Andrew Meng1 Michael Braun1 Colleen Fenrich1 Muyu Xue1 Ann Marshall2 James Harris3 Paul McIntyre1

1, Materials Science and Engineering, Stanford University, Stanford, California, United States
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.