Estudios de nitruros aleados mediante técnicas de haces de electronesimagen, difracción y espectroscopía

Resumo

Group III-Nitride semiconductors have proven to be ideal candidates for a number of electronic applications and due to their immense success, are a subject of active research, both academically and industrially. To expedite the progress of these materials, characterization techniques need to be adapted to fit the necessity of this III-N research field. In order to improve the already existing methods of study and contribute to develop new methods for the fabrication of more efficient devices, a detailed understanding of the fundamental processes governing the functioning of these devices is necessary. Although Transmission Electron Microscopy (TEM) is a tool with the capability and versatility to provide information on an atomic length scale, with the reduction in the size of the active components and an increase in the inner complexity of these devices, new subtechniques of characterization need to be developed. The research presented in this thesis focuses on the use of TEM techniques to characterize several III-N nanostructures. This thesis can be divided into two main sections: Chapter 3, 4 and 5 present the development of novel techniques to advance the characterization of these heterostructures. In chapter 3, an improvement in the measurement of interplanar distances using electron diffraction is reported. The thin films studied here were a few hundred nanometres in height, thus making classical electron diffraction an ideal tool for their characterization. In chapter 4 and 5, the height of the layers of interest was only 2-3 nm, thus making use of selected area electron diffraction inappropriate. To overcome this problem, two novel methods were developed depending on nature of the information required from each sample. In chapter 4, a method to acquire accurate chemical information with high spatial resolution from InGaN quantum wells using high angle annular dark field scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy and Rutherford backscattering is presented. Chapter 5 presents a technique, to measure the electric field using nanobeam electron diffraction in a multi-quantum well (MQW) heterostructure with AlN barriers of 2nm high nanolayers. On the other hand, chapter 6 investigates the response of a GaN/AlN supperlattice to ion implantation. The structure did not show the expected degradation because of the implantation and its response deviated from the classically predicted behaviour. To explain the change in behaviour a model is developed and presented in this final results chapter.