BACKGROUND

1. Field

The present disclosure relates to an optical sensor, an image sensor, and/or more particularly, to an optical sensor and/or image sensor including graphene quantum dots to which a functional group is bonded.

2. Description of Related Art

Silicon semiconductors commonly used in optical sensors and/or image sensors exhibit significantly lower quantum efficiencies for the infrared ray band compared to quantum efficiencies thereof for the visible ray band. Therefore, other materials are being developed for optical sensors and/or image sensors. Optical sensors may be used for various purposes, including as a biometric authentication sensor, a low-light sensitivity enhancing device, a night vision sensor, and an autonomous navigation sensor.

SUMMARY

According to some example embodiments, an optical sensor includes a first electrode, a graphene quantum dot layer, and a second electrode on the graphene quantum dot layer. The graphene quantum dot layer includes a plurality of first graphene quantum dots bonded to a first functional group and a plurality of second graphene quantum dots bonded to a second functional group that is different from the first functional group. The graphene quantum dot layer may be on the first electrode.

In some example embodiments, the first functional group may be bonded to one or more carbon atoms at an outermost portion of the plurality of first graphene quantum dots, and the second functional group may be bonded to one or more carbon atoms disposed at an outermost portion of the plurality of second graphene quantum dots.

In some example embodiments, the plurality of first graphene quantum dots may be configured to absorb light of a first wavelength band, and the plurality of second graphene quantum dots may be configured to absorb light of a second wavelength band that is different from the first wavelength band.

In some example embodiments, the graphene quantum dot layer may further include a plurality of third graphene quantum dots bonded to a third functional group that is different from the first functional group and the second functional group, and the plurality of third graphene quantum dots may be configured to absorb light of a third wavelength band that is different from the first and second wavelength bands.

In some example embodiments, each of the first functional group and the second functional group may include at least one of —NO2, —NH2, —CH3, —OH, —COOH, ═O, —CHO, —COCH3, —(C═O)—, —F, —H, —CO—N(CH3)2, —CH2—OH, —CO—NH2, —N(CH3)2, alkylamine, aniline, or polyethylene glycol (PEG).

In some example embodiments, the plurality of first graphene quantum dot may have a first size, and the plurality of second graphene quantum dots may have a second size that is different from the first size.

In some example embodiments, the graphene quantum dot layer may have a thickness that ranges from about 50 nm to about 100 μm, for example.

In some example embodiments, the optical sensor may further include a semiconductor layer between the first electrode and the graphene quantum dot layer.

In some example embodiments, the semiconductor layer may include at least one of silicon, a compound semiconductor material, an organic semiconductor material, and a 2-dimensional semiconductor material having a band gap and a 2-dimensional crystal structure, and the semiconductor material may form a Schottky barrier between the semiconductor layer and the first electrode.

In some example embodiments, an energy difference between the lowest unoccupied molecular orbital (LUMO) energy level of the graphene quantum dot layer and the valence band of the semiconductor layer may be smaller than an energy difference between the work function of the first electrode and the conduction band of the semiconductor layer.

In some example embodiments, the 2-dimensional semiconductor material may include a transition metal dichalcogenide (e.g., a compound of a transition metal and a chalcogen element).

In some example embodiments, the transition metal may include at least one of tin (Sn), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), hafnium (Hf), titanium (Ti), or rhenium (Re), and the chalcogen element may include at least one of sulfur (S), selenium (Se), or tellurium (Te).

In some example embodiments, the semiconductor layer may include a first semiconductor layer on the first electrode and a second semiconductor layer on the first semiconductor layer. The first semiconductor layer may be doped to a first conductivity type, and the second semiconductor layer may be doped to a second conductivity type that is electrically opposite the first conductivity type.

In some example embodiments, the second electrode may be a transparent electrode.

In some example embodiments, the optical sensor may include an optical sensing layer on the first electrode and the optical sensing layer may include the graphene quantum dot layer.

According to some example embodiments, an optical sensor includes a first electrode, a semiconductor layer on the first electrode, a graphene quantum dot layer on the semiconductor layer, and a second electrode on the graphene quantum dot layer. The graphene quantum dot layer includes a plurality of first graphene quantum dots bonded to a first functional group, A material of the semiconductor layer forms a Schottky barrier between the semiconductor layer and the first electrode.

In some example embodiments, an energy difference between the lowest unoccupied molecular orbital (LUMO) energy level of the graphene quantum dot layer and the valence band of the semiconductor layer may be smaller than an energy difference between the work function of the first electrode and the conduction band of the semiconductor layer.

In some example embodiments, the graphene quantum dot layer may further include a plurality of second graphene quantum dots bonded to a second functional group that is different from the first functional group. The plurality of first graphene quantum dots may be configured to absorb light of a first wavelength band, and the plurality of second graphene quantum dots may be configured to absorb light of a second wavelength band that is different from the first wavelength band.

In some example embodiments, the semiconductor layer may include a first semiconductor layer on the first electrode and a second semiconductor layer on the first semiconductor layer. The first semiconductor layer may be doped to a first conductivity type, and the second semiconductor layer may be doped to a second conductivity type that is electrically opposite the first conductivity type.

In some example embodiments, the optical sensor may include a plurality of semiconductor layers and a plurality of graphene quantum dot layers that are alternately disposed between the first electrode and the second electrode. The first electrode and the second electrode may face each other. The second electrode may be on the first electrode. The graphene quantum dot layer may include a plurality of first graphene quantum dots bonded to a first functional group. The plurality of semiconductor layers may include a first semiconductor layer on the first electrode and a second semiconductor layer between two adjacent graphene quantum dot layers among the plurality of graphene quantum dot layers. The first semiconductor layer may be the semiconductor layer such that a material of the first semiconductor layer may form a Schottky barrier between the plurality of semiconductor layers and the first electrode.

In some example embodiments, an energy difference between the lowest unoccupied molecular orbital (LUMO) energy level of the graphene quantum dot layer and the valence band of the first semiconductor layer may be smaller than an energy difference between the work function of the first electrode and the conduction band of the first semiconductor layer, and an energy difference between the highest occupied molecular orbital (HOMO) energy level of the graphene quantum dot layer and the conduction band of the second semiconductor layer may be smaller than an energy difference between the work function of the first electrode and the conduction band of the first semiconductor layer.

In some example embodiments, thicknesses of each of the second semiconductor layers may be configured to allow tunneling in each of the second semiconductor layers.

According to some example embodiments, an image sensor includes the above-described optical sensor and a signal processing layer configured to process an optical signal detected by the optical sensor into an electric signal. The image sensor may include an optical sensing layer on the first electrode. The optical sensing layer may include a first optical sensing layer configured to sense light of a first wavelength band and a second optical sensing layer configured to sense light of a second wavelength that is different from the first wavelength band. The first optical sensing layer may include the first graphene quantum dot layer including the plurality of graphene quantum dots bonded to the first functional group, and the second optical sensing layer including the second graphene quantum dot layer including the plurality of graphene quantum dots bonded to the second functional group that is different from the first functional group.

In some example embodiments, the optical sensing layer may further include a third graphene quantum dot layer including a plurality of graphene quantum dots bonded to a third functional group that is different from the first and second functional groups; and a fourth graphene quantum dot layer including a plurality of graphene quantum dots bonded to a fourth functional group that is different from the first through third functional groups.

In some example embodiments, sizes of the first through fourth graphene quantum dots may be different from one another.

According to some example embodiments, an optical sensor includes a first electrode, a graphene quantum dot layer on the first electrode, and a second electrode on the graphene quantum dot layer. The graphene quantum dot layer includes a plurality of first graphene quantum dots bonded to a first functional group and a plurality of second graphene quantum dots bonded to a second functional group that is different from the first functional group.

In some example embodiments, the plurality of first graphene quantum dots may be configured to absorb light of a first wavelength band, and the plurality of second graphene quantum dots may be configured to absorb light of a second wavelength band that is different from the first wavelength band.

In some example embodiments, each of the first functional group and the second functional group may include at least one of —NO2, —NH2, —CH3, —OH, —COOH, ═O, —CHO, —COCH3, —(C═O)—, —F, —H, —CO—N(CH3)2, —CH2—OH, —CO—NH2, —N(CH3)2, alkylamine, aniline, or polyethylene glycol (PEG).

In some example embodiments, the optical sensor may further include a semiconductor layer between the first electrode and the graphene quantum dot layer.

In some example embodiments, an image sensor may include the optical sensor and a signal processing layer configured to process an optical signal detected by the optical sensor into an electric signal.

