Tuning Performance Parameters of Ge-on-Si Avalanche Photodetector–Part II: Large Bias Operation

The carrier multiplication phenomenon involves hot carriers, which gain kinetic energy while accelerating to equilibrium with the established avalanching electric fields, and is typically explained via the local avalanche model. This work presents two vertical Ge-on-Si avalanche photodetectors fabricated in a separate absorption, charge, and multiplication configuration. Uniformity in materials, doping densities, and device dimensions is maintained, except for the multiplication width, which is used as a control parameter to manipulate avalanching fields under identical electric biasing and illumination schemes. Nonlocal carrier multiplication model is implemented during analysis of the extracted current-voltage signatures under small and large reverse biasing arrangements. For such an APD characterized by thinner multiplication region
$\left ({{W_{m}=0.1 ~\mu m}}\right)$
, reduced linear and Geiger-mode multiplication regimes are perceived to be at play, outperforming the device having thicker multiplication region in almost all related figures of merit, e.g., responsivity
$(22.58 \mathrm {A/W})$
, photo-to-dark current ratio
$(\sim {10}^{5})$
, normalized photo-to-dark current ratio
$(2.5\times {10}^{9} \mathrm {W}^{-1})$
, specific detectivity
$(7.45\times {10}^{12}\mathrm {Jones})$
, and noise equivalent power
$(\sim 2.42\times {10}^{-15} \mathrm {W/}\sqrt {\mathrm {Hz}})$
. The enhanced performance characteristics are due to excessively strong avalanching fields, reduced thermal charge density, and negligible dead space compared to its counterpart characterized by thicker multiplication width.