Phosphorus Surface Segregation And The Influence Of Pre-deposited Phosphorus Atoms On The Formation Of Ge Quantum Dots

The study of impurity segregation during Si epitaxial growth is essential both technologically and scientifically. With the further reduction of device dimensions to deep-submicron and nanometer scale, precise control of dopant profiles and diminishing unintentional doping are essential for the electronic performance of devices. Most studies in this field have been concentrated on Sb doping in Si, P doping and P segregation behavior were much less studied, especially at low growth temperatures. Further understanding of the segregation behavior of P in Si MBE is required.In the first part of the thesis, the surface segregation of phosphorus in silicon at the temperature range of 250-450 ℃ is studied by using 5 doping structures grown by molecular beam epitaxy (MBE). The samples are characterized by synchrotron radiation X-ray crystal truncation rod (CTR) scattering and small angle X-ray reflectivity. The 1/e decay length of P segregation and segregation barrier energy are obtained by fitting the CTR curves within kinematical approximation of X-ray diffraction theory. The results show that surface segregation of P is strong at a growth temperature of 450 ℃, with a 1/e decay length of 14 nm. For growth temperatures below 350 ℃, P segregation is negligible with a 1/e decay length not larger than 4 nm, which means at these temperatures sharp dopant profiles and 8 doping structures can be achieved. The segregation barrier energy is determined to be 0.43 eV.Besides, the preparation of Ge quantum dots (QDs) of small size, high areal density and high uniformity (both in size distribution and spatial distribution) has been the target of numerous researches. It still remains a great challenge up to now. Surfactant- or impurity-mediated growth by various elements such as Sb and C has been shown to be able to change dot size and density significantly. However, the influence of P atoms on the growth of Ge QDs has not been studied. On the other hand, it has been shown that adding PH3 during Ge growth in chemical vapor deposition can greatly change the dot morphology.In the second part of this thesis, the influence of pre-deposited phosphorus atoms on the formation of self-assembled Ge QDs on Si(001) is investigated. The samples...