Infrared (IR) photoresistors based on recrystallized amorphous germanium films on silicon using liquid phase epitaxy

In this work a heterogeneously integrated germanium (Ge) NIR photo-resistor fabricated on CMOS-compatible silicon substrates is presented. The resistor is fabricated on an epitaxial germanium films grown on silicon using a novel liquid phase crystallization (LPC) process. First, silicon wafers were coated with amorphous germanium deposited using PECVD. Next, Ge film is crystallized into epitaxial germanium using a thermal anneal cycle during which Ge undergoes melting and controlled cooling. The LPE Ge films is polycrystalline but epitaxial with threading dislocation density of ~10⁹ cm^-2. On the LPE germanium, NIR photo-resistors were fabricated with metal-semiconductor-metal (MSM) inter-digitated structure with an active area of 150 μm x 300 μm. Responsivity of the devices was characterized using a fiber laser, tunable from 1500 to 1600 nm. With 1550 nm excitation, a photocurrent of 100 μA was measured at a bias of 4V with laser power of 25 mW, corresponding to a responsivity of 4 mA/W.