含鍺之Si(100)-2x1表面上矽鍺原子的鑑別與分佈

Abstract

本論文研究含鍺之Si(100)-2□1表面上矽鍺原子的鑑別以及分佈。實驗方法是將Cl曝滿在Ge/Si(100)-2x1表面上，利用掃瞄穿隧顯微鏡(STM)觀察樣品表面。實驗結果顯示，由於電子親和力的差別，和Ge鍵結的Cl會比和Si鍵結的Cl擁有較大的電子雲密度，因而在掃描穿隧式顯微鏡下看起來會比較明亮，據此我們可以從STM以影像上清楚分辨Ge原子和Si原子的位置。藉由數點STM影像上Ge-Ge,Ge-Si,和Si-Si雙原子單體(dimer)的比例，並對照機率運算的模擬結果，可以得知在磊晶過程當中，Ge原子是隨機和基板上的Si原子作交換的。當含鍺的Si(100)-2x1樣品升溫到690K時，經由先前的同步輻射光譜可以得知此時表面的Ge會和第二層的Si作交換，表面不再有Ge原子存在。在STM影像中我們確實看到此現象，並且發現Ge/Si混合表面原有的2xN結構在此時消失，而表面缺陷的長軸方向變成沿著dimer row 的方向。表面缺陷的長軸長度均為奇數個雙原子單體，此因缺陷底部的斷鍵重構而造成。

Growth of Ge on Si substrate is an prototipical system for the study of strained semiconductor heteroepitaxy. However, there are no effective ways to identify individual Ge atoms from Si on the Ge/Si(100)-2x1 surface. On the chlorine saturated Ge/Si(100)-2x1 surface, with the help of the different electron density of state, Ge atoms are identified from Si clearly in the STM images. Through the comparison of the mathematical simulation and the data counted on the STM images, we proved that either atom in a Si-Si dimer and the Si atom in a Si-Ge dimer is equally likely to exchange with the deposited Ge atom during the kinetic, replacive adsorption process. On the Cl:Ge/Si(100)-2x1 surface, Cl induced Si surface segregation will take place at ~650K. This phenomenon has been monitored by the synchrotron radiation photoemission spectroscopy. From STM images of the Cl:Ge/Si(100)-2x1 surface taken at 690K, no germanium bonded with surface chlorine were observed. After the Ge/Si exchange reaction taking place at 650K, the long axis of the vacancy island tends to be parallel to the dimer raw direction. It is very different from the ( 2 x N ) reconstruction of the Ge/Si surface. The length of the vacancy islands is counted from STM images, and it tends to be (2n+1) missing dimers. This could be reasonable explaned by the stable reconstructed configuration of nDVs. Based upon the analysis of density of dangling bonds per unit cell we demonstrate that the vacancy islands with (2n+1)DVs in length are more stable than the vacancy islands with (2n)DVs in length.