JP2003329988A - Semiconductor multi-layered structure and optical control element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an element structure which reduces the energy consumption of an optical control element using inter-subband transition up to a level adaptive to a large-capacity optical communication system. <P>SOLUTION: Disclosed are: a semiconductor multi-layered structure including as a basic constitutional element a quantum well structure which has a compound barrier layer in which an AlAs barrier layer of ≥1 nm film thickness is arranged between an InGaAs well layer and an Al(Ga)AsSb barrier layer; and a semiconductor optical control element formed by arranging the semiconductor multi-layered structure on an InP substrate. By irradiating the multi- quantum well structure with a light resonating to the inter-subband transition energy of the conduction band of a multi-quantum well structure, and the absorption coefficient, refractive index, or optical gain to the light corresponding to energy of inter-subband transition are varied. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor multilayer structure for optical devices used in optical communication and optical information processing systems, and in particular to a broadband optical control device using the conduction band intersubband transition of a semiconductor quantum well structure, And a semiconductor multilayer structure used therefor.

[0002]

2. Description of the Related Art In recent years, research and development on all-optical / optical control elements have been actively developed for application to ultrahigh-speed time division multiplex optical communication systems and optical information processing systems. Among them, optical switches using semiconductors are easy to reduce in size and weight, can be monolithically integrated with semiconductor elements such as semiconductor lasers and optical modulators, and have quantum structures such as superlattices and quantum wells. With the adoption of, there is an advantage that the efficiency of optical switching can be improved.

The conventional semiconductor optical switch utilizing absorption due to band-to-band transition has a problem that the switch-off time is limited by the band-to-band recombination time (several nanoseconds) of the actually excited carriers. On the other hand, the relaxation time of the conduction band inter-subband transition of the semiconductor quantum well structure is several picoseconds or less, and the speed can be increased 1,000 times or more as compared with the interband transition. For this reason, studies are underway on switches that utilize the high-speed transition between subbands.
We also have Electronics Letter 37 (2001)
Year) 129 to 131 (Electronics Lett. 3
7, (2001) pp129-131), an absorption recovery time of 0.69 ps, which is an index of switching speed, and Photonics Technology Letter 14 (2002), pages 495 to 4
Page 97 (Photonics Techn. Lett. 14 (2002) PP 495-4
97), OTDM-D with a control light pulse at 1ps intervals
We have reported a simulation experiment of EMUX and obtained an operation prospect in an ultrahigh-speed optical communication system of 1 Tb / s. However, there are many problems to be solved in order to put into practical use an optical control element using inter-subband transition excellent in high speed as described above. Among them, the power of the control light for controlling the signal light is It is important to reduce by at least 2 digits.

However, in the InGaAs / AlAsSb heterostructure, unlike the GaAs / AlGaAs heterostructure, when the impurity addition amount is increased in order to increase the intersubband absorption intensity, substitution of constituent elements and mutual diffusion are promoted. It became clear that the structure was significantly disturbed.
Therefore, an interface layer is formed between the InGaAs layer and the AlAsSb layer, and the absorption strength is reduced. Conventionally, in order to suppress the formation of this interface layer and form a steep interface, when forming a quantum well structure, for example, Al
When switching the growth from the AsSb layer to the InGaAs layer, the growth is temporarily stopped at the stage when the growth of the AlAsSb layer is finished, and only the arsenic is irradiated on the substrate surface.
A so-called interface termination method for starting the growth of the aAs layer has been adopted. However, although a certain improvement was observed by this interface termination method, sufficient absorption intensity was not obtained.

[0005]

As described above, the conventional optical control element using the inter-subband transition has a problem that the control optical power which is about two orders of magnitude higher than the practical level is required.

The present invention has been made in consideration of the above problems, and an object thereof is to perform optical modulation or optical switching at ultra-high speed by utilizing the above inter-subband transition.
An object of the present invention is to provide an optical control element compatible with a large-capacity optical communication system of terabits / second or more, and a semiconductor multilayer structure capable of realizing the same.

[0007]

In order to solve the above problems, the present invention employs the following configurations. That is, according to the present invention, in the multiple quantum well structure which is a basic constituent element of the light control element, the composition x of In in the well layer is 0.5 to 0.5.
1.0 In _x Ga _1-x As, and As for the barrier layer.
Composition y of 0.3-0.7 Al (Ga) As _y Sb
Adopting a composite barrier layer consisting of _1-y and AlAs, an AlAs layer with a thickness of 1 nm or more is an InGaAs well layer and an Al
A semiconductor multi-layer structure characterized by being inserted between the (Ga) AsSb barrier layer is adopted.

The absorption intensity of the intersubband absorption transition depends largely on the interface characteristics. The interface termination method, which has been used conventionally, shows some improvement, but is still insufficient. Therefore, with the aim of further improvement, In
Insert the AlAs layer between the GaAs layer and the AlAsSb layer,
The sharpness of the interface was improved. As a result of investigating the AlAs layer film thickness dependence of the absorption coefficient between sub-bands by using the multi-quantum well structure, no remarkable improvement was observed in many cases where the AlAs layer of 0.6 nm was inserted. 0.0 nm AlA
By inserting the s layer, an absorption coefficient of 10,500 cm ^-1 was obtained, which was about five times larger. Therefore, by inserting an AlAs layer with a thickness of 1.0 nm or more, the InGaAs layer and the A
The formation of the interface layer between the 1AsSb layers is suppressed, and the absorption intensity can be significantly increased.

Now, the excitation carrier accompanying the intersubband transition
The relaxation rate of A is higher than that of a single quantum well.
The door is faster. Therefore, it requires a large amount of communication.
In case of
In the coupled multiple quantum well structure consisting of quantum well layers,
The composition x of In in the door layer is 0.5 to 1.0_xGa_1
-XAs, and the composition y of As in the barrier layer is 0.3 to
0.7 Al (Ga) As _ySb_1-yAnd AlAs
Is used for the barrier layer 1 between the adjacent InGaAs well layers.
An AlAs layer or an Al (Ga) AsSb layer, and
The barrier layer 2 sandwiching the InGaAs well layers is formed of AlAs.
Adopt a composite barrier layer consisting of a layer and Al (Ga) AsSb layer
The AlAs layer is the InGaAs well layer and the Al (Ga) A layer.
A semiconductor which is inserted between the sSb barrier layer and the semiconductor layer
It is desirable to employ a body multilayer structure.

When the light transmission characteristics of the waveguide structure are examined, as shown in FIG.
μm, the surface side clad layer is 2 μm, the refractive index of the clad layer is 3.1, and the thickness of the quantum well structure forming the core layer is 0.8.
In the case of μm, good optical waveguide characteristics can be obtained.
When the core layer has a thickness of 0.3 μm as shown in FIG. 5, good transmission characteristics cannot be obtained. Further, even when the film thickness of the substrate-side cladding layer is reduced from 3 μm to 2 μm, sufficient transmission characteristics cannot be obtained (FIG. 11). Further, when the refractive index of the clad layer is 3.15, it can be seen that the incident light leaks to the substrate and hardly propagates in the waveguide (FIG. 12).

In view of the above results, preferred embodiments of the present invention will be shown below. (1) The thickness of the InGaAs well layer is 1 to 3 nm, AlAs
The thickness of the barrier layer is 1 to 5 nm, and also Al (Ga) AsSb
The thickness of the semiconductor multilayer structure in which single or coupled quantum well layers having a barrier layer thickness of 3 to 20 nm are laminated is at least 0.4 μm or more. (2) The semiconductor multilayer structure according to (1) above is used as the InP substrate and the core layer, and the refractive index is 3.
A semiconductor waveguide structure having a cladding layer made of a material of 1 or less, at least one of which is an Al (Ga) AsSb layer, and further having a cap layer. (3) A semiconductor waveguide structure in which the substrate-side clad layer has a thickness of 3 μm or more, the surface-side clad layer has a thickness of 2 μm or more, and the core layer has a film thickness of 0.4 μm or more. (4) A semiconductor optical switch that irradiates light that resonates with the intersubband transition energy of the conduction band of the multiple quantum well structure to change the absorption coefficient, refractive index, or optical gain of light at the energy of the intersubband transition 2. A light control element using the above semiconductor multilayer structure or semiconductor waveguide structure.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a schematic diagram showing the basic structure of a semiconductor multilayer structure according to an embodiment of the present invention. AlAs
0.55Sb0.45 barrier layer 11, AlAs barrier layer 1
The core layer 1 was formed by stacking 80 sets of 5 layers each including 2 and Si-added In0.8Ga0.2As well layers 13 as a basic unit. The amount of Si added is 1x
It was 10 ¹⁹ cm ³ . The well width is 1.8 nm, A
The lAs barrier layer was 1.5 nm, and the AlAsSb barrier layer was 5.5 nm. FIG. 2 shows the pulse energy dependence of the optical pulse transmittance of this structure. Here, as the incident light,
Pulsed light with a wavelength of 1.55 μm (pulse width 100
fs) was used. Further, FIG. 2 shows InGaAs / without the AlAs barrier layer 82, which is a conventionally adopted structure.
The light transmission characteristics of the semiconductor multi-layer structure using the AlAsSb quantum well layer structure are also shown. As is clear from the figure, in the structure according to the present invention, the incident light intensity at which absorption saturation occurs and the transmittance becomes high is approximately two orders of magnitude lower than in the case of the conventional structure. When applied to, it is possible to reduce power consumption by two digits.

Next, FIG. 3 shows the basic structure of the semiconductor multilayer structure according to the second embodiment of the present invention.

Two In0.8Ga0.2A having the same width
s Well layers 13a and 13b, Al between two well layers
As barrier layer 14 and AlAs sandwiching two well layers
0.5Sb0.5 barrier layer 11 and AlAs barrier layer 12
A coupled quantum well structure 1 having 7 layers as a basic unit
The core layer 1 was formed by laminating 80 sets. Each film thickness is
The well layers 13a and 13b are 2.3 nm, and the AlAs barrier layer 1 is
4 was 1.5 nm, the barrier layer 11 was 5.5 nm, and the barrier layer 12 was 1.7 nm. In the absorption spectrum of this structure, two absorption peaks are observed as shown in FIG. 4, the peak on the short wavelength side is 1.55 μm, and the peak on the long wavelength side is 1.8 μm. 1.55 with a pulse width of 100 fs
FIG. 5 shows the transient response characteristics of the absorption coefficient at 1.55 μm when irradiated with μm light. As can be seen from this figure, the full width at half maximum of the absorption recovery time is 2 to 10 in the multiple quantum well structure.
It is 3 ps or less than 1 ps in the coupled multiple quantum well structure, and both can be applied to terabit class optical switches.

The adoption of the waveguide structure is preferable for integration with other semiconductor elements such as a semiconductor laser and a semiconductor photodetector. The basic structure of the semiconductor multilayer structure having the waveguide structure according to the third embodiment of the present invention is shown below in FIG. On the semi-insulating InP substrate 2, the refractive index is 3.
A clad layer 3 made of a material of 1 or less and a core layer 1 made of the semiconductor multi-layer structure shown in the first or second embodiment are sequentially laminated, and a refractive index of 3.
The surface-side clad layer 4 and the cap layer 5 made of a material of 1 or less are laminated, and then the cap layer 5 and a part of the clad layer 4 are removed by etching, and the optical guide layers (4b, 5
a) has been formed.

A more specific configuration example will be described below. The lower clad layer 3 is made of AlAs0.5 having a film thickness of 3 μm.
Sb is 0.5, and the coupled multiple quantum well structure shown in the second embodiment is adopted as the core layer. That is, two In0.8Ga0.2As well layers 13a and 13b having the same width, an AlAs barrier layer 14 between the two well layers, and an AlAs0.5Sb sandwiching the two well layers.
7 consisting of 0.5 barrier layer 11 and AlAs barrier layer 12
Using the layer as a basic unit, 80 sets were laminated. The thickness of each well layer 13a, 13b is 2.3 nm, AlA
s barrier layer 14 is 1.5 nm, barrier layer 11 is 5.5 nm,
Further, the barrier layer 12 has a thickness of 1.7 nm. The upper clad layer 4 is AlAs0.5Sb0.5 having a film thickness of 2 μm,
The InAlAs cap layer 5 was laminated thereon to a thickness of 0.2 μm. After that, the InAlAs cap layer 5 and AlAs0.
A part of the 5Sb0.5 cladding layer 4 is removed by etching,
A ridge type waveguide structure having a width of 4 μm and a thickness of 2 μm was formed.
The absorption saturation intensity at 1.55 μm of this structure is approximately 200 fJ, and by adopting this structure, a terabit-class optical signal switching element can be realized.

An embodiment of the light control element adopting the semiconductor multilayer structure according to the present invention will be described below with reference to FIG.
In FIG. 7, the ridge type waveguide structure is adopted as the basic configuration of the light control element. In the figure, 6 indicates control light, 7 indicates signal light, and 71 indicates controlled signal light. Control light 6
Is a wavelength that resonates with the intersubband transition energy of the coupled quantum well structure 1, and the signal light 7 has a wavelength that is substantially equal to the same intersubband transition energy or another intersubband transition energy. In such a structure, the quantum well layers 13a and 13b are doped with n-type impurities, and electrons are accumulated in the conduction band subbands (first and second). By irradiating with light, electrons are excited from the low order subbands to the high order subbands, and intersubband light absorption occurs. It is possible to modulate or switch the signal light by utilizing the absorption coefficient, the refractive index, etc. accompanying the inter-subband absorption by the control light, and it is possible to realize a terabit-class light control element.

Although the waveguide structure with the optical guide layer is adopted in this embodiment, the optical control element may be used in the multi-pass waveguide structure as shown in FIG. 8a or the single-pass waveguide structure in FIG. 8b. There is no change in what can be achieved.

[0020]

As described above, according to the present invention, the quantum well structure, which constitutes the all-optical semiconductor light control element, is
The absorption saturation strength of the intersubband transition of the quantum well is significantly increased by configuring the barrier layer adjacent to the well layer with a thickness of 1 nm or more by using two types of barrier layers made of different materials from the well layer. Since it can be reduced, it becomes possible to support an optical communication system of terabits / second or more.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor multilayer structure according to a first embodiment.

FIG. 2 is a diagram showing the pulse energy dependence of the optical pulse transmittance of the embodiment.

FIG. 3 is a sectional view of a semiconductor multilayer structure according to a second embodiment.

FIG. 4 is a diagram showing an intersubband optical absorption spectrum characteristic of the embodiment.

FIG. 5 is a diagram showing an optical pulse response of an intersubband optical absorption coefficient according to the embodiment.

FIG. 6 is a schematic diagram showing a basic structure of a semiconductor multilayer structure according to a third embodiment.

FIG. 7 is a schematic diagram showing a basic configuration of a semiconductor light control element according to one embodiment.

FIG. 8 is a schematic diagram showing a basic configuration of a semiconductor light control element according to one embodiment.

FIG. 9 is a diagram showing light transmission characteristics in a waveguide structure.

FIG. 10 is a diagram showing light transmission characteristics in a waveguide structure.

FIG. 11 is a diagram showing light transmission characteristics in a waveguide structure.

FIG. 12 is a diagram showing light transmission characteristics in a waveguide structure.

[Explanation of symbols]

1: Core layer (InGaAs / AlAs / AlAsSb multiple quantum well layer) 2: InP substrate 3: AlAsSb lower clad layer 4: AlAsSb upper clad layer 5: InAlAs cap layer 6: Control light 7: Signal light 8: InGaAs / AlAsSb quantum well layer 9: (AlAs mixed crystal ratio = 0.56) 11: AlAsSb barrier layer 12: AlAs barrier layer 13: InGaAs well layer 14: AlAs barrier layer.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor collection Teruo             1-280, Higashi Koikekubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Minamoto Shimoyama             4-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa             No. 1 within Fujitsu Limited (72) Inventor Haruhiko Yoshida             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center F-term (reference) 2H079 AA08 AA12 AA13 AA14 BA01                       CA05 DA16 EA03 EA07

Claims (10)

[Claims] 1. A multi-quantum well structure composed of a well layer and a barrier layer, having two or more different materials having a band gap of at least 1.6 eV and a conduction band offset from the InGaAs layer of 1.0 eV. A semiconductor multi-layer structure having a composite barrier layer composed of a film made of. 2. The semiconductor multilayer structure according to claim 1, wherein the barrier layer adjacent to the well layer of the composite barrier layer has a film thickness of 1 nm or more. 3. The composite barrier layer comprises a ternary, quaternary or quaternary compound semiconductor layer containing AlAsSb as a component and a binary, ternary or quaternary compound semiconductor layer containing AlAs as a main component. , Of which the barrier layer adjacent to the well layer is
2. The semiconductor multi-layer structure according to claim 1, which is composed of a binary, ternary or quaternary compound semiconductor containing AlAs as a main component. 4. In a multi-quantum well structure comprising a well layer and a barrier layer, the well layer is made of In _x Ga _1-x As having an In composition x of 0.5 to 1.0, and the barrier layer is made of As. Al composition y is _{0.3~0.7 (Ga) As y Sb 1} -y and a
A binary, ternary or quaternary compound semiconductor containing lAs as a main component is used, and a binary, ternary or quaternary compound semiconductor layer containing AlAs as a main component is an InGaAs well layer and an Al (Ga) A layer.
It is inserted between the sSb barrier layer and its thickness is 1 nm to 5 nm.
The semiconductor multi-layer structure according to claim 1, wherein 5. In a coupled multiple quantum well structure comprising two well layers and a barrier layer, the In composition x of the well layer is 0.5.
~ 1.0 In _x Ga _1-x As and As in the barrier layer.
Composition y of 0.3-0.7 Al (Ga) As _y Sb
Binary, ternary or quaternary compound semiconductors containing _1-y and AlAs as main components are used, and a binary, ternary or quaternary compound semiconductor mainly containing AlAs is used for the barrier layer 2 between adjacent InGaAs well layers. As the barrier layer 1 sandwiching the two layers and the InGaAs well layer, a composite barrier layer of a binary, ternary or quaternary compound semiconductor layer containing AlAs as a main component and an Al (Ga) AsSb layer is used. The binary, ternary or quaternary compound semiconductor layer containing as a main component is an InGaAs well layer and an Al
It is placed between the (Ga) AsSb layer and its thickness is 1 nm.
2. The semiconductor multi-layer structure according to claim 1, wherein the thickness is about 5 nm. 6. The thickness of the InGaAs well layer is 1 nm to 3 nm,
A single quantum well layer or a coupled quantum well in which a binary, ternary or quaternary compound barrier layer containing AlAs as a main component has a thickness of 1 nm to 5 nm and an Al (Ga) AsSb barrier layer has a thickness of 3 nm to 20 nm. The thickness of the well layers stacked is at least 0.4μ
The semiconductor multi-layer structure according to claim 2 or 3, wherein the thickness is at least m. 7. An InP substrate and a semiconductor multilayer structure according to claim 4 as a core layer, and a cladding layer made of a material having a refractive index of 3.1 or less on both sides of the InP substrate, at least one of which is provided. Is an Al (Ga) AsSb layer and has a cap layer on the outermost surface. 8. The substrate-side clad layer has a film thickness of 3 μm or more, the surface-side clad layer has a film thickness of 2 μm or more, and the core layer has a film thickness of 0.4 μm or more. Semiconductor waveguide structure. 9. A semiconductor that irradiates light that resonates with the intersubband transition energy of a conductor of the multi-quantum well structure and changes the absorption coefficient, refractive index, or optical gain of light at the energy of the intersubband transition. In the optical switch,
A light control element comprising the semiconductor multilayer structure according to any one of claims 1, 2, 3, 4, 5 and 6. 10. A light absorption coefficient, a refractive index, and a refractive index of light at the energy of the intersubband transition are irradiated by irradiating light that resonates with the intersubband transition energy of the conductor having the multiple quantum well structure.
Alternatively, in a semiconductor optical switch for changing the optical gain, the semiconductor waveguide structure according to claim 7 is used.