Self-assembling SiGe and SiGeC nanostructures for light emitters and tunneling diodes

Abstract

We report structural and photoluminescence (PL) investigations of self-assembling typically 100 nm lateral size Ge islands and 10 nm size C-induced Ge quantum dots in Si. The different recombination pathways are discussed for single and stacked dot layers. The aim is to evaluate different ways of using self-assembling quantum structures for Si-based emitters in the wave length range of 1.3 to 1.55 μm. The pre-growth of a small fraction of a monolayer C on Si(100) introduces nucleation centers for the subsequent formation of Ge islands which results in the formation of a high density of extremely small 10 nm size quantum dots. PL-studies indicate a spatially indirect radiative recombination mechanism with the no-phonon line strongly dominating. For larger 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 wave length. This is attributed to a spatially indirect transition between heavy holes confined within the compressively strained Ge dots and two-fold degenerated Δ state electrons in the tensile strained Si spacer layers between the stacked Ge dots. In the second part we present the preparation and I–V characteristics of Si/SiGe/Si p+/i/n+ Esaki diodes. The incorporation of a maximum amount of Ge within the i-zone increases the interband tunneling probability and thus, gives rise to an increased peak current density of about 3 kA/cm2 and a peak to valley current ratio of 4.2 at room temperature. The further increase of Ge content by incorporation of self assembling Ge islands within the intrinsic cone of the diode is discussed.