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

We report the demonstration of a Ge_0.95Sn_0.05 on silicon (Ge_0.95Sn_0.05/Si) avalanche photodiode (APD) having a separate-absorption-charge-multiplication structure, wherein a Ge_0.95Sn_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_0.95Sn_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.