Preparation and optical properties of Ge and C-induced Ge quantum dots on Si

Pure Ge epitaxially grown on Si(100) at high temperatures forms typically 1 00-nm lateral size islands on top of a three- to four-monolayer-thick wetti ng layer. In stacked layers of Ge dots pronounced vertical alignment is obs erved if the thickness of the Si spacer layers is smaller than approximatel y 50 nm. Pre-growth of a small amount of C on Si substrate induces very sma ll 10 nm size Ge quantum dots after deposition of approximately two to thre e monolayers of Ge. Photoluminescence (PL) studies indicate a spatially ind irect radiative recombination mechanism with the no-phonon line strongly do minating. Strong confinement shift in the 1-2-nm-high and 10-nm lateral siz e dots results in low activation energies of 30 meV, which causes luminesce nce quenching above 50 K. For large stacked Ge islands with 13 nm thin Si s pacer layers we observe a significantly enhanced Ge dot-related PL signal u p to room temperature at 1.55 mum wavelength. This is attributed to a spati ally indirect transition between heavy holes confined within the compressiv ely strained Ge dots and twofold degenerated Delta state electrons in the t ensile strained Si between the Ge stacked dots. (C) 2000 Elsevier Science S .A. All rights reserved.