Germanium-Tin on Si Avalanche Photodiode: Device Design and Technology Demonstration

We report the demonstration of a Ge
_0.95
Sn
_0.05
on silicon (Ge
_0.95
Sn
_0.05
/Si) avalanche photodiode (APD) having a separate-absorption-charge-multiplication structure, wherein a Ge
_0.95
Sn
_0.05
layer and a Si layer function as an absorption layer and a multiplication layer, respectively. Material characterization was performed by atomic force microscopy, X-ray diffraction, and transmission electron microscopy. The dark current I
_dark
of the APD is dominated by the area-dependent bulk leakage rather than the surface leakage. The temperature dependence of breakdown voltage of the Ge
_0.95
Sn
_0.05
/Si APD was characterized and a thermal coefficient of 0.05% K
^-1
was obtained, achieving a lower thermal sensitivity than the conventional III-V-based APDs. In the wavelength range of 1600-1630 nm, a responsivity of ~1 A/W (bias voltage V
_bias
= -9.8 V) was achieved due to the internal avalanche gain.