JPH06175173A - Nonlinear optical device - Google Patents

Abstract

PURPOSE:To enable high speed moving without decreasing an exciton absorption peak intensity and without damaging nonlinear optical properties by having almost the same tunneling time of hole as electrons and having strong confinement of electrons in an active layer. CONSTITUTION:The device is provided with a longitudinal structure pn type superlattice SL in which a first material layer A1, a second or third material layer A2 being a quantum well containing p type impurities, a fourth material layer B2 being a potential barrier only to electrons a first material layer A3, a second material layer A4 being an active layer of the quantum layer and having the thickness capable of existing of two dimensional excitons, a first material layer A5 and a second or third material layer A6 being a quantum well containing (n) type impurities are respectively laminated to form one cycle. Energy difference between a first quantum level of an electron and a first quantum level of a hole generated in the second or third material layer A2 and A6 is larger than the energy difference between the first quantum level of an electron and the first quantum level of a hole generated in the second material layer A4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to TBQ (tunnel).
The present invention relates to improvement of a non-linear optical device having an ing bi-quantum well (TBQ) structure and functioning as an optical / optical switch, an optical bistable device, an optical / optical memory, or the like.

[0002] Normally, this type of non-linear optical device operates so as to switch between an operating state and a non-operating state depending on irradiation and non-irradiation of operating light, and control transmission of non-operating light input to the device. Which is currently high speed operation and S
/ N is required to be improved.

[0003]

2. Description of the Related Art Generally, as a non-linear optical device, a device using a semiconductor superlattice is known, which utilizes a non-linear operation characteristic associated with light absorption and recovery of two-dimensional excitons. Can be controlled at high speed.

However, in the above-mentioned nonlinear optical device, although the two-dimensional excitons are produced quickly, the recovery time depends on the recombination time of electrons and holes, and hence the recovery time becomes slower. The operation as is decided by the slower one.

In an attempt to solve the above problems, T
A non-linear optical device having a BQ structure has been developed (see Japanese Patent Application No. 63-224547, if necessary).

FIG. 5 is an energy band diagram for explaining a non-linear optical device having a conventional TBQ structure. In FIG. 5, reference numerals 31, 33, 35, and 37 denote potential barriers generated in the semiconductor layer made of a material having a wide band gap.
2 and 36 are wide quantum wells formed by a thick semiconductor layer made of a narrow bandgap material, 34 is a narrow quantum well formed by a thin semiconductor layer made of a narrow bandgap material, and E _V is the top of the valence band. , E _C is the bottom of the conduction band, e ₁ is the first quantum level of the electron in the quantum well, and h ₁ is the first quantum level of the hole in the quantum well.

As can be seen from FIG. 5, this non-linear optical device is a thin semiconductor layer of a narrow bandgap material sandwiched by potential barriers 33 and 35 created by a semiconductor layer of a wide bandgap material. A TBQ structure in which the entire structure including the generated narrow quantum wells 34 and the wide quantum wells 32 and 36 formed on both sides of the narrow quantum wells 34 with thick semiconductor layers made of a material having a narrow forbidden band as one unit is adopted. Contains.

In this nonlinear optical device, the narrow quantum well 3
4 semiconductor layers act as actual active layers, and
The semiconductor layer forming the wide quantum wells 32 and 36 is used as a waste field of electrons, that is, as an inactive layer.

Therefore, by irradiating the non-linear optical device with the controlled light and irradiating the control light with a stronger intensity, the transmission or non-transmission of the controlled light is controlled. Narrow quantum well 34 which is an active layer depending on control light
The electrons generated in the above and the electrons of the holes easily tunnel through the potential barriers 33 or 35 on both sides and move to the wide quantum well 32 or 36 which is an inactive layer. This phenomenon is caused by the first quantum level e of electrons in the narrow quantum well 34.
_This is because the first quantum level e ₁ in the wide quantum well 32 or 36 is lower than that in ₁ .

As is clear from the above description, the recovery time of this nonlinear optical device depends on the time taken for the electrons generated in the narrow quantum well 34 to tunnel the potential barrier 33 or 35, and is usually , 0.5 [p
s] to 500 [ps], which is extremely high speed, and the time for recovering the light absorbing ability can be remarkably shortened as compared with the nonlinear optical device described at the beginning.

However, this non-linear optical device has a problem that light absorption occurs even in the non-active layer, which is a place where electrons are discarded, that is, in the semiconductor layers forming the wide quantum wells 32 and 36, and the active layer is active. Layers, ie narrow quantum wells 32 and 3
There is also a problem that the relaxation of holes in 6 is slow.

Therefore, in order to solve the above-mentioned problems, a non-linear optical device using a vertical structure pn type superlattice has been developed (see Japanese Patent Application No. 2-411915, if necessary). Figure 6
Is an energy band diagram for explaining a non-linear optical device using a vertical structure pn type superlattice.

In FIG. 6, C1 is a first material layer having a first forbidden band, C2 is a second material layer having a second forbidden band, and C3 is a first material layer having a first forbidden band. Material layer, C4 is a third material layer having a third forbidden band, C5 is a first material layer having a first forbidden band, C6 is a fourth material layer having a fourth forbidden band, E _V is the top of the valence band, E _C is the bottom of the conduction band, E _g1 is the energy band gap in the first material layers C1, C3, C5, and E _g2 is in the second material layer C2. Energy band gap, E _g3 is the energy band gap in the third material layer C4, E _g4 is the fourth material layer C
6, the energy band gap, e ₁ is the first quantum level of the electron, and h ₁ is the first quantum level of the hole.

As is apparent from FIG. 6, in this non-linear optical device, the second material layer C2 and the fourth material layer C6, which are inactive layers which are carriers for discarding, have been described with reference to FIG. Compared with the non-linear optical device, the band gap is remarkably widened, and the second material layer C2 is in contact with the third material layer C4 through the first material layer C3.
The fourth material layer C6, which is in contact with the first material layer C5 via the first material layer C5, is doped with the n-type impurity.

In the non-linear optical device of FIG. 6, the second material layer C2 is caused by an internal electric field resulting from the addition of impurities to the second material layer C2 and the fourth material layer C6. C2,
The energy levels of the first quantum levels of the electrons generated in the third material layer C4 and the fourth material layer C6 are inclined stepwise, and the second material layer C2> the third material layer C4> The fourth material layer C6 is formed, and the energy level of the first quantum level of holes is also graded in a stepwise manner so that the second material layer C2 <the third material layer C4 <the fourth material layer C6.

That is, the electrons of the two-dimensional excitons generated in the third substance layer C4 and the holes in the third substance layer C4 are independent of the composition of the semiconductor material forming the quantum well. Energy band structures have been created that tunnel into separate layers into the two material layers C2. The energy difference between the electron and hole first quantum levels e ₁ and h ₁ of the third material layer C4 is calculated as the second material layer C2 and the fourth material layer C6.
The light absorption is mainly made in the third material layer C4 so as not to be larger than that.

[0017]

In the non-linear optical device using the vertical structure pn type superlattice described with reference to FIG. 6, light absorption occurs only in the third material layer C4 which is an active layer, and Since the electrons and holes photoexcited in the material layer C4 escape to the different wells in the opposite directions, that is, the fourth material layer C6 and the second material layer C2, the electrons and holes are tunneled. It became possible to control the time separately.

However, in order to make the barrier layer tunneling times of electrons and holes comparable, it is necessary to make the barrier layer for holes having a large effective mass extremely thin as compared with the barrier layer for electrons. When the barrier layer for holes becomes thinner, the coupling of the electron wave function between the active layer and the quantum well, which is a hole waste field, becomes stronger, and the exciton absorption peak intensity in the active layer decreases. Problems occur.

The present invention relies on taking simple measures,
The hole barrier layer tunneling time is comparable to the electron barrier layer tunneling time, and moreover, the electrons are strongly confined in the active layer so that the exciton absorption peak intensity does not decrease. We aim to enable high-speed operation without impairing the nonlinear optical properties due to two-dimensional excitons.

[0020]

FIG. 1 is a perspective view of a main part of a nonlinear optical device for explaining the principle of the present invention, and FIG. 2 is an energy diagram of the nonlinear optical device shown in FIG.・
It is a band diagram.

In the figure, 1 is a substrate, 2 is an etching stop layer, SL is a vertical structure pn type superlattice, A1 is a first material layer having a first forbidden band, and A2 is a second or third layer. A second or third material layer having a forbidden band, A3 is a first material layer having a first forbidden band, A4 is a second material layer having a second forbidden band,
A5 is a first material layer having a first forbidden band, A6 is a second or third material layer having a second or third forbidden band, and B1 and B2 have a fourth forbidden band and are electrons. A fourth material layer acting only as a barrier against only, D is a defect layer, e ₁ is a first quantum level of an electron, h ₁ is a first quantum level of a hole, and the second or third The material layer A2 is doped with p-type impurities such as Be, and the second or third material layer A6 is formed.
Is doped with an n-type impurity such as Si.

The defect layer D can be replaced by a groove, and in any case, at the interface between them and the vertical structure pn type superlattice SL, the recombination velocity of carriers is large, and therefore, there is a recombination of carriers there. Therefore, less carriers are accumulated in the second or third material layer A2 and A6, which is a waste place for carriers.

Of course, the doping may be performed uniformly on the second or third material layer A2 or the second or third material layer A6, but the central portion of each material layer A2 or A6 may be planarized. It can also be doped, in which case the first material layer A1 or the fourth material layer B1 or the first material layer A3 or the fourth material layer B2 or the first material layer It is advantageous to obtain a large internal electric field because there is little risk of impurity diffusion during growth of each of A5 and high-concentration doping is possible as compared with uniform doping.

The non-linear optical device shown in FIGS. 1 and 2 has a structure in which the first material layer A1 to the second or third material layer A6 are set as one cycle and are continuously folded in a continuous manner. It consists of a super lattice.

Further, due to the internal electric field resulting from the addition of impurities to the second or third material layer A2 and the second or third material layer A6, the second or third material layer A2 , The energy level of the first quantum level e ₁ of electrons generated in the second material layer A4 and the second or third material layer A6 respectively is stepwise inclined, A2> third material layer A4> second or third material layer A6, and the energy level of the first quantum level h ₁ of holes also inclines stepwise. A2 <third material layer A4 <second or third material layer A6.

As is apparent from the above description, the second material layer A4 is an active layer composed of quantum wells,
The second or third material layer A2 is a quantum well for releasing holes generated in the second material layer A4 which is an active layer, and the second or third material layer A6 is a second active layer. Material layer A
4 function as quantum wells for releasing the electrons generated in 4.

Now, comparing the non-linear optical device shown in FIGS. 1 and 2 with the non-linear optical device shown in FIG.
The second material layer A4 (FIG. 6) which is an active layer composed of quantum wells.
Corresponds to the third material layer C4) and the second material layer A2 (corresponding to the second material layer C2 in FIG. 6) which is a quantum well for releasing holes generated in the second material layer A4. First material layer A3 that acts as a barrier to both electrons and holes during
The structure for providing (corresponding to the first material layer C3 in FIG. 6) is the same, but in the nonlinear optical device shown in FIGS. 1 and 2, the first material layer A3 is provided with a barrier against only electrons. A significant difference is that a fourth material layer B2 acting as the above is added.

Due to the formation of the fourth material layer B2, the second material layer A4 which is an active layer composed of quantum wells is formed.
And a second material layer A2 which is a quantum well for releasing holes
The coupling of the electron's wave function during the period is weakened, and the confinement of the electron in the second material layer A4 becomes strong.

From the above, the non-linear type according to the present invention
In the optical device, (1) electron with the first forbidden band
It acts as a potential barrier against holes and the holes are fully tunneled.
Of a first material layer A1 (eg
Dope In_0.52Al _0.48As layer) and the first material layer
Is formed adjacent to A1 and has a fourth forbidden band
Fourth material layer that acts as a potential barrier only for electrons
B1 (eg undoped (GaAs_0.51Sb_0.49)
_x(In_0.52Al_0.48As)_1-xLayer) and the fourth object
Second or third forbidden formed adjacent to the quality layer B1
Electrons and holes that have a band and are doped with p-type impurities
Second or third material acting as a quantum well for
Layer A2 (eg p-type In_0.53Ga_0.47As layer) and the above
Formed adjacent to the second or third material layer A2 and
It has a forbidden band of four and acts as a potential barrier only for electrons.
The fourth material layer B2 (for example, undoped (Ga)
As_0.51Sb_0.49)_x(In_0.52Al_0.48As)
_1-xLayer) and adjacent to the fourth material layer B2
And has a first forbidden band and potential for electrons and holes
Thickness that acts as a barrier and allows tunneling of holes
A first material layer A3 (eg undoped In)_0.52
Al_0.48As layer) and adjacent to the first material layer A3
Is formed and has a second forbidden band and pairs with electrons and holes.
Two-dimensional excitation that is an active layer acting as a quantum well
A second material layer A4 having a thickness in which the child may be present (eg
Undoped In_0.53Ga_0.47As layer) and the second object
Is formed adjacent to the texture layer A4 and has a first forbidden band
Both act as potential barriers for electrons and holes, and
First material layer A5 having a thickness capable of tunneling
(For example, undoped In_0.52Al_0.48As layer) and the above
Is formed adjacent to the first material layer A5 and
It has three forbidden bands and is doped with n-type impurities
Second or acting as a quantum well for children and holes
Third material layer A6 (eg p-type In_0.53Ga_0.47As
Vertical structure pn type in which each material layer of
A second or third material layer as described above, which comprises a superlattice
A2 and the second or third material layer A6, respectively.
The difference in energy between the first quantum levels of electrons and holes
The first quantum of electrons and holes generated in the second material layer A4
It is characterized in that it is large compared to the energy difference between levels.
Or

(2) In the above (1), the positions of the fourth substance layer B2 and the first substance layer A3 are exchanged, and the first substance layer A3 and the second or third substance layer A2 are formed. The fourth material layer B2 and the second material layer A4 are adjacent to each other, or

(3) In the above (1) or (2),
The positions of the fourth material layer B1 and the first material layer A1 are exchanged, and the first material layer A1 and the second or third material layer A2 and the fourth material layer B1 and the second material layer A4 are replaced. Characterized by being adjacent to each other, or

(4) In the above (1), (2) or (3), holes are removed from the second or third material layer A2 and electrons are removed from the second or third material layer A6. In order to achieve this, the vertical structure pn-type superlattice is divided into lines or meshes, and a defect layer (for example, the defect layer D) that acts from the front surface side to the back surface side of the vertical structure pn-type superlattice to act as a recombination center. ) Is formed, or

(5) In the above (1), (2) or (3), holes are removed from the second or third material layer A2 and electrons are removed from the second or third material layer A6. In order to achieve this, the vertical structure pn-type superlattice is divided into lines or meshes, and a groove is formed from the front surface side to the back surface side of the vertical structure pn-type superlattice to act as a recombination center. Or

(6) In the above (1) or (2) or (3) or (4) or (5), the vertical structure pn
Type superlattice formed on the front surface and the back surface of the optical mirror including a semiconductor multilayer film or a dielectric film (for example, the semiconductor multilayer film mirror 3
And 4) are formed.

[0035]

According to the above-mentioned means, in the non-linear optical device of the present invention, in the barrier to act on both holes and electrons, the thickness of the barrier for holes is determined by the tunneling time of holes. Is sufficiently thin to be comparable to that of electrons, the barrier for electrons can be made substantially thick enough, so that electrons generated in the second material layer A4, which is an active layer composed of quantum wells, are generated. Is strongly confined, and prevents the electron wave function there from coupling with the second or third material layer A2 which is also a quantum well for escaping holes generated in the second material layer A4. You can
Therefore, even if the tunneling probability of the holes is made to be similar to that of electrons, it does not lead to a decrease in exciton peak intensity, and high-speed operation without impairing the nonlinear optical property due to the two-dimensional excitons. You can

[0036]

EXAMPLES Main data when the configuration of the non-linear optical device described with reference to FIGS. 1 and 2 is embodied as examples will be described by way of example. 2 shows a vertical structure pn type superlattice (one cycle + two layers),
All of them are explained.

(1) Regarding the first material layer A1 Material: Undoped In _0.52 Al _0.48 As Thickness: 1.17 [nm] (2) About the fourth material layer B1 Material: Undoped (GaAs _0.51 Sb _0.49 ) _x (In
_0.52 Al _0.48 As) _1-x Thickness: 2.94 [nm]

(3) Second or Third Material Layer A2 Material: p-type In _0.53 Ga _0.47 As or p-type (In _0.53 G
_{a 0.47 As) y (In 0.} 52 Al 0.48 As) 1-y thickness: 2.94 [nm] Doping: the Be 1 × 10 ¹² in the center portion of the layer [cm ^-2]
(4) Regarding the fourth material layer B2 Material: Undoped (GaAs _0.51 Sb _0.49 ) _x (In
_0.52 Al _0.48 As) _1-x Thickness: 2.94 [nm]

(5) First Material Layer A3 Material: Undoped In _0.52 Al _0.48 As Thickness: 1.17 [nm] (6) Second Material Layer A4 Material: Undoped In _0.53 Ga _0.47 As Thickness : 4.50 [nm]

(7) First material layer A5 Material: undoped In _0.52 Al _0.48 As Thickness: 4.11 [nm] (8) Second or third material layer A6 Material: n-type In _0.53 Ga _0.47 As or n type (In _0.53 G
_{a 0.47 As) y (In 0.} 52 Al 0.48 As) 1-y thickness: 3.52 nm, doping: 1 × the Si in the central portion of layer 10 ¹² [cm ^-2]
As planar doping

(9) First Material Layer A5 Material: Undoped In _0.52 Al _0.48 As Thickness: 4.11 [nm] (10) Second Material Layer A4 Material: Undoped In _0.53 Ga _0.47 As Thickness : 4.50 [nm]

(11) Stacking period number of superlattice A1, B1, A2, B2, A3, A4, A5, A6 are set as one period and folded back at A6 for 50 periods. In the superlattice, A1 and B1 are interchanged. , Again, B2 and A
Replace 3, replace B1, A1, A2, A3, B2, A
It can also be 4, A5, A6. (12) About Substrate 1 Material: InP

(13) Regarding the defect layer D Width: eg 0.5 [μm] Number: The occupied area of the plane is 100 [μm] × 100 [μ
m] for vertical structure pn superlattice 25 [pieces] (same width and number of grooves)

The above-described embodiment can be manufactured extremely easily by applying the semiconductor device manufacturing technique which has been widely used in the past. (1) For example, molecular beam epitaxial growth (molec
ultra beam epitaxy (MBE) method or metalorganic chemical vapor deposition (metalorgani)
c chemical vapor deposit
(ion: MOCVD) method, an appropriate compound semiconductor crystal growth method is applied to stack and grow the etching stop layer 2 and the vertical structure pn type superlattice SL on the substrate 1.

(2) For example, chemical vapor deposition (chemi)
cal vapor deposition: CVD)
By applying the method, a protective film made of, for example, SiO ₂ is formed.

(3) A resist film is formed by applying a resist process in the lithography technique, and then a line shape or a mesh shape depending on a light beam, an electron beam, a focused ion beam, etc., if necessary. Exposure and develop.

(4) CHF ₃ as etching gas
Reactive Ion Etching (react)
By applying the ive ion etching (RIE) method, SiO _{2 is used} with the resist film as a mask.
The protective film made of is patterned.

(5) Using the protective film made of SiO ₂ as a mask, Si or Be ions are implanted to form a line-shaped defect layer D or a mesh-shaped defect layer D. The focused ion beam may be used to directly draw Si ions or Be ions on the surface of the stacked layers without going through the processes (2) to (4).

(6) The backside etching of the substrate 1 made of InP is performed by applying a resist process in the lithography technique and a wet etching method using an etchant as an HBr-based etching solution. Since this etching is automatically stopped by the etching stop layer 2, there is no difficulty even if the substrate 1 is thick. Needless to say, such etching is performed to reduce the loss of incident light.

Although the above description has been made with respect to the step of forming the defect layer D, in the case of forming the groove D, a protective film also made of SiO ₂ is similarly formed in the step (6). The trench D may be completed by selectively etching the vertical structure pn type superlattice SL by applying the RIE method using the mask as the mask and the etching gas as the Cl-based gas.

FIG. 3 is a perspective view of an essential part showing an embodiment in which the non-linear optical device described with reference to FIGS. 1 and 2 is applied as an etalon element. The same symbols as those used in FIGS. They represent the same part or have the same meaning. In the figure, 3 and 4 denote semiconductor multilayer film mirrors, specifically, for example, InAlAs layer and InGaAs.
Repetitive multi-layer laminated film with layers or GaAs layer and AlA
It is composed of a repeating multilayer film including an s layer. As the mirror, a dielectric film mirror may be used instead of the semiconductor multilayer film mirror.

FIG. 4 is a diagram showing the static light absorption characteristics obtained according to the embodiment of the present invention, in which the vertical axis represents the light absorption rate (arbitrary scale) and the horizontal axis represents the wavelength [! nm] respectively. The figure shows the characteristic line AB according to the invention.
1 and the characteristic line AB2, which is based on the conventional technique for reference.
It can be seen that the characteristic line AB1 has a clear two-dimensional exciton peak as compared with the characteristic line AB2.

[0053]

In the non-linear optical device of the present invention, the first material layer A which acts as a potential barrier against electrons and holes.
A second or third material layer A2 doped with 1 and p-type impurities and acting as a quantum well for electrons and holes, and a fourth material layer B2 acting as a potential barrier only for electrons and electrons and holes. On the other hand, a first material layer A3 that acts as a potential barrier and a second material layer A4 that acts as a quantum well for electrons and holes and has a thickness such that two-dimensional excitons can exist and electrons. The first material layer A5 that acts as a potential barrier for holes and the second or third material layer A6 that is doped with n-type impurities and acts as a quantum well for electrons and holes are stacked. A vertical structure pn-type superlattice forming one cycle, and
The energy difference between the first quantum levels of electrons and holes generated in the second or third material layer A2 and the second or third material layer A6, respectively, is equal to that in the second material layer A4. It is large compared to the energy difference between the first quantum levels of generated electrons and holes.

By adopting the above-mentioned structure, in the non-linear optical device of the present invention, in the barrier to act on both holes and electrons, the thickness of the barrier for holes is set to the tunneling time of holes. Is sufficiently thin to be comparable to that of electrons, the barrier for electrons can be made substantially thick enough, so that electrons generated in the second material layer A4, which is an active layer composed of quantum wells, are generated. Is strongly confined, and prevents the electron wave function there from coupling with the second or third material layer A2 which is also a quantum well for escaping holes generated in the second material layer A4. Therefore, even if the tunneling probability of the holes is made to be similar to that of electrons, it does not cause a decrease in exciton peak intensity and impairs the nonlinear optical property due to the two-dimensional excitons. Not fast It can be created.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of a nonlinear optical device for explaining the principle of the present invention.

2 is an energy band diagram of the non-linear optical device seen in FIG. 1. FIG.

FIG. 3 is a perspective view of a principal part showing an example in which the nonlinear optical device described with reference to FIGS. 1 and 2 is applied as an etalon element.

FIG. 4 is a diagram showing static light absorption characteristics obtained according to an example of the present invention.

FIG. 5 is an energy band diagram for explaining a non-linear optical device having a conventional TBQ structure.

FIG. 6 is an energy band diagram for explaining a non-linear optical device using a vertical structure pn type superlattice.

[Explanation of symbols]

1 Substrate 2 Etch Stop Layer SL Vertical Structure pn Superlattice A1 First Material Layer with First Forbidden Band A2 Second or Third Material Layer with Second or Third Forbidden Band A3 First Forbidden Band First material layer with band A4 Second material layer with second forbidden band A5 First material layer with first forbidden band A6 Second or third with second or third forbidden band Material layer B1 A fourth object layer having a fourth forbidden band and acting as a barrier only to electrons B2 A fourth object layer having a fourth forbidden band and acting as a barrier only to electrons D Defect layer e ₁ electron first quantum level h ₁ hole first quantum level

Claims (6)

[Claims] 1. A first material layer A1 and a first material layer A1 which have a first forbidden band, act as a potential barrier against electrons and holes, and have a thickness capable of sufficiently tunneling holes. A fourth material layer B1 formed adjacently and having a fourth forbidden band and acting as a potential barrier only against electrons, and a second or third material layer B1 formed adjacently to the fourth material layer B1. A second or third material layer A2 which has a forbidden band and is doped with p-type impurities and acts as a quantum well for electrons and holes, and is formed adjacent to the second or third material layer A2. A fourth material layer B2 having four forbidden bands and acting as a potential barrier only for electrons, and a fourth forbidden band formed adjacent to the fourth material layer B2 and having electrons and holes. Acts as a potential barrier against holes A first material layer A3 having a sufficiently tunnelable thickness and an active layer formed adjacent to the first material layer A3 and having a second forbidden band and acting as a quantum well for electrons and holes. And a second material layer A4 having a thickness such that two-dimensional excitons can exist, and a second forbidden band formed adjacent to the second material layer A4, and having a first forbidden band and for electrons and holes. Is formed adjacent to the first material layer A5 and the first material layer A5 having a thickness that allows electrons to tunnel sufficiently by acting as a potential barrier and has a second or third forbidden band and n A vertical structure pn-type superlattice in which each material layer of the second or third material layer A6, which is doped with a type impurity and acts as a quantum well for electrons and holes, is stacked to form one cycle; Second or third material layer Second material layer A the energy difference between the first quantum level of 2 and the second or the third of electrons and holes generated respectively material layer A6 has the
4. A non-linear optical device having a large energy difference between the first quantum level of electrons and holes generated in 4. 2. The positions of the fourth material layer B2 and the first material layer A3 are exchanged, and the first material layer A3 and the second or third material layer A2 and the fourth material layer B2 and the second material layer A2 are replaced. The nonlinear optical device according to claim 1, wherein the material layers A4 are adjacent to each other. 3. The positions of the fourth material layer B1 and the first material layer A1 are exchanged, and the first material layer A1 and the second or third material layer A2 and the fourth material layer B1 and the second material layer A1 are replaced. 3. The non-linear optical device according to claim 1 or 2, wherein the material layers A4 are made adjacent to each other. 4. A vertical structure pn-type superlattice is divided into lines or meshes for removing holes from the second or third material layer A2 and electrons from the second or third material layer A6, respectively. The defect layer is formed so as to reach from the front surface side to the back surface side of the vertical structure pn type superlattice and act as a recombination center. Non-linear optical device. 5. A vertical structure pn-type superlattice is divided into lines or meshes for removing holes from the second or third material layer A2 and electrons from the second or third material layer A6, respectively. The non-linear optical device according to claim 1, 2 or 3, further comprising a groove extending from the front surface side to the back surface side of the vertical structure pn type superlattice. 6. An optical mirror made of a semiconductor multilayer film or a dielectric film is formed on the front surface and the back surface of the vertical structure pn type superlattice. The nonlinear optical device according to claim 4 or 5.