Near-infrared light sensors including 2-dimensional insulator

Abstract

A near infrared light sensor includes a 2D material semiconductor layer on a substrate, a tunneling layer on the 2D material semiconductor layer, and first and second electrodes on opposite edge regions of an upper surface of the tunneling layer. The 2D material semiconductor layer may be a TMDC layer having a thickness in a range of about 10 nm to about 100 nm. The tunneling layer and the substrate may each include hBN.

Claims

1. A near infrared light sensor, comprising: a two-dimensional (2D) material semiconductor layer on a substrate; a tunneling layer on the 2D material semiconductor layer; and first and second electrodes on the tunneling layer, the first and second electrodes on opposite edge regions of an upper surface of the tunneling layer, wherein the 2D material semiconductor layer has a thickness in a range of about 10 nm to about 100 nm, and the tunneling layer has a thickness in a range of about 3 nm to about 10 nm.

2. The near infrared light sensor of claim 1, wherein the 2D material semiconductor layer includes a transition metal di-chalcogenide (TMDC).

3. The near infrared light sensor of claim 1, wherein the 2D material semiconductor layer includes MoS.sub.2, MoSe.sub.2, MoTe.sub.2, WS.sub.2, WSe.sub.2, WTe.sub.2, ZrS.sub.2, ZrSe.sub.2, HfS.sub.2, HfSe.sub.2, NbSe.sub.2, ReSe.sub.2, or CuS.

4. The near infrared light sensor of claim 1, wherein the tunneling layer includes hBN, alumina, or hafnium oxide.

5. The near infrared light sensor of claim 1, wherein the substrate includes hBN.

6. The near infrared light sensor of claim 1, further comprising: a gate electrode on the substrate, the gate electrode and the 2D material semiconductor layer on opposite sides of the substrate.

7. The near infrared light sensor of claim 1, wherein the substrate has a thickness in a range of about 3 nm to about 10 nm.

8. The near infrared light sensor of claim 1, wherein each electrode of the first and second electrodes includes a transparent conductive oxide.

9. A near infrared light sensor, comprising: a semiconductor layer on a substrate, the semiconductor layer including MoTe.sub.2, the substrate including hBN; a tunneling layer on the semiconductor layer, the tunneling layer including hBN; and first and second electrodes on the tunneling layer, the first and second electrodes on opposite edge regions of an upper surface of the tunneling layer, wherein the semiconductor layer has a thickness in a range of about 10 nm to about 100 nm, and the tunneling layer has a thickness in a range of about 3 nm to about 10 nm.

10. The near infrared light sensor of claim 9, further comprising: a gate electrode on the substrate, the gate electrode and the semiconductor layer on opposite sides of the substrate.

11. The near infrared light sensor of claim 10, wherein the substrate has a thickness in a range of about 3 nm to about 10 nm.

12. The near infrared light sensor of claim 9, wherein each electrode of the first and second electrodes includes a transparent conductive oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and/or other aspects will become apparent and more readily appreciated from the following description of the example embodiments, taken in conjunction with the accompanying drawings in which:

(2) FIG. 1 is a schematic cross-sectional view of a configuration of a near infrared light sensor according to some example embodiments of the inventive concepts;

(3) FIG. 2 is a graph showing a dark current of a near infrared light sensor according to some example embodiments of the inventive concepts;

(4) FIG. 3 is a graph showing a reactivity of a near infrared light sensor according to some example embodiments of the inventive concepts; and

(5) FIG. 4 is a schematic cross-sectional view of a configuration of a near infrared light sensor according to some example embodiments of the inventive concepts.

DETAILED DESCRIPTION

(6) Hereinafter, example embodiments of the inventive concepts will now be described in detail with reference to the accompanying drawings. In the drawings, thicknesses of layers or regions are exaggerated for clarity of specification. The embodiments of the inventive concepts are examples and capable of various modifications and may be embodied in many different forms.

(7) It will be understood that when an element or layer is referred to as being on or above another element or layer, the element or layer may be directly on another element or layer or intervening elements or layers.

(8) FIG. 1 is a schematic cross-sectional view of a configuration of a near infrared light sensor 100 according to some example embodiments of the inventive concepts. The near infrared light sensor 100 may include a few millions of pixels, and FIG. 1 shows one of the pixels of the near infrared light sensor 100.

(9) Referring to FIG. 1, the near infrared light sensor 100 may include a two-dimensional (2D) material semiconductor layer 120 and a tunneling layer 130, which are sequentially formed on a substrate 110. Restated, the 2D material semiconductor layer 120 is on the substrate 110, and the tunneling layer 130 is on the substrate 110, and the tunneling layer 130 is on the 2D material semiconductor layer 120. The 2D material semiconductor layer 120 is formed directly on the substrate 110, and the tunneling layer 130 may be formed directly on the 2D material semiconductor layer 120. First and second electrodes 141 and 142 may be respectively formed on both sides of the tunneling layer 130. Restated, and as shown in at least FIG. 1, the first and second electrodes 141 and 142 may be on the tunneling layer 130, such that the first and second electrodes 141 and 142 are on opposite edge regions 130e-1 and 130e-2 (also referred to herein as simply edges) of an upper surface 130a of the tunneling layer 130. As shown in FIG. 1, a near infrared ray (near infrared light beam 199) may be irradiated on a central portion 130c of the tunneling layer 130 that is between the opposite edge regions 130e-1 and 130e-2 on which the first and second electrodes 141 and 142 are located.

(10) Where an element is described as being on another element, it will be understood that the element may be above or beneath the other element. Additionally, an element that is on another element may be directly on the other element, such that the element contacts at least a portion of the other element, or may be indirectly on the other element, such that the element is isolated from contacting the other element by an interposing element, empty space, or combination thereof.

(11) The 2D material semiconductor layer 120, which may be interchangeably referred to herein as simply a semiconductor layer, generates carriers when the 2D material semiconductor layer 120 receives a near infrared ray of a wavelength of approximately 800 nm to 900 nm. The 2D material semiconductor layer 120 may be a channel for passing the carriers. The 2D material semiconductor layer 120 is a layer that transforms received light into an electrical signal. The 2D material semiconductor layer 120 may have a bandgap of approximately 1 eV at which the 2D material semiconductor layer 120 may well absorb a near infrared ray. The 2D material semiconductor layer 120 may have a layer structure including one or more transition metal di-chalcogenides (TMDC). Restated, the 2D material semiconductor layer 120 may include a transition metal di-chalcogenide (TMDC) monolayer (also referred to herein as simply a transition metal di-chalcogenide (TMDC)). The 2D material semiconductor layer 120 may include a plurality of TMDC monolayers as a stack of such monolayers. The TMDC may include one of transition metals, such as Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc, Re, and Cu and one of chalcogen elements, such as S, Se, and Te. The TMDC may include MoS.sub.2, MoSe.sub.2, MoTe.sub.2, WS.sub.2, WSe.sub.2, WTe.sub.2, ZrS.sub.2, ZrSe.sub.2, HfS.sub.2, HfSe.sub.2, NbSe.sub.2, ReSe.sub.2, or CuS. Accordingly, for example, the 2D material semiconductor layer 120 may include MoTe.sub.2. Materials described above are only examples, and besides the materials above, other materials may also be used as the TMDC materials.

(12) The 2D material semiconductor layer 120 may have a thickness 120t in a range of about 10 nm to about 100 nm. If the thickness 120t of the 2D material semiconductor layer 120 is less than 10 nm, an amount of light absorption is small. Therefore, a near infrared light sensor that includes a 2D material semiconductor layer having a thickness less than 10 nm may be difficult to perform as a sensor. If the thickness of the 2D material semiconductor layer 120 is greater than 100 nm, a size of the near infrared light sensor 100 may be increased, and thus, it may not be used as a small near infrared light sensor. The thickness of the 2D material semiconductor layer 120 may be in a range from about 20 nm to about 50 nm.

(13) The tunneling layer 130 includes a two-dimensional (2D) insulator. The 2D insulator may include hexagonal boron nitride (hBN), alumina, or hafnium oxide. For example, the tunneling layer 130 may include hBN. The tunneling layer 130 may have a thickness 130t in a range of about 3 nm to about 10 nm. If the thickness of the tunneling layer 130 is less than 3 nm, a dark current may be increased. If the thickness of the tunneling layer 130 is greater than 10 nm, a tunneling current may be small, and thus, light detectivity may be reduced.

(14) If the tunneling layer 130 includes hBN, a dangling bond is hardly present on a surface of the tunneling layer 130 and a defect state inside a bandgap of the tunneling layer 130 is very small, and thus, a dark current is hardly generated in the near infrared light sensor 100 that uses hBN as the tunneling layer 130.

(15) Each electrode of the first and second electrodes 141 and 142 may include a general metal or a transparent conductive oxide. The general metal may be at least one selected from the group consisting of Al, Cu, Ti, Au, Pt, Ag, and Cr, but the general metal according to the example embodiments are not limited thereto.

(16) The transparent conductive oxide may include at least one selected from the group consisting of, for example, indium tin oxide (ITO), indium zinc oxide (IZO), ZnO, SnO.sub.2, antimony-doped tin oxide (ATO), Al-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), TiO.sub.2, and fluorine-doped tin oxide (FTO), but the transparent conductive oxide according to the example embodiments are not limited thereto.

(17) The substrate 110 may have a thickness 110t in a range of about 3 nm to about 10 nm. The substrate 110 may include a generally used insulating material, for example, silicon, glass, plastic, etc. The substrate 110 may include hBN. When the substrate 110 including hBN is used, resistance to carriers passing through the 2D material semiconductor layer 120 is low, and thus, the mobility of the carriers in the 2D material semiconductor layer 120 is increased. As a result, the photo-detection effect is increased, the sensitivity of the near infrared light sensor 100 is increased, and the photo-responsivity of the near infrared light sensor 100 is increased since recombination of electrons and holes generated in the 2D material semiconductor layer 120 is reduced.

(18) When the terms about or substantially are used in this specification in connection with a numerical value, it is intended that the associated numerical value include a tolerance of 10% around the stated numerical value. When ranges are specified, the range includes all values therebetween such as increments of 0.1%.

(19) When light of a near infrared wavelength spectrum (e.g., near infrared light beam 199) is irradiated onto an upper surface of the near infrared light sensor 100, that is, onto the tunneling layer 130 as shown in FIG. 1, the irradiated near infrared light beam 199 generates electron-hole pairs in the 2D material semiconductor layer 120 after passing through the tunneling layer 130. The generated electron-hole pairs are separated into electrons and holes. The separated electrons move towards one of the first and second electrodes 141 and 142 to which a higher potential voltage is applied, and accordingly, a tunneling current that passes through the tunneling layer 130 is generated. By measuring this tunneling current, an amount of light of a near infrared wavelength spectrum irradiated on a corresponding pixel of the near infrared light sensor 100 may be detected.

(20) FIG. 2 is a graph showing a dark current of a near infrared light sensor 100 according to some example embodiments of the inventive concepts. In some example embodiments, a MoTe.sub.2 layer (e.g., a 2D material semiconductor layer 120 that includes MoTe.sub.2) having a thickness of 50 nm is used as the 2D material semiconductor layer 120 of the near infrared light sensor 100, and an hBN layer having a thickness of 5 nm is used as the tunneling layer 130. In some example embodiments, the substrate 110 is formed of (at least partially comprises) hBN. In some example embodiments, the tunneling layer 130 and the substrate 110 may each include hBN. A near infrared wavelength spectrum of 850 nm is used as the near infrared wavelength spectrum. FIG. 2 shows a measured dark current according to a voltage applied between the first and second electrodes 141 and 142 in a dark environment.

(21) Referring to FIG. 2, when a voltage is applied between the first and second electrodes 141 and 142 in a dark environment, a dark current of approximately 0.7 pA or less is detected. When the value of the dark current is converted to unit area, it is 0.7 A/cm.sup.2 or less, and this value of the dark current is a few hundred times lower than a silicon-based near infrared light sensor of the related art.

(22) FIG. 3 is a graph showing a reactivity of a near infrared light sensor 100 according to some example embodiments of the inventive concepts. The configuration of the near infrared light sensor 100 is the same as the configuration of the near infrared light sensor 100 of FIG. 2. FIG. 3 shows optical currents measured in a dark state and states under amounts of light irradiation of 20 nW, 50 nW, and 150 nW.

(23) Referring to FIG. 3, it is known that the dark current in the dark state is a sub-pico ampere, and the optical currents increase as the amount of light of the near infrared wavelength spectrum (irradiation of 850 nm) irradiating the near infrared light sensor 100 increases. The photo-responsivity is 1 A/W or above, which is a favorable photo-responsivity. The near infrared light sensor 100 according to some example embodiments uses the tunneling layer 130 having defectless hBN, and thus, has a low dark current. In some example embodiments, since the near infrared light sensor 100 uses the substrate 110 including hBN, after electron-hole pairs generated by light of the near infrared wavelength spectrum (e.g., near infrared light beam 199) are separated into electrons and holes, the electrons and holes are transferred to the first and second electrodes 141 and 142 without recombination therebetween, and thus, it is seen that the photo-responsivity of the near infrared light sensor 100 is increased. In some example embodiments, a response time of the near infrared light sensor 100 that uses the substrate 110 including hBN is reduced as compared to a near infrared light sensor that uses an oxide substrate of the related art.

(24) In some example embodiments, the near infrared light sensor 100 according to some example embodiments includes the 2D material semiconductor layer 120 having a relatively small thickness, and thus, a camera that employs the near infrared light sensor 100 may be miniaturized.

(25) FIG. 4 is a schematic cross-sectional view of a configuration of a near infrared light sensor 200 according to some example embodiments of the inventive concepts. Like reference numerals are used to indicate elements that are substantially identical to the elements of FIG. 1, and thus, the detailed description thereof will be omitted.

(26) Referring to FIG. 4, the near infrared light sensor 200 may include a gate insulating layer 210, a 2D material semiconductor layer 120, and a tunneling layer 130, which are sequentially formed on a gate electrode 250. In some example embodiments, the gate insulating layer 210 is the substrate 110. As shown in FIG. 4, the gate electrode 250 and the 2D material semiconductor layer 120 may be on opposite sides of the gate insulating layer 210. Accordingly, where the gate insulating layer 210 is the substrate 110, the gate electrode 250 and the 2D material semiconductor layer 120 may be on opposite sides of the substrate 110. The 2D material semiconductor layer 120 is formed directly on the gate insulating layer 210, and the tunneling layer 130 may be formed directly on the 2D material semiconductor layer 120. First and second electrodes 141 and 142 may be formed respectively on both sides of the tunneling layer 130 in contact with the tunneling layer 130. Light of a near infrared wavelength spectrum may be irradiated onto the tunneling layer 130 between the first and second electrodes 141 and 142.

(27) The gate insulating layer 210 may have a thickness in a range of about 5 nm to about 10 nm. The gate insulating layer 210 may include silicon oxide or silicon nitride generally used in semiconductor processes. The gate insulating layer 210 may include a 2D insulator, for example, hBN. When the gate insulating layer 210 including hBN is used, impurities between the 2D material semiconductor layer 120 and the gate insulating layer 210 may be reduced, and thus, a gating effect therebetween may be increased.

(28) The gate electrode 250 may include a general metal. The general metal may be at least one material selected from the group consisting of Al, Cu, Ti, Au, Pt, Ag, and Cr, but the general material according to the example embodiments is not limited thereto.

(29) When a particular (or, alternatively, predetermined) voltage is applied to the gate electrode 250, charges in the 2D material semiconductor layer 120 move towards the gate electrode 250, and thus, an optical absorption in the 2D material semiconductor layer 120 may be increased. Accordingly, a photo-responsivity of the near infrared light sensor 200 is increased. The tunneling layer 130 reduces a dark current.

(30) The near infrared light sensor according to some example embodiments uses the tunneling layer including a 2D insulator, and thus, a dark current is reduced. In some example embodiments, a photo-responsivity is increased by using a TMDC semiconductor layer in which an amount of optical absorption is increased.

(31) In some example embodiments, the hBN substrate and the hBN gate insulating layer increase the photo-responsivity of the near infrared light sensor.

(32) In some example embodiments, the gate electrode increases the optical absorption in the 2D material semiconductor layer, and thus, the photo-responsivity and response time of the near infrared light sensor may be improved.

(33) While one or more example embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.