JPH0743757A - Semiconductor quantum well optical element - Google Patents

Abstract

PURPOSE:To provide a semiconductor quantum well optical element of such a strain quantum well structure having the highest possible optical nonlinear effect while maintaining a light absorption characteristic of a blue shift. CONSTITUTION:This semiconductor quantum well optical element is formed by utilizing quantum wells or superlattice structures consisting of compd. semiconductors and is constituted by alternately laminating InGaAs compressive strain layers 11 having the lattice constant larger than the lattice constant of a GaAs substrate 10 and the quantum well structures 12 consisting of two kinds of the compd. semiconductors AlGaAs/GaAs having the lattice constant equal to the lattice constant of the GaAs substrate 10 on the GaAs substrate 10 having a (111) face at its main face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical element which is indispensable for constructing an optical information processing system for controlling light by an optical signal or an electric signal, and particularly utilizes a quantum well or a superlattice structure made of a compound semiconductor. Semiconductor quantum well optical element.

[0002]

2. Description of the Related Art Recently, a semiconductor quantum well optical element utilizing a semiconductor quantum well or a superlattice structure has been researched and developed in order to realize a highly efficient and ultrafast nonlinear optical element.
Semiconductor quantum wells or superlattice structures have good electrical properties in addition to large nonlinear constants compared to other nonlinear materials (eg, organic nonlinear materials), so electrical means are introduced to further improve optical nonlinearity. It can be enhanced, or the electronic element and the non-linear optical element can coexist.

Recently, unlike a normal quantum well nonlinear device formed in the [100] direction, as shown in FIG.
[00] Quantum well structure on substrate (called intrinsic region i)
And n-type and p-type doped layers are stacked, so-called ni
A p-i structure has been proposed (DSMcCallum et al,
J. Appl. Phys 70, 6891 (1991)).

In this structure, space charges are formed because some of the impurities in the n and p layers are ionized. As a result, an internal electric field is applied to the quantum well region i in the direction perpendicular to the layer. By applying this internal electric field, the energy band structure is largely bent in the thermal equilibrium state as shown in FIG. Therefore, the peak of exciton absorption in the quantum well is red-shifted to the longer wavelength side as compared with the case of no electric field.

When light is irradiated in this state, the electrons and holes excited in the quantum well are separated into an n-type doped layer and a p-type doped layer by the internal electric field. Since the carriers excited by these lights electrically neutralize the ionized impurities, the electric field strength in the quantum well is lowered as shown in FIG. Become. Therefore, the exciton absorption peak in the quantum well is blue-shifted to the shorter wavelength side as compared with the case where light is not irradiated.

Then, due to the shift of the absorption peak,
Changes occur in the absorption coefficient and refractive index.
Utilizing this, application to optical elements such as optical modulators, optical switches, and optical memories can be considered.

[0007]

However, in the above n-i-p-i structure, the magnitude of the internal electric field is completely determined by the density of ionized space charges, that is, the doping concentration in the n-layer and the p-layer. To be done. As is well known, the impurity concentration that can be doped into a semiconductor material is limited (usually 10 ¹⁶ to 10 ¹⁹ cm ⁻³ ), and some semiconductors cannot be doped at all (for example, GaN), that is, p and n layers cannot be formed. possible. Furthermore, since the internal electric field is weak (-10 ⁴ V / cm), the shift amount of the exciton absorption peak is small, and a very large nonlinear effect cannot be expected.

From the above reasons, when applied to an optical switch which is a typical non-linear optical element, the controllable range with respect to the internal electric field due to the externally applied electric field is quite narrow, so that the change amount of the refractive index is small and The intensity ratio becomes smaller when the switch turns on and off. Also, since the internal electric field is weak,
When the externally applied electric field is unstable, it is easily affected,
Not only is the device lacking in stability, but the wavelength of light that can be controlled is also limited to a fairly narrow range.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor having a strained quantum well structure having a large optical nonlinear effect while maintaining the blue-shift optical absorption characteristics. It is to provide a quantum well optical element.

[0010]

In order to solve the above problems, the present invention employs the following configurations. That is, the present invention provides a semiconductor quantum well optical element utilizing a quantum well or superlattice structure made of a compound semiconductor, in which the main surface is (1
On a compound semiconductor substrate of the 11) plane, a compound semiconductor having a lattice constant different from that of the substrate and a quantum well or a superlattice structure composed of two kinds of compound semiconductors A and B having the same lattice constant of the substrate are alternately laminated. It is characterized by

Here, the following are preferred embodiments of the present invention. (1) On a compound semiconductor substrate whose main surface is a (111) plane, a compound semiconductor (compressive strain layer) having a larger lattice constant than the substrate 1
And a quantum well or a superlattice structure 2 composed of two kinds of compound semiconductors A and B matching the lattice constant of the substrate are alternately laminated. (2) On the compound semiconductor substrate whose main surface is the (111) plane, a compound semiconductor (tensile strain layer) with a lattice constant smaller than that of the substrate 3
And the quantum well or the superlattice structure 2 are alternately laminated. (3) A semiconductor 1, a quantum well or a superlattice structure 2, a semiconductor 1, a semiconductor 3, a quantum well or a superlattice structure 2, and a semiconductor 3 are sequentially and alternately laminated on a compound semiconductor substrate having a (111) main surface. The periodic structure in which the structure (including both the compressive strain layer and the tensile strain layer) is used alone or repeatedly is used.

[0012]

According to the present invention, when a semiconductor material having a lattice constant of a substrate is laminated on a compound semiconductor substrate having a (111) plane as a main surface, a piezoelectric effect due to strain caused by lattice mismatching causes A large internal electric field is generated in the strained layer.
The direction of this internal electric field is determined by the nature of the strain (compressive strain or tensile strain).

For example, when a semiconductor having a lattice constant larger than that of a substrate is stacked on a compound semiconductor substrate having a (111) B plane as a main surface, a compressive strain is generated in a direction parallel to the substrate surface, so that the crystal surface is moved from the substrate to the crystal surface. An internal electric field is generated in the strained layer. On the other hand, when a semiconductor having a lattice constant smaller than that of the substrate is stacked on the (111) B-plane substrate, tensile strain is generated in a direction parallel to the substrate surface, so that the directions of the internal electric fields are reversed.

The magnitude of the internal electric field is determined by the magnitude of strain, that is, the magnitude of lattice mismatch between the laminated semiconductor material and the substrate. For example, (11
1) When GaAs _1-x P _x is laminated on the B-plane GaAs substrate, the magnitude of the internal electric field generated by the piezoelectric effect is about 2 × 10 ⁵ V /
cm is extremely large. Needless to say, GaAs _1-x P
By varying the P content x in the _x, it can be freely controlled according to need the size of the internal electric field.

Further, it is also a great merit that a doping process, which is indispensable for previously giving an internal electric field to a quantum well structure, like the nip structure, is not necessary at all. As a result, for example, p-type materials such as GaN, which is expected to be a blue light emitting diode material but has not yet been put to practical use
Even semiconductor materials that cannot be type-doped can be used according to the present invention.

When the quantum structure of the present invention is applied to, for example, an optical switch, which is a typical nonlinear optical element, the internal electric field is strong, so that the blue shift amount of the exciton absorption peak due to incident light or an externally applied electric field is large, The amount of change in the refractive index is considered to be quite large. Therefore, the transmitted light intensity ratio in the on / off state is extremely large as compared with the conventional n-i-p-i element.

Further, since the internal electric field is strong, it is not easily affected by the instability of the externally applied electric field, and not only the element stability is excellent, but also the controllable wavelength range of light is considerably widened. Since the quantum well of the lattice matching system or the superlattice structure can be used as it is, it is very advantageous in manufacturing the device.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is for explaining a semiconductor quantum well optical element according to a first embodiment of the present invention.
1] shows a quantum structure including a compression strained layer in the [1] direction.

GaAs substrate 10 having a plane orientation of (111) B
InG having a lattice constant larger than that of the GaAs substrate 10
aAs (compressive strain layer) 11 and Al composed of AlGaAs and GaAs whose lattice constant matches the GaAs substrate 10.
GaAs / GaAs quantum well or superlattice structure 12,
The layers are stacked alternately. At this time, InGaAs11 is subjected to compressive strain in a direction parallel to the substrate surface, and
ssion) Region c is formed.

On the other hand, the AlGaAs / GaAs quantum well or superlattice structure 12 does not undergo strain and is intrinsic (intrinsic).
) Forming region i. Here, since the layer thickness of InGaAs11 is selected to be sufficiently smaller than its critical thickness, misfit dislocations due to strain relaxation do not occur, and
11 is a strained layer that is elastically and uniformly strained.

The present embodiment is characterized in that a c-i-c-i periodic structure in which the above-mentioned c-i structure is used alone or repeatedly is used. FIG. 2 is an energy band diagram corresponding to the quantum structure of FIG. As described in detail in the above [Action] section, since compressive strain is generated in the direction parallel to the layers, the internal electric field from the GaAs (111) B substrate 10 to the crystal surface is changed by the piezoelectric effect.
s quantum well or superlattice structure 12 will be applied. Due to the presence of this internal electric field, the energy band structure is greatly tilted as shown in FIG. 2A in the thermal equilibrium state (without light irradiation). Quantum confined Stark effect (Quantu
Due to the m Confined Stark Effect), the exciton absorption peak in the quantum well or superlattice structure 12 is red-shifted to the longer wavelength side as compared with the case where there is no internal electric field.

However, the above-mentioned c-i or c-i-c-
When a quantum structure having a period like i is irradiated with light, electrons and holes excited by the quantum well or superlattice structure 12 are separated by the internal electric field and accumulated in the InGaAs 11. This lowers the internal electric field, and therefore the inclination of the energy band structure becomes small as shown in FIG. 2 (b). As a result, the exciton absorption peak in the quantum well or superlattice structure 12 is blue-shifted to the short wavelength side as compared with the case where light is not irradiated. This blue shift causes a large change in the absorption coefficient and the refractive index.

Utilizing such characteristics, c- of this embodiment is used.
When the i or c-i-c-i structure is applied to, for example, an optical switch, since the change in the refractive index due to the application of an external electric field is large, the intensity ratio of transmitted light in the on / off state is the same as that of the conventional n-i. It is much higher than the p-i structure. Moreover,
Since the internal electric field is strong, the element is less likely to be affected by the instability of the externally applied electric field and not only has excellent stability, but also the controllable wavelength range of light is considerably wide.

Further, since the doping process is not necessary, the lattice-matched quantum well or the superlattice structure such as AlGaAs / GaAs, which is technically mature, and the semiconductor material such as GaN which cannot be p-type doped are fully utilized. can do. Furthermore, In in InGaAs11
It goes without saying that the strain and the magnitude of the internal electric field can be freely adjusted as needed by changing the composition. (Embodiment 2) FIG. 3 is a schematic view showing a quantum structure including a [111] direction compression strained layer according to a second embodiment of the present invention. On a GaAs substrate 20 having a plane orientation of (111) B, an AlGaAs / GaAs quantum well or superlattice structure 21 made of AlGaAs and GaAs having a lattice constant matching GaAs, and In having a lattice constant larger than GaAs.
GaAs (compressive strain layers) 22 are alternately laminated in sequence. At this time, the AlGaAs / GaAs quantum well or the superlattice structure 21 forms the intrinsic region i without being subjected to strain.

On the other hand, the InGaAs 22 is subjected to compressive strain in the direction parallel to the surface of the substrate and forms the compressed region c. Here, since the layer thickness of InGaAs22 is selected to be sufficiently smaller than the critical film thickness, misfit dislocations due to strain relaxation do not occur, and InGaAs22 is a strained layer that is elastically uniformly strained.

The present embodiment is characterized by using the above-mentioned i-c structure alone or using an i-c-i-c periodic structure which is repeated many times. The energy band diagram corresponding to the ic-ic quantum structure of FIG. 3 is c- of the first embodiment.
It is clear from the principle described in the above [Action] that the energy band diagram in the ic quantum structure (FIG. 2) is very similar. Therefore, i-c-i of the present embodiment
The -c quantum structure can be applied to all devices in the c-i-c-i quantum structure of the first embodiment, and the principle of operation is exactly the same. (Embodiment 3) FIG. 4 is a schematic view showing a quantum structure including a [111] direction tensile strained layer according to a third embodiment of the present invention. GaAs substrate 30 having plane orientation (111) B
GaAsP (tensile strain layer) 31 having a lattice constant smaller than GaAs and A having a lattice constant matching GaAs
AlGaAs / GaA consisting of 1GaAs and GaAs
s quantum wells or superlattice structures 32 are sequentially stacked alternately. At this time, the GaAsP 31 is subjected to tensile strain in a direction parallel to the substrate surface and forms a tensile region t.

On the other hand, the AlGaAs / GaAs quantum well or superlattice structure 32 forms the intrinsic region i without being strained. Here, since the layer thickness of GaAsP31 is selected to be sufficiently thinner than its critical thickness, misfit dislocations due to strain relaxation do not occur, and GaAsP31 is a strained layer that is elastically uniformly strained.

The present embodiment is characterized by using a t-i-t-i periodic structure obtained by repeating the above-mentioned t-i structure alone or repeatedly. FIG. 5 is an energy band diagram corresponding to the quantum structure of FIG. As described in detail in the above [Action], tensile strain is generated in the direction parallel to the layers, so that an internal electric field from the crystal surface to the substrate is generated in the AlGaAs / GaAs quantum well or superlattice structure 32 by the piezoelectric effect. Will be applied. By the application of this internal electric field, the energy band structure is greatly inclined in the thermal equilibrium state (without light irradiation) as shown in FIG. Due to the quantum confined Stark effect, a quantum well or superlattice structure 32
The exciton absorption peak at 1 is red-shifted to the longer wavelength side as compared with the case where there is no internal electric field.

However, the above t-i or t-i-t-
When a quantum structure having a period like i is irradiated with light, the electrons and holes excited by the quantum well or superlattice structure 32 are separated by the internal electric field and accumulated in GaAsP 31. This lowers the internal electric field, and therefore the inclination of the energy band structure becomes small as shown in FIG. 5 (b). As a result, the exciton absorption peak in the quantum well or superlattice structure 32 is blue-shifted to the short wavelength side as compared with the case where light is not irradiated. This blue shift causes a large change in the absorption coefficient and the refractive index.

The t-i-t-i quantum structure of the present embodiment is the c-i-c-i of the first embodiment or the i-c of the second embodiment.
It is clear that they are functionally similar to the -ic quantum structure, except that the direction of the internal electric field and the slope of the energy band structure are opposite. Therefore, t-i-t-
Like the c-i-c-i or i-c-i-c quantum structure, the i-quantum structure has a large change in the refractive index due to the application of an external electric field when applied to an optical switch.
The intensity ratio of transmitted light in the off state is
-Much higher than the i structure. In particular, since a doping process is not required to form an internal electric field, even a semiconductor material having a wide bandgap such as GaN, which cannot be p-type doped, is applied to the t-i-t-i quantum structure of this embodiment. can do. (Embodiment 4) FIG. 6 is a schematic view showing a quantum structure including a [111] direction tensile strained layer according to a fourth embodiment of the present invention. GaAs substrate 40 having a plane orientation of (111) B
On top of it, an AlGaAs / GaAs quantum well or superlattice structure 41 made of AlGaAs and GaAs having a lattice constant matching GaAs, and a lattice constant smaller than G
and aAsP (tensile strain layer) 42 are alternately laminated in sequence. At this time, the AlGaAs / GaAs quantum well or the superlattice structure 41 forms the intrinsic region i without being strained.

On the other hand, GaAsP 42 is subjected to tensile strain in a direction parallel to the surface of the substrate and forms a tensile region t.
Here, since the layer thickness of GaAsP42 is selected to be sufficiently smaller than its critical thickness, misfit dislocations due to strain relaxation do not occur, and GaAsP42 is a strained layer that is elastically and uniformly strained.

The present embodiment is characterized in that the above-mentioned ti structure is used alone or an it-it periodic structure in which the ti structure is repeated many times is used. The energy band diagram corresponding to the it-it quantum structure of FIG. 6 is t of the third embodiment.
It is apparent from the principle described in the above [Action] that the energy band diagram in the -it-i quantum structure (Fig. 5) is very similar. Therefore, it-i of the present embodiment
The -t quantum structure is c-i-c-of the first, second, and third embodiments.
It can be applied to all devices in an i, ic-ic or t-i-t-i quantum structure,
The principle of operation is exactly the same as the t-i-t-i quantum structure of the third embodiment. (Embodiment 5) FIG. 7 is a schematic view showing a quantum structure including both a [111] direction compressive strain layer and a tensile strain layer according to a fifth embodiment of the present invention. On a GaAs substrate 50 having a plane orientation of (111) B, InGaAs (compressive strain layer) 51 having a lattice constant larger than GaAs, and a lattice constant GaA.
A consisting of AlGaAs and GaAs matching the s substrate
lGaAs / GaAs quantum well or superlattice structure 52, I
nGaAs51, GaA having a lattice constant smaller than GaAs
sP (tensile strain layer) 53, quantum well or superlattice structure 5
2 and GaAsP53 are sequentially laminated alternately. At this time, in the direction parallel to the substrate surface, the InGaAs 51 receives a compressive strain to form a compressed region c, and the GaAsP 53 receives a tensile strain to form a tensile region t.

On the other hand, the AlGaAs / GaAs quantum well or superlattice structure 52 forms the intrinsic region i without being strained. Here, since the layer thicknesses of InGaAs51 and GaAsP53 are selected to be sufficiently smaller than their critical thicknesses, misfit dislocations due to strain relaxation do not occur, and I
The nGaAs 51 and GaAsP 53 are strained layers that are elastically uniformly strained.

In this embodiment, the above c-i-c-t is used.
It is characterized by using a periodic structure in which the -it quantum structure is used alone or repeatedly. FIG. 8 is a diagram of FIG.
It is an energy band diagram corresponding to a c-t-it quantum structure. As described in the above [Operation], when InGaAs 51 having a lattice constant larger than that of GaAs is stacked on the GaAs substrate 50 having a (111) B main surface, a compressive strain is generated in a direction parallel to the layer, so that the piezoelectric effect is produced. By Ga
The internal electric field from the As substrate 50 toward the crystal surface is InGa
It is applied to the AlGaAs / GaAs quantum well or superlattice structure 52 sandwiched by As51. Similarly, GaAsP in which the opposite internal electric field has tensile strain
It will be applied to the AlGaAs / GaAs quantum well or superlattice structure 52 sandwiched between 53.

The energy band structure due to the application of these internal electric fields is shown in FIG. 8 (a) in the thermal equilibrium state (without light irradiation).
It bends greatly as shown in. Due to the quantum confined Stark effect, the exciton absorption peak in the quantum well or superlattice structure is red-shifted to the longer wavelength side compared to the case without an internal electric field.

However, when the above-mentioned c-ict-it quantum structure is irradiated with light, the quantum well or superlattice structure 52 is obtained.
The excited electrons and holes in are separated by the internal electric field and become strained layers of InGaAs51 and GaAs.
It accumulates in P53. On the contrary, this lowers the internal electric field. Therefore, the energy band structure becomes relatively flat as shown in FIG. as a result,
The exciton absorption peak in the quantum well or superlattice structure 52 is blue-shifted to the short wavelength side as compared with the case where light is not irradiated. This blue shift causes a large change in the absorption coefficient and the refractive index.

Utilizing this, in this embodiment, similar to the quantum structures of the first to fourth embodiments, novel nonlinear optical elements such as optical switches, optical modulators and optical memories can be manufactured.

7 and 8 are compared with FIGS. 13 and 14, the c-i-c-t-i-t quantum structure of the present embodiment has not only the structure but also the operating mechanism (mechanism for forming an internal electric field). , Conventional n-
It is clear that it is quite different from the ipi structure. The only thing that they have in common is that an internal electric field is applied to the quantum well or superlattice structure that is the intrinsic region.

As described in the above [Problem] section, in the conventional n-i-p-i structure, the magnitude of the internal electric field is small and can reach a practical level due to the limitation of the doping process. It's extremely difficult. In particular, a very important blue light-emitting material such as GaN cannot be p-type doped, so that it is impossible to form an n-i-p-i structure.

On the other hand, the c-i-c-t of this embodiment is used.
In the -it quantum structure, the doping process is completely eliminated in order to create the internal electric field, so there are no restrictions associated with doping. Moreover, the magnitude and direction of the internal electric field can be freely controlled as needed by changing the magnitude and direction of strain due to lattice mismatch.

For example, on a GaAs- (111) B substrate,
When GaAsP is laminated, the magnitude of the internal electric field is about 2 × 10 ⁵ even if the lattice mismatch (strain) is only 1%.
V / cm, which is more than 10 times larger than that of the conventional nip-i structure. In particular, it goes without saying that semiconductor materials such as GaN can be applied to the c-ict-it quantum structure of the present invention. Furthermore, since it is possible to make full use of the technically matured lattice-matched AlGaAs / GaAs quantum well or superlattice structure, it can be expected that the device can be manufactured relatively easily.

Further, c-i-c-t-i-t of the present embodiment.
Since there are two kinds of internal electric fields whose directions are opposite to each other in the quantum structure, a novel nonlinear optical element which cannot be considered in the quantum structures of the first to fourth examples (the internal electric field has only one direction) (details) Can refer to the seventh embodiment). (Embodiment 6) FIG. 9 is a schematic view showing a quantum structure including both a [111] direction compressive strain layer and a tensile strain layer according to a sixth embodiment of the present invention. On a GaAs substrate 60 having a plane orientation of (111) B, a GaAsP (tensile strain layer) 61 having a lattice constant smaller than GaAs, and a lattice constant GaA.
A consisting of AlGaAs and GaAs matching the s substrate
lGaAs / GaAs quantum well or superlattice structure 62, G
aAsP61, InGa having a lattice constant larger than GaAs
As (compressive strained layer) 63, quantum well or superlattice structure 6
2. InGaAs 63 are sequentially stacked alternately. At this time, in the direction parallel to the substrate surface, GaAsP61 receives tensile strain to form a tensile region t, and InGaAs63
Undergoes compressive strain to form a compressed region c.

On the other hand, the AlGaAs / GaAs quantum well or superlattice structure 62 does not undergo strain and is intrinsic (intrinsic).
) Forming region i. Where GaAsP61 and I
Since the layer thickness of nGaAs 63 is selected to be sufficiently smaller than the critical film thickness, misfit dislocations due to strain relaxation do not occur, and GaAsP 61 and InGaAs 63 are strained layers elastically and uniformly strained.

In this embodiment, the above-mentioned t-i-t-c-i- is used.
It is characterized by using a c-quantum structure alone or a periodic structure in which it is repeated many times. T-i-t-c-i-c in FIG.
The energy band diagram corresponding to the quantum structure is very similar to the energy band diagram (FIG. 8) in the c-ict-i-t quantum structure of the fifth embodiment. It is clear from the principle described in Section. Therefore, the t-i-t-c-i-c quantum structure of this embodiment can be applied to all devices in each quantum structure of the first to fifth embodiments, and the principle of operation is also the first. C of Example 5
It is exactly the same as the -ict-i-t quantum structure. (Embodiment 7) FIG. 10 is a diagram showing a configuration of an optical switch according to a seventh embodiment of the present invention including any of the strained quantum structures of the fifth and sixth embodiments. n-type GaAs (111)
An n grid layer (n region) 72 is grown on the substrate, one of the quantum structures of the fifth and sixth embodiments (quantum structure 71) is grown on it, and a p grid layer (p is formed on it). The region 73 has a grown structure. Then, the n region 72,
An external rectangular electric field is applied between the p regions 73.

As described in the fifth and sixth embodiments, c-i-
In the case of using the c-t-i-t or t-i-t-t-c-i-c strained quantum structure, two kinds of internal electric fields in opposite directions due to the piezoelectric effect due to the lattice mismatch are iG regions.
It will be applied to an aAs / GaAs quantum well or superlattice structure. It is assumed that the wavelength of light incident on the quantum structure of FIG. 10 coincides with the absorption peak in exciton transition when the external electric field E = 0.

When an external electric field with E ≠ 0 is applied to the quantum structure, the internal electric field in the same direction as the external electric field in the quantum well is further enhanced. Therefore, the exciton absorption peak in the quantum well to which it is applied is As indicated by A in 11, red shifts to the long wavelength side. On the other hand, since the internal electric field in the opposite direction to the external electric field in the quantum well is slightly reduced, the exciton absorption peak in the quantum well to which it is applied is blue-shifted to the short wavelength side as shown by B in FIG. To do.

As a result, the incident light almost absorbed when E = 0 (not transmitted through the quantum structure) is almost not absorbed (because the absorption coefficient is lowered) by the application of the external electric field of E ≠ 0. In the state, the quantum structure can be transmitted.

FIG. 12 shows the optical switching characteristics when the (+) rectangular external electric field is applied to the quantum structure (the same applies to the (-) rectangular external electric field). (A) shows the input power Pin, (b) shows the output power Pout, and (c) shows the rectangular externally applied electric field E. As is clear from this figure, for incident light with wavelength λ and input power Pin (constant),
The output power Pout is modulated by the rectangular externally applied electric field E into a rectangular shape having a high extinction ratio. That is, the efficiency of the optical switch of this embodiment is extremely high.

The present invention is not limited to the above embodiments. In the embodiment, mainly GaAs (11
1) B substrate, InGaAs, GaAsP and AlGaA
Although the case of the s / GaAs quantum well is specifically described, the material system is not limited to these, and Zinc
-blend type All semiconductor quantum well optics including compressive strain layer, tensile strain layer or combination thereof formed on III-V semiconductor (111) surface and quantum well or superlattice structure lattice-matched with substrate The present invention can be applied to an element.

Further, in the intrinsic region i, not the quantum well or the superlattice structure lattice-matched with the substrate but two patents of the present inventors (Japanese Patent Application No. 4-225770 and Japanese Patent Application No. 4-3281).
55), which is lattice-mismatched to the substrate, that is, a strained quantum well structure can be incorporated. further,
Instead of GaAs (111) B substrate, GaAs (11
1) A substrate may be used. In this case, the direction of the generated internal electric field is reversed, but it is clear that the same effect as that of the GaAs (111) B substrate is produced. In addition, various modifications can be made without departing from the scope of the present invention.

[0051]

As described in detail above, according to the present invention, a compound semiconductor having a lattice constant different from that of the substrate and a quantum well or a superlattice structure made of two kinds of compound semiconductors having the lattice constant of the substrate are alternately arranged. Since it is possible to realize a semiconductor quantum well structure having a strong internal electric field that can be freely controlled, the strained quantum well structure that has as large an optical nonlinear effect as possible while maintaining the blue-shift optical absorption characteristics. The semiconductor quantum well optical element can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a quantum structure including a [111] -direction compressive strained layer according to a first embodiment.

FIG. 2 is an energy band diagram corresponding to the c-i-c-i quantum structure of FIG.

FIG. 3 is a schematic diagram showing a quantum structure including a [111] -direction compressive strain layer according to a second embodiment.

FIG. 4 is a schematic diagram showing a quantum structure including a [111] -direction compressive strained layer according to a third embodiment.

5 is an energy band diagram corresponding to the t-i-t-i quantum structure of FIG.

FIG. 6 is a schematic view showing a quantum structure including a [111] direction tensile strained layer according to a fourth example.

FIG. 7 is a schematic diagram showing a quantum structure including both a [111] direction compressive strain layer and a tensile strain layer according to a fifth example.

8 is an energy band diagram corresponding to the c-ict-i-t quantum structure of FIG. 7.

FIG. 9 is a schematic diagram showing a quantum structure including both a [111] -direction compressive strain layer and a tensile strain layer according to a sixth example.

FIG. 10 is a schematic diagram showing a configuration of an optical switch according to a seventh embodiment including a strained quantum structure.

FIG. 11 is a diagram illustrating the operating principle of the optical switch of FIG.

12 is a switching characteristic diagram of the optical switch of FIG.

FIG. 13 is a schematic diagram showing the structure of a conventional semiconductor quantum well optical element.

14 is an energy band diagram corresponding to the n-i-p-i structure of FIG.

[Explanation of symbols]

10, 20, 30, 40, 50, 60 ... GaAs (11
1) B substrate 11, 22, 51, 63 ... InGaAs compression strain layer 12, 21, 32, 41, 52, 62 ... AlGaAs /
GaAs quantum well structure 31, 42, 53, 61 ... GaAsP tensile strain layer 71 ... Strain quantum structure portion 72 ... N-type compound semiconductor region 73 ... P-type compound semiconductor region

Claims (1)

[Claims] 1. A semiconductor quantum well optical device using a semiconductor quantum well or a superlattice structure, a compound semiconductor substrate having a (111) plane as a main surface, a compound semiconductor having a lattice constant different from that of the substrate, and a lattice of the substrate. A semiconductor quantum well optical element, characterized in that quantum wells or superlattice structures made of two kinds of compound semiconductors having a constant value are alternately laminated.