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

Abstract

Pure Ge epitaxially grown on Si(100) at high temperatures forms typically 100-nm lateral size islands on top of a three- to four-monolayer-thick wetting layer. In stacked layers of Ge dots pronounced vertical alignment is observed if the thickness of the Si spacer layers is smaller than approximately 50 nm. Pre-growth of a small amount of C on Si substrate induces very small 10 nm size Ge quantum dots after deposition of approximately two to three monolayers of Ge. Photoluminescence (PL) studies indicate a spatially indirect radiative recombination mechanism with the no-phonon line strongly dominating. Strong confinement shift in the 1–2-nm-high and 10-nm lateral size dots results in low activation energies of 30 meV, which causes luminescence quenching above 50 K. For large stacked Ge islands with 13 nm thin Si spacer layers we observe a significantly enhanced Ge dot-related PL signal up to room temperature at 1.55 μm wavelength. This is attributed to a spatially indirect transition between heavy holes confined within the compressively strained Ge dots and twofold degenerated Δ state electrons in the tensile strained Si between the Ge stacked dots.