JP2010225844A - Optical semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent stress deterioration and characteristics variation of an embedded type laser diode. <P>SOLUTION: A current constriction layer 18 is made to have a multilayer structure and the averaging of the Al composition value of the current constriction layer 18 is facilitated. Then, the average Al composition value of a ridge portion 9 and the average Al composition value of the current constriction layer 18 are made to be equal. As a result, since immanent stress which is applied to an active layer 3 is made to be a minimum value and stress variation caused by temperature variation in an element can be controlled, the deterioration of a laser diode chip caused by stress can be prevented and the stress deterioration and the characteristics variation of the element can be reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical semiconductor device, and more particularly to a technique effective when applied to an AlGaAs laser diode in the near-infrared wavelength band.

  AlGaAs laser diodes (semiconductor lasers) that emit light in the near-infrared region are widely used in reading and writing of optical disks such as CDs and MDs, laser printers, and medical / measurement equipment. The above laser diode is mainly used for the purpose of information industry, and a buried ridge structure is generally adopted as its structure.

  A general method of manufacturing a conventional laser diode is to first grow a multilayer of AlGaAs / GaAs on a GaAs substrate, then form a ridge portion (width W = 2 to 5 μm) by etching, and form a current confinement layer beside the ridge portion. By forming, the chip structure of the laser diode is formed. The current confinement layer on the side of the ridge portion uses a structure in which AlGaAs and GaAs are stacked, or a GaAs single layer. However, in order to perform current confinement and light confinement at the same time, what is the AlGaAs layer constituting the ridge portion? Layers with different Al compositions and lattice constants are used.

  As for a laser diode having a striped ridge portion, a technique is known in which a cavity is not generated in a current confinement layer for the purpose of improving output characteristics (for example, Patent Document 1).

JP 2004-342957 A

  A near-infrared laser diode in which a laser structure is formed of an AlGaAs / GaAs crystal on a GaAs substrate has a problem that strain stress is inherent in the laser diode chip due to the difference in lattice constant between AlGaAs and GaAs. In particular, in the vicinity of the ridge structure that performs current confinement and light confinement and becomes the light emitting portion of the element, the active layer portion is uneven due to the difference in the composition of the ridge portion that becomes the convex portion and the buried layer that becomes the current confinement layer Stress will be applied. In this state, when the laser diode chip is assembled and operated with solder on the package, the stress of the element is deteriorated and the characteristics are changed.

  FIG. 1 is a cross-sectional view of a main part showing a buried laser diode having a conventional ridge portion having a general stripe structure. As shown in FIG. 1, in the conventional general embedded laser diode, the strain stress is particularly large on the stress generating portion 21 in the active layer 3 below the side surface of the ridge portion 9, and the current confinement layer 22 is made of Al. In the case where one GaAs layer 19 is formed on the AlGaAs layer 20 having a high content ratio (the Al composition is large), the second p-type cladding layer 6 constituting the ridge portion 9 and the AlGaAs layer 20 constituting the current confinement layer Since the lattice constant difference between the GaAs layer 19 and the GaAs layer 19 is large, a large strain stress is inherent in the stress generating portion 21.

  One of the factors that reduce the reliability of AlGaAs laser diodes is the problem that the generation and growth of crystal defects is facilitated by the strain stress inherent in the element. In this material-based laser diode, AlGaAs used for the cladding layer and GaAs of the semiconductor substrate have different lattice constants, and have a structure that inherently contains strain stress. In the laser diode fabrication process, there are processes with various thermal histories, such as a buried growth / electrode formation process in the previous process and a die bonding process in the subsequent process, and even greater strain stress is generated depending on the device structure. As a result, life deterioration due to this strain stress may occur. In general, the thermal expansion coefficient of the heat sink part of the package in which the product is incorporated is different from that of the crystal part of the laser diode chip. The mount / heat sink is deformed, and the strain stress applied to the active layer portion of the chip changes. As a result, there is a problem that the internal stress becomes too large depending on the operating temperature, and the element deteriorates due to temperature fluctuation.

  The object of the present invention is to reduce the stress degradation and characteristic fluctuation of the element by minimizing the internal stress applied to the active layer portion of the laser diode and suppressing the element degradation due to long-term operation and the stress change in the element due to temperature fluctuation. To provide technology to prevent.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

An optical semiconductor device according to an embodiment of the present invention includes:
An optical semiconductor element having a laser diode formed on a main surface of a III / V group semiconductor substrate containing Ga,
The laser diode is formed on the main surface of the semiconductor substrate, and has a first conductivity type clad layer having a multilayer crystal structure using a III / V group mixed crystal semiconductor containing at least Al.
An active layer formed on the cladding layer of the first conductivity type;
A clad layer of a second conductivity type formed on the active layer and having a multilayer crystal structure using a group III / V mixed crystal semiconductor containing at least Al;
A ridge portion including a cladding layer of the second conductivity type and having a stripe structure;
A current confinement layer formed of a composite layer of two or more layers using a group III / V mixed crystal semiconductor containing Al in at least one layer formed on the main surface of the semiconductor substrate and on the side surface of the ridge portion;
A contact layer formed on the ridge and the current confinement layer;
Electrodes formed on the contact layer and on the back surface of the semiconductor substrate;
Have
The ridge portion and the current confinement layer are configured such that the Al composition average values of the crystals constituting each of them are substantially equal.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  A highly reliable laser diode can be easily manufactured by preventing concentration of local intrinsic stress, which is a deterioration factor of the conventional AlGaAs laser diode.

It is principal part sectional drawing of the conventional optical semiconductor element. It is principal part sectional drawing which shows the manufacturing method of the optical semiconductor element of this invention. FIG. 3 is a fragmentary cross-sectional view showing the method for manufacturing the optical semiconductor device following FIG. 2. FIG. 4 is an essential part cross-sectional view showing a method for manufacturing the optical semiconductor device following FIG. 3; FIG. 5 is a fragmentary cross-sectional view showing the method for manufacturing the optical semiconductor device following FIG. 4. 6 is a fragmentary cross-sectional view showing the method for manufacturing the optical semiconductor element continued from FIG. 5. FIG. FIG. 7 is a fragmentary cross-sectional view showing the method for manufacturing the optical semiconductor element continued from FIG. 6. FIG. 8 is an essential part cross-sectional view showing a method for manufacturing the optical semiconductor element following FIG. 7; FIG. 9 is an essential part cross-sectional view showing a method for manufacturing the optical semiconductor element following FIG. 8; FIG. 10 is an essential part cross-sectional view showing a method for manufacturing the optical semiconductor element following FIG. 9; It is principal part sectional drawing which shows the manufacturing method of the optical semiconductor element following FIG.

  In the following embodiments, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other. There are some or all of the modifications, details, supplementary explanations, and the like.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.

  Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. In addition, in the embodiment, etc., when “consisting of A” or “consisting of A” is used to exclude other elements, unless specifically stated that only those elements are stated. It goes without saying that it is not.

  Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  In addition, when referring to materials, etc., unless specified otherwise, or in principle or not in principle, the specified material is the main material, and includes secondary elements, additives It does not exclude additional elements. For example, unless otherwise specified, the silicon member includes not only pure silicon but also an additive impurity, a binary or ternary alloy (for example, SiGe) having silicon as a main element.

  Also, components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof is omitted.

  In the drawings used in the following embodiments, even a plan view may be partially hatched to make the drawings easy to see.

  The optical semiconductor device of this embodiment is applied to an embedded laser diode having a stripe-shaped ridge portion, and the manufacturing process will be described with reference to FIGS. 2 to 11 are fragmentary cross-sectional views of the laser diode of the present embodiment during the manufacturing process.

  First, as shown in FIG. 2, a GaAs substrate (hereinafter simply referred to as a substrate) 1 is prepared. In addition to GaAs, this substrate 1 may use other III / V group semiconductor substrates containing Ga, such as GaP.

  Next, as shown in FIG. 3, an n-type cladding layer 2 containing AlGaAs, an active layer 3 and a p-type AlGaAs are formed on the main surface of the substrate 1 by MOCVD (Metal Organic Chemical Vapor Deposition). A first p-type cladding layer 4 containing Al, an etch stop layer 5 containing AlGaInP, a second p-type cladding layer 6 containing p-type AlGaAs, and a contact layer 7 containing p-type GaAs are sequentially deposited. The active layer 3 is composed of five thin films and is formed by depositing layers of AlGaAs, GaAs, AlGaAs, GaAs, and AlGaAs in order from the bottom, although not shown. As a material for the n-type cladding layer 2, the first p-type cladding layer 4 and the second p-type cladding layer 6, a III / V group mixed crystal semiconductor containing Al, such as AlGaP, may be used.

  Next, as shown in FIG. 4, after depositing a silicon oxide film on the main surface of the substrate 1 by MOCVD, a part of the silicon oxide film is removed by dry etching using a photoresist film (not shown) as a mask. Then, an insulating film 8 made of the remaining silicon oxide film is formed. Thereafter, the photoresist film on the insulating film 8 is removed by ashing.

  Next, as shown in FIG. 5, using the insulating film 8 as a mask, the contact layer 7 and a part of the second p-type cladding layer 6 are removed by wet etching, and the ridge having the second p-type cladding layer 6 and the contact layer 7 is obtained. Part 9 is formed. In forming the ridge portion 9, a dry etching method with good controllability may be used instead of wet etching. The etch stop layer 5 may be made of another material such as GaAs or may have a structure in which the etch stop layer 5 itself is eliminated.

  Next, as shown in FIG. 6, an n-type AlGaAs layer 10, an n-type GaAs layer 11, an n-type AlGaAs layer 12, and an n-type GaAs layer 13 are formed as a current confinement layer 18 on the main surface of the substrate 1 by MOCVD. The four layers are sequentially deposited. At this time, the current confinement layer 18 is not deposited on the upper portion of the ridge because it is not vapor-phase grown at the portion covered with the insulating film 8. The thickness of the current confinement layer 18 is set so that the upper end of the current confinement layer 18 is flush with the upper end of the contact layer 7. The average value of the Al composition value in the current confinement layer 18 is, for example, 0.48, the average value of the Al composition value in the ridge portion 9 is, for example, 0.49, and the absolute value of the difference is within 0.1 So that the values are almost equal. At this time, the current confinement layer 18 has a structure composed of two or more composite layers using a group III / V mixed crystal semiconductor containing Al in at least one layer. In the case of another configuration, for example, a configuration in which GaP is used for the substrate 1 and the current confinement layer 18 is a composite layer of AlGaP and GaP may be used. Further, the upper end of the current confinement layer 18 is formed so as to have the same height as the upper end of the ridge portion 9 so as to be substantially equal.

  Here, by forming the current confinement layer 18 in a four-layer structure, the Al composition value in the current confinement layer 18 is higher than that of the current confinement layer having a two-layer structure that is common in conventional laser diodes. Makes it easy to average. For this reason, the average value of the Al composition values of the ridge portion 9 and the average value of the Al composition values of the current confinement layer 18 can be easily made equal.

  As shown in FIG. 1, many portions of the current confinement layer 22 are conventionally formed of GaAs, and the lattice constant of the cladding layer 6 constituting the ridge portion 9 and the current confinement layer 22 on the side surface of the ridge portion 9. When the lattice constants of the formed AlGaAs layer 20 or GaAs layer 19 are different, local stress concentration occurs in a part of the active layer 3 (stress generation part 21), which causes stress deterioration and characteristic variation of the laser diode element. It was.

  In the present embodiment, the average value of the Al composition value of the ridge portion 9 and the average value of the Al composition value of the current confinement layer 18 shown in FIG. The average value of the constant is also equal. For this reason, the local stress concentration to the specific location by the lattice constant difference with the board | substrate 1 and the shape influence of the ridge part 9 can be suppressed, and the distortion stress to the ridge part side surface downward direction can be reduced. As a result, the internal stress applied to the active layer 3 can be minimized, and when the completed laser diode chip is bonded to the package and operated, the stress change due to temperature fluctuations in the element can be suppressed. Therefore, it is possible to prevent the deterioration of the stress of the element and reduce the characteristic variation.

  In the case of using the present invention, it is desirable that the height of the ridge portion 9 and the height of the upper end of the current confinement layer 18 are aligned so that the upper ends of both are substantially on the same plane. There is no need to align. When the heights of both are not equal, the average value of the Al composition is taken in the range from the upper end of the etch stop layer 5 to the higher upper end of either the ridge portion 9 or the current confinement layer 18, and the ridge portion If the structure is determined so that the composition average value is approximately equal between 9 and the current confinement layer 18, the same effect as described above can be obtained.

  Next, as shown in FIG. 7, after the insulating film 8 is removed by wet etching using a hydrofluoric acid (HF) etching solution, a contact layer 14 mainly made of GaAs is formed on the main surface of the substrate 1 by MOCVD. It accumulates by.

  Next, as shown in FIG. 8, the contact layer 14, the current confinement layer 18, the etch stop layer 5, the first p-type cladding layer 4, the active layer 3, n by dry etching using a photoresist film (not shown) as a mask. After removing the mold cladding layer 2 and a part of the substrate 1, the photoresist film on the contact layer 14 is removed by ashing.

  Next, as shown in FIG. 9, after a silicon oxide film 15 is deposited on the main surface of the substrate 1, a part of the silicon oxide film 15 is removed by dry etching using a photoresist film (not shown) as a mask. Then, the photoresist film on the silicon oxide film 15 is removed by ashing.

  Next, as shown in FIG. 10, a main surface electrode 16 is deposited on the main surface of the substrate 1. The main surface electrode 16 is formed of a layer in which Ti / Pt / Au are sequentially stacked.

  Next, as shown in FIG. 11, after depositing a back electrode 17 on the back surface of the substrate 1, a part of the back electrode 17 is removed by dry etching using a photoresist film (not shown) as a mask, and then by ashing. The photoresist film on the back surface is removed. The reason why a part of the back electrode 17 is removed here is to facilitate the operation of cleaving the substrate 1 in the subsequent process.

  Thereafter, although not shown in the figure, the substrate 1 is cleaved and divided into a plurality of rows, and a protective film is coated on the front and rear light output end faces by electron beam evaporation or the like, and then the substrate 1 divided into the plurality of rows is pelletized. By separating (cutting) into individual laser diode chips, the pre-process of the embedded laser diode having the stripe-shaped ridge portion is completed.

  The laser diode divided into chips is used as a product by assembling it into a package using AuSn solder as an adhesive with the main surface side with the ridge portion 9 as the submount side.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  For example, although the current confinement layer 18 has a four-layer structure in the above embodiment, similarly, an AlGaAs layer and a GaAs layer may be alternately deposited to form an eight-layer structure, a ten-layer structure, or a twenty-layer structure. In the current confinement layer, the more the number of layers constituting the current confinement layer, the easier it is to average the Al composition value inside.

  In addition, if the current confinement layer is not a structure in which AlGaAs and GaAs layers are alternately stacked, but if the average value of the Al composition is almost equal, all layers are made of AlGaAs and the Al composition is adjusted for each layer. You may make it match | combine an average value.

  The present invention relates to a technique effective when applied to an embedded laser diode.

1 Substrate (GaAs substrate)
2 n-type cladding layer 3 active layer 4 first p-type cladding layer 5 etch stop layer 6 second p-type cladding layer 7 contact layer 8 insulating film 9 ridge portion 10 n-type AlGaAs layer 11 n-type GaAs layer 12 n-type AlGaAs layer 13 n Type GaAs layer 14 Contact layer 15 Silicon oxide film 16 Main surface electrode 17 Back electrode 18 Current confinement layer 19 GaAs layer 20 AlGaAs layer 21 Stress generating portion 22 Current confinement layer

Claims (7)

An optical semiconductor element having a laser diode formed on a main surface of a III / V group semiconductor substrate containing Ga,
The laser diode is formed on the main surface of the semiconductor substrate, and has a first conductivity type clad layer having a multilayer crystal structure using a III / V group mixed crystal semiconductor containing at least Al.
An active layer formed on the cladding layer of the first conductivity type;
A clad layer of a second conductivity type formed on the active layer and having a multilayer crystal structure using a group III / V mixed crystal semiconductor containing at least Al;
A ridge portion including a cladding layer of the second conductivity type and having a stripe structure;
A current confinement layer formed of a composite layer of two or more layers using a group III / V mixed crystal semiconductor containing Al in at least one layer formed on the main surface of the semiconductor substrate and on the side surface of the ridge portion;
A contact layer formed on the ridge and the current confinement layer;
Electrodes formed on the contact layer and on the back surface of the semiconductor substrate;
Have
The ridge portion and the current confinement layer are configured so that the Al composition average values of crystals constituting each of them are substantially equal.   The semiconductor substrate includes GaAs, the first conductive type cladding layer and the second conductive type cladding layer include AlGaAs, and the current confinement layer includes an AlGaAs or GaAs composite layer. 1. The optical semiconductor device according to 1.   2. The optical semiconductor device according to claim 1, wherein the ridge portion and the current confinement layer have substantially the same height, and the upper ends of the ridge portion and the current confinement layer are substantially in the same plane.   The height of the upper end of each of the ridge portion and the current confinement layer is set to a different height, and either the ridge portion or the current confinement layer is higher from the lower end of the ridge portion or the current confinement layer. 2. The optical semiconductor device according to claim 1, wherein an average value of the Al composition up to the upper end position of the other part is taken and the composition average value at both parts is substantially equal.   2. The optical semiconductor device according to claim 1, wherein the laser diode has the ridge portion, the main surface side of the semiconductor substrate being a submount side, and being bonded to the inside of the package by AuSn solder.   2. The optical semiconductor element according to claim 1, wherein the current confinement layer has a structure in which AlGaAs and GaAs are alternately laminated.   The semiconductor substrate includes GaP, the first conductivity type cladding layer and the second conductivity type cladding layer include AlGaP, and the active layer is a III / V group mixed crystal including at least one of In or As; 2. The optical semiconductor element according to claim 1, wherein the current confinement layer includes a composite layer of AlGaP and GaP.

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