Sub-Bandgap Photo-Response of Chromium Hyperdoped Black Silicon Photodetector Fabricated by Femtosecond Laser Pulses

As the main component of silicon (Si)-based Optic Electronics Integrated Circuit (OEIC) chip, Si-based infrared photodetector operating at communication wavebands is very important. In this paper, we report a kind of chromium (Cr)-hyperdoped black Si material fabricated using femtosecond laser pulses irradiation. The concentration of the Cr atoms in the black Si layer exceeds 10
²⁰
cm
⁻³
and the Cr-hyperdoped Si has a large sub-bandgap absorptance (~60% for
$1.31 \boldsymbol {\mu }\text{m}$
). The deep-energy level introduced by Cr impurity is 0.39 eV below the bottom of conduction band and thus the ionized electron concentration is very low (~10
¹⁵
cm
⁻³
). Owing to the excellent sub-bandgap absorption of Cr-hyperdoped Si, face-to-face black Si photodiodes are fabricated. Under illumination of
$1.31 \boldsymbol {\mu }\text{m}$
light, the responsivity of the photodiodes based on N
⁺
-N junction reaches 0.57 A/W at 4.3 V bias. In addition, the rise and delay time of the device to the infrared light are on the order of milliseconds.