JPH0536286A - Semiconductor optical element - Google Patents

Abstract

PURPOSE:To modulate the light absorbing intensity with different wavelength by 2 elements by constituting a non-symmetrical SEED element with 2 types of different pin diodes to be operated by different wavelength. CONSTITUTION:When the switch light of constant wavelength (lambda1) and constant intensity Pin1 is made incident on a diode element 31 at the wavelength area in which the light absorption is reduced by the increase of a reverse bias voltage, a low impedance condition is obtained, the reverse bias voltage is impressed to a diode element 32 and a high impedance is obtained. When the light of different wavelength lambda2 is made incident on the element 32 to be operated by the wavelength different from the element 31, and when trigger light intensity Pin2(lambda2) to be made incident on the element 32 is smaller than switch light intensity Pin1(lambda1), the reverse bias voltage impressed condition of 31 and 32 is not changed. At the time of Pin2>Pin1, the element 32 becomes the low impedance and the element 31 is changed to a high impedance condition (B). At this time, for the element 31, the light absorption becomes small and the light switching action of switch light intensity Pout1 is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor nonlinear optical device, and to a new optical bistable device that operates at two different wavelengths.

[0002]

2. Description of the Related Art FIGS. 1 and 2 show, for example, the paper by Rentin et al. (AL Lentine et al., Applied Physics Letter).
s, 52, No. 17, 1419-1421 (1988)), which is a conventional semiconductor optical device. Symmetric Self-electrooptic-effect-devic
e, S-SEED), and FIG. 5 shows its operating principle.

This S-SEED element is a pin diode element 1 of two heterojunction semiconductors connected in series.
1 and 12, and a reverse bias constant voltage source 13 is connected to both. And the intensity of light absorption at the optical absorption edge,
Or to change the transmitted light intensity electro-optically,
The same multi-quantum well (Multiple Quantum Wells, MQ) is used for the intrinsic semiconductor layer (i) in the two pin diode structures.
W) structure is used. Each diode element 11, 1
As shown in FIG. 2, the substrate semiconductor 1 includes an n-type semiconductor contact layer 2, an n-type semiconductor clad layer 3, an intrinsic semiconductor layer 4 including a multiple quantum well structure, and a p-type semiconductor clad layer 5.
Are sequentially laminated, and the p-type semiconductor contact layer 6 is further laminated on a part of the p-type semiconductor clad layer 5. As shown in the figure, the side surfaces of each of the diode elements 11 and 12 are covered with an insulator 8, and further the metal 7 for electrodes is used.
Is connected to the p-type semiconductor contact layer 6 of the diode element 11, the electrode metal 7 ′ is connected between the n-type semiconductor contact layer 2 of the diode element 11 and the p-type semiconductor contact layer 6 of the diode element 12, and the electrode The metal 7 ″ for connection is connected to the n-type semiconductor contact layer 2 of the diode element 12. The metal 7 and 7 ″ for electrode is connected to the constant voltage source 13. Thus, the electric field can be applied from the direction perpendicular to the multiple quantum well structure. A superlattice structure (SL) may be used instead of the multiple quantum well.

Next, the operation will be described. A circuit (FIG. 1) in which two diode elements 11 and 12 including a multiple quantum well structure are connected in series and a reverse bias constant voltage (Vo) source 13 is connected is formed. In the wavelength region where the light absorption decreases with the increase of the reverse bias voltage, a constant wavelength (λ ₁ ) and a constant intensity Pi
When the light of n ₁ enters the switching diode element 11,
The diode element 11 is in a low impedance state due to the presence of charge carriers generated by light absorption, and a reverse bias voltage is applied to the diode element 12. That is, the diode element 12 is in a high impedance state. At this time, the so-called quantum Stark effect (see the above-mentioned Lentin et al. Article) causes the diode element 11 to absorb light.
The (transmission) becomes large (small) and the diode element 1
In No. 2, light absorption (transmission) is small (large).

When light of the same wavelength (λ ₂ = λ ₁ ) having a light intensity Pin ₂ is incident on the diode element 12 operating at the same wavelength as the diode element 11 and the intensity thereof is increased, the diode element 12 is caused to increase in intensity. The generated photocurrent increases as shown by the solid line in FIG. 5 (corresponding to one Pin ₂ respectively), and the current flowing through the circuit is determined by the intersection (A) with the load curve of the diode element 11 (dotted line in FIG. 5). It becomes the current value. When the light intensity Pin ₂ applied to the diode element 12 is smaller than Pin ₁ , the way of applying the reverse bias voltage to the diode elements 11 and 12 is the same as that described above.

However, when Pin ₂ > Pin ₁ , when the threshold value is exceeded, the intersection (A) of the load curves where the diode element 12 remains in the high impedance state does not exist, so the diode element 12 enters the low impedance state. , As a result of switching the applied bias voltage value, the diode element 11 changes from the low impedance state to the high impedance state.
Switch to (B). At this time, the light absorption (transmission) of the diode element 11 is in a small (large) state. That is,
The increase of Pin _2, Pout ₁ of optical switching operation (OF
F → ON) is obtained.

On the other hand, when Pin ₂ is decreased, the low impedance state of the diode element 12 is maintained until the intersection (C) with the load curve, so that the ON state (high impedance state) of the diode element 11 is maintained. The result is optical memory operation. Pin ₂ decreases and intersection point C with the load curve
Beyond C, there is no intersection with the load curve below C, so the optical switching operation to the initial state (D) (C (ON) →
D (OFF) occurs, and the optical bistable operation is obtained.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention S-SE described above
In the ED element, since the two pin diode elements use the same multiple quantum well structure, the light emitted to the diode element 11 and the light emitted to the diode element 12 have the same wavelength. Therefore, it is difficult to distinguish them and guide them to a minute element opening, and there is a problem of so-called crosstalk, and it is necessary to distinguish the light radiated to the diode elements 11 and 12 by polarizations orthogonal to each other (eg. GD Boyd et al., Applied Physics, 57, N
18), 1843-1845, 1990) and other fundamental problems. The present invention has been made to solve the above problems, and two elements have different wavelengths (λ ₁ ≠
It is an object of the present invention to provide a semiconductor optical device configured so that the light absorption intensity can be modulated by λ ₂ ).

[0009]

A semiconductor optical device according to the present invention has a multiple quantum well structure or a superlattice structure as an intrinsic semiconductor layer, and an electric field is applied from a direction perpendicular to the multiple quantum well structure or the superlattice structure. The first pin diode of the heterojunction semiconductor capable of changing the light transmittance in the wavelength region near the optical absorption edge by doing so, and having the multiple quantum well structure or the superlattice structure as the intrinsic semiconductor layer, the multiple quantum well structure Alternatively, it is possible to change the light transmittance in the wavelength region near the optical absorption edge by applying an electric field from a direction perpendicular to the superlattice structure.
The n-diode is composed of a second pin diode of a heterojunction semiconductor capable of changing the light transmittance in a wavelength range different from that of the n-diode, and a constant voltage source capable of applying a constant reverse bias voltage. The first pin diode and the second pin diode are connected to each other. A feedback circuit can be constructed electro-optically by connecting in series with a constant voltage source.

[0010]

The semiconductor optical device according to the present invention is a self-electro-optical effect (SEED) device composed of two heterojunction type semiconductor pin diode devices for switching and for triggering, and is provided in the intrinsic semiconductor region of each pin diode device. The multi-quantum well or superlattice structure used is composed of layers having different structures designed to work in mutually different wavelength ranges. The semiconductor optical device according to the present invention includes two types of different pin diodes that operate at different wavelengths from each other and has an asymmetric SEED (Asymme).
(tric-SEED, A-SEED) is configured,
The wavelengths of switch light and trigger light can be different.
Therefore, it is not necessary to distinguish the two types of light by the polarized light, and there is an advantage that the configuration of the optical device for operating the element is greatly simplified. In addition, pi grown on GaAs substrate
In the n-diode structure, when one of the two SEED elements (diode element) is composed of a multiple quantum well or a superlattice having an InGaAs strained quantum well, one wavelength can be set to a wavelength at which the GaAs substrate becomes a transparent body. Therefore, there is an advantage that the element can be easily configured without removing the substrate.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Here, the same reference numerals indicate the same or corresponding parts. 3 and 4 are views showing the structure of an asymmetric self-electro-optical effect (A-SEED) device according to an embodiment of the present invention. The A-SEED element is composed of two serially connected heterojunction semiconductor pin diode elements 31 and 32, and a reverse bias constant voltage source 33 is connected to both.
Then, in order to electro-optically change the intensity of light absorption at the optical absorption edge or the intensity of transmitted light, multiple quantum wells (Multiple Quantum Wells, The MQW) structure is used.

As shown in FIG. 4, the diode element 31 includes a GaAs substrate semiconductor 21, an n-type semiconductor contact layer (n-GaAs) 22, and an n-type semiconductor cladding layer (n).
-AlGaAs) 23, undoped InGaAs / Al
An intrinsic semiconductor layer 24 including a GaAs multiple quantum well structure (MQW) or a superlattice (SL) and a p-type semiconductor clad layer (p-AlGaAs) 25 are sequentially stacked, and a p-type semiconductor contact layer (p- GaAs) 26
It is stacked on a part of the p-type semiconductor clad layer 25. Similarly, the diode element 32 is a substrate semiconductor 2 of GaAs.
1, a p-type semiconductor contact layer (p-GaAs) 2
6 ', p-type semiconductor clad layer (p-AlGaAs) 2
5 ', an intrinsic semiconductor layer 24' including an undoped GaAs / AlGaAs multiple quantum well structure (MQW) or a superlattice (SL), an n-type semiconductor cladding layer (n-AlGaA).
s) 23 'is sequentially laminated, and an n-type semiconductor contact layer (n-GaAs) 22' is further laminated on a part of the n-type semiconductor clad layer (n-AlGaAs) 23 '. As shown in the figure, the side surface of each diode element 31, 32 is covered with an insulator 28, and the electrode metal 27 is connected to the p-type semiconductor contact layer 26 of the diode element 31, and the electrode metal 27 ′. Is the diode element 3
1 is connected between the n-type semiconductor contact layer 22 and the p-type semiconductor contact layer 26 ′ of the diode 32 element, and the electrode metal 27 ″ is connected to the n-type semiconductor contact layer 22 ′ of the diode element 32. The electrode metals 27 and 27 ″ are connected to a constant voltage source 33. Thus, the electric field can be applied from the direction perpendicular to the multiple quantum well structure or the superlattice.

The intrinsic semiconductor layers 24 and 24 'are composed of multiple quantum wells or superlattice structures having different compositions and film thicknesses, and operate in different wavelength regions. Therefore, the wavelengths of the switch light (λ ₁ ) and the trigger light (λ ₂ ) can be made different, and it is not necessary to distinguish the two types of light by polarization. The operating principle of the A-SEED element is that the wavelengths used are different between the diode element 31 (λ ₁ ) and the diode element 32 (λ ₂ ≠ because the multiple quantum wells or superlattice structures used for the diode element 31 and the diode element 32 are different. λ ₁ ) is different, and there are two types of photoresponse curves that modulate the optical absorption intensity due to the electric field when a photocurrent is generated.
The principle of optical switch operation and optical memory operation is the conventional S
-SEED element can be easily explained by the same mechanism as the operation principle. However, when a superlattice structure is used for the intrinsic semiconductor layer 24 or 24 ', the mechanism by which the optical absorption intensity is modulated by the electric field is the Wannier-Stark localization (for example, K. Fujiw).
ara, Optical and Quantum Electrics, 32, S99
-S320, 1990)).

Next, the operation of the A-SEED element will be described. Two diode elements 31, 32 including a multiple quantum well structure or a superlattice are connected in series to form a circuit (FIG. 3) in which a reverse bias constant voltage (Vo) source 33 is connected. In this element, the light response curve that modulates the light absorption intensity by the electric field when the photocurrent is generated has diode elements 31 and 32.
There are two types for each diode element 31, 3
The principle of the optical switch operation and the optical memory operation of FIG.
It can be explained by the photoresponse curve shown in FIG. The bias voltage applied to the switching diode element 31 is changed by the trigger light incident on the trigger diode element 32, whereby the diode element 31 transmits or blocks the switch light (having a wavelength different from that of the trigger light).

That is, in the wavelength region where the light absorption decreases due to the increase of the reverse bias voltage, the switch light having the constant wavelength (λ ₁ ) and the constant intensity Pin ₁ is the switching diode element 3
Upon entering 1, the diode element 31 is in a low impedance state due to the existence of charge carriers generated by light absorption, and a reverse bias voltage is applied to the diode element 32. That is, the trigger diode element 32 is in a high impedance state. At this time, due to the so-called quantum Stark effect (see the above-mentioned Lentin et al. Article), the diode element 31 enters a state in which light absorption (transmission) is large (small) and does not transmit light (OFF state), but the diode element 31 32 is in a state where light absorption (transmission) is small (large).

The trigger diode element 32, which operates at a wavelength different from that of the switching diode element 31, has a light intensity Pi at a wavelength λ ₂ (λ ₂ ≠ λ ₁ ) different from the wavelength λ _{1 of the} switch light.
When the trigger light of n ₂ is incident and its intensity is increased, the photocurrent generated in the diode element 32 increases as shown by the solid line in FIG. 5 (each corresponding to one light intensity Pin ₂ ), The current flowing through the circuit has a current value determined by the intersection (A) with the load curve (dotted line in FIG. 5) of the diode element 31. When the trigger light intensity Pin ₂ (λ ₂ ) applied to the diode element 32 is smaller than the switch light intensity Pin ₁ (λ ₁ ), the state in which the reverse bias voltage is applied to the diode elements 31 and 32 is the same as before. Absent.

However, when Pin ₂ > Pin ₁ , when the threshold value is exceeded, the intersection point (A) of the load curve where the trigger diode element 32 may exist in the high impedance state does not exist, so that the trigger diode element 32 does not exist. The element 32 enters the low impedance state, and as a result of switching the applied bias voltage value, the switching diode element 31 changes from the low impedance state to the high impedance state (B).
At this time, the diode element 31 is in a state in which light absorption (transmission) is small (large) and allows the light having the switch light intensity Pout ₁ to pass therethrough. That is, by increasing the intensity Pin ₂ of the trigger light,
Optical switching operation with switch light intensity Pout ₁ (OFF →
ON) is obtained.

On the other hand, when the trigger light intensity Pin ₂ is decreased, the low impedance state of the trigger diode element 32 is maintained until the intersection (C) with the load curve, so that the switch diode element 31 is turned on (high). (Impedance state) is retained, resulting in optical memory operation. The trigger light intensity Pin ₂ decreases and the intersection point C with the load curve
Beyond C, since there is no intersection with the load curve below C, an optical switching operation (C (ON) → D (OFF)) to the initial state (D) of the switching diode element 31 occurs, and Stable operation can be obtained.

In FIGS. 3 and 4, since the intrinsic semiconductor layer 4 of the diode element 31 is constructed using a multiple quantum well or superlattice structure operating at a wavelength at which it is transparent to the substrate 1,
An example is shown in which the elements are configured by changing the incident directions of light incident on the diode element 31 and the diode element 32 by 180 degrees without removing the substrate. Also, FIG. 3 and FIG.
Then, layers 24 and 24 'having two different compositions and thicknesses
However, the step is formed in advance at the position where the diode element 31 and the diode element 32 are formed, and two different layers 24 and 24 ′ are formed by one growth. It is also possible to form it.
In this case, if the wavelength λ _{1 of the} light used for the diode element 31 is set to be longer than the wavelength λ _{2 of} the light used for the diode element 32, the light incident on the diode element 31 will be transmitted to the diode element 32. Is transparent, so it is an optical switch due to leakage light, ON / OFF when operating an optical memory
Level fluctuations can be eliminated.

Heterojunction p grown on GaAs substrate
In the in-diode structure, when the intrinsic semiconductor layer of one diode element of the SEED element is composed of a multiple quantum well or a superlattice having an InGaAs strained quantum well, one wavelength should be set to a wavelength at which the GaAs substrate becomes a transparent body. Therefore, the semiconductor optical device can be easily constructed without removing the substrate for the incidence and emission of light unlike the conventional symmetrical SEED device (FIG. 2).

In a heterojunction type semiconductor pin diode structure, InP is used as a substrate, and InGaAs / InP or InGaAs / InP is used as an intrinsic semiconductor layer on the InP substrate.
A multiple quantum well structure or a superlattice structure composed of AlAs may be formed. Further, in the configuration of the asymmetric SEED element, even if the substrate semiconductor 1 is not transparent to the multiple quantum well or the superlattice layer, the conventional symmetric SEE
Similar to the D element, a symmetrical SEED element that operates at two different wavelengths λ ₁ and λ ₂ can be configured by adding a reflective film formed of a multilayer thin film between the pin diode layer and the substrate. ..

[0022]

In the semiconductor optical device according to the present invention,
Since the asymmetric SEED element is composed of two different types of pin diodes operating at different wavelengths λ ₁ and λ ₂ ,
The wavelength multiplicity of light, which allows the wavelengths λ ₁ and λ ₂ of the signal switch light and the trigger light to be different, can be fully utilized. Further, for this reason, the configuration of an optical signal processing system such as an optical arithmetic system including an asymmetric SEED element as a component can be greatly simplified.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a conventional symmetrical SEED.

FIG. 2 is a structural diagram of a conventional symmetrical SEED.

FIG. 3 is a circuit diagram of an asymmetric SEED according to an embodiment of the present invention.

FIG. 4 is a structural diagram of an asymmetric SEED according to an embodiment of the present invention.

FIG. 5 is a diagram showing an operation principle of an optical switch and an optical memory.

[Explanation of symbols]

21: substrate, 23, 23 ': n-type semiconductor cladding layer, 24, 24': multiple quantum well (MQW) or superlattice (S
L) structure, 25, 25 ': p-type semiconductor clad layer, 31: diode element for switch, 32: diode element for trigger, 33: constant voltage power supply.

Claims (4)

[Claims] 1. The intrinsic semiconductor layer has a multiple quantum well structure or a superlattice structure, and an electric field is applied from a direction perpendicular to the multiple quantum well structure or the superlattice structure to transmit light in a wavelength region near an optical absorption edge. A first pin diode of a heterojunction semiconductor capable of changing the ratio, and an intrinsic semiconductor layer having a multiple quantum well structure or a superlattice structure, and an electric field is applied from a direction perpendicular to the multiple quantum well structure or the superlattice structure. As a result, the light transmittance can be changed in the wavelength region near the optical absorption edge, and
The first diode and the second pin diode are composed of a second pin diode of a heterojunction semiconductor capable of changing the light transmittance in a wavelength region different from that of the in diode, and a constant voltage source capable of applying a constant reverse bias voltage. A semiconductor optical device characterized by being connected in series with a constant voltage source to form a feedback circuit electro-optically. 2. A heterojunction semiconductor pin diode structure is formed on a GaAs substrate, and an intrinsic semiconductor layer is strained In.
2. The semiconductor optical device according to claim 1, wherein the GaAs substrate is composed of a GaAs layer and has a multiple quantum well structure or a superlattice structure capable of operating in a transparent wavelength region. 3. The semiconductor optical device according to claim 1, wherein a heterojunction semiconductor pin diode structure is formed on a GaAs substrate, and a multiple thin film reflective film is provided between the GaAs substrate and the diode structure. 4. A heterojunction semiconductor pin diode structure is formed on an InP substrate, and an intrinsic semiconductor layer is InGa.
2. The semiconductor optical device according to claim 1, which has a multiple quantum well structure or a superlattice structure composed of As / InP or InGaAs / InAlAs.