and other structural parameters, such as average grain size, crystallinity, strain, and crystal defects. The aim of this thesis is to explore different configurations of the XRD system and measurement methods on different materials, and to understand better that for different materials which techniques provide the fastest and simplest approach to acquire the results. Different semiconductor materials including InAs & InGaAs thin films, and InAs nanowires were characterized in this project. All the materials were grown by molecular beam epitaxy (MBE). The InAs and InGaAs thin films were grown on GaAs substrate, with the layer partially or fully relaxed. High resolution XRD (HRXRD) measurements were carried out on these samples. Two methods, based on rocking curve (RC) scans and reciprocal space mapping (RSM), respectively, were used to calibrate In composition and to characterize strain relaxation. The two methods show consistent results, implying the accuracies. Considering the simplicity of the two methods, it is much easier and faster to get the tilt using the rocking curve method, whereas the RSM method requires less effort on measurement set up and calculation. However, the RSM method takes much longer scanning time compared to the RC method. The InAs nanowires were grown on Si (111) substrate. This is because nanowires with cubic crystal typically grow in the (111) direction and therefore they are often epitaxial grown on (111) substrate to achieve vertical aligned nanowire growth. However, it is widely observed that the crystallographic structure of GaAs, InAs, and some other III-V nanowires embody occasional staking faults (SFs) originating from the presence of mixed wurtzite (WZ) and zincblend (ZB) structures. Transmission Electron Microscopy (TEM) has been a powerful tool to characterize the crystalline phase in atomic scale, however, it usually require complex sample preparation and extremely high image resolution. In this work, different XRD configurations havebeen used to characterize the InAs nanowire crystalline structures. RC scans seems invalid to provide full information since the diffraction peaks from the WB and ZB structures appears at different offsets. RSM measurements were carried out under both HRXRD and x-ray lens configurations, showing similar results. TEM measurements were carried out to verify the XRD results.
Informations- och kommunikationsteknik , Materialvetenskap , Nanovetenskap och nanoteknik , Materialteknik , Nanoteknik , Information & Communication Technology , Materials Science , Nanoscience & Nanotechnology , Materials Engineering , Nano Technology