Sb mediated Ge/Si(100) quantum dots for Si based photonics

Nowadays the search for an efficient silicon based light emitting source attracts a lot of attention, because the niche of the light emitter device for chip to chip communications is not yet occupied. Low quantum efficiency of radiative recombination in the bulk Si caused by an indirect nature of its band gap is the challenge to be bypassed. Up to the date the hybrid III-V on Si technology dominates, but other approaches are intensively investigated. Among of them there are promising SiGe/Si heterostructures, which can be grown by epitaxy on Si (100) substrates, e.g., in the form of quantum wells or quantum dots (QD). Thereby a Si p-n junction can be used to supply carriers to the light-emitting Ge/Si nanostructure. In spite of the fact that the bulk Ge itself has an indirect band gap, the energy band diagram of strained SiGe on Si is modified due to the elastic strain and the quantum confinement effect. The hetero junction SiGe/Si is characterized by so-called `type-II´ band alignment, where carriers are located on the opposite sides of the junction: electrons - in Si, but holes - in Ge. This fact might lead to a small overlap of the electron and hole wave functions and a low oscillator strength causing a low light emission. A possible solution of the latter problem might be found, if the carriers are strongly confined at the sharp Si/Ge hetero-interface. This can be realized via small Ge QDs of a very high density. In particular, high density of Ge QDs leads to the higher luminescence probability of Δ_xy - HH transitions [2]. Here Δ_xy are electronic states localized in the compressively strained Si between the QDs, HH is the heavy hole state in the QD.