Si–Ge–Sn alloys grown by chemical vapour deposition: a versatile material for photonics, electronics, and thermoelectrics

Abstract

Si–Ge–Sn alloys are offering unusual material properties with a strong potential to add a variety of functionalities to advanced CMOS technology. Being a group IV alloy, SiGeSn can be monolithically integrated on Si. The discovery of a direct band gap at Sn concentration above 8%, the extremely small effective mass for electrons and holes as well as the pronounced phonon scattering are opening new opportunities for Si photonics, high frequency devices and thermoelectrics. Si–Ge–Sn alloys with Sn concentration far beyond the solid solubility limit are metastable, artificial materials, which request challenging growth conditions. In this paper the epitaxial conditions for Si–Ge–Sn alloys to achieve precise control of the Sn content, to manage the lattice mismatch and defects, as well as to fabricate doped layers are discussed. The applied process control allows for epitaxy of group-IV heterostructures, required for typical devices for photonic and electronic applications. In this context, lasers and nanowires MOSFETs are discussed in this paper. In additions, the thermal conductivity is investigated as a critical material parameter to obtain a high thermoelectric figure of merit in GeSn alloys.

Isothermal Heteroepitaxy of Ge1–xSnx Structures for Electronic and Photonic Applications

“…Different from laser structures, which typically require thick layers and very large Sn contents, to widely separate the Γ and L- valleys of the conduction band, for electronic transport thin defect-free Ge 1– x Sn x layers or quantum wells (QWs) heterostructures are desirable. Such advanced heterostructures, which employ Ge or Si 1– x –y Ge y Sn x barrier layers to define Ge 1– x Sn x QWs, are extremely challenging for the epitaxial growth . For example, even the simple growth of a stack in which a Ge 1– x Sn x layer is deposited on another Ge 1– y Sn y , x < y layer (inverse step Sn composition) cannot be easily performed.…”

“…Such advanced heterostructures, which employ Ge or Si 1– x –y Ge y Sn x barrier layers to define Ge 1– x Sn x QWs, are extremely challenging for the epitaxial growth. 12 For example, even the simple growth of a stack in which a Ge 1– x Sn x layer is deposited on another Ge 1– y Sn y , x < y layer (inverse step Sn composition) cannot be easily performed. Indeed, to get a lower Sn content, one typically has to increase the deposition temperature.…”

Synthesis of High Sn Content Ge1–x–ySixSny (0.1 < y < 0.22) Semiconductors on Si for MWIR Direct Band Gap Applications

“…Since their experimental demonstration in 2003, Ge 1– x – y Si x Sn y alloys have not attracted the level of attention that Ge 1– y Sn y analogues have generated, even though the addition of Si introduces important benefits for semiconductor applications, including improved thermal stability and an additional degree of freedom that decouples lattice engineering from band structure tuning . A few review articles have summarized the work done to date and described possible applications. − The enhanced thermal stability of the ternary alloy with respect to that of the binary Ge 1– y Sn y analogues is important due to the inherent thermodynamic metastability of this system, which might not be compatible with the unavoidable heating that occurs during the operation of light-emitting optical systems. Therefore, the Ge 1– x – y Si x Sn y films integrated on Si may have important advantages over Ge 1– y Sn y as active layers in infrared (IR)-emitting devices.…”