A photocurrent amplifier operable
at low bias voltages with high
responsivity and detectivity is highly demanding for various optoelectronic
applications. This study shows majority carrier graphene-native oxide-silicon
(GOS) photocurrent amplifiers complying with the demands. The photocurrent
amplification is primarily attributed to the photoinduced Schottky
barrier height (SBH) lowering for majority carriers. The unavoidably
formed thin native oxide layer between graphene and silicon during
the wet graphene transfer process plays significant roles in lowering
of the dark leakage current as well as photoinduced SBH lowering.
As a result, the photocurrent to dark current ratio is as high as
∼12.7 at the optical power density of 1.45 mW cm–2. These GOS devices show a high responsivity of 5.5 AW–1 at an optical power (458 nm in wavelength) of 15 μWcm–2, which corresponds to ∼1400% quantum efficiency.
Further the response speed is as fast as a few ten-microseconds. Thus,
these GOS majority carrier photodiodes show the highest detectivity
(2.35 × 1010 cm Hz1/2 W1–) among previously reported graphene-silicon photodiodes. However,
the responsivity decreases with the optical power density due to the
increasing recombination rate through the interface states proportional
to the optical power density.