Research of High-Efficiency Silicon-Based Light-Emitting Devices

利用sps^*紧密结合模型研究了Si/Ge人造晶体的电子结构。对于由两层Si和Ge单分子层叠加而成的晶体，电子在GAMMA点的波函数与块体Ge中L点的波函数非常相似，因此在GAMMA点的导带能量取局部最小值。通过拉长键长，晶体呈现直接跃迁型结构。这种晶体具有潜在的可见光发射特性，是传统的基于原子随机化学吸附的外延方法难以形成的。因此，研究了一种原子层外延（ALE）方法，其中晶体以一层接一层的方式生长。采用新引入的原子氢和SiH_2Cl_2，首次实现了Si-ALE方法，并获得了理想的（每循环一个单层）生长速率。在400 ~ 518‰的温度范围内，原子氢和GeH_2 (CH_3) _2交替暴露，也证明了Ge-ALE具有理想的生长速率。研究了锗和硅异质晶体，即锗在硅上的生长和硅在锗上的生长。对于前者，存在一个问题，即表面被单层的Ge所覆盖。对于后者，存在一个问题，即大量的碳原子被吸附在表面。

Electronic structures are investigated for Si/Ge manmade crystals using an sps^* tight binding model. For the crystal stacked with two monolayrs of Si and Ge, wavefunction of electrons at the GAMMA point is very similar to that at the L point in bulk Ge, and thus the energy takes the local minimum in the conduction band at the GAMMA point. By elongating the bond length, the crystal takes the direct-transition type structure.This crystal, having potentially visible light emission characteristics, is difficult to be formed by conventional epitaxial methods based on random chemisorption of atoms. Thus an atomic layr epitaxy (ALE) method has been investigated where the crystal is grown with a layr-by-layr manner. The Si-ALE method has been achieved using newly introduced atomic hydrogen and SiH_2Cl_2, for the first time, with an ideal (one monolayr per cycle) growth rate. And the Ge-ALE with the ideal growth rate has been also demonstrated by alternative exposure to atomic hydrogen and GeH_2 (CH_3) _2 for a wide temperature range from 400ﾟC to 518ﾟC.Ge- and Si- hetero ALEs, i.e., growth of Ge on Si and that of Si on Ge, has been investigated for making the manmade crystals. As for the former, there was a problem that the surface is covered by Ge of one monolayr. As for the latter, there was a problem that a lot of carbon atoms are adsorbed on the surface.