Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate-controlled graphene-silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈10 ), a very high photoresponsivity (≈70 A W ), and a low dark current in the order of µA cm in a wide wavelength range (395-850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene-field-effect transistor-based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.

A high‐responsivity near‐infrared photodetector is demonstrated using a transparent ZnO top gate‐modulated graphene/Ge Schottky junction. The responsivity of a graphene/Ge junction photodetector characterized with a scanning photocurrent microscopy system is improved to 0.75 A W−1. This result is 5 to 35 times higher than the previously reported graphene/Ge photodetectors that did not use gate modulation. The detectivity is also improved to 2.53 × 109 cm Hz1/2 W−1 at Vg = −10 V from 0.43 × 109 cm Hz1/2 W−1 at Vg = 0 V. The performance of this gate‐modulated graphene/Ge Schottky junction base infrared (IR) detector is comparable to a commercially available IR photodetector, but the fabrication process is much simpler and compatible with glass or flexible substrates.

The performance of a graphene/Ge Schottky junction near-infrared photodetector is significantly enhanced by inserting a thin Al2O3 interfacial layer between graphene and Ge. Dark current is reduced by two orders of magnitudes, and the specific detectivity is improved to 1.9 × 1010 cm ⋅ Hz1/2W−1. The responsivity is improved to 1.2 AW−1 with an interfacial layer from 0.5 AW−1 of the reference devices. The normalized photo-to-dark current ratio is improved to 4.3 × 107 W−1 at a wavelength of 1550 nm, which is 10–100 times higher than those of other Ge photodetectors.

A graphene photodetector decorated with Bi2Te3 nanowires (NWs) with a high gain of up to 3 × 104 and wide bandwidth window (400–2200 nm) has been demonstrated. The photoconductive gain was improved by two orders of magnitude compared to the gain of a photodetector using a graphene/Bi2Te3 nanoplate junction. Additionally, the position of photocurrent generation was investigated at the graphene/Bi2Te3 NWs junction. Eventually, with low bandgap Bi2Te3 NWs and a graphene junction, the photoresponsivity improved by 200% at 2200 nm (~0.09 mA/W).

Simultaneous optimization of detectivity and dark current is successfully achieved by modulating the Schottky barrier height of a graphene/p‐type silicon photodetector from 0.42 to 0.68 eV by doping graphene with polyethyleneimine (PEI). At a barrier height modulation of 0.26 eV, the dark current is reduced by three orders of magnitude from 980 nA to 219 pA, and the detectivity is improved by 529% at 850 nm when compared to undoped graphene/p‐type silicon photodetectors. Such a significant performance enhancement confirms that the chemical doping of graphene before device fabrication is a simple yet highly efficient approach to improve the detectivity of heterojunction photodetectors.