JP2665324B2 - Polariton waveguide and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polariton waveguide and a method for producing the same, through which a polariton and a corresponding exciton propagate.

[0002]

2. Description of the Related Art Among waveguides that have been conventionally considered, an electron waveguide is formed by cutting a two-dimensional electron gas into a plurality of thin lines by using a Schottky electrode, and by making the interval between these thin lines approximately equal to the tunnel length of electrons. In most cases, a bond between them was obtained (Japanese Patent Application No. 3-223352, Japanese Patent Application No. 1-294368).

In the case of an optical waveguide, the wavelength of light used for propagation is usually about 1 μm, and the diameter of the waveguide is larger than the wavelength of the light because light must be confined in the waveguide (applied).・ Physics Letters (Appl.Phy
s. Lett.) 1991, 58, 6, p. 562).

[0004]

However, in the case of a material such as GaAs which is usually used for an electron waveguide, the electron tunnel length is about 1 to 2 nm, which corresponds to about 3 atomic layers. In addition, since the behavior of electrons is extremely sensitive to the shape of the walls of the several atomic layers, a high degree of controllability is required for waveguide design.

[0005] Further, in a coupler using an optical waveguide, since the wavelength of light is usually as large as about 1 μm, the diameter of the waveguide itself becomes large, and the size of the coupler becomes large. In addition, in the manufacturing method, a thin film epitaxially grown on a semiconductor substrate is usually formed by lithography and etching, but the number of steps is large, so that the crystal is likely to be damaged, and it is necessary to manufacture a large number of waveguides. It is difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide a waveguide and a coupler which are smaller in size than an optical waveguide without requiring a high degree of controllability in the design of the waveguide. It is easy to obtain a method of manufacturing a large quantity of high quality and small waveguides.

[0007]

The object of the present invention is to use polariton as a propagation medium and to form a plurality of waveguides having a diameter smaller than the wavelength of the incident light by providing an interval between the waveguides equal to or more than the de Broglie wavelength of electrons or holes. By forming the polariton propagation waveguide and the coupler, the diameter of the waveguide is smaller than that of the optical waveguide, and therefore, the overall size is smaller, and the manufacturing restrictions are not as severe as those of the electron waveguide.
Further, according to the present invention, it is possible to obtain a polariton waveguide and a coupler in which the diameter of the waveguide is 100 nm or less and the distance between the waveguides is 10 nm or more. Further, by configuring the waveguide with a needle-like crystal, a polariton waveguide and a coupler can be easily manufactured.

Further, when the waveguide is formed of a needle-like crystal, the needle-like crystal can be formed at a desired position by combining oblique vapor deposition of aluminum with a ridge formed on a semiconductor substrate, which can be easily achieved. Thus, a polariton waveguide and a coupler can be obtained.

[0009]

In the physical phenomena of polaritons, the signal intensity is extremely small, so it has been considered that it is usually difficult to put to practical use. However, the quantum phenomena of a waveguide in which a quantum well is formed in a core for guiding light is used. When a polariton is confined and propagated in a well, light and excitons are not separated by the guide mechanism of the waveguide, but are integrated and propagate as exciton polaritons to increase the density and stabilize the interaction of polaritons. And can be greatly increased. The exciton polariton propagating in the waveguide is a hybrid wave of light and an electron-hole pair constituting the exciton. However, if there is no exciton between two adjacent waveguides, the polariton couples between adjacent waveguides via light. For this reason, it is possible to sufficiently couple the adjacent waveguides even if they are separated by about the wavelength of light, and it is possible to easily configure a polariton coupler.

The exciton polariton has a large effective refractive index involved, and can propagate even in an extremely fine waveguide, and propagates through a waveguide having a diameter of 100 nm or less, which is smaller than the wavelength of light. It is possible to propagate even in a waveguide having a diameter of about a wavelength. In such a waveguide, a wave of an undesired wavelength is not mixed, so that control becomes easier. In addition, the exciton polariton has a smaller size than the optical waveguide as described above, utilizing the property that the exciton polariton can also be coupled to a waveguide that is larger than the conventional coupling waveguide interval and that exists at a distance of about the wavelength of light. Waveguides can be formed more easily than electronic waveguides. That is, when the diameter of the polariton waveguide exceeds 100 nm and the interval is less than 10 nm, a waveguide having a size smaller than that of the conventional waveguide cannot be obtained.

In addition, since it can easily propagate even in a fine waveguide having a diameter of about the de Broglie wavelength as described above, it is possible to use a needle-like crystal for a polariton waveguide. The oblique vapor deposition of aluminum and the ridge formed on the substrate forms a gold vapor-deposited portion at a desired position on the side of the ridge, and grows a fine needle-like crystal on the gold vapor-deposited portion to form a polariton waveguide. A polariton waveguide smaller in size than the optical waveguide can be easily formed.

[0012]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual view showing a first embodiment of a coupler using a polariton waveguide according to the present invention, FIG. 2 is a sectional view of the coupler, FIG. 3 is a perspective view of the polariton waveguide and the coupler, and FIG. Is a perspective view showing a second embodiment of a coupler using a polariton waveguide made of a needle-shaped crystal, FIG. 5 is a view showing the formation of a waveguide made of a needle-shaped crystal, and (a) to (e) are views showing respective steps. FIG. 6 shows a third example of a polariton waveguide made of a needle crystal.
FIGS. 7A, 7B, and 7C are views showing an example, and FIGS. 7A and 7B are views showing another method for obtaining the polariton waveguide. FIGS.

First Embodiment FIG. 1 is a view showing a coupler using a parallel polariton waveguide as a first embodiment of the present invention. Light incident from a light input / output portion 2 formed of a diode or the like is coupled between adjacent waveguides 1 via light. By modulating the refractive index of the coupling portion by designing the coupling portion or providing the electrode 4, for example,
The incident light can be extracted from either side of the waveguide 1 shown in the figure. Here, in a normal optical waveguide, the distance d between the waveguides is about 1 μm,
The width r of the waveguide 1 is also several μm. On the other hand, in the case of an electronic waveguide, the width r of the waveguide 1 is as small as about 10 nm, and the distance d between the waveguides is as extremely small as about 1 nm, which makes it difficult to design the waveguide. In a polariton waveguide, the width r of the waveguide is about 10 nm and the distance d between the waveguides is 1 μm.
That is, it is possible to construct an element in a region that can be sufficiently designed even with current technology.

In this embodiment, means for constructing a polariton waveguide and a coupler using the same using the conventional technique will be described. First, a GaAs or AlGaAs multiple quantum well structure (MQ) is formed on a gallium arsenide substrate (hereinafter referred to as a GaAs substrate) by using a technique such as molecular beam epitaxy (MBE).
W) is formed, and is formed as shown in FIG. 2 by wet etching. The quantum well layer 3 in FIG. 2 is a clad through which polaritons propagate. Here, Ga
As and AlGaAs layers were laminated at 5 nm each in five layers. Therefore, the height h of the waveguide is about 50 nm, the width r of the waveguide is 100 nm, and the distance d between the waveguides is d.
Was set to about 1 μm. Although light having a wavelength of about 1 μm cannot be guided to such a thin waveguide, it can be guided by polaritons. In addition, since the light is coupled to a nearby waveguide via light, sufficient coupling can be obtained even when the distance d between the waveguides is about 1 μm. In this embodiment, the incident light is 750 nm. The guided polaritons can be coupled to either waveguide depending on the length of the waveguide. The manner of this coupling can be freely controlled by modulating the refractive index of the waveguide. In order to modulate the refractive index, the electrode 4 is provided in the middle of the polariton waveguide 1 as shown in FIG.
Can be easily performed by applying a voltage to the. Polaritons are more susceptible to applied voltage than light,
The coupling distance required for coupling including the waveguide and the distance between the waveguides can be reduced.

Second Embodiment A second embodiment of a polariton coupler provided with a waveguide made of a needle crystal
An example is shown in FIG. By using needle-like crystals,
The polariton waveguide can be configured more easily than in the case of using the related art, and therefore, the configuration of the polariton coupler is also easier. In FIG. 4, the light 21 incident from the needle-shaped crystal waveguide 5 on the near side propagates as polaritons,
It is shown that the light is extracted from the right side as light 21 by being coupled to the waveguide 5 made of a needle-like crystal on the back side by the control electrode 4.

Next, a method for manufacturing the polariton waveguide having the above structure will be described. First, as shown in FIG. 5A, a normal semiconductor substrate (for example, a GaAs substrate) 7 is etched by about 0.5 μm to form a ridge 6. At this time, since the needle-like crystal grows on the {111} arsenic surface in the <111> B direction, the side surface of the ridge 6 is set to the {111} arsenic surface. Therefore, the substrate 7 has (110)
It is preferable to use a substrate or (211) B. Next, the SiO ₂ film 10 is formed to a thickness of 50 nm by a thermal chemical vapor deposition (T-CVD) method or the like.
After growing, a resist 9 that is exposed to an electron beam is applied thereon. Then, a pattern having a width of about 0.1 μm, which traverses the ridge 6 with the electron beam 8, is formed as shown in FIG.
, And etching is performed up to the underlying SiO ₂ film 10. Next, as shown in FIG. 5C, aluminum is vapor-deposited from the oblique direction 11 to about 200 nm. Aluminum incident from the oblique direction 11 is not deposited on the opposite side surface of the ridge 6 due to the shadow of the ridge 6. Next, gold is deposited from the opposite oblique direction 13 this time. The deposition amount of gold may be about 0.1 nm in average thickness. afterwards,
When the aluminum and SiO ₂ films are peeled off, as shown in FIG. 5D, a small area drawn by the electron beam remains as the Au vapor deposition section 14. The substrate in this state is annealed at 500 ° C. in an arsine atmosphere, and GaAs needle crystals are grown at a substrate temperature of 420 ° C. using trimethylgallium and arsine. Needle-like crystals having a growth time of at most about 10 minutes and a length of about 2 μm are obtained as shown by 15 in FIG. As shown in the third embodiment, a polariton coupler as shown in FIG. 4 can be formed by providing two or more ridges.

Third Embodiment Another simple manufacturing method of a waveguide structure using a needle-shaped crystal will be described below as a third embodiment. Using a GaAs (110) substrate or a (211) B substrate, the <110> B direction is set to the direction shown in FIG.
After depositing an iO ₂ film by T-CVD, it is etched as shown in FIG. Next, the GaAs substrate 7 is
After etching about 0.5 μm as shown in (b), the SiO ₂ film 16 is deposited again. Thereafter, gold is deposited from the oblique direction 13 so that the average thickness is about 0.1 nm. When the crystal is grown by annealing in the same manner as shown in the second embodiment, a waveguide structure of a needle-like crystal can be obtained at an appropriate interval as shown by 15 in FIG. it can. However, in this method, since the position control of the needle crystal in the horizontal direction is not performed, the crystal grows randomly in the horizontal direction.

[0018] Alternatively, SiO ₂ film 1 as shown in FIG. 7
After depositing on the substrate such that 0 is opposed to each other, a concave step is formed by etching, and a SiO ₂ film is deposited again, and then gold is deposited from the oblique direction 13 as shown in FIG. Then, a polariton waveguide can also be obtained by growing a needle-shaped crystal through the following steps.

As a seed for growing a needle-like crystal, the second
In the embodiment and the third embodiment, the gold vapor-deposited portion is formed. However, this is not necessarily gold, but may be any metal that forms an alloy droplet with GaAs, and aluminum used for oblique vapor deposition is not limited to this. Absent.

In each of the above embodiments, GaAs is used as the substrate. However, the material of the substrate is not limited to GaAs.
For example, Si, InP, InAs, GaN, ZnS, Z
By using a material such as nAs, it is possible to obtain the polariton waveguide and the coupler as described above.

[0021]

As described above, the polariton waveguide according to the present invention comprises a plurality of waveguides having a diameter smaller than the wavelength of the incident light.
By forming them at a distance equal to or longer than the de Broglie wavelength of the electrons or holes of the polariton used as the propagation medium, a waveguide smaller in size than the optical waveguide can be formed without requiring a high degree of controllability. A small coupler can be obtained using the formed polariton waveguide.
Further, a polariton waveguide and a coupler can be easily manufactured by forming a ridge on a semiconductor substrate, performing oblique evaporation of aluminum, and growing a needle-like crystal on the side surface of the ridge.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a first embodiment of a coupler using a polariton waveguide according to the present invention.

FIG. 2 is a cross-sectional view of the coupler.

FIG. 3 is a perspective view of a coupler using the polariton waveguide.

FIG. 4 is a perspective view showing a second embodiment of a coupler using a polariton waveguide made of a needle-like crystal.

FIGS. 5A to 5C show the formation of a waveguide using a needle-like crystal, and FIGS.
(E) is a figure which shows each process.

FIG. 6 is a view showing a third embodiment of a polariton waveguide made of a needle-like crystal, and (a), (b) and (c) are views showing manufacturing steps, respectively.

FIG. 7 is a diagram showing another method for obtaining the polariton waveguide.

[Explanation of symbols]

Reference Signs List 1 polariton waveguide 5 needle-shaped crystal polariton waveguide 6 ridge 11 aluminum oblique deposition direction 15 needle-shaped crystal

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshio Katsuyama 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-2-106726 (JP, A) JP-A-63 −110414 (JP, A)

Claims (4)

(57) [Claims] A plurality of waveguides having a diameter equal to or less than the wavelength of incident light are formed with a spacing of at least the de Broglie wavelength of electrons or holes of polaritons used as a propagation medium. Polariton waveguide. 2. The waveguide according to claim 1, wherein the waveguide has a diameter of 100 nm or less, and a plurality of waveguides having an interval of 10 nm.
2. The polariton waveguide according to claim 1, wherein the polariton waveguides are separated from each other. 3. The polariton waveguide according to claim 1, wherein said waveguide is made of a needle-like crystal. 4. A method for manufacturing a polariton waveguide having a diameter equal to or smaller than the wavelength of incident light, wherein oblique deposition of aluminum is combined with a ridge formed on a semiconductor substrate, and a needle-like crystal is grown on a side surface of the ridge. Forming a polariton waveguide.