阅读说明：本技术 波导集成等离子体激元辅助场发射检测器 (Waveguide integrated plasmon auxiliary field emission detector ) 是由 W.M.琼斯 L.B.德罗斯 A.谢勒 于 2020-02-27 设计创作，主要内容包括：将场发射与表面等离子体激元极化相结合的光检测器。描述了允许在THz范围内且在高频下检测和测量光的方法和器件。所公开的器件包括具有窄纳米尺寸间隙的等离子体激元金属触点,以将光波导模态耦合到等离子体激元模态,从而通过偏置所述触点来产生场发射电流。(A photodetector that combines field emission with surface plasmon polarization. Methods and devices are described that allow detection and measurement of light in the THz range and at high frequencies. The disclosed device includes a plasmonic metal contact with a narrow nano-sized gap to couple an optical waveguide mode to a plasmonic mode to generate a field emission current by biasing the contact.)

1. A method of detecting and measuring light, comprising:

providing first and second plasmonic metal contacts separated by a gap in the range of 10 to 50nm to form a plasmonic waveguide;

coupling first and second plasmonic metal contacts with an on-chip optical waveguide having a first refractive index, the optical waveguide being vertically separated from the plasmonic waveguide by a dielectric layer having a second refractive index, the second refractive index being greater than 1 and less than the first refractive index;

coupling light into the optical waveguide to produce an optical mode;

applying a bias voltage to the first and second plasmonic metal contacts; and

the plasmonic waveguide is configured such that the optical mode couples to a plasmonic mode within the gap, thereby generating a field emission current as a function of light intensity, the field emission current flowing from the first plasmonic metal contact through the gap and to the second plasmonic metal contact.

2. The method of claim 1, wherein the first and second plasmonic metal contacts are selected from gold, silver, copper, aluminum, or a combination thereof.

3. The method of claim 1 or 2, wherein the dielectric layer has a width in the range of 15nm to 25 nm.

4. The method of claim 3, wherein the dielectric layer comprises silicon dioxide and the optical waveguide is made of silicon.

5. The method according to any of claims 1-4, wherein light is coupled into the optical waveguide from an optical fiber.

6. The method of claim 3 or 4, wherein the dielectric layer has a width of 20 nm.

7. A photodetector, comprising:

an optical waveguide coupled to a plasmonic waveguide, the plasmonic waveguide comprising first and second plasmonic metal contacts separated by a gap of 10nm to 50nm, wherein:

the optical waveguide is configured to receive light to generate an optical mode; and

the plasmonic waveguide is configured to allow the optical mode to couple to a plasmonic mode within the gap.

8. The photodetector of claim 7, wherein the first and second plasmonic metal contacts are configured to receive a bias voltage to generate a field emission current that flows from the first plasmonic metal contact, through the gap, and to the second plasmonic metal contact.

9. The photodetector of claim 8, wherein the first and/or second plasmonic metal contact is selected from gold, silver, copper, aluminum, or combinations thereof.

10. The photodetector of any one of claims 7 to 9, wherein the optical waveguide is coupled with a dielectric layer having a thickness in a range of 15nm to 25nm, having a first side and a second side.

11. The photodetector of claim 10, wherein the optical waveguide is configured to receive light and couple the light to a plasmonic waveguide.

12. The photodetector of claim 11, wherein the dielectric layer comprises silicon dioxide and the optical waveguide comprises silicon.

13. The photodetector of claim 12, wherein the dielectric layer is connected to the first and second plasmonic metal contacts on the first side and to the optical waveguide on the second side.

14. The photodetector of any one of claims 7 to 13, wherein the optical waveguide receives light from an optical fiber.

15. The photodetector of any one of claims 10 to 13, wherein the low index dielectric layer has a thickness of 20 nm.

16. The photodetector of claim 8 or 9, further comprising a gate metal contact connected to the optical waveguide, the gate metal contact configured to receive a voltage to bias the optical waveguide to control a field emission current.

Technical Field

Throughout this document, the term "surface plasmon polarization" is used to refer to a quasiparticle (i.e., a combination of electromagnetic waves in a dielectric and collective motion of electrons in a metal). The combination of the two creates a wave phenomenon, i.e., surface plasmons, that propagate along the surface of the dielectric and metal.

The present disclosure relates to photodetectors, and more particularly to plasmon-assisted field emission detectors, a novel photodetector that combines the physical properties of field emission with the focusing properties of surface plasmons on light.

Background

The photodetector includes devices such as a photomultiplier tube, a bolometer, and a semiconductor detector. Fast detectors typically require the use of semiconductor materials to convert photons into electron-hole pairs and to change conductivity or provide a photocurrent. Generally, the energy of a photon must exceed a threshold energy, usually the bandgap, which enables an electron or hole to be generated and measured. These carriers must be moved to the electrical contacts to be detected and this carrier transit time typically limits the final frequency response of the photodetector. In designing high frequency detectors, the capacitance of the device and the distance between the carrier generation and the contacts are typically minimized. Amplification of the electrical signal is achieved by incorporating transistors or carrier multiplication mechanisms, such as avalanche photodiodes or integrated phototransistors.

Fig. 1 shows a prior art germanium (Ge) p-n diode detector (100) integrated on a silicon (Si) waveguide. By coupling light from a mode of a 6 micron diameter glass fiber (110) into a 200x400 nanometer silicon waveguide (120), the concentration of the optical field is over 300 times. Typically, the waveguide is composed of a different material than the detection material, since the light should not be absorbed before reaching the detection area. In fig. 1, light is detected by a reverse biased in-plane p-n diode (130) and the current between contact (141) and contact (142) is measured. In this case, light is coupled from the silicon waveguide (120) to the germanium detector region and electron-hole pairs are generated in the depletion region of the p-n diode (130).

The operating frequency limit of the detector (100) of fig. 1 is generally determined by the distance between the contacts and the carrier generation region. It should be noted that the maximum velocity of electrons in semiconductors is limited by the saturation velocity, which is about 1x10 cm/sec for silicon and about 2 times for InP and GaAs. This translates into a transit time of about 10^12 seconds for carriers moving 100 nanometers in the semiconductor waveguide/detector region, or the fundamental frequency of the photodetector is limited to 1 THz. Therefore, there is a need for faster photodetectors that operate at higher frequencies above 1 THZ.

Disclosure of Invention

The methods and devices disclosed herein address the above-mentioned problems. Photodetectors of the type described are able to exceed the above-mentioned limits and speed problems and to operate at higher frequencies, while offering the potential for high sensitivity and low noise.

According to a first aspect of the present disclosure, a method of detecting and measuring light is disclosed, providing first and second plasmonic metal contacts separated by a gap in the range of 10 to 50nm to form a plasmonic waveguide; coupling first and second plasmonic metal contacts with an on-chip optical waveguide having a first refractive index, the optical waveguide being vertically separated from the plasmonic waveguide by a dielectric layer having a second refractive index, the second refractive index being greater than 1 and less than the first refractive index; coupling light into the optical waveguide to produce an optical mode; applying a bias voltage to the first and second plasmonic metal contacts; and configuring the plasmonic waveguide such that the optical mode couples to a plasmonic mode within the gap, thereby generating a field emission current as a function of light intensity, the field emission current flowing from the first plasmonic metal contact through the gap and to the second plasmonic metal contact.

According to a second aspect of the present disclosure, there is provided a photodetector comprising an optical waveguide connected to a plasmonic waveguide, the plasmonic waveguide comprising first and second plasmonic metal contacts separated by a gap of 10nm to 50nm, wherein the optical waveguide is configured to receive light to produce an optical mode; and the plasmonic waveguide is configured to allow the optical mode to couple to a plasmonic mode within the gap.

Other aspects of the disclosure are provided in the description, drawings, and claims of the disclosure.

Drawings

Fig. 1 shows a prior art Ge PN diode detector.

Fig. 2 shows exemplary modeling results of the relevant field strength within a plasmonic waveguide.

Fig. 3 illustrates an exemplary photodetector according to an embodiment of the present disclosure.

Fig. 4 illustrates the response of an exemplary light field transmitter in accordance with an embodiment of the present disclosure.

Fig. 5A illustrates an exemplary gate voltage response of a field emission voltage in accordance with the teachings of the present disclosure.

Fig. 5B illustrates an exemplary photodetector according to further embodiments of the present disclosure.

Detailed Description

In accordance with the teachings of the present disclosure, light can be used to generate very high electromagnetic fields by surface plasmons in appropriately designed nanostructures made of plasmonic metals (plasmonic metals), such as gold, silver, copper, and aluminum, or combinations thereof. Such a large light field can in turn be used to change the Fowler-Nordheim emission characteristics of the field emitter. For example, by illuminating gold field emitters with light, their electronic properties can be altered and an optically active electronic amplifier can be obtained that can be used as a high frequency photodetector.

Embodiments according to the present disclosure may be realized by introducing a gap between, for example, two gold contacts forming a plasmonic waveguide (plasmon waveguide). The plasmonic waveguide may be efficiently coupled to an on-chip (on-chip) photonic layer comprised of a high index dielectric waveguide by overlaying a metal layer on top of the high index waveguide with a thin, lower index dielectric layer, such as silicon dioxide, between the metal layer and the high index waveguide. Fig. 2 shows exemplary modeling results of the optical field intensity in such a plasmon waveguide cross section. The inventors have noted that reducing the gap width may lead to localization of the optical field (localization), with an accompanying increase in field strength. Throughout this document, the equivalent terms "small gap" and "narrow gap" are used interchangeably to describe a gap in the nanometer range between two metal contacts, both coupled to and fabricated on the same surface of a dielectric waveguide, where electrons can move through the gap from one metal contact to the other through the presence of an optical field and field emission, while avoiding direct tunneling between the metal contacts, which can undesirably lead to device breakdown. The width of such a gap is in the range of 10 to 50 nanometers.

As an example of an embodiment, and in accordance with an embodiment of the present disclosure, a plasmonic transistor (plasmonic triodes) may be fabricated, wherein a gate of the plasmonic transistor may be provided by biasing a doped silicon dielectric waveguide below a plasmonic metal (e.g., gold) contact. Light in the silicon waveguide can be efficiently coupled into the plasmonic waveguide defined by the plasmonic metal contact structure by the adiabatic mode converter to efficiently connect the optical silicon waveguide modes to the focused hybrid plasmonic mode and minimize insertion loss. The hybrid plasmon mode results in an optical field that is enhanced by a factor of about 100 compared to the optical field in a silicon waveguide, which results in a reduction in the absolute magnitude of the optical power required to affect field emission.

Furthermore, because the light is concentrated by mode matching rather than by resonator geometry, the switching time is not limited by the resonator lifetime, and operating frequencies above 1THz are possible. In the following, some exemplary embodiments of the present disclosure will be used to further describe the principles disclosed above.

Fig. 3 shows a photodetector (300) according to an embodiment of the present disclosure. The photodetector (300) is essentially a plasmon assisted field emission diode comprising an optical waveguide (320) and two plasmonic metallic contacts (341, 342) separated by a narrow gap (330) in the nanometer range, the two metallic contacts being coupled with the optical waveguide (320), a thin dielectric layer (350) in the nanometer range being placed i) below the two metallic contacts and ii) between the two metallic contacts and the optical waveguide (320). In other words, the thin dielectric layer is provided with a first side connected to the metal contacts (341, 342) and a second side connected to the optical waveguide (320). The optical waveguide (320) may have a structure of slab waveguide or other waveguide geometries. According to an embodiment of the present disclosure, the thin dielectric layer (350) may have a refractive index greater than 1 and less than a refractive index of the optical waveguide (320). In other words, the optical waveguide (320) may also be made as a dielectric layer with a refractive index greater than the refractive index of the thin dielectric layer (350). According to further embodiments of the present disclosure, the thin dielectric layer (350) may have two functions of 1) making the plasmonic portion less lossy during focusing, and 2) reducing the dark current (dark current) of the photodetector (300) by allowing undercutting of the metal contacts (341, 342), thereby removing the leakage path from the high electric field region.

During operation, the photodetector (300) is configured such that light from the optical fiber (310) couples into the high index optical waveguide (320) and then into a plasmonic waveguide defined by the gap between the contact (341) and the contact (342). The optical field that has been increased by modal conversion into the high index optical waveguide (320) is again increased by coupling from the high index dielectric waveguide mode to the plasmonic mode, with an even smaller modal area and corresponding further electric field concentration. Insertion and absorption losses will reduce the final optical field, but in principle it is possible to obtain very high field strengths. According to embodiments of the present disclosure, the optical waveguide (320) may be made of a high index dielectric semiconductor, such as silicon, and the low index dielectric layer comprises silicon dioxide or some other low index material. The thickness of the low refractive index dielectric layer is in the range of 15 to 25nm, for example 20 nm.

Fig. 4 shows a feasibility test in which the response of the light field emitter (emitter voltage) to light (light induced current) was measured. Light is coupled into the silicon through a grating coupler that is very lossy and therefore the quantum efficiency of the detector is less than expected. As can be seen in fig. 4, the field emission current between the source and the anode, sensitive to the light intensity, is focused by the plasmonic waveguide into the gap between the two contacts.

Referring again to fig. 3, and considering the geometry of the photodetector (300), the field emission current can be varied by introducing a gate close to the contacts (341, 342). The method of gating (gate) such a device is to apply a gate voltage to the optical waveguide (320), in which case the optical waveguide will be lightly doped with a solid dopant such as boron or phosphorous. Fig. 5A shows the field emitter current/voltage characteristics (when not illuminated) at different gate bias values, indicating that this device functions similarly to a three-terminal vacuum triode.

Fig. 5B shows an optical photodetector (500) constructed in accordance with the above considerations. The photodetector (500) has a structure and features similar to those described with respect to the photodetector (300) of fig. 3, except that the optical photodetector (500) further includes an additional contact (543) for applying a gate voltage to control the field emission current. The combination of the optical and electrostatic field concentrations during operation with illumination enables optimization of the maximum sensitivity and frequency response of the device while biasing the device to achieve signal amplification.

Similar to phototransistors, but without saturation speed limitations, plasmon-assisted triodes can operate at frequencies above 1THz and can match the bit-scale data introspection requirements in optical systems transmitting Tb/s data without the need for complex serial demultiplexing circuits.

Because carrier scattering does not limit speed, the nanoscale field emission triode is expected to work at THz frequency, which is much faster than a traditional transistor. However, in practical circuits, as previously mentioned, the electronic frequency response is limited by electron scattering in the contacts of the connected device. In summary, based on the above teachings of the present disclosure, such scattering can be avoided by optically connecting the triode to the plasmonic waveguide, for example, as shown in the embodiment of fig. 5B, to transmit signals between these devices at the speed of light. An optoelectronic field emitter constructed in accordance with the present disclosure is capable of combining high electrostatic and electromagnetic fields at the nanometer level. The use of contacts made of metals such as gold, silver, copper and aluminum, or combinations thereof, as plasmonic waveguide and electrostatic field emitting electrodes allows for reduction of interconnect delay times and development of more complex integration and simpler circuit design.

According to the teachings of the present disclosure, a field emission triode may be integrated with a plasmonic and silicon waveguide to define a phototransistor circuit. By integrating ultrafast electronics directly on the optical waveguide, the multiplexing and demultiplexing circuitry required for modern silicon photonics data communication links will be simplified. In addition, by combining the electronic optical device with the nano-scale photonic device, one class of devices can be manufactured, which lays a foundation for the next generation of photoelectric devices and is not limited by carrier scattering any more.

Most electro-optic modulators rely on the absorption of light or a change in refractive index. Electro-optic polymers with high nonlinearity have recently been developed for use in nonlinear modulators, in which a high electrostatic field is applied to a small gap to adjust the refractive index, thereby producing an electro-optic (EO) device. Thus, by incorporating electro-optic materials into a small high electric field device as described in this disclosure, an EO modulator will be constructed. The change in electron density results in a change in refractive index even in vacuum, thereby realizing an electro-optical vacuum electronic device. However, greater nonlinearity can be found in EO polymers, particularly after these polymers are polarized in a very high electrostatic field at high temperatures. According to embodiments of the present disclosure, a micro-scale electro-optic modulator may be fabricated by using a plasmonic waveguide to fabricate a small Mach-Zehnder interferometer in which one leg of the interferometer may be biased while the other leg is undisturbed.