2, Stanford Nano Shared Facilities, Stanford University, Stanford, California, United States
3, Electrical Engineering, Stanford University, Stanford, California, United States
Germanium-tin is a promising material for novel devices for optical sensing in the mid-IR region. For sufficiently high Sn compositions, the material has a direct band-gap near 0.5 eV, and could have applications either as a detector or as an emitter. The main challenge to growth of high-quality single crystals is the large lattice mismatch of the system (~14% for diamond cubic Sn on Ge) and the low equilibrium solubility of Sn in Ge (~1%). Demonstrations of core-shell Ge/GeSn nanowire structures have shown that it is possible to take advantage of a thin nanowire as a compliant substrate for high quality single crystal growth.1,2 In this work, we show that a Ge nanowire can act as a template for both axial and radial growth of Ge/GeSn heterostructures by controlling H2 partial pressure during CVD growth of GeSn. We are also able to achieve different Sn compositions varying from 2% to 10% using this method as confirmed by STEM-EDS and photoluminescence measurements. With control over axial to radial growth of GeSn heterostructures, a much wider possibility of device architectures can be achieved.
1Meng, A. C., et al., Nano Letters (2016) 16 (12), 7521.
2Assali, S., et al., Nano Letters (2017) 17 (3), 1538.