Development of Si-based light emitter has been eagerly anticipated in Si photonics. However, its realization is difficult because group IV semiconductors such as Si and Ge are indirect-transition semiconductors. Si or Ge quantum dots (QDs) on Si substrates have drawn much attention as Si-based light emitting materials because their optical transition probability can be enhanced by their quantum confinement effect. There are some kinds of QDs fabricated by various methods: Stranski Krastanov (SK) QDs (Eaglesham & Cerullo, 1990; Schmidt & Eberl, 2000), Ge nanoparticles in SiO2 matrix (Maeda, 1995), Si QDs by anodic oxidation (porous Si) (Wolkin et al., 1999; Cullis & Canham, 1991), and so on. In terms of the crystal orientation control, SK QDs have intensively attracted much interest. In general, the density of SK QDs is approximately 1010-11 cm-2 and the size is about 50-100 nm. In order to get strong light emission and quantum confinement effect, the higher density and smaller size are required.