Group IV elements are essential for modern standards of life including Si-based science and technology in a multitude of applications. Even though semiconductor technology based on group IV is a very mature field, the physical properties can be altered by the formation of metastable solid solutions possessing significantly altered physical properties.[1] The contribution will address challenges and strategies for the synthesis of metastable Ge-based solid solutions including hyperdoped compounds. In this context, the crystal growth of single crystalline nanowires (NWs) will be discussed and the changes in physical properties associated with their composition shall be highlighted.
All the crystal growth studies have been carried out at low temperatures using the solute as a metallic growth seed. Hence, this process could be described as a self-seeding of the targeted Ge_1-xSn_x solid solutions. This approach allowed the formation of highly crystalline, metastable Ge1-xSnx substitutional solid solutions.[2] A highlight is the transformation of Ge representing a typical indirect bandgap material into a direct bandgap material upon incorporation of 19 at% Sn. The high crystal quality and efficient incorporation following our strategy has been demonstrated for Ge_0.81Sn_0.19 NWs by recording their photoluminescence.[2] The absorption and emission in the mid-IR range (<~0.55 eV) makes Ge_1-xSn_x very attractive materials for CMOS-compatible optoelectronic devices based purely on group IV elements.
Our latest results demonstrate the formation of Ge_1-xSi_x and Ge_1-x-ySi_xSn_y nanowires by using Si-Ge single source precursors, which should enable the tailoring of bandgap and strain by compositional modulation in the solid solutions.    
 

References:
[1] S. Barth, M. S. Seifner and S. Maldonado,  Chem. Mater. 2020, 32, 2703.   
[2] M. S. Seifner, A. Dijkstra, J. Bernardi, A. Steiger-Thirsfeld, M. Sistani, A. Lugstein, J.E.M. Haverkort, S. Barth,   ACS Nano 2019, 13, 8047.
[3] R. Behrle, V. Krause, M. S. Seifner, B. Köstler, K. Dick-Thelander, M. Wagner, M. Sistani, S. Barth, submitted.