Characterization of Wide-Bandgap Heterostructures by Reflectance-Difference Spectroscopy

点击翻译按钮获取中文摘要

The purpose of this research is to establish the technique to analyze electronic structures of wide-gap heterostructures. In this research, we developed the new optical characterization technique so called reflectance-difference spectroscopy(RDS). This technique achieves in-situ characterizations during the crystal growth. The RDS spectra reveal the electronic structures localized at the surface and interface. In the case of heteroepitaxial growth, especially heterovalent system such as GaN/GaAs, understanding and control of the electronic structures at the heterointerface are very important to control the interface. RDS and reflection-high-energy-electron diffraction(RHEED) include information of short- and long-range ordering of the crystal structures, respectively. Therefore, simultaneous observation of both RDS and RHEED realize detailed in-situ characterization of heterointerfaces. For our goal, RDS and RHEED systems mounted on a molecular-beam epitaxy(MBE) were developed. We appl … More ied this newly developed characterization technique to GaN grown on GaAs(001), and got the following important resuts.(1)We used a RE-plasma source for nitrogen. Spectroscopy of plasma luminescence enables us to control precisely the plasma conditions.(2)RDS spectra of GaN were observed for the first time. The gand gap of GaN is about 3.5 eV, which acts as a window when we characterize the heterointerface. This is the most important feature in this technique.(3)We measured RDS spectra under various growth conditions. The results give relations between the growth conditions and the interface electronic conditions.(4)Furthermore, we succeeded to characterize the interface during the GaN growth. These dynamic characterizations will open new field of growth monitoring.From our research results, we confirmed that the newly developed spectroscopy, RDS, combined with RHEED is most suitable for the evaluation of the wide-gap semiconductor heterostructures. Moreover, an outlook to the realization of this new technique was made. Less