JP3043797B2 - Semiconductor optical device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device, and more specifically, is expected to be a component of a system having a new function in addition to being a semiconductor light emitting device and a light receiving device. The present invention relates to a semiconductor optical device.

2. Description of the Related Art Heretofore, several semiconductor optical devices having both a semiconductor light emitting device and a light receiving device have been proposed, and are applied to various systems as multifunctional devices.

The most common conventional example is shown in FIG. In this conventional example, by providing a parallel groove 78 having a vertical end face beyond the active layer 75 in a part of the resonator of the semiconductor laser element, and further comprising independent electrodes 79a and 79b in each part ( 80 is a common electrode), a light emitting portion 76 formed on one side, and a light receiving portion 77 formed on the other side and receiving light emitted from the light emitting portion 76 and input to the active layer 75 again. In this conventional example, the light emitting and light receiving functions are partially shared by using the same active layer 75, and the optical signal from the light receiving unit 77 is fed back to the light emitting unit 76 to perform APC (automatic light emission amount control). ) Has been proposed.

[Problem to be Solved by the Invention] In such an element having both light emission and light reception, a method of light and electrical separation between the two (light-emitting part and light-receiving part) is important, and the functions used thereby. Is also determined. Therefore, the more flexible the optical and electrical separation is,
The degree of freedom in design increases, and new functions can be expected.

However, in the above conventional example, the optical separation and the electrical separation are performed simultaneously, and the functions are limited. For example, what can be detected by the light receiving unit 77 is the light emitted from the light emitting unit 76, and the light inside the light emitting unit 76 cannot be detected.

In order to detect light inside the light emitting section, it is necessary to perform electrical separation without optical separation between the light emitting section and the light receiving section. There is no freedom.

Further, in the above conventional example, since the same active layer 75 is used for light emission and light reception, it is difficult to optimize the characteristics of both at the same time. Even if the characteristics (emission spectrum and the like) of the light emitting section are optimized, the light receiving efficiency (sensitivity) is not always optimized by the emission wavelength.

Therefore, an object of the present invention is to provide a semiconductor optical device having a high degree of freedom in design and a configuration capable of flexibly responding to requests in view of the above-mentioned problems.

[Means for Solving the Problems] In a semiconductor optical device according to the present invention for achieving the above object, an active layer and an absorption layer laminated with a first clad layer made of a semi-insulating material interposed therebetween; Second and third cladding layers stacked so as to sandwich these layers, and first n-type semiconductor layers provided on both sides of the active layer so as to sandwich the active layer in a direction orthogonal to the stacking direction. A first p-type semiconductor layer, a second n-type semiconductor layer and a second p-type semiconductor layer provided on both sides of the absorption layer in a direction orthogonal to the stacking direction, and a second p-type semiconductor layer in the stacking direction. A high-resistance layer provided between the first n-type semiconductor layer and the second n-type semiconductor layer and between the first p-type semiconductor layer and the second p-type semiconductor layer; Electrically connected to the n-type semiconductor layer and the first p-type semiconductor layer, respectively. The first
N-type electrode and a first p-type electrode, and a second n-type electrode and a second p-type electrode electrically connected to the second n-type semiconductor layer and the second p-type semiconductor layer, respectively. Wherein the active layer and the absorption layer are formed so as to be in the same optical waveguide, and a current is caused to flow between the first n-type electrode and the first p-type electrode, so that light is emitted from the active layer. Is generated, light generated in the active layer is detected by the absorption layer, and extracted as an electric signal from the second n-type electrode and the second p-type electrode. By adopting such a configuration, it is possible to perform the current injection into the active layer and the light detection by the absorption layer independently of each other without generating crosstalk.

More specifically, the active layer and the absorption layer each have a quantum well structure, the first cladding layer has a superlattice structure, and an external optical signal is input to and output from the optical waveguide. This optical signal is amplified while propagating through the optical waveguide, and the second n-type electrode and the second p-type electrode are connected so that the amplification factor between input and output is always constant. The current flowing between the first n-type electrode and the first p-type electrode is controlled in accordance with an electric signal taken out of the device.

As described above, according to the present invention, two regions formed to be the light emitting unit or the light receiving unit are manufactured in the same waveguide, and are configured to be controlled separately.
A semiconductor optical device, such as a light emitting and receiving device with a high degree of freedom, is realized.

FIG. 1 is a perspective view of a first reference example, and FIG.
An example of a system using a reference example is shown.

In FIG. 1, semi-insulating (hereinafter, referred to as SI) GaAs
1 μm thick SI-GaAs buffer layer 12 on substrate 11, thickness
1.5 μm SI-Al _0.3 Ga _0.7 As cladding layer, 0.1 μm thickness
Non-doped Al _0.05 Ga _0.95 As active layer 14, 0.3 μm thick S
I-Al _0.2 Ga _0.8 As cladding layer 15, non-doped Al _0.05 Ga _0.95 As absorbing layer 16 having a thickness of 0.1 μm, SI-Al _{0.3 having} a thickness of 1 μm
Ga _0.7 As cladding layers 17 were sequentially laminated using a molecular beam epitaxy method.

Next, etching was performed to extend over the active layer 14 to the cladding layer 13 except for the stripe region. Thereafter, the stripe and one side of the stripe were masked, and only one side (the right side in FIG. 1) of the stripe was buried in the p-Al _0.3 Ga _0.7 As cladding layer 18 using the liquid phase epitaxial method.

Further, the mouse was removed, and the other side (left side in FIG. 1) of the stripe left before was covered with a first n-Al _0.3 Ga _0.7 As clad layer 19, an Al _0.3 Ga _0.7 As high resistance layer 20, and a second n-Al _0.3 Ga _0.7
It was buried in the As cladding layer 21 using liquid phase epitaxy. At this time, the thicknesses of the respective layers were controlled such that the high-resistance layer 20 was located substantially at an intermediate position of the SI-Al _0.2 Ga _0.8 As clad layer 15.

Further, the high resistance layer 20 was partially removed along the stripe at a distance of several μm from the stripe by etching.

Further, the p-electrode 22 was formed on the p-cladding layer 18 and the n-electrodes 23 and 24 were formed on the first and second n-cladding layers 19 and 21, respectively, after performing pre-treatment so that ohmic contact could be obtained.

The present embodiment is characterized in that the light emitting section and the light receiving section are provided in the same waveguide, and has an electrode structure capable of giving electrical control to each of the light emitting section and the light receiving section.

 The operation of the first reference example will be described.

In the light emitting portion, since the electrical connection is made through a path passing through the p-electrode → p-cladding layer 18 → active layer 14 → first n-cladding layer 19 → n-electrode 24, the connection between both electrodes 22 and 24 is established. When a forward bias is applied, current flows through this path, carriers are injected into the active layer 14, a population inversion is formed, and stimulated emission occurs.

On the other hand, in the light receiving section, electrical connection is established through the path of the p-electrode 22 → the p-cladding layer 18 → the light absorbing layer 16 → the second n-cladding layer 21 → the n-electrode 23. Therefore, both electrodes 22, 23
When a reverse bias is applied to the light, the light is detected by the light absorbing layer 16.

At this time, since the active layer 14 and the light absorbing layer 16 are optically coupled and form one waveguide, the optical power inside the light emitting section can be detected. That is, in the present embodiment, what is detected is the optical power inside the element, not the light emitted to the outside of the light emitting section as in the above-described conventional example. Therefore, when using the semiconductor laser of the present embodiment as a semiconductor laser, it is necessary to keep in mind that what is detected is the optical power inside the element.

In the configuration of the above reference example, between the electrodes 22 and 23 and the electrode 2
If a forward bias is applied to both the portions 2 and 24, both the light emitting portion and the light receiving portion become light emitting portions and can function as a normal semiconductor laser.

Alternatively, only one set of the electrodes 22 and 23 or the electrodes 22 and 24 may be used, and only each function may be individually performed. If a forward bias is applied only to the light emitting section, the semiconductor laser will be used.
-Functions as a PD.

Further, as in the conventional example shown in FIG.
It is also possible to provide a groove up to 14, and use one side as a light emitting unit and the other side as a light receiving unit. Thus, APC control can be performed. Further, in the device of the present reference example, the light absorption layer 16 can be designed in accordance with the light emission characteristics of the light emitting section. That is, the layer configuration (composition and doping amount) of the light absorbing section 16 can be independently changed to improve characteristics such as improvement of light receiving efficiency.

Now, the present embodiment has a new function that the light emitting unit and the light receiving unit can be driven simultaneously and independently, and the optical power inside the light emitting unit can be detected. Will be explained. In FIG. 2, reference numeral 25 denotes an AR coating applied to both end surfaces to use the first reference example as the optical amplification element 30, reference numeral 26 denotes an optical fiber, and reference numeral 27 denotes an AGC circuit.

This system is an optical repeater system, in which a signal transmitted through the optical fiber 26 is amplified when guided through the inside of the semiconductor optical element, and is output to the other optical fiber 26.

At that time, it is desired that the amplification degree is always constant. In this system, the light inside the amplifier 30 is received by the light receiving section, and the gain is returned to the light emitting section to perform an auto gain control such that the amount of current therethrough is controlled. The signal light is detected by providing the light receiving section with a demodulation circuit that matches the frequency of the signal light (this is provided in the AGC circuit 27). Can be performed.

AG by detecting the level of spontaneous emission light without signal light
It is also possible to do C.

Furthermore, the electrode 23 of the light receiving section is divided in the resonance direction, the signal level received at the input side is compared with the signal level received at the output side, and feedback is applied to the light emitting section so that the ratio is constant, and the AGC is performed. You can also do

AGC is required even in a conventional optical amplifier, and a beam splitter, a fiber type duplexer, or the like is generally used to separate a part of output signal light. By comparison,
The system does not require separation and greatly simplifies the equipment.

In the first reference example shown in FIG. 1, the active layer 14 and the light absorbing layer 16 have the same composition and the same thickness. Therefore, as can be seen from the above, the electrodes 22 and 23 and
If the bias state between 22 and 24 is completely reversed, the active layer 14 is used as a light receiving section and the light absorbing layer 16 is used as a light emitting section. However, the light receiving unit is a loss for the light emitting unit, and the characteristics of the light emitting unit are degraded. Therefore, it is not always necessary to make the light emitting unit and the light receiving unit equal. Rather, it is better to optimize the light emitting unit according to the light emitting characteristics and the light receiving unit according to the light receiving characteristics, and it is a feature of this embodiment that each can be designed independently. The design should be tailored to the expected function.

FIGS. 3A to 3D show design examples of the optical amplification element 30 in the system shown in FIG.

FIG. 3A shows the band structure of the conduction band having the configuration described in the first reference example of FIG.

In the system shown in FIG. 2, it is better that the amplification characteristics do not deteriorate. Therefore, the characteristics of the light emitting section are emphasized.
If the active layer 14 is arranged at the center of the waveguide mode and the light absorbing layer 16 is formed at the bottom of the waveguide mode as shown in FIG. You.

Further, as shown in FIG. 3 (c), the active layer 14 and the light absorbing layer 16 have a quantum well structure, and GRIN (graded) is provided on both sides of the waveguide structure.
It is also conceivable to provide an index) structure. When a quantum well is used, light emission and light reception characteristics suitable for the intended use can be arbitrarily designed by changing the composition, the width of the barrier, and the like.

Further, as shown in FIG. 3 (d), a layer 31 having a superlattice structure is provided between the active layer 14 and the light absorbing layer 16 to realize a structurally high-resistance layer to ensure semi-insulation between them. The design to be considered is also conceivable.

FIG. 4 shows an embodiment of the present invention. This embodiment is composed of four electrodes. The same members as those in FIG. 1 are given the same numbers. In this embodiment, in order to form a four-electrode structure, the substrate is removed and an electrode is provided below the substrate. Thus,
The electrical connection is completely separated vertically from the light emitting part (lower part) and the light receiving part (upper part) with the high resistance 20 and the SI-cladding layer 15 as boundaries. The light emitting portion is a p-type electrode 45 → p-type layer 41 → active layer 14
The n-type layer 43 is connected by an n-type electrode 47, and the light receiving section is connected by a p-type electrode 46 → p-type layer 42 → light absorbing layer 16 → n-type layer 44 → n-type electrode 48. Optically, as in the first reference example,
The operation and effects are the same except for the above-described effects unique to the present invention.

FIG. 5 shows a second reference example. In FIG.
On an As substrate 51, an n-GaAs buffer layer 52 having a thickness of 1 μm, an n-Al _0.3 Ga _0.7 As cladding layer 53 having a thickness of 1.5 μm, a thickness of 0.1
μm non-doped Al _0.05 Ga _0.95 As active layer 54, thickness 1.5μ
An m-type p-Al _0.3 Ga _0.7 As clad layer 55 is laminated. Next, a stripe is formed by etching, and a high-resistance layer 56 is formed on the bottom surface other than the stripe. Furthermore, a non-doped Al _0.05 Ga layer having a thickness of 0.1 μm
_0.95 As light absorbing layer 57, n
-An Al _0.3 Ga _0.7 As cladding layer 58 is laminated. Further, a p-type electrode 60 is provided above the stripe, and an n-type electrode 61 is provided below the substrate 51.
And n on the n-cladding layer 58 on both sides of the stripe.
A mold electrode 62 is formed.

The electrical connection of this embodiment is as follows. First,
The light emitting portion is a p-type electrode 60 → p-cladding layer 55 → active layer 54 → n
-Cladding layer 53-> n-buffer layer 52-> n-substrate 51-> n-electrode 61. Next, the light receiving section is a p-type electrode 60 → a p-cladding layer 55 → a light absorbing layer 57 → a n-cladding layer.
58 → n-electrode 62 are connected.

In the present embodiment, unlike the first embodiment and the embodiment of the present invention, the waveguide mode is substantially determined by the configuration of the light emitting section. For this reason, in the present reference example, improvement of the characteristics (emission spectrum and the like) of the light emitting portion is expected as an effect.
That is, in the present reference example, the light receiving unit is located in a part of the field distribution of the guided mode mainly including the light emitting unit. FIG. 6 shows a third reference example. The configuration of the present embodiment will be described.

A 1 μm thick p-GaAs buffer layer on a p-GaAs substrate 63
64, 1.5 μm thick p-Al _0.3 Ga _0.7 As clad layer 65,
A non-doped Al _0.05 Ga _0.95 As active layer 66 having a thickness of _0.1 μm and an n-Al _0.2 Ga _0.8 As cladding layer 67 having a thickness of 0.15 μm are laminated. Next, etching is performed over the active layer 66 to the p-clad layer 65 to form a stripe. Thereafter, the portions other than the stripes are buried with the SI-Al _0.3 Ga _0.7 As cladding layer 68. Further, a 0.1 μm thick n-Al _0.2 Ga _0.8 As cap layer 69 and a 0.1 μm thick n-Al _0.2 Ga _0.8 As clad layer 7
0, non-doped Al _0.05 Ga _0.95 As light absorption layer 7 of 0.1 μm thickness 7
1. A 1.5 μm-thick p-Al _0.3 Ga _0.7 As clad layer 72 is formed. Next, an n-cap layer is left while leaving a stripe portion
Steps 69 and 69 are removed, and an n-electrode 73 is formed thereon. The p-electrode 74 is located above the stripe and the p-electrode is located below the substrate 63.
Form 75.

The electrical connection of this embodiment is as follows. The light emitting section is connected to the p-electrode 75 → p substrate 63 → p-buffer layer 64 → p-cladding layer 65 → active layer 66 → n-cladding layer 67 → n-cap layer 69 → n-electrode 73. On the other hand, the light receiving section
It is connected to a p-electrode 74 → p-cladding layer 72 → light absorbing layer 71 → n-cladding layer 70 → n-cap layer 69 → n electrode 73.

Optically, the stripe is temporarily interrupted by the n-cap layer 69, but the effect of the upper and lower stripes causes the stripe to temporarily stop.
It can be treated as one waveguide, and is almost the same as the first reference example.

Therefore, this element also has the same effect as the first reference example.

In the above example, the constituent material is described as a GaAs-based material. However, the constituent material is not limited to the GaAs-based material, and may be formed of another semiconductor material such as an InP-based III-V-based or II-VI-based.

Although the active layer and the light absorbing layer have been described with quantum wells and the like, each may have a multiple quantum well structure or a quantum wire.

As the manufacturing method, any known film forming apparatus and etching apparatus having excellent controllability and reproducibility may be used.

Further, the waveguide on which the active layer and the light absorbing layer are formed may be configured as a single mode rectangular waveguide, a multimode waveguide, or the like suitable for the application.

[Effects of the Invention] As described above, according to the present invention, the first region and the second region configured to be the active layer or the light absorbing layer are manufactured in the same waveguide, and the first and second regions are formed. Since the means for independently controlling the two regions is provided, for example, the degree of freedom in designing an optical element having both light emission and light reception is increased.

Thus, a unique design of the light emitting unit and the light receiving unit can be performed, and the characteristics are improved. In addition, it is possible to configure a system having new functions in addition to the conventional configuration.

[Brief description of the drawings]

FIG. 1 is a view showing a first reference example of a semiconductor device according to the present invention, FIG. 2 is a view showing an optical repeater system configured using the first reference example, and FIGS. 3 (a) to 3 (d). FIG. 4 is a view for explaining some examples of the layer structure, FIG. 4 is a view showing an embodiment of the present invention, FIG. 5 is a view showing a second reference embodiment, and FIG.
FIG. 7 is a diagram showing a conventional example. 11, 51, 63 ... substrate, 12, 52, 64 ... buffer layer, 13,
15, 18, 19, 21, 53, 55, 58 ... clad layer, 14, 54,
66 ... active layer, 16, 57, 71 ... light absorption layer, 20, 56 ... high resistance layer, 22, 23, 24, 45, 46, 47, 48, 60, 62, 73, 7
4, 75 ... electrode, 25 ... AR coating, 26 ... optical fiber, 27 ... AGC circuit, 30 ... optical amplifier, 31 ... superlattice layer (SL layer), 41, 42 ... p-type layer , 43, 44 ... n-type layer, 69
..... n-cap layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-128589 (JP, A) JP-A-57-35392 (JP, A) JP-A-64-7583 (JP, A) JP-A 63-128 9163 (JP, A) JP-A-62-12180 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (4)

(57) [Claims] An active layer and an absorption layer laminated with a first cladding layer made of a semi-insulating material interposed therebetween, and second and third cladding layers laminated so as to sandwich these layers. A first n-type semiconductor layer and a first p-type semiconductor layer provided on both sides of the active layer so as to sandwich the active layer in a direction perpendicular to the laminating direction, and the absorbing layer in a direction perpendicular to the laminating direction. The second provided on each side to sandwich
N-type semiconductor layer and the second p-type semiconductor layer, between the first n-type semiconductor layer and the second n-type semiconductor layer in the stacking direction, and between the first p-type semiconductor layer and the second p-type semiconductor layer. A high-resistance layer provided between the first n-type semiconductor layer and the first n-type electrode and a first n-type electrode electrically connected to the first n-type semiconductor layer and the first p-type semiconductor layer, respectively. a p-type electrode; a second n-type electrode and a second p-type electrode electrically connected to the second n-type semiconductor layer and the second p-type semiconductor layer, respectively; The absorption layer is formed so as to be in the same optical waveguide, and light is generated in the active layer by flowing a current between the first n-type electrode and the first p-type electrode. The detected light is detected by the absorption layer, and the second n-type electrode and the second
A semiconductor optical element which is extracted as an electric signal from the p-type electrode. 2. The semiconductor optical device according to claim 1, wherein each of said active layer and said absorption layer has a quantum well structure. 3. The semiconductor optical device according to claim 2, wherein said first cladding layer has a superlattice structure. 4. The optical waveguide has means for inputting / outputting an external optical signal to / from the optical waveguide, and the optical signal is amplified while propagating through the optical waveguide, so that an input / output amplification factor is always constant. The first n-type electrode and the first p-type electrode are connected to each other in accordance with an electric signal taken out between the second n-type electrode and the second p-type electrode.
4. A current flowing between the p-type electrode and the p-type electrode is controlled.
The semiconductor optical device according to any one of the above.