Study of semiconductor heterointerface using low-energy electron transmission spectroscopy

利用低能电子衍射（LEED）、俄歇电子能谱（AES）和低能电子透射能谱（LEETS）研究了Ge在Si及其异质界面上生长的初始阶段。对于在Si（001）表面上的Ge生长，LEED和AES测量显示，在5ML的覆盖范围内，Ge的生长以一层接一层的伪晶方式进行。超过5ML的覆盖范围，具有{015}刻面的小3D团簇外延生长，保持衬底取向。此外，LEED光斑分布的能量依赖性表明，晶格畸变仍然存在于由小的三维团簇组成的这一阶段。当使用As表面活性剂在Si（111）表面生长时，覆盖面积达到8ML， Ge以一层接一层的伪晶方式生长。进一步沉积Ge会导致晶格失配的松弛，并生长出与本体Ge具有相同晶格常数的Ge薄膜。相反，在没有表面活性剂As的情况下，Ge的生长以stranski - krstanov模式进行。LEED测量表明，锗岛的晶格常数比体锗岛小1.5%。由于生长温度高（500 C），生长速度非常慢（0.07ML/min），我们认为生成的岛是Si和Ge的合金。根据实验结果，我们推测As表面活性剂阻止了生长膜的合金化。LEET测量已用于在Si（001）和Si（111）表面生长的Ge薄膜。当表面活性剂为As时，在500℃的温度下，Ge在Si（111）表面生长时，LEET光谱表现出典型的量子尺寸特征，表明Ge/Si界面突变。相比之下，当表面活性剂As在600℃的温度下在Si（001）和Si（111）上生长时，没有观察到LEET光谱的量子特征。这些结果表明，LEETS提供了有关半导体异质界面结构的信息。

Initial stages of Ge growth on Si and its heterointerface have been investigated using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and low-energy electron transmission spectroscopy (LEETS).For Ge growth on Si(001) surface, LEED and AES measurements reveal that up to a coverage of 5ML, Ge growth proceeds in the pseudomorphic layer-by-layer fashion. Beyond a coverage of 5ML, small 3D clusters with {015} facets grow epitaxially keeping the substrate orientation. Moreover, energy dependence of the LEED spot profiles reveals that the lattice distortion still remains in this phase consisting of small 3D clusters.When growing on Si(111) surface with an As surfactant, up to a coverage of 8ML, Ge growth proceeds in the pseudomorphic layer-by-layer fashion. Further deposition of Ge leads to the relaxation of lattice misfit and growth of Ge films having the same lattice constant as bulk Ge. In contrast, Ge growth without the As surfactant proceeds in the Stranski-Krastanov mode. LEED measurements reveal that Ge islands have the smaller lattice constant by 1.5% than that of bulk Ge. We believe that the resulting island is an alloy of Si and Ge, since growth temperature is high (500ﾟC) and growth rate is very slow (0.07ML/min). Based on the results, we speculate that the As surfactant prevents the alloying of growing films.LEET measurements have been employed for Ge films grown on both Si(001) and Si(111) surfaces. For Ge growth on Si(111) at 500ﾟC with the As surfactant, LEET spectra exhibit characteristic quantum size features, suggesting the abrupt Ge/Si interface. In contrast, when growing not only on Si(001) but on Si(111) at 600ﾟC with the As surfactant, no quantum feature characteristic of LEET spectra was observed. These results indicate that LEETS provides information on the structure of semiconductor heterointerfaces.