EELS-HAADF combination for characterization of a new AlN/GaN DBRs growth method.

摘要: Group III nitride materials promise production of optoelectronic devices that cover the entire visible range thanks to their widely–tunable room–temperature band gap energy. Nevertheless, in–plane lattice mismatch between the binary components is an issue affecting their design and growth. This causes proneness of the structures to present defects at the interfaces between compounds, finally decreasing the overall performance of the devices. In the present case we deal with a heterostructure of the binaries AlN/GaN for the configuration of distributed Bragg reflectors (DBR)[1-3].This work proposes a new method for the growth of high reflectivity, crack–free, AlN/GaN DBRs. This new method has been tested by growing 6, 10 and 20 period samples that are presented and characterized through various techniques. Reflectivity and X-ray diffraction reciprocal space mapping (XRD–RSM) measurements have been performed. These methods are useful for testing optical and structural properties of the samples, viewed as a whole. Moreover, the sample is thoroughly probed at a local scale through combined high angle annular dark field (HAADF) and low-loss electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) equipped with an aberration corrected and a monochromator. Our own-made computer routines are presented as they are useful in the automatization of the analysis of this kind of spectra [4-5]. The combination of these techniques and the great quality of the measured data allows us to recover information of the sample at the nanoscale, with sub-eV energy resolution (for the EEL spectra [6 …