Atomic level characterization and property control of surface and interface in nitride semiconductor heterostructures

在该项目中，进行了原子级表征，以了解GaN异质外延1。UHVMBE-STM/AFM的构建为了在原子水平上表征和控制III族氮化物分子束外延生长，构建了新型无As UHVMBE-STM/AFM，能够对绝缘体进行原子分辨率成像. Si（111）衬底上GaN的生长及其极性控制通过富Ga重构的STM成像研究了Ga/N流量比对Si（111）衬底上直接生长GaN极性的影响。发现成核阶段的富氮生长条件对单N极性GaN的生长至关重要.金属-GaN接触的形成用STM研究了在GaN（0001）上沉积金属时出现的金属-Ga合金结构。在Au的情况下，形成c（2 × 12），并且在Ag的情况下，形成Ag膜。Ag薄膜在室温下是不稳定的，这表明形成良好欧姆接触的可能性很低.研究了GaN（0001）的卤素刻蚀，通过对GaN（0001）进行Cl暴露，利用STM观察退火前后的表面形貌。在Ga终止表面的情况下，蚀刻逐层进行，并且根据退火温度观察到台阶边缘蚀刻或平台蚀刻。通过ZrB_2缓冲层在Si（111）衬底上生长GaN二硼化锆作为Si衬底上生长GaN的缓冲层，近年来引起了人们的注意。用扫描隧道显微镜（STM）和原子力显微镜（AFM）研究了Si（111）衬底上外延生长的ZrB_2薄膜的表面结构和GaN在其上的生长过程。我们发现N极性GaN的生长与生长条件无关，而单极性GaN的起源是N极性GaN和Zr封端的ZrB_2的GaN（0001）-ZrB_2（0001）界面的稳定性。

In this project, atomic-level characterization was carried out in order to understand GaN heteroepitaxy1. Construction of UHVMBE-SPMIn order to characterize and control III-nitride MBE growth in atomic level, new As-free UHVMBE-STM/AFM, which is capable of atomic-resolution imaging of insulators, was constructed.2. Growth of GaN on Si(111) and its polarity controlThe effect of Ga/N flux ratio on the polarity of GaN directly grown on Si(111) was studied by the STM imaging of Ga-rich reconstructions. We found that the N-rich growth condition at nucleation stage is critical for mono N-polar GaN growth.3. Formation of metal-GaN contactMetal-Ga alloyed structures which appear upon depositing metals on GaN(0001) were studied by STM. In the case of Au, c(2x12) was formed, and in the case of Ag, ultrathin film was formed. The ultrathin Ag film was unstable at room temperature, which indicates that the possibility of forming a good ohmic contact is low.4. Halogen etching of GaNEtching process of GaN was studied by exposing GaN(0001) to Cl, and observe the surface before and after annealing using STM. In the case of Ga-terminated surface, the etching proceeds bilayer-by-bilayer, and either step-edge etching or terrace etching was observed depending on the annealing temperature.5. Growth of GaN on Si(111) via ZrB_2 buffer layerZirconium diboride is recently attracting attention as a buffer layer for GaN growth on Si. The surface structure of thin ZrB_2 film epitaxially grown on Si(111), and the growth process of GaN on it was studied using STM and AFM. We found that N-polar GaN grows regardless of the growth conditions, and that the origin of mono-polarity is the stableness of GaN(0001)-ZrB_2(0001) interface of N-polar GaN and Zr-terminated ZrB_2.