Characterization of Wide-Bandgap Heterostructures by Reflectance-Difference Spectroscopy

本研究的目的是建立分析宽禁带异质结电子结构的技术。在这项研究中，我们开发了一种新的光学表征技术，称为反射差分光谱(RDS)。该技术实现了晶体生长过程中的原位表征。RDS谱揭示了定域在表面和界面的电子结构。在异质外延生长中，尤其是GaN/GaAs等异价体系中，对异质界面电子结构的理解和控制对于控制界面是非常重要的。RDS和反射高能电子衍射(RHEED)分别包含晶体结构的短程和长程有序化信息。因此，RDS和RHEED的同时观测实现了异质界面的详细原位表征。为了达到我们的目标，我们开发了安装在分子束外延(MBE)上的RDS和RHEED系统。我们应用…进一步将这一新发展起来的表征技术应用于生长在GaN(001)衬底上，得到了以下重要的结果：(1)我们使用了稀土等离子体源作为氮源。等离子体发光光谱使我们能够精确地控制等离子体条件。(2)首次观测到GaN的RDS光谱。GaN的禁带宽度约为3.5 eV，这是表征异质界面的窗口。这是该技术最重要的特点。(3)测量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)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，我们确认了新发展的光谱RDS和RHEED相结合最适合于宽禁带半导体异质结构的评估。并对这一新技术的实现进行了展望。较少

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