Characterization of Wide-Bandgap Heterostructures by Reflectance-Difference Spectroscopy

本研究的目的是建立分析宽间隙异质结构电子结构的技术。在这项研究中，我们开发了一种新的光学表征技术，即反射-差分光谱（RDS）。该技术在晶体生长过程中实现了原位表征。RDS谱揭示了表面和界面的电子结构。在异质外延生长的情况下，特别是像GaN/GaAs这样的异质体系，了解和控制异质界面上的电子结构对控制界面非常重要。RDS和反射高能电子衍射（RHEED）分别包含晶体结构的短期和长期有序信息。因此，同时观察RDS和RHEED可以实现异质界面的详细的原位表征。为此，我们开发了安装在分子束外延（MBE）上的RDS和RHEED系统。我们将这种新开发的表征技术应用于GaAs（001）上生长的GaN，得到了以下重要结果。(1)我们使用re -等离子体作为氮源。等离子体发光光谱学使我们能够精确地控制等离子体条件。(2)首次观察到GaN的RDS光谱。GaN的GaN隙约为3.5 eV，这是表征异质界面的一个窗口。这是该技术中最重要的特性。(3)测定了不同生长条件下的RDS光谱。给出了生长条件与界面电子条件之间的关系。(4)此外，我们成功地表征了GaN生长过程中的界面。这些动态表征将为生长监测开辟新的领域。从我们的研究结果中，我们证实了新开发的RDS与RHEED相结合的光谱最适合于宽间隙半导体异质结构的评价。并对该新技术的实现作了展望。少

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