JP2009087977A - Semiconductor light-emitting element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element having high light emitting efficiency even if a driving current increases, and to provide a manufacturing method thereof. <P>SOLUTION: Since a position P of an interface between a first embedding layer 31 and a second embedding layer 32 in an embedding layer 30 is higher than a position Q of a lower surface of a second conductivity-type cladding layer 22 in a semiconductor mesa 20 and is lower than a position R of the upper surface, at least one part of a side surface 22s of the second conductivity-type cladding layer 22 is covered with the second embedding layer 32. Since the second embedding layer 32 is made of an insulative material, a leak current in the second conductivity-type cladding layer side surface 22s can be efficiently suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor optical device and a manufacturing method thereof.

As one of the main structures of a semiconductor optical device used in the field of optical information communication, the active layer and its peripheral layer are etched in a mesa stripe shape, and both end faces thereof are embedded with a current blocking region (embedded layer) made of a semiconductor layer. There is a buried heterostructure (Buried Heterostructure, hereinafter referred to as “BH structure”). In the BH structure, light and current can be strongly confined in the active layer by the current blocking regions on both sides, so that stimulated emission is efficiently generated. In particular, a BH structure type semiconductor optical device using a semiconductor material in the current block region is frequently used as a laser for optical communication because of its small parasitic capacitance and excellent high speed. For example, Patent Document 1 discloses a semiconductor optical device having the above structure.
JP-A-8-111565

  In recent years, with an increase in information transmitted by optical communication, there is a high demand for an optical communication laser capable of high output, and there is a demand for an optical communication laser with high luminous efficiency, particularly when the drive current increases. In the conventional BH structure type semiconductor optical device, sufficient luminous efficiency cannot be obtained. The cause of this is considered to be an increase in leakage current from the side surface of the semiconductor mesa to the buried layer.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor optical device having high luminous efficiency even when the drive current increases and a method for manufacturing the same.

  In order to achieve the above object, a semiconductor optical device according to the present invention is provided on (a) a semiconductor substrate and (b) a semiconductor substrate, and on the first conductivity type cladding layer and the first conductivity type cladding layer. A semiconductor mesa including an active layer provided and a second conductivity type clad layer provided on the active layer; and (c) a semiconductor mesa provided on the semiconductor substrate and embedded in the semiconductor mesa. And (d) an interface between the first buried layer and the second buried layer. The buried layer includes a first buried layer and a second buried layer made of an insulating material provided on the first buried layer. The position is higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface.

  In the case of the above structure, the position of the interface between the first buried layer and the second buried layer in the buried layer is higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface. At least a part of the side surface of the second conductivity type cladding layer is covered with the second buried layer. Since the second buried layer is made of an insulating material, the leakage current on the side surface of the second conductivity type cladding layer is effectively suppressed. Therefore, the semiconductor optical device according to the present invention can achieve high luminous efficiency even when the drive current increases.

  The method for producing a semiconductor optical device of the present invention includes: (a) a first conductivity type cladding layer, an active layer provided on the first conductivity type cladding layer, and a second conductivity type cladding layer provided on the active layer. And (b) embedding the semiconductor mesa, and the position of the upper surface of the semiconductor mesa is lower than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa. A step of forming a first buried layer made of a semiconductor material that is higher than a position of the upper surface; and (c) forming a second buried layer made of an insulating material and filling a semiconductor mesa on the first buried layer. And a process.

  With the above manufacturing method, the first buried layer of the buried layers is formed such that the position of the upper surface is higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface. For this reason, at least a part of the side surface of the second conductivity type cladding layer in the semiconductor mesa is covered with the second buried layer made of an insulating material. As a result, a leakage current from the side surface of the second conductivity type cladding layer to the buried layer is suppressed, and a semiconductor optical device having high light emission efficiency can be manufactured even when the drive current is increased.

  Further, in the method of manufacturing a semiconductor optical device of the present invention, (b) the step of forming the first buried layer on the semiconductor substrate is (b1) the step of forming the first buried layer to a position higher than the semiconductor mesa. (B2) etching the first buried layer to form a position of the upper surface at a height higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface. The aspect which has may be sufficient.

  When the first buried layer is grown on the semiconductor substrate, the epi layer may creep up near the side surface of the semiconductor mesa, which may cause a variation in thickness. However, by forming the first buried layer up to a position higher than the semiconductor mesa as described above, it is possible to suppress the creeping of the epi layer in the vicinity of the side surface of the semiconductor mesa. Furthermore, by adjusting the height of the first buried layer by etching, it is possible to reduce the influence of the rising of the epi layer, and to make the first buried layer uniform in height.

  The manufacturing method of the present invention further includes (b2) a step of etching the first buried layer, (b2-1) a step of removing a part of the first buried layer by deep etching, and (b2-2) first The first buried layer is partially etched by wet etching so that the position of the upper surface of the first buried layer is higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface. And a step of removing.

  According to the above process, when etching the first buried layer, the upper surface of the first buried layer is flattened by making the etching rate in the surface direction of the semiconductor substrate higher than the etching rate in the thickness direction of the semiconductor substrate. Can be.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor optical element which has high luminous efficiency even if a drive current increases, and its manufacturing method are provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted.

(Configuration of semiconductor optical device)
FIG. 1 is a cross-sectional view showing a semiconductor optical device according to an embodiment of the present invention. This semiconductor optical device emits light in the 1.55 μm band, and is used for long-wavelength optical communication, for example. As shown in FIG. 1, the semiconductor optical device 1 </ b> A includes a semiconductor substrate 10, a semiconductor mesa 20, and a buried layer 30 that embeds the semiconductor mesa 20.

  The semiconductor substrate 10 is a first conductivity type (n-type) substrate having conductivity, for example, an InP substrate.

  The semiconductor mesa 20 is provided on the semiconductor substrate 10 and has a lower first conductivity type cladding layer 21, an active layer 23, an upper second conductivity type cladding layer 22, and an upper contact of the second conductivity type cladding layer. Layer 24.

  As the first conductivity type cladding layer 21 constituting the semiconductor mesa 20, for example, InP doped with Si is preferable. Alternatively, the first conductivity type cladding layer 21 and the first conductivity type semiconductor substrate 10 may be configured integrally. As the second conductivity type cladding layer 22, for example, an InP layer doped with Zn is preferable.

  The active layer 23 employs a quantum well structure including well layers and barrier layers. For example, the active layer 23 may be a layer having a multiple quantum well structure including well layers and barrier layers that are alternately stacked. The well layer and the barrier layer are made of, for example, InGaAsP semiconductors having different compositions. Alternatively, a separate confinement heterostructure (SCH structure) including guide layers above and below the quantum well structure may be used.

  As the contact layer 24, for example, an InGaAs layer or the like is preferable.

The buried layer 30 includes two layers, and includes a lower first buried layer 31 and an upper second buried layer 32. The first buried layer 31 is made of a semiconductor material, and for example, Fe-doped InP or the like is preferable. The second buried layer 32 provided on the first buried layer 31 is made of an insulating material, and for example, SiO ₂ is preferable.

  The interface between the first buried layer 31 and the second buried layer 32 is parallel to the main surface 10 s of the semiconductor substrate 10, and its position P is higher than the position Q on the lower surface of the second conductivity type cladding layer 22, It is lower than the position R. Therefore, a part of the side surface 22 s of the second conductivity type cladding layer 22 is covered with the second buried layer 32.

  The semiconductor optical device 1A according to the present embodiment further includes an electrode 41 (for example, an anode) formed on the uppermost contact layer 24 of the semiconductor mesa 20 and an electrode 42 (for example, the back surface of the semiconductor substrate 10). Cathode).

In addition, the more specific aspect of said embodiment is as follows.
Semiconductor substrate 10: InP substrate First conductivity type cladding layer 21: Si-doped InP layer (thickness: 1.0 μm)
Active layer 23: InGaAsP layer (thickness 0.2 μm)
Second conductivity type cladding layer 22: Zn-doped InP layer (thickness 1.5 μm)
Contact layer 24: InGaAs layer (thickness 0.2 μm)
First buried layer 31: Fe-doped InP layer (Fe concentration 1 × 10 ¹⁷ atoms / cm ³ )
Second buried layer 32: SiO ₂ layer

The effect by embodiment of this invention shown above is demonstrated compared with a prior art. FIG. 2 is a diagram showing a semiconductor optical device 2A according to the prior art. As shown in FIG. 2, the semiconductor mesa 20 of the semiconductor optical device 2 </ b> A is embedded only with the semi-insulating embedded layer 60. An SiO ₂ insulating layer 61 is interposed between the buried layer 60 and the electrode 41. For this reason, the leakage current from the semiconductor mesa 20 to the buried layer 60 is large, and sufficient light emission efficiency has not been obtained.

  On the other hand, in the semiconductor optical device 1A according to the embodiment of the present invention, the position P of the interface between the first buried layer 31 and the second buried layer 32 is the position of the lower surface of the second conductivity type cladding layer 22 as shown in FIG. Since it is higher than Q and lower than the position R of the upper surface, the leakage current from at least a part of the side surface 24s of the contact layer 24 and the side surface 22s of the second conductivity type cladding layer located above the interface P is reduced. Therefore, even when the drive current is large, high luminous efficiency can be realized as much as when the drive current is small.

  When the position P of the interface between the first buried layer 31 and the second buried layer 32 is lower than the position Q on the lower surface of the second conductivity type cladding layer 22, the side surface of the active layer 21 is not covered with the first buried layer 31. Then, it is exposed to the outside until the second buried layer 32 is formed at least around the active layer 21. For this reason, the crystallinity of the active layer 21 may be deteriorated due to the influence of the atmosphere at the time of exposure or the high temperature treatment at the time of forming the second buried layer 32, and the light emission efficiency may be lowered. Further, when the interface position P is higher than the position R of the upper surface of the second conductivity type cladding layer 22, the side surface 22s of the second cladding layer is not covered with the second buried layer 32, so that the leakage current is not suppressed, It is thought that luminous efficiency falls.

(Method for manufacturing semiconductor optical device)
3-5 is a figure which shows typically each process of the manufacturing method of 1 A of semiconductor optical elements which concern on this embodiment. The semiconductor optical device 1A is manufactured, for example, through the following steps.

[Semiconductor layer forming step]
As shown in FIG. 3A, a semiconductor layer 20 a is formed over the semiconductor substrate 10. The semiconductor layer 20a includes a layer 21a to be the first conductivity type cladding layer 21, a layer 23a to be the active layer 23, a layer 22a to be the second conductivity type cladding layer 22, and a layer 24a to be the contact layer 24 on the semiconductor substrate 10. The cap layer 51 is formed by sequentially growing. For the growth of these layers, for example, a metal organic chemical vapor deposition (MOVPE) method can be used.

[Mask layer forming step]
Next, as shown in FIG. 3B, a mask layer 52 having a thickness of about 1 μm is formed on the cap layer 51. The mask layer 52 is made of an insulating material, and for example, SiO ₂ and SiN are preferable. The mask layer 52 is formed by, for example, a plasma CVD method.

  Subsequently, as shown in FIG. 3C, the mask layer 52 is patterned to form a stripe mask 53 having a width of 1.8 μm. The mask 53 is formed by, for example, a normal photolithography method and dry etching.

[Semiconductor mesa formation process]
Next, as shown in FIG. 3D, the semiconductor layer 20a is etched using the mask 53 as a mask to obtain the semiconductor mesa 20. At this time, the conditions of the etching process are adjusted to form the semiconductor mesa 20 having a predetermined height (for example, 3 μm). This etching is performed, for example, by dry etching using a mixed gas of H ₂ and CH ₄ . As a result, a semiconductor mesa 20 is formed that extends in a predetermined axial direction and includes the first conductivity type cladding layer 21, the active layer 23, the second conductivity type cladding layer 24, and the contact layer 24.

[First buried layer forming step]
Next, as shown in FIG. 4A, a semiconductor layer 31a to be the first embedded layer 31 of the embedded layer 30 in which the semiconductor mesa 20 is embedded is formed. The semiconductor layer 31a is formed by, for example, the MOVPE method. The thickness of the semiconductor layer 31 a is not less than the semiconductor mesa 20 (for example, 3 μm) and does not grow on the semiconductor mesa 20 covered with the mask 53. In this way, by making the semiconductor layer 31 a thicker than the semiconductor mesa 20, it is possible to suppress the creeping that occurs near the side surface of the semiconductor mesa 20.

  After forming the semiconductor layer 31a, the mask 53 is removed. The mask 53 is removed by, for example, hydrofluoric acid (DHF) diluted to 25%.

  Next, the semiconductor layer 31a is etched, and the position of the upper surface thereof is made higher than the position of the lower surface of the second conductivity type cladding layer 22 of the semiconductor mesa 20 and lower than the position of the upper surface, so that the first buried layer 31 is formed. obtain. The detailed method is as follows.

  First, as shown in FIG. 4B, grooves 33 extending in parallel along the semiconductor mesa 20 are formed in each of the semiconductor layers 31a on both sides of the semiconductor mesa 20 by dry etching. The two grooves 33 are deep-etched to the same depth and adjusted so that the position of the bottom surface is the same as the position of the top surface of the first buried layer 31. The position of the bottom surface can be adjusted by changing the etching conditions.

Subsequently, as shown in FIG. 4C, the first buried layer 31 is formed by etching the semiconductor layer 31 a by wet etching to make the semiconductor layer 31 a flat near the bottom surface position of the groove 33. The depth of etching is 1 μm, for example. In the wet etching, an etching solution in which CH ₃ COOH and HCl are mixed and diluted with H ₂ O is used. By adjusting the mixing ratio of CH ₃ COOH and HCl, the horizontal etching rate of the semiconductor layer 31a is sufficiently higher than the vertical etching rate, so that the upper surface of the first buried layer 31 after etching Can be flattened.

  In this way, by forming the semiconductor layer 31a up to a position higher than the semiconductor mesa 20, it is possible to suppress creeping or the like in the vicinity of the side surface of the semiconductor mesa 20. Further, the height of the semiconductor layer 31a is adjusted by deep etching by dry etching and wet etching to form the first embedded layer 31, thereby reducing the influence of the above-mentioned creeping up and making the first embedded layer 31 uniform. Height.

  Note that the cap layer 51 is also etched away during the wet etching of the semiconductor layer 31a. Further, since the etching rate in the vertical direction of the semiconductor layer 31a is sufficiently higher than the etching rate in the vertical direction of the contact layer 24, the etching of the contact layer 24 hardly proceeds and the semiconductor layer 31a is selectively etched. Can do.

[Second buried layer forming step]
Next, as shown in FIG. 4D, an insulating layer 32 a made of an insulating material is formed so as to integrally cover the semiconductor mesa 20 and the first buried layer 31. The formation method is, for example, by plasma CVD so that the upper surface is higher than the semiconductor mesa 20.

  Then, a part of the formed insulating layer 32a is etched by the following method, for example. That is, as shown in FIG. 5A, after forming the photoresist 54 having an opening in the semiconductor mesa 20, the insulating film is insulated with 25% diluted hydrofluoric acid using the photoresist 54 as a mask. The layer 32a is etched to expose the contact layer 24 of the semiconductor mesa 20. The photoresist 54 used for the etching is removed, and the second embedded layer 32 after molding is obtained.

[Electrode formation process]
Next, an electrode is formed on the contact layer 24. As shown in FIG. 5B, a photoresist 55 (thickness: 2 μm) is formed in which an opening is provided in a portion where the electrode 41 is to be formed. Thereafter, an Au / Pt / Ti electrode is deposited and lifted off to form an electrode 41 having a thickness of 3 μm or more as shown in FIG. Further, the electrode 42 is formed on the back surface of the semiconductor substrate by the same method.

  Thereby, the semiconductor optical device 1A shown in FIG. 1 is manufactured.

  According to the above manufacturing method, the position P of the interface between the first buried layer 31 and the second buried layer 32 is higher than the position Q on the lower surface of the second cladding layer 22 and lower than the position R on the upper surface. It is possible to provide a semiconductor optical device having high luminous efficiency even when the driving current increases.

  In addition, the said embodiment can be changed in the range which does not deviate from the summary of this invention. For example, the conductivity type of the semiconductor substrate 10 is n-type, but may be p-type. In this case, the conductivity type of the first conductivity type cladding layer 21 is changed to p-type, and the conductivity types of the second conductivity type cladding layer 22 and the contact layer 24 are changed to n-type.

It is sectional drawing which shows typically the structure of the semiconductor optical element concerning embodiment of this invention. It is sectional drawing which shows the structure of the conventional semiconductor optical element typically. It is sectional drawing which shows a part of process of the manufacturing method of the semiconductor optical element concerning embodiment of this invention. It is sectional drawing which shows a part of process of the manufacturing method of the semiconductor optical element concerning embodiment of this invention. It is sectional drawing which shows a part of process of the manufacturing method of the semiconductor optical element concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A, 2A ... Semiconductor optical element, 10 ... Semiconductor substrate, 20 ... Semiconductor mesa, 21 ... 1st conductivity type clad layer, 22 ... 2nd conductivity type clad layer, 23 ... Active layer, 24 ... Contact layer, 30 ... Buried layer 31 ... 1st embedding layer, 32 ... 2nd embedding layer, 41, 42 ... electrode.

Claims (4)

A semiconductor substrate;
A first conductivity type cladding layer; an active layer provided on the first conductivity type cladding layer; a second conductivity type cladding layer provided on the active layer; A semiconductor mesa containing
A first embedded layer made of a semiconductor material, and a second embedded layer made of an insulating material provided on the first embedded layer; An embedded layer;
The position of the interface between the first buried layer and the second buried layer in the buried layer is higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface. A semiconductor optical device that is characterized. A semiconductor mesa including a first conductivity type cladding layer, an active layer provided on the first conductivity type cladding layer, and a second conductivity type cladding layer provided on the active layer is formed on a semiconductor substrate. Forming, and
A step of embedding the semiconductor mesa and forming a first buried layer made of a semiconductor material, the position of the upper surface being higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface; When,
Forming a second buried layer made of an insulating material and filling the semiconductor mesa on the first buried layer;
A method for producing a semiconductor optical device, comprising: Forming the first buried layer on the semiconductor substrate;
Forming the first buried layer to a position higher than the semiconductor mesa;
Etching the first buried layer to form a position of the upper surface at a height higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface;
The method of manufacturing a semiconductor optical device according to claim 2, comprising: Etching the first buried layer comprises:
Removing a portion of the first buried layer by deep etching;
The remaining portion of the first buried layer is wet so that the upper surface of the first buried layer is higher than the position of the lower surface of the second conductivity type cladding layer in the semiconductor mesa and lower than the position of the upper surface. Removing by etching;
The method of manufacturing a semiconductor optical device according to claim 3, comprising:

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