JP2810862B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element used in the field of optical communication or information processing, and more particularly to a semiconductor device using a waveguide for transmitting a quantum wave.

[0002]

2. Description of the Related Art Polaritons, which are a type of polarization coupled wave in which an exciton, which is an electron-hole pair, and light are coherently coupled, have been considered as a type of quantum wave. Conventionally, it has been proposed to form a modulation element, a logic element, a gate circuit, and the like by propagating this polariton through a quantum well waveguide (Japanese Patent Application No. 59-159346, Japanese Patent Application No. 61-25).
5649).

[0003]

An element using the above-mentioned polariton has an advantage that signal switching can be performed at an ultra-high speed. However, the polariton has an energy substantially corresponding to the resonance energy of the waveguide through which it propagates. Therefore, there is a disadvantage that the propagation loss is essentially increased.

An object of the present invention is to solve the above problems and to provide a semiconductor device with small propagation loss.

[0005]

In order to achieve the above object, according to the present invention, first, carriers are artificially injected into a waveguide through which polaritons propagate, and excitons are generated inside the waveguide. Next, the exciton interacts with polaritons,
Thereby, polaritons are amplified. In addition, the above-described polariton-propagating waveguide is achieved by using a waveguide having any one of slab, rectangular, circular, and elliptical cross-sectional shapes.

[0006]

The waveguide through which the polariton propagates has four types of sectional structures: 1) slab type, 2) rectangular, 3) circular, and 4) elliptical. Here, the slab waveguide of 1) will be described first. The slab-type waveguide refers to a waveguide having a flat plate shape.

In order to inject carriers artificially into a waveguide through which polariton propagates and to generate excitons inside the waveguide, according to the present invention, as shown in FIG. A p-type semiconductor layer 3 is formed above the layer 2 and an n-type semiconductor layer 4 is formed below the layer 2. Next, electrodes 5 are formed above the p-type semiconductor layer and below the n-type semiconductor layer, and carriers are injected from these into the waveguide layer. Naturally, there is no difference in the effect even if the n-type semiconductor layer is arranged at the upper part and the p-type semiconductor layer is arranged at the lower part. At this time, in order to prevent impurities such as dopants for carrier injection from being contained in the region where the polariton electromagnetic field exists, the region where the polariton electromagnetic field 6 shown in FIG. Between the semiconductor layer 3 and the lower n-type semiconductor layer 4. That is,
It is necessary that the space between the p-type semiconductor layer 3 and the lower n-type semiconductor layer 4 be the semiconductor clad layer 2 with a small amount of impurities such as dopants, and the thickness d be a certain value or more. In this case, the dopant concentration of the semiconductor layer having a small amount of impurities such as a dopant is
It is necessary to be not more than 10 17 / cubic cm. Above that value, the scattering of polaritons increases. Further, the semiconductor layer containing few impurities such as a dopant is preferably a semi-insulating semiconductor layer.

[0008] The minimum value of the thickness d, refractive index n ₁ of the thickness a and the waveguide layer 1 of the waveguide layer in the center, when determined using the refractive index n ₂ of the cladding layer 2, the following Become like First, the electromagnetic field of a guided polariton is expressed by Equations 1 and 2.

[0009]

E = Ae cos (κx) (Equation 1) where | x | ≦ a / 2

[0010]

E = Ae cos (κa / 2) exp [−γ (| x | −a / 2)] (Expression 2) where | x |> a / 2 where κ, γ, and β are This is a variable represented by the following equation (3).

[0011]

[Number 3] κ = (2π / λ) √ (n 1 2 -n 0 2) γ = (2π / λ) √ (n 0 2 -n 2 2) β = (2π / λ) n 0 ··· (Equation 3) The relationship shown in the following Equation 4 exists between these variables from the boundary condition that the electromagnetic field is continuous at the boundary between the waveguide layer 1 and the cladding layer 2.

[0012]

Γ = κtan (κa / 2) (Equation 4) Here, it is natural that it is desirable that the bottom of the electromagnetic field of the polariton does not completely touch the p and n layers containing impurities. In such a case, it is necessary to make the thickness of the semi-insulating cladding layer 2 infinite, as can be seen from Equation 2.
For this reason, it was experimentally examined to what extent the thickness of the polariton transmission loss due to impurities can be neglected. As a result, when the carrier concentration of the p-type and n-type semiconductor layers is equal to or higher than 10 18 / cubic cm necessary for actual carrier injection, the semi-insulating cladding layer 2 It has been clarified that when the magnitude of the electromagnetic field at the boundary between the layer and the p and n layers becomes 1/10 or less, the transmission loss of polaritons due to impurities can be ignored. At this time, the thickness d ₀ of the semi-insulating cladding layer 2 is obtained as follows.

Since the electric field strength at the coordinate x is expressed by the equations (1) and (2), the electric field strength at the center of the waveguide 1 is Ae, the coordinate d ₀ at the boundary between the semi-insulating cladding layer 2 and the p, n layer. / 2
Field strength of the obtained by substituting x = d _0/2 in Equation 2. Therefore, the conditional expression in which the magnitude of the electric field intensity is 1/10 or less is as follows:

[0014]

Ae / 10 = Ae cos (κa / 2) exp [−γ (d ₀ / 2−a / 2)] (Equation 5) When rearranging Equation 5,

[0015]

D ₀ = (2 / γ) ln (10 · cos (κa / 2)) + a (Equation 6) Here, γ and κ are quantities obtained from Equations 3 and 4.

In this way, if the cladding thickness is made larger than d ₀ given by the _equation 6, a polariton waveguide or element that can reduce the transmission loss and amplify the polariton can be manufactured.

Although the above-described polariton waveguide has a slab structure, this concept can be similarly applied to other rectangular, circular, and elliptical shapes. First, as shown in FIG. 2, in the case of a rectangular waveguide having a waveguide 7 having a height a and a width b and a cladding 8 having a height d and a width c, the height d of the cladding 8 made of a semi-insulating semiconductor material is used. From the height a of the waveguide to d ₀ given by the _{equation (} 6). Further, in the lateral direction, it was found that the width c of the clad 8 should be larger than d ₀ obtained from Equation 6 by replacing the height a with the width b.

Next, as shown in FIG. 3, in the case of a circular waveguide 9 having a diameter a, if the thickness d of the clad 10 is made larger than d ₀ given by the _equation 6 from the diameter a of the waveguide 9. It turned out to be good. Here, there is no problem even if the cross-sectional shape of the clad is the same as the waveguide as shown by the dotted line in FIG.

Furthermore, in the case of the waveguide 11 having an elliptical cross section, the thickness d of the cladding 12 is shifted from the length a in the height direction by a _value larger than d ₀ given by the _{equation (} 6), as shown in FIG. I just found out. Further, the shape of the clad 12 may be any shape as long as the distance between the p-layer and the n-layer is larger than d ₀ within a range corresponding to the width b of the elliptical waveguide.

As described above, the condition given by Expression 6 is a universal condition for producing a polariton waveguide or element capable of amplifying polariton with a small transmission loss regardless of the shape of the waveguide. I understand.

[0021]

EXAMPLES (Example 1) As shown in FIG. 5, a waveguide for propagating the polariton center are made from GaAs quantum well layer 13, the semi-insulating clad layer 14 around its Al _{0. 3} G
a _0. slab structure consisting of ₇ As was formed by molecular beam epitaxy. Further, a p-type GaAs layer 15 is formed thereon.
(Dopant: C, carrier concentration: 10 18 / cubic cm), and an n-type GaAs layer 16 (dopant: S
i, carrier concentration: 10 to the 18th power / cubic cm). On the p-type GaAs layer, an Au electrode layer 17 and an n-type G
An Au / Ge / Ni electrode layer 18 was provided under the aAs substrate.

With such a structure, the thickness a of the central quantum well waveguide 13 was set to 200 °. In this case, as compared with the electromagnetic field of the magnitude of the waveguide central, Al ₀ the size of the electromagnetic field at the boundary between the semi-insulating clad layer 14 and the p, n layers is less than one tenth. ₃ Ga ₀ . ₇ the thickness d of as semi-insulating cladding layer 14, will be asked about 2000 angstroms,
The 2000 angstrom is applied to the semi-insulating cladding layer 14.
And the thickness. As a result, it has been confirmed that polaritons propagating in the quantum well waveguide are transmitted without loss by carrier injection.

[0023] (Example 2) As shown in FIG. 2, a waveguide 7 for propagating polariton center are made from quantum wire GaAs, semi-insulating cladding layer 8 around its Al _0.
3 Ga _0. The rectangular structure waveguide made ₇ As is formed using a molecular beam epitaxy and microfabrication technologies. Further thereon, a p-type GaAs layer 19 (dopant: C, carrier concentration: 10 to the 18th power / cubic cm) and an n-type GaAs layer thereunder
Layer 20 (dopant: Si, carrier concentration: 10-18)
Squared / cubic cm). On the p-type GaAs layer,
Au / Ge / N under the Au electrode layer and the n-type GaAs substrate
An i-electrode layer was provided.

With such a structure, the thickness a of the central quantum wire waveguide 7 was set to 200 angstroms, and the width b was set to 400 angstroms. In this case, as compared with the electromagnetic field of the magnitude of the waveguide central, Al ₀ to p and the semi-insulating cladding layer 8, the electromagnetic field magnitude at the boundary between the n layer becomes less than 1/10.
₃ Ga _{0. 7} the thickness of the As semi-insulating cladding layer, since it is determined to be about 2000 angstroms, and the 2000 Å and the thickness d of the semi-insulating clad layer. As a result, it has been confirmed that polaritons propagating in the quantum well waveguide are transmitted without loss by carrier injection.

(Embodiment 3) As shown in FIG. 3, a waveguide for propagating a central polariton is a quantum wire Ga having a circular cross section.
Are made from AS9, and the circular structure waveguide 9 semi-insulating clad layer 10 around it consists of _{Al 0. 3 Ga 0. 7} As prepared using the whiskers grow. In other words, parallel to grow the columnar whiskers on a substrate, to produce a circular structure waveguide embedded Thereafter cylindrical whiskers at _{Al 0. 3 Ga 0. 7} As. Further thereon, a p-type GaAs layer 19 (dopant: C, carrier concentration: 10 to the 18th power / cubic c)
m) and an n-type GaAs layer 20 thereunder (dopant: S
i, carrier concentration: 10 to the 18th power / cubic cm). On the p-type GaAs layer, an Au electrode layer, an n-type GaAs
An Au / Ge / Ni electrode layer was provided under the s substrate.

With such a structure, the diameter a of the central quantum wire waveguide was set to 200 angstroms. in this case,
Compared to the magnitude of the electromagnetic field at the center of the waveguide 9, the magnitude of the electromagnetic field at the boundary between the semi-insulating cladding layer 10 and the p and n layers is 10
Al ₀ to less than or equal to 1 minute. ₃ Ga _{0. 7} the thickness of the As semi-insulating cladding layer 10, will be asked about 2000 angstroms, and the 2000 Å and the thickness d of the semi-insulating clad layer 10. As a result, it has been confirmed that polaritons propagating in the quantum well waveguide are transmitted without loss by carrier injection.

Example 4 In Example 3, the quantum wire waveguide having a circular cross section was used. However, a quantum wire waveguide 11 having an elliptical cross section was manufactured in the same manner as in Example 3. Al ₀ to the waveguide becomes semi-insulating clad layer 12. ₃ Ga _{0. 7} As
And a p-type GaAs layer 19 (dopant:
C, carrier concentration: 10 18 cubic cm), and an n-type GaAs layer 20 (dopant: Si, carrier concentration: 10 18 cubic cm) was formed thereunder. p-type GaAs
An Au electrode layer was provided on the s layer, and an Au / Ge / Ni electrode layer was provided below the n-type GaAs substrate 21.

With such a structure, the minor axis a of the central quantum wire waveguide was set to 200 angstroms. in this case,
The magnitude of the electromagnetic field at the boundary between the semi-insulating cladding layer 12 and the p and n layers is 1 compared to the magnitude of the electromagnetic field at the center of the waveguide 11.
Al ₀ to less than or equal to 1 0 minutes. ₃ Ga _{0. 7} the thickness of the As semi-insulating cladding layer 12, will be asked about 2000 angstroms, and the 2000 Å and the thickness d of the semi-insulating clad layer 12. As a result, it has been confirmed that polaritons propagating in the quantum well waveguide are transmitted without loss by carrier injection.

[0029]

According to the present invention, carriers are artificially injected into a waveguide through which polaritons propagate, and excitons are generated inside the waveguide. Next, the excitons and polaritons interacted with each other, thereby amplifying the polaritons, thereby enabling polariton propagation with small propagation loss.
Further, by limiting the thickness of the layer containing no dopant around the waveguide, the transmission loss of polaritons could be significantly reduced.

[0030]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a principle of reducing transmission loss of polaritons.

FIG. 2 is an explanatory diagram showing a structure when a polariton waveguide is rectangular.

FIG. 3 is an explanatory diagram showing a structure when a polariton waveguide is circular.

FIG. 4 is an explanatory diagram showing a structure when the polariton waveguide is elliptical.

5 is a diagram illustrating GaAs waveguide as polariton waveguides, the Al _{0. 3} Ga _0. Slab structure waveguide in the case of using the ₇ As a semi-insulating cladding layer.

[Explanation of symbols]

1 ··· waveguide layer, 2 ··· clad layer, 3 ··· p-type semiconductor layer 4 ··· n-type semiconductor layer, 5 ··· electrode, 6 ··· electromagnetic field distribution of polariton, 7 ··· rectangular waveguide, 8 ..Clad,
9 .. circular waveguide, 10 ... clad, 11 ... elliptical waveguide, 12 ... clad, 13 ... GaAs quantum well layer, 14 ·· Al _0.3 Ga _0.7 As semi-insulating layer, 15 ... p
-Type GaAs layer, 16... N-type GaAs layer, 17... Au
Electrode, 18 ·· Au / Ge / Ni electrode, 19 ·· p-type G
aAs layer, 20 n-type GaAs layer, 21 n-type Ga
As substrate.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-197915 (JP, A) PHYS. REV. B. , VOL. 46 NO. 20 PP. 13289-13292 (Issued November 15, 1992) 13TH SYMPOSIUM ON FUTURE ELECTRON DE VICES Proceedings (October 1994) PP. 59-64 (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1 / 015 505 G02F 1/35 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A waveguide that can generate exciton polaritons, and a waveguide that can generate the exciton polaritons in order to amplify the exciton polaritons in the waveguide in a direction that intersects the transmission direction of the exciton polaritons. Between the means for injecting carriers provided over the region where the polariton propagates and the waveguide and the means for injecting carriers, at least a thickness of d ₀ (where d ₀ = (2 / γ)) ln (10
× cos (κa / 2)) + a, where a is the thickness of the waveguide, γ = (2π / λ) √ (n 0 2 -n 2 2), κ = (2π
/ Λ) √ (n ₁ ² −n ₀ ² ), where n ₁ is the refractive index of the waveguide,
n ₂ is a refractive index of the cladding layer), and the dopant concentration of the semi-insulating cladding layer is 10 17 tatami / cubic cm or less. 2. A waveguide capable of producing exciton polaritons, and a waveguide capable of producing said exciton polaritons in order to amplify said exciton polaritons in a direction intersecting the transmission direction of said exciton polaritons. Means for injecting carriers having an n-type or p-type semiconductor layer and an electrode layer provided over a region where the polariton propagates, and means for injecting the waveguide and the carriers. A thickness of at least d ₀ (where d ₀ = (2 / γ)
ln (10 × cos (κa / 2)) + a, where a is the thickness of the waveguide, γ = (2π / λ) √ (n 0 2 -n 2 2),
κ = (2π / λ) √ (n 1 2 -n 0 2), n 1 is the refractive index of the waveguide, n ₂ has a refractive index of the cladding layer), and 17-mat 10 of dopant concentration / Square cm or less, and a boundary between the semi-insulating cladding layer and the n-type and p-type semiconductor layers compared to the magnitude of the electromagnetic field at the center of the waveguide. Wherein the magnitude of the electromagnetic field at the point is 1/10 or less, and the presence of the electromagnetic field of the exciton polariton is substantially in a region including the waveguide and the cladding layer. apparatus.