Laser-Crystallized Epitaxial Germanium on Silicon-Based Near-Infrared Photodetector

This work reports the fabrication of near-infrared (NIR) photodetectors based on laser-crystallized epitaxial germanium (100 nm) on silicon (001). The laser crystallized epitaxial germanium has an extracted dislocation density of $\approx 10$ ⁹ cm ⁻² . Metal-Semiconductor-Metal photodetectors fabricated on these films using Cr/Au as contact showed remarkable responsivity values of 0.64 A/W at 1550 nm and 0.71 A/W at 1310 nm for a 1V bias. Au/Cr-Ge contact exhibited ohmic characteristics with a contact resistance of $\approx 340$ ± $13~\Omega $ . The devices showed a time response with a rise time (10%-90%) of 3 s and fall time (90%-10%) of 5.2 s. The obtained high value of dark current is reduced by one order after passivating the Ge layer below contact with TiO ₂ (5 nm). TiO ₂ based devices showed a contact resistance of 3400± $283\Omega $ . Kelvin probe force microscopy (KPFM) was employed to map the surface potential across the MSM photodiodes to understand the current transport mechanisms. KPFM yields an Ohmic and Schottky contact in MSM diodes without and with TiO ₂ passivation layer, respectively. With further improvement in the device architecture; and optimization of the laser crystallization conditions of Ge film; these devices can be used as a potential candidate for various low-cost NIR applications, like on-chip integration of photonic circuits.