Two-Dimensional Material Detector Based on Asymmetrically Integrated Optical Microstrip Antenna

Abstract

The present disclosure provides a two-dimensional material detector with an asymmetrically integrated optical microstrip antenna, structurally including a metal reflecting surface, a dielectric spacer layer, a two-dimensional active material layer, a top source electrode, and a drain electrode integrated with a metal strip array. Self-driven photoresponse of a metal/two-dimensional material/metal structure is induced by a Schottky junction formed due to contact between the two-dimensional material and the metal. The asymmetrically integrated optical microstrip antennas break the symmetry between the two contact/two-dimensional material junctions. Light absorption in the contact/two-dimensional material junction integrated with optical patch antennas is significantly enhanced by efficient light in-coupling and intensified light localization; meanwhile, the extended boundary of the contact/two-dimensional material junction enlarges the photocurrent collection area. The light absorption in the other contact/two-dimensional material junction is significantly inhibited by a metal bottom surface which is very close to the two-dimensional material.

Claims

1. A two-dimensional material detector with an asymmetrically integrated optical microstrip antenna array, structurally comprising from bottom to top: a metal reflecting surface, a dielectric spacer layer, a two-dimensional active material layer, a source electrode, and a drain electrode integrated with a metal strip array, wherein the drain electrode integrated with a metal strip array, the dielectric spacer layer and the metal reflecting surface are combined to form an optical microstrip antenna; wherein the metal reflecting surface is a metal reflecting layer with a thickness no less than twice a skin depth of electromagnetic waves in the metal; wherein the metal reflecting surface also works as a gate to electrostatically control the two-dimensional material and is made of a metal with high electrical conductivity; wherein the dielectric spacer layer is a layer of a dielectric transparent to a working waveband, and an optical thickness is smaller than one-quarter of the wavelength; wherein the two-dimensional active material is a material with an atomic thickness; wherein the source electrode and the drain electrode integrated with a metal strip array are formed by a layer of a high electrical conductivity metal with a thickness no less than twice a skin depth of the electromagnetic waves in the metal, with a structure being determined by a strip array period, a strip line width a strip length and a channel length, wherein the strip length is half of the channel length; and wherein the strip array period ranges from one quarter to one half of an optical wavelength, and the strip line width ranges from one third to one half of the strip array period.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a schematic diagram of a graphene photodetector asymmetrically integrated with an optical microstrip antenna.

[0017] FIG. 2 is a photovoltage waveform diagram obtained by irradiating a laser spot at two positions (marked in FIG. 1).

[0018] FIG. 3 is a schematic diagram of a graphene photodetector asymmetrically integrated with an optical microstrip antenna under floodlighting.

[0019] FIG. 4 is a diagram showing the responsivity spectra of two devices under floodlighting.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] According to the present disclosure, the fabrication of the two-dimensional material detector with asymmetrically integrated optical microstrip antennas for self-driven photoresponse enhancement is compatible with a traditional semiconductor process. For ease of description, a specific embodiment of the present disclosure will be described below by taking a graphene detector with asymmetrically integrated optical microstrip antennas working at 1.55 μm as an example:

[0021] 1. A silicon wafer substrate is first ultrasonically cleaned with acetone, and the surface of the silicon wafer is rinsed with isopropanol to remove excess acetone. The silicon wafer is then rinsed with deionized water and dried to ensure that the surface of the silicon wafer substrate is clean and pollution-free.

[0022] 2. A metal layer of Cr (20 nm)/Au (90 nm) is deposited on the clean silicon wafer substrate as a bottom metal reflecting layer.

[0023] 3. A dielectric spacer layer (2) that is transparent to a working waveband is deposited by using plasma-enhanced atomic layer deposition (PEALD) on the bottom metal reflecting layer. The thickness of layer (2) is specifically designed according to the requirement of the optical microstrip antenna.

[0024] 4. A single layer of graphene grown by copper-based chemical vapor deposition (CVD) was transferred to the surface of the dielectric spacer layer (2) by using wet transfer techniques.

[0025] 5. Patterns are defined by electron beam lithography. An electron beam photoresist is used as a mask to protect the underlying graphene, and oxygen plasma is used to etch the graphene that is not protected by the photoresist. Thus, the graphene patterning is achieved.

[0026] 6. Metal contacts and photonic structures are created by electron beam lithography, metal deposition, and lift-off processing. With a photoresist as a mask, Cr (5 nm) and Au (45 nm) are deposited in sequence by electron beam evaporation. Finally, the source and drain electrodes and a metal strip array are obtained by the lift-off process.

EXAMPLE

[0027] The graphene detector with asymmetrically integrated optical microstrip antennas in this example works at a wavelength of 1.65 μm. An optimized periodic unit was designed with the following structural dimensions: P=590 nm, W=283 nm, L.sub.1=5 μm, L.sub.2=10 μm, h.sub.1=110 nm, h.sub.2=30 nm, and h.sub.3=45 nm. The metal reflecting layer (1) was formed by Cr (20 nm)/Au (90 nm). The dielectric spacer layer (2) was an aluminum sesquioxide dielectric layer that was transparent to the working waveband. The thickness of layer (2) is specifically designed according to the requirement of the optical microstrip antenna. The two-dimensional active material (3) was a single layer of graphene grown by copper-based CVD and transferred by a wet chemistry method. The source electrode (4) and the drain electrode (5) integrated with the metal strip array were made of Cr (5 nm)/Au (45 nm). As a reference control, a common graphene device was asymmetrically integrated with a light-coupling grating with the same structural dimensions of the top metal strip array in the graphene detector with asymmetrically integrated optical microstrip antennas. The substrate of the control device was 500 μm thick silicon and the intermediate dielectric spacer layer was 300 nm silicon dioxide.