MBE-Grown Ge0.92Sn0.08 Diode on RPCVD-Grown Partially Relaxed Virtual Ge0.92Sn0.08 Substrate

The binary alloy semiconductor
$\text{Ge}_{1-\mathrm{x}}\text{Sn}_{\mathrm{x}}$
is a promising candidate for the monolithic integration of optoelectronic circuits on Si due to its reported direct bandgap at specific Sn concentration and strain. However, while the directness of
$\text{Ge}_{1-\mathrm{x}}\text{Sn}_{\mathrm{x}}$
improves with increasing Sn concentration, compressive strain counteracts with this trend. Since too high Sn concentrations lead to high amount of crystal defects due to Sn segregation, the growth of strain relaxed
$\text{Ge}_{1-\mathrm{x}}\text{Sn}_{\mathrm{x}}$
would allow a decreasing Sn concentration and therefore an increasing crystal quality at once. The key issue is the growth of strain relaxed virtual
$\text{Ge}_{1-\mathrm{x}}\text{Sn}_{\mathrm{x}}$
substrates for the subsequent epitaxy of
$\text{Ge}_{1-\mathrm{x}}\text{Sn}_{\mathrm{x}}$
device structures, which seems to be the biggest obstacle with molecular beam epitaxy (MBE) so far. In this work, we report the epitaxy of partially relaxed Ge
0.92
Sn
0.08
layers via reduced pressure chemical vapor deposition (RPCVD), which serve as virtual substrate for the consecutive MBE of Ge
0.92
Sn
0.08
diode structures. This consecutive epitaxy process requires an extensive surface cleaning sequence, which had to be developed first. The quality of the grown diode structures was verified using X-ray diffraction (XRD). Furthermore, diodes were fabricated and electrically characterized. We will show that our approach is promising for high quality
$\text{Ge}_{1-\mathrm{x}}\text{Sn}_{\mathrm{x}}$
devices on Si.