JP2012256712A - Semiconductor optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the characteristics of a laser active layer or a light absorption layer in a ridge type semiconductor device having an optical waveguide of mesa stripe structure.SOLUTION: A stress applied to a laser active layer or a light absorption layer 24 is reduced by separating an electrode 29 provided on a mesa stripe into more than one region in the light propagation direction by means of a stress reduction slit 29-1. Furthermore, stress is especially reduced near the end of the mesa stripe where the stress is concentrated, by reducing the size of the separation region near the end of the mesa stripe of the electrode 29, as required.

Description

  The present invention relates to a semiconductor optical device having an optical waveguide having a mesa stripe structure used for optical communication and various optical signal processing.

  The structure of a conventional semiconductor optical device is shown in FIG. A first cladding layer 12 made of n-InP is stacked on a substrate 11 made of n-InP. On the first cladding layer 12, a first optical confinement layer 13 made of a non-doped InGaAsP-based bulk is laminated. On the first optical confinement layer 13, a laser active layer or a light absorption layer of an electroabsorption modulator (hereinafter referred to as "laser activity") composed of non-doped InGaAsP-based MQW (Multiple-Quantum-Well) or bulk. 14) are laminated. On the laser active layer or the light absorption layer 14, a second light confinement layer 15 made of a non-doped InGaAsP bulk is laminated. A second cladding layer 16 made of p-InP is stacked on the second optical confinement layer 15. A contact layer 17 made of p-InGaAs is stacked on the second cladding layer 16.

In each of the layers 12 to 17, the laminated structure of unnecessary regions is removed by etching so as to have a mesa stripe structure, and the p-type electrode 19 is provided on the contact layer 17, so that an insulating material (for example, SiO ₂ or Both sides 18 of the mesa stripe are widely embedded with polyimide (Toray: UR3800) (hereinafter referred to as “insulating layer”). Further, an n-type electrode 20 is provided through a contact hole formed so as to be in contact with the lower surface of the substrate 11 made of n-InP or the upper surface of the substrate 11 made of n-InP (see Non-Patent Document 1). ).

  Incidentally, in FIG. 2, in order to clarify the mesa stripe structure, the insulating layer 18 on the right side of the mesa stripe is expressed as transparent, and the structure is as if the inside is visible (FIG. 1, The same applies to FIG.

  In the ridge type semiconductor optical device having such a pin diode structure, the laser oscillation from the laser active layer or the light absorption layer 14 or the light in the layer 14 is generated by injecting a current into the optical confinement layer or applying a reverse bias. By utilizing the shift of the absorption peak wavelength from the short wavelength to the long wavelength side, the laser output and intensity modulation of the input light can be performed. That is, it is designed to function as an optical device by utilizing the electro-optical conversion characteristics in the laser active layer or the light absorption layer 14.

Patent 4607235

“InGaAsP / InGaAsP Multiple-Quantum-Well Modulator with Improved Saturation Intensity and Bandwidth Over 20 GHz”, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 4, NO. 7, JULY 1992

  The semiconductor optical device as described above exhibits characteristics as an optical device by converting the injected current into laser light, or by absorbing part of the incident signal light and converting the intensity of transmitted light. . Therefore, in the semiconductor optical device, the control efficiency of the optical characteristics by the electric signal is very important. Therefore, it is desired that the characteristics of the laser active layer or the light absorption layer in the semiconductor optical device be uniform over the light propagation direction.

  However, as a problem related to the reliability of semiconductor optical devices, it is found that a large strain stress is applied to the laser active layer or the light absorption layer and the surrounding layers depending on the device structure near the edge of the mesa stripe corresponding to the input / output part of the optical signal. (See Patent Document 1).

  Furthermore, when the stress applied to the laser active layer was simulated, it was found that the stress load increased as the distance from the end of the mesa stripe approached the conventional electrode structure.

  This may be a factor of degrading the characteristics of the semiconductor optical device as well as reducing the reliability of the semiconductor optical device. That is, there is a possibility that the uniformity of the characteristics of the laser active layer or the light absorption layer may be lost by applying a large strain stress to the laser active layer or the light absorption layer near the edge of the mesa stripe and the surrounding layers. This is an important problem to be solved in order to improve the characteristics of the semiconductor optical device.

  Regarding this strain stress, the difference in thermal expansion coefficient between the insulating layer and the semiconductor to protect the semiconductor surface from dirt and electrical problems, the electrode metal formed on the insulating layer (hereinafter referred to as "electrode") and It has been found that this is caused by a difference in thermal expansion coefficient between the insulating layer and the semiconductor and a film stress caused by bonding different materials such as a semiconductor, an insulating layer, and a metal.

For example, as shown in FIG. 3A, a metal film (eg, Au / 14.2 × 10 ⁻⁶ / ° C.) a having a large thermal expansion coefficient is applied to a semiconductor substrate (eg, InP / 4.56 × 10 ⁻⁶ / In the case of the structure on [° C.] b, it is also observed as a shape change such as the semiconductor substrate warping due to the difference in thermal expansion coefficient between the metal film and the semiconductor.

  Therefore, it is very important to reduce the influence of this stress in improving the characteristics of the semiconductor optical device. The present invention provides a structure in which variations in characteristics of a laser active layer or a light absorption layer can be suppressed in the device by reducing stress applied to the laser active layer or the light absorption layer of the semiconductor optical device and its surrounding layers. The purpose is to provide.

A semiconductor optical device according to a first invention for solving the above-mentioned problems is as follows.
In a ridge-type semiconductor optical device having at least an optical waveguide having a mesa stripe structure, electrodes separated by stress reduction slits are provided on at least two regions in the light propagation direction on the mesa stripe. It is characterized by.

A semiconductor optical device according to a second invention for solving the above-mentioned problems is as follows.
In the semiconductor optical device according to the first invention,
The electrode is configured to be inclined with respect to the mesa stripe.

A semiconductor optical device according to a third invention for solving the above-mentioned problem is as follows.
In the semiconductor optical device according to the first or second invention,
The size of each area | region of the said electrode is comprised unevenly, It is characterized by the above-mentioned.

A semiconductor optical device according to a fourth invention for solving the above-mentioned problems is as follows.
In the semiconductor optical device according to the third invention,
The size of each region of the electrode separated into at least three or more regions is configured to be smaller as it approaches the end of the mesa stripe.

A semiconductor optical device according to a fifth invention for solving the above-mentioned problem is as follows.
In the semiconductor optical device according to any one of the first to fourth inventions,
The electrode is a single electrode in a region away from the mesa stripe.

  According to the first aspect of the invention, the strain stress applied to the laser active layer or the light absorption layer can be reduced, and variations in characteristics of the laser active layer or the light absorption layer can be suppressed.

  According to the second aspect, the strain stress applied to the laser active layer or the light absorption layer can be further reduced.

  According to the third and fourth aspects of the present invention, the stress at the end of the laser active layer or the light absorption layer having a large strain stress can be particularly suppressed.

  According to the fifth aspect of the invention, the same electric signal can be supplied from one place to each of the divided electrode regions, and the drive circuit configuration and the simple driving similar to those of the conventional semiconductor optical device can be realized.

1 is a structural diagram of a semiconductor optical device according to Example 1 of the present invention. It is a structural diagram of a conventional semiconductor optical device. It is a schematic diagram of the curvature of the semiconductor substrate using the material from which a thermal expansion coefficient differs. (A) is related to the semiconductor substrate which comprised the uniform metal film, (b) is related with the semiconductor substrate into which the metal film was divided | segmented. It is a stress distribution figure concerning the laser active layer of the mesa stripe edge part of each of the conventional semiconductor optical device and the semiconductor optical device according to Example 1 of the present invention. FIG. 6 is a structural diagram of a semiconductor optical device according to Example 2 of the present invention. It is the top view which looked at the structure of the semiconductor optical device which concerns on Example 2 of this invention from the top.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a semiconductor optical device according to the present invention will be described in detail with reference to the drawings by way of examples.

  FIG. 1 shows the structure of a semiconductor optical device according to Example 1 of the present invention. On the substrate 21 made of n-InP, a first clad layer 22 made of Si-doped or Sn-doped n-InP is laminated. A first optical confinement layer 23 made of a non-doped InGaAsP bulk is laminated on the first cladding layer 22. On the first optical confinement layer 23, a laser active layer or a light absorption layer 24 made of non-doped InGaAsP-based MQW is laminated. On the laser active layer or the light absorption layer 24, a second light confinement layer 25 made of a non-doped InGaAsP bulk is laminated. A second cladding layer 26 made of Zn-doped p-InP is stacked on the second optical confinement layer 25. A contact layer 27 made of p-InGaAs is stacked on the second cladding layer 26.

  The region 28 has a width of about 2 μm and a depth of about 3 μm from the substrate surface by, for example, methane-based RIE (Reactive Ion Etching) so that the layers 22 to 27 have a mesa stripe structure. It is etched and filled with an insulating layer such as UR3800 polyimide manufactured by Toray.

  An n-type electrode 30 is provided on the lower surface of the substrate 21 made of n-InP. Each device is cut by cleavage so that the chip width and the chip length are 300 μm and 200 μm, respectively, and a non-reflective coating or the like is applied to the cleaved end face.

  Incidentally, the p-type electrode 29 provided on the contact layer 27 in FIG. 1 is divided into several regions on the mesa stripe via the stress reducing slit 29-1.

  Compared to the conventional semiconductor substrate as shown in FIG. 3A, when the metal film a is divided into several regions as shown in FIG. 3B, it is expected that the stress is relaxed and the warpage is reduced. The

  Furthermore, as shown in FIG. 4, in the conventional electrode structure, it was found by simulation that the stress load increases as the laser active layer 24 approaches the end of the mesa stripe, so that the electrode is made smaller at the end of the mesa stripe. It is designed to eliminate the stress concentration of the electrode by dividing.

  That is, compared with the conventional electrode structure, in the semiconductor optical device of Example 1, for example, the p-type electrode 29 is divided into seven regions via the stress reducing slit 29-1 (in FIG. In order to avoid complexity, the p-type electrode 29 is divided into five regions), and the p-type electrode 29 is largely divided near the center of the mesa stripe where the influence of stress is relatively small. Since the size of the electrode is divided into smaller portions as it approaches the end, the influence of large stress received from the electrode can be reduced, and as shown in FIG. 4, the laser activity at the end of the mesa stripe where the stress is most concentrated The stress applied to the layer 24 is 8 to 46 MPa for the device having the conventional structure, but is reduced to 14 to 33 MPa in this embodiment.

  Further, as shown in FIG. 1, the number of electrodes divided on the mesa stripe is one in a region away from the mesa stripe. As a result, the same electric signal can be supplied from one place to the divided electrode regions, and a drive circuit configuration and simple driving similar to those of a conventional semiconductor optical device can be realized.

  The material used for the laser active layer or the light absorption layer 24 may be other than InGaAsP. Further, the substrate 21 is not limited to the InP substrate, and may be a substrate made of another material such as GaAs. Further, in this embodiment, an example in which a semiconductor device is configured on an n-type substrate 21 is shown, but a semiconductor device configured on a p-type conductive substrate or a semi-insulating substrate may be used.

  5 and 6 show the structure of the semiconductor optical device according to Example 2 of the present invention. A first cladding layer 32 made of Si-doped or Sn-doped n-InP is laminated on a substrate 31 made of n-InP. On the first cladding layer 32, a first optical confinement layer 33 made of a non-doped InGaAsP bulk is laminated. On the first optical confinement layer 33, a laser active layer or light absorption layer 34 made of non-doped InGaAsP-based MQW is laminated. On the laser active layer or the light absorption layer 34, a second light confinement layer 35 made of a non-doped InGaAsP bulk is laminated. A second cladding layer 36 made of Zn-doped p-InP is stacked on the second confinement layer 35. A contact layer 37 made of p-InGaAs is stacked on the second cladding layer 36.

  The region 38 is etched to have a width of about 2 μm and a depth of about 3 μm from the substrate surface by methane-based RIE processing so that the layers 32 to 37 have a mesa stripe structure, and an insulating material such as UR3800 polyimide manufactured by Toray. Embedded in layers.

  A p-type electrode 39 is provided on the contact layer 37. Each device is cut by cleavage so that the chip width and the chip length are 300 μm and 200 μm, respectively, and a non-reflective coating or the like is applied to the cleavage end surface.

  In order to reduce the stress that the laser active layer or the light absorption layer receives from the electrode while simplifying the chip design, in the semiconductor optical device of Example 2, a part of the electrode configured on the mesa stripe is formed in a comb shape. The slit 39-1 for stress reduction is included.

  A thin electrode metal that covers the entire surface of the mesa stripe (hereinafter referred to as “thin film electrode”) so that the current injection into the laser active layer or the light absorption layer does not become non-uniform by forming a part of the electrode in a comb shape. And a comb-shaped electrode is formed on the thin film electrode. For example, if the thickness of the thin film electrode is set to 1000 mm or less, the influence of stress is reduced to a negligible level.

  For example, the comb-shaped electrode may be configured such that the divided electrode region has a width of 10 μm and the stress reduction slit 39-1 has a width of 10 μm therebetween.

  Furthermore, it is also possible to disperse the stress load applied to the optical waveguide by arranging the comb-shaped electrodes to be inclined with respect to the mesa stripe.

  The material used for the laser active layer or the light absorption layer 34 may be other than InGaAsP. Further, the substrate 31 is not limited to the InP substrate, and may be a substrate made of another material such as GaAs. Further, in this embodiment, an example in which a semiconductor device is configured on an n-type substrate 31 is shown, but a semiconductor device configured on a p-type conductive substrate or a semi-insulating substrate may be used.

  The present invention is suitable as a semiconductor optical device used for optical communication and various optical signal processing.

11, 21, 31 n-InP substrates 12, 22, 32 n-InP first cladding layers 13, 23, 33 InGaAsP first optical confinement layers 14, 24, 34 InGaAsP laser active layers or light absorption layers 15, 25, 35 InGaAsP second optical confinement layer 16, 26, 36 p-InP second cladding layer 17, 27, 37 p-InGaAsP contact layer 18, 28, 38 Buried region (insulating layer) beside mesa stripe
19, 29, 39 p-type electrode 20, 30, 40 n-type electrode 29-1, 39-1 Stress reducing slit a Metal film (Au)
b Semiconductor substrate (InP)

Claims (5)

  In a ridge-type semiconductor optical device having at least an optical waveguide having a mesa stripe structure, electrodes separated by stress reduction slits are provided on at least two regions in the light propagation direction on the mesa stripe. A semiconductor optical device characterized by the above.   The semiconductor optical device according to claim 1, wherein the electrode is formed obliquely with respect to the mesa stripe.   3. The semiconductor optical device according to claim 1, wherein the size of each region of the electrode is configured to be non-uniform.   4. The semiconductor optical device according to claim 3, wherein the size of each region of the electrode separated into at least three or more regions is configured so as to decrease toward the end of the mesa stripe.   5. The semiconductor optical device according to claim 1, wherein the electrode is a single electrode in a region away from the mesa stripe. 6.

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