Fabrication of SiGe nanostructures for infrared devices


F. Schäffler



The prospect of light emission from the indirect band gap SiGe material system was always a driving force for dealing with low-dimensional structures in this material system. Within IR ON, Project P02 is responsible for most of the SiGe-related material base and for nanostructuring of SiGe heterostructures, with the aim of near- and mid-infrared device applications.

P02 pursues on the one hand epitaxial Stranski-Krastanow (SK) growth of compressively strained Ge on Si, and quantum well (QW) growth of both compressively strained Ge and tensile strained Si on Si, Ge and SiGe substrates. On the other hand, a new material base will be introduced into the IR-ON consortium with the alloys GeSn and Ge:C, which aim toward direct-gap group-IV semiconductors. While Ge:C is an entirely new material class, interest in GeSn is presently being revived as a potentially superior alternative to heavily doped Ge, which has led to the recent demonstration of band gap lasing. Both Ge-based alloys exploit material and strain engineering to shift the conduction band minimum of Ge from the L point to the Γ point.

Compressively strained Ge-on-Si is an advanced material system that has become prototypal for the investigations of SK growth. A particular feature of this material combination is the feasibility of introducing a high degree of order and size homogeneity into SK growth by providing preferential nucleation sites via nanostructured substrates. Significant contributions to this field were made during the first funding periods of IR-ON, which are now being exploited for the implementation of a SiGe-based near infrared emitter. For this purpose, we will continue our attempts from the last funding period, where we developed a technology platform for the implementation of photonic crystals (PhC) with embedded, ordered Ge islands that are located on well-defined positions of the PhC with a high density of states. The aim here is to demonstrate superior room temperature (RT) light emission, as compared to hitherto reported group-IV emitters.

Besides epitaxial growth and nanostructuring, P02 will also provide structural characterization of the SiGe material base, in particular plan view and cross sectional transmission electron microscopy. This is of special importance for both the elemental QWs and the new Ge-based alloys, which require optimized growth conditions for the suppression of defects and dislocations.

P02 is closely related to P12, which is responsible for most of the optical characterization. There are also close connections to P06, P07, and P11, especially with regard to the newly introduced Ge-based alloys, and new attempts to shift radiative recombination further into the infrared range by combining strained QWs of pure Si and pure Ge on a SiGe pseudosubstrate.