Fig. 1. Schematic of bonding and layer transfer technique for GOI p-i-n structure fabrication.

Fig. 2. (a) SIMS doping profiles of B and As in Ge vertical p-i-n structure. Inset shows a corresponding cross-sectional TEM image of the fabricated GOI p-i-n structure at bonding interface. (b) HRXRD (004) 2θ−ω scan of as-grown Ge-on-Si and GOI p-i-n structure with that of bulk Ge as reference. Tensile strain of ∼0.15% for the Ge layer in the GOI was obtained. The values in the plot correspond to the respective peak 2θ−ω angles.

Fig. 3. (a) Cross-sectional schematic of a GOI vertical p-i-n photodetector (PD) and (b) its optical microscope image with a mesa diameter of 80 μm. The FESEM image above presents the cross-sectional view of the detector along the green solid line across the mesa.

Fig. 4. (a) Dark current density-voltage characteristic of GOI vertical p-i-n PDs with different mesa diameters. (b) Temperature-dependent study on dark current of GOI vertical p-i-n PD at −0.5  V.

Fig. 5. (a) Photocurrent of a GOI vertical p-i-n PD (mesa diameter of 250 μm) as a function of applied bias, with its dark I-V characteristic as a reference. Inset shows the corresponding measurement configuration. (b) Optical responsivity spectrum of GOI vertical p-i-n PD across C- and L- telecommunication bands. Inset shows the corresponding first-order derivative of the responsivity spectrum.

Fig. 6. Performance comparison of Ge-based PDs. i-Ge thicknesses for the corresponding Ge-on-Si and Ge-on-SOI devices (without AR coating) in the references (numbers in square brackets) were indicated. The i-Ge thicknesses for GOI PDs were not indicated due to their discrepant configurations (interdigitated lateral p-i-n [19] and waveguide-integrated [21]).

Fig. 7. (a) Frequency response of GOI vertical p-i-n PD (mesa diameter of 60 μm) at −2  V. Inset shows device series resistance extracted from I-V characteristics. (b) Calculated 3 dB bandwidth of GOI vertical p-i-n detector (Rs=30 Ω) with respect to its mesa diameter (red solid line). The dashed line represents the corresponding carrier transit-limited bandwidth. Inset shows linear interpolation of device capacitances at −2  V for de-coupling of junction and parasitic capacitances. (c) Calculated 3 dB bandwidth of the PD with mesa diameter of 10 μm with respect to i-Ge thickness.