Electronicband modulation and formation of quantum tunneling structures by atomic-layer control of group-IV semiconductors

本课题的目的是通过对第四族半导体的原子层控制和原子序异质结构的引入，研究电子能带调制和量子隧道结构的形成，以阐明载流子输运/产生/重组过程的新特性，并创造新的电子能带调制半导体。利用B_2H_6和PH_3在Si，Si_<1-x bb_0 Ge_x和Ge表面上的表面反应，在抑制混合和低温孤岛的条件下，找到了B和P原子层形成的条件。此外，发现Si_2H_6作为比SiH_4更活泼的反应气体，可以有效抑制P在P吸附的Si（100）上的盖层生长过程中的P偏析，并使许多P原子聚集在厚度小于2 nm的界面薄膜区域，最大P浓度为3x10^<21> cm^<-3>（原子比6%）。此外，还发现这种P原子层掺杂结构比常规的均匀P掺杂Si具有更高的霍尔迁移率。通过不加热衬底的ECR等离子体CVD，在原子级平面的Si和Ge（100）表面实现了高应变的Ge和Si外延生长，并显示了高应变的族iv半导体异质结构的可能性（这是传统热CVD工艺难以实现的）。为了获得更高性能的p型共振隧道二极管，通过研究高质量Si_<1-x>Ge_x/Si异质结构外延生长的新条件，得出了在异质结构中增加Ge分数是达到室温工作的有效方法。这些结果对制造新型电子带调制半导体非常有用。

Purpose of this project is, by atomic-layer control of group-IV semiconductors and introduction of atomic-order heterostructures, investigation of electronic-band modulation and formation of quantum tunneling structures in order to clarify new properties of carrier transport/generation/recombination processes and creation of novel electronic-band modulated semiconductors. Utilizing surface reactions of B_2H_6 and PH_3 on Si,Si_<1-x>Ge_x and Ge surfaces, conditions for atomic-layer formation of B and P were found under suppression of intermixing and islanding at low temperatures. Additionally, it was found that, by using Si_2H_6 as a more reactive reactant gas than SiH_4,P segregation during capping Si layer growth on a P adsorbed Si(100) could be effectively suppressed and many of P atoms were incorporated in a thin film region at the interface with the thickness below 2 nm and the maximum P concentration of 3x10^<21> cm^<-3>(atomic ratio 6%). Moreover, it was also found that such P atomic-layer doped structures showed higher Hall mobility than the conventional uniformly P doped Si. By using ECR plasma CVD without substrate heating, highly strained Ge and Si epitaxial growth on a (100) surface of Si and Ge with atomic-order flatness was achieved, and possibility of highly strained group-IV semiconductor heterostructures was shown (which was difficult to be achieved by conventional thermal CVD processes). In order to achieve higher-performance p-type resonant tunneling diodes, by investigating new conditions for epitaxial growth of high quality Si_<1-x>Ge_x/Si heterostructures, it is concluded that increase of Ge fraction in the heterostructure is quite effective to reach room temperature operation. These results are very useful to create novel electronic-band modulated semiconductors.