JP4984514B2 - Semiconductor light emitting device and method for manufacturing the semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light-emitting device including a high-power superluminescent diode (hereinafter referred to as “SLD”) suitable for optical fiber communication and a light source for measurement / diagnosis, and a method for manufacturing the same.

  In recent years, SLDs have attracted attention as incoherent light sources required in the field of optical measurement such as fiber gyros and high-resolution OTDR. The SLD is an element in which spontaneous emission light generated by recombination of injected carriers is amplified by receiving a high gain due to stimulated emission while traveling in the direction of the light emission end face, and emitted from the light emission end face, as in the semiconductor laser. SLDs differ from semiconductor lasers in that they prevent the formation of resonators due to end-face reflection and prevent FP (Fabry-Perot) mode oscillation. The SLD is incoherent like a normal light emitting diode, exhibits a broad spectrum shape, and can output up to several tens of mW.

  In such an SLD, (1) a method using a structure in the waveguide direction of light (see, for example, Patent Document 1) and (2) an active layer as a method for obtaining a broader spectrum distribution (over a wide wavelength range). A method using a structure in the thickness direction is known (for example, see Non-Patent Document 1).

  The method (2) is a method in which a plurality of layers having mutually different band gaps are used as active layers, the light spectra emitted in the respective band gaps are superimposed, and the emitted light spectrum is broadened. However, in this structure, when the number of active layers and the thickness of the active layer are increased, the drive current density increases, so that a large load is applied to a broadband device that requires a plurality of active layers and the life of the device is improved. It was difficult.

  On the other hand, in the method (1), after forming masks having different widths, an active layer is formed so that the active layer has a thickness distribution and a composition distribution in the waveguide direction, and a band gap is continuously formed in the waveguide direction. This is a method of widening the band by changing the power or discontinuously, and no load such as an increase in driving current is generated by the widening of the band. This utilizes the fact that the gain wavelength varies depending on the thickness and composition of the active layer.

Conventionally, as a method of providing thickness distribution and composition distribution in the waveguide direction as in (1), a selective growth mask is produced with an insulating film such as SiO ₂ or SiN before the active layer is formed. A method of selectively growing the active layer using the method is used. Specifically, two stripe-like SiO ₂ masks are formed on the laminated surface in parallel at regular intervals, and the thickness of the active layer grown in the region sandwiched between the masks by changing the mask width A method for changing the composition in the direction of the resonator axis is known.
JP-A-6-196809 Published by Ching-Fuh Lin and Bor-Lin Lee, Applied Physics Letters, 1997, Vol. 71, No. 1, 1598

  The SLD manufactured using the method (1) and having a structure that generates light having a different gain wavelength in the waveguide direction has a wider bandwidth than an SLD that generates only light having a single gain wavelength. Can be obtained.

  On the other hand, since this method utilizes the fact that the raw material on the mask portion surface migrates outside the active layer and other masks, it is necessary to increase the amount of change in the mask width in order to further increase the bandwidth. . In order to increase the amount of change in the mask width, it is necessary to increase the mask area as a whole. In general, however, in the selective growth of MOCVD, if the mask area increases, it is removed by an etching process after the selective growth. There is a problem that polycrystals that cannot be easily deposited on the mask surface, and the mask area is limited. Therefore, there is a limit to the expansion of the device bandwidth.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a semiconductor light emitting device having a novel structure capable of increasing the gain wavelength in a semiconductor light emitting device such as an SLD and a method for manufacturing the same.

The semiconductor light-emitting device of the present invention is formed by laminating a plurality of semiconductor layers including a lower clad layer, an active layer, and an upper clad layer on a substrate. In a semiconductor light emitting device having
Of the plurality of semiconductor layers, a recess is formed on the laminated surface of the semiconductor layer on the substrate side of the active layer,
The active layer and the layer above the active layer are laminated above the lamination surface,
The optical waveguide is arranged so as to overlap with at least a part of the recess in plan view.

  The shape of the concave portion may be any shape, but by forming the concave portion on the laminated surface, a surface having a different plane orientation from the plane parallel to the substrate is exposed, and the plane having the different plane orientation is exposed. It is assumed that a semiconductor layer above the semiconductor layer having the stacked surface is stacked on a stacked surface having a plurality of surfaces having different plane orientations. Note that the recess is preferably formed by etching.

  When the concave portion is in a stripe shape, the optical waveguide may be arranged to extend in a direction intersecting the concave portion in the plan view, or the optical waveguide and the concave portion may be arranged to extend in the same direction. Good.

  The semiconductor light emitting device of the present invention may be used as a superluminescent diode or an optical amplifier.

In the method for manufacturing a semiconductor light emitting device of the present invention, a plurality of semiconductor layers including a lower clad layer, an active layer, and an upper clad layer are laminated on a substrate. A method of manufacturing a semiconductor light emitting device having an optical waveguide,
Laminating a semiconductor layer below the active layer among the plurality of semiconductor layers on the substrate,
Forming a recess in the laminated surface of the semiconductor layer;
The active layer and the layer above the active layer are laminated above the laminated surface where the concave portion is formed, and the optical waveguide is formed so as to overlap with at least a part of the concave portion in plan view. It is characterized by doing.

  Here, the concave portion is formed to expose a surface having a plane orientation different from the surface parallel to the substrate on the laminated surface, and may have any shape. For example, an etching method can be used to form the recess. Moreover, you may form a recessed part using the selective growth method.

  In the semiconductor light emitting device of the present invention, a recess is formed on the stacking surface of the semiconductor layer on the substrate side of the active layer, and the recess is formed so that a different plane orientation is exposed on the stacking surface, and another active layer or the like is exposed. Since the layers are laminated, the thickness of the layer above the laminated surface is grown with a different thickness in the region along the recess and in other regions, and the optical waveguide is at least part of the recess. Since they are arranged so as to overlap in plan view, the thickness of the active layer in the optical waveguide is also different between the portion overlapping the recess and the other portion. Accordingly, since the gain wavelength has a width due to the change in the thickness of the active layer, a broadband optical output can be obtained.

  Since the semiconductor light emitting device of the present invention can obtain a broadband optical output, it can be suitably used as a light source for optical measurement such as OTDR as a superluminescent diode.

  According to the method for manufacturing a semiconductor light emitting device of the present invention, by forming a recess in the laminated surface, it is possible to expose a surface having a different surface orientation on the laminated surface, and when the surface orientation is different, the surface is grown thereon. Since the growth rate of the semiconductor layer differs, the active layer to be laminated above the lamination surface is grown with different thicknesses in the region along the recess and in other regions. Since the optical waveguide is formed so as to overlap with a part of the recess in plan view, the thickness of the active layer in the optical waveguide can be different between the part overlapping the recess and the other part. . Since the gain wavelength changes when the thickness of the active layer changes, the semiconductor light emitting device manufactured by this manufacturing method has a gain wavelength width due to the change of the thickness of the active layer, and can obtain a broadband optical output. Become.

  As a method for changing the thickness of the active layer, since a conventional selective growth mask is not used, a wide band can be realized without causing a problem of polycrystals being deposited on the mask.

  Embodiments of the present invention will be described below.

  FIG. 1 is a cross-sectional view of a semiconductor light emitting device according to a first embodiment of the present invention, and FIG. 2 is a plan view schematically showing a relationship between a recess and an optical waveguide in the semiconductor light emitting device shown in FIG. It is.

  In the semiconductor light emitting device of this embodiment, a plurality of semiconductor layers including a lower clad layer 3, an active layer 5, and upper clad layers 7 and 9 are laminated on a substrate 1, and an optical waveguide having a mesa stripe ridge structure 25 is formed. A semiconductor light emitting device having Of the plurality of semiconductor layers, a recess 20 is formed in the laminated surface of the lower cladding layer 3 on the substrate 1 side of the active layer 5, and the active layer 5 and the layers above the active layer 5 are above the laminated surface. Are stacked, and the optical waveguide 27 is disposed so as to overlap at least a part of the recess 20 in plan view. The optical waveguide 27 is defined by the mesa stripe type ridge structure 25, and the shape and arrangement of the mesa stripe in plan view are substantially the same as those of the optical waveguide 27.

  In this element, as shown in FIG. 2, the optical waveguide is arranged so as to be inclined in the normal direction of the end faces 18 and 19, and the AR films are applied to both end faces 18 and 19, so that the resonator No structure is formed and light is emitted as SLD.

  3A to 3E are perspective views showing manufacturing steps of the semiconductor light emitting device shown in FIGS. 1 and 2. The semiconductor light emitting device of this embodiment is an SLD that emits infrared light. With reference to FIGS. 3A to 3E, a specific layer structure and a manufacturing method of the semiconductor light emitting element will be described.

The semiconductor layer is stacked by crystal growth using a metal organic chemical vapor deposition (MOCVD) method. The raw material TEG (triethyl gallium), TMA (trimethyl aluminum), TMI (trimethyl indium), AsH ₃ (arsine), PH ₃ (phosphine), SiH ₄ as a dopant (silane), using DEZ (diethylzinc).

An n-type GaAs buffer layer (0.2 μm thick, carrier concentration 5.0 × 10 ¹⁷ cm) on the (100) surface of the n-type GaAs substrate 1 under the conditions of a growth temperature of 600 ° C. to 700 ° C. and a growth temperature of 10.3 kPa by MOCVD. ^-3 ) 2, n-type In _0.49 Ga _0.51 P lower clad layer (2.0 μm thickness, carrier concentration 5.0 × 10 ¹⁷ cm ^-3 ) 3 is grown (see FIG. 3A).

  A stripe-shaped opening having a width of 5 μm is formed on the laminated surface of the lower clad layer 3 in the normal direction of the end face by a lithography process, and the lower clad layer 3 is etched into a stripe shape by 100 nm as shown in FIG. 3B. A concave portion 20 is formed.

After removing the resist, the non-doped GaAs lower light guide layer (0.034 nm thickness) 4, InGaAs multiple quantum well active layer (1.1 μm emission) 5, non-doped GaAs upper light guide layer (0.034 nm thickness) 6, p-type by MOCVD In _0.49 Ga _0.51 P upper first cladding layer (0.2 μm thick, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 7, p-type GaAs etching stop layer (100 mm thick, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 8, p Type In _0.49 Ga _0.51 P upper second cladding layer (0.5 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 9 and p-type GaAs cap layer (0.2 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 10 The layers are sequentially stacked (see FIG. 3C).

A SiO ₂ selective growth mask serving as a dielectric mask is formed on the cap layer 10 (not shown), and the p-GaAs cap layer 10 and the p-type In _0.49 Ga _0.51 P upper second cladding layer 9 are etched, A mesa stripe ridge structure 25 is formed (see FIG. 3D). Here, the optical waveguide formed by the mesa stripe ridge structure 25 is inclined with respect to the light emitting end faces 18 and 19 and forms an angle of 7 ° with the stripe-shaped recess 20 formed in the lower cladding layer 3. So cross.

After that, n-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P current blocking layer (0.5 μm thick) is formed on the p-GaAs etching stop layer 8 except the mesa stripe ridge 25 by selective growth using a SiO ₂ mask. , Carrier concentration 1.0 × 10 ¹⁸ cm ⁻³ ) 11 is formed by the third crystal growth. Further, after removing the SiO ₂ mask, the p-type Al _0.58 Ga _0.42 As upper third cladding layer (1.3 μm thick, carrier concentration 7.0 × 10 ¹⁷ cm ^{− over} the entire surface of the mesa stripe ridge 25 and the current blocking layer 11. ³ ) 12, p-GaAs contact layer (2.0 μm thick, carrier concentration 1.0 × 10 ¹⁹ cm ⁻³ ) 13 is formed by the fourth crystal growth (see FIG. 3E).

  Thereafter, the substrate is polished until the total thickness becomes about 100 μm, and finally the n-side electrode 14 is formed on the back surface of the substrate 1 and the p-side electrode 15 is formed on the contact layer 13 by vapor deposition and heat treatment. An SLD bar having a length of about 0.50 to 2.0 mm between the end faces 18 and 19 is cut out from the wafer by cleaving, and AR film coating having a reflectance of 0.5% or less with respect to the emission wavelength of the element is performed on the end faces 18 and 19. . Thereafter, a chip is formed by cleavage to form an SLD element. It is desirable to mount the chip on the heat sink with the pn junction part with the light emitting part facing down in order to enhance the heat dissipation effect.

  In general, it is known that when a thin film is crystal-grown, it grows at different growth rates depending on the crystal plane orientation of the laminated surface. Therefore, when the crystal is grown on the concave portion as described above, the (100) plane parallel to the substrate of the concave portion (the surface indicated by reference numeral 21 in FIG. 3B) and the inclined surface generated by etching (indicated by reference numeral 22 in FIG. 3B). Since the growth rate is different from that on the surface), the thicknesses of the films grown on the respective surfaces differ when grown in the same crystal growth time. For example, when the In composition ratio of InGaAs in the active layer is 5%, the growth rate ratio between the (100) plane parallel to the substrate and the inclined surface (011) is 8: 5 at a growth temperature of 750 ° C. Therefore, when the thickness of the active layer is set to 80 mm for crystals grown on the (100) plane, the thickness on the slope is 50 mm. Therefore, when the optical waveguide is formed so as to intersect with the recess, the active layer in the optical waveguide includes a portion whose thickness varies between 50 and 80 mm.

  On the other hand, FIG. 4 shows the active layer thickness and gain wavelength (transition wavelength) for each InGaAs In composition ratio (0%, 5%, 10%, 20%, 30%, 40%, 50%). It shows the relationship. As shown in FIG. 4, the gain wavelength changes as the thickness of the active layer changes. As described above, in the device in which the In composition ratio of InGaAs is 5% and the active layer thickness is changed from 50 to 80 mm, the gain wavelength is changed with a width of about 30 nm. Therefore, the active layer thickness is constant. Compared with, a broad spectrum is obtained.

  When the In composition is increased, the In composition has a plane orientation dependency, and it is considered that the composition ratio is changed by growing on a plane having a different plane orientation, and further broadening of the band can be expected. Further, since the ratio of the growth rate between the (100) plane and the slope may change when the growth temperature is changed, the band can be expanded depending on the growth temperature.

  In addition, since the growth temperature in each composition and the growth rate in each plane orientation differ depending on the material, if the growth temperature and the growth rate for each plane orientation (or the ratio of the growth rate) are unknown, they are preliminarily determined. In view of the above, it is necessary to set the temperature, time, etc. during growth by obtaining the active layer thickness width that can obtain a desired wavelength width in light of the relationship between the composition, the active layer thickness, and the wavelength.

  In the above embodiment, the material composition and layer thickness of the light guide layer, the material composition and layer thickness of the current blocking layer, and the material composition and layer thickness of the cladding layer show an example of the conditions for emitting light in a single mode. Therefore, the present invention is not limited to the above-described material composition and layer thickness. In this example, the SLD element with an optical waveguide with a buried ridge stripe structure that combines a refractive index waveguide type and a gain waveguide type is mentioned. However, other structures such as those with a refractive index guided type internal stripe structure are mentioned. An element including an optical waveguide according to the above may be used.

  Moreover, in the said embodiment, although one stripe-shaped recessed part was formed as a recessed part provided in the lamination | stacking surface of the semiconductor layer of the substrate side from an active layer, a recessed part is a surface different from a surface parallel to a board | substrate. It is provided to expose the azimuth plane, and the shape does not need to be a stripe shape and can be an arbitrary shape, and the number of recesses may be singular or plural. Further, the number of stripe-shaped recesses is not limited to one, and a plurality of stripe-shaped recesses may be provided. Further, it may be a concave portion whose width changes in a tapered shape. When providing a plurality of stripe-shaped recesses perpendicular to the optical waveguide, the formation period of the stripe-shaped recesses is 1/2 wavelength of the emission spectrum wavelength in order to avoid the formation of the resonator structure due to the periodic stripe-shaped recesses. Therefore, it is desirable not to form periodic stripe-shaped concave portions perpendicular to the optical waveguide.

  Note that an arbitrary spectral shape can be obtained by arbitrarily setting the relationship between the ridge forming the waveguide and the recess. For example, when it is desired to obtain a spectral shape with a large spectral intensity on the long wavelength side, the concave portion or the mesa stripe ridge is formed so that the area overlapping the region emitting light of the long wavelength (for example, the region having an active layer thickness of 80 mm) is large. What is necessary is just to make it a structure which gives a curvature and the overlap part of a long wavelength region becomes large with respect to the overlap part of a short wavelength region.

  In the above embodiment, the concave portion is formed on the upper surface of the lower clad layer. However, any layer may be used as long as it is a layer closer to the substrate than the active layer. For example, the upper surface of the buffer layer or the lower cladding layer may have a two-layer structure, and a recess may be provided on the upper surface of the lower cladding layer on the substrate side.

  Hereinafter, another example in which the arrangement of the concave portion and the optical waveguide is different will be described. The layer configuration and manufacturing method can be the same as those in the above-described embodiment. FIGS. 5 to 7 are plan views of the semiconductor light emitting devices of the second to fourth embodiments, in which concave portions and optical waveguides formed in the device are indicated by broken lines.

  The semiconductor light emitting device of the second embodiment shown in FIG. 5 includes a tapered concave portion 31 whose width gradually increases from the front end surface 18 to the rear end surface 19 of the device, and the optical waveguide 32 has a concave portion 31 on the rear side. Are arranged so as to overlap.

  The semiconductor light emitting device of the third embodiment shown in FIG. 6 is arranged so that a striped recess 34 extending in a direction parallel to the end surfaces 18 and 19 of the device and a normal direction of the end surface and perpendicular to the recess 34. The optical waveguide 35 is provided.

  The semiconductor light emitting device of the fourth embodiment shown in FIG. 7 has a striped recess 36 extending in the normal direction of the end faces 18 and 19 of the device, a width wider than the width of the recess 36, and parallel to the recess 36. And an optical waveguide 37 disposed on the substrate. When the optical waveguide 37 overlaps the entire area of the recess 36 as in the semiconductor light emitting device of FIG. 7, the width of the recess 36 is desirably equal to or less than the width of the optical waveguide 37.

  In any of the embodiments, the optical waveguide is formed so as to overlap with the recess in plan view, and the thickness of the active layer in the optical waveguide is partially changed. A broadband optical output can be obtained. Therefore, it can be suitably used as a light source of an apparatus for optical measurement.

  In addition, the semiconductor light emitting device of each of the above embodiments can be used not only as an SLD but also as an optical amplifier.

Sectional drawing of the semiconductor light-emitting device of one Embodiment of this invention The top view which represented typically the recessed part and optical waveguide in the semiconductor light-emitting device shown in FIG. The perspective view which shows the manufacturing process of a semiconductor light-emitting device (the 1) The perspective view which shows the manufacturing process of a semiconductor light-emitting device (the 2) The perspective view which shows the manufacturing process of a semiconductor light-emitting device (the 3) The perspective view which shows the manufacturing process of a semiconductor light-emitting device (the 4) The perspective view which shows the manufacturing process of a semiconductor light-emitting device (the 5) Diagram showing the relationship between InGaAs active layer thickness and gain wavelength (transition wavelength) The top view which represented typically the recessed part and optical waveguide in the semiconductor light-emitting device of 2nd Embodiment The top view which represented typically the recessed part and optical waveguide in the semiconductor light-emitting device of 3rd Embodiment The top view which represented typically the recessed part and optical waveguide in the semiconductor light-emitting device of 4th Embodiment

Explanation of symbols

1 n-type GaAs substrate 2 n-type GaAs buffer layer 3 n-type In _0.49 Ga _0.51 P lower cladding layer 4 non-doped GaAs lower light guide layer 5 InGaAs multiple quantum well active layer 6 non-doped GaAs upper light guide layer 7 p-type In _0.49 Ga _0.51 P upper first cladding layer 8 p-type GaAs etching stop layer 9 p-type In _0.49 Ga _0.51 P upper second cladding layer
10 p-type GaAs cap layer
11 n-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P current blocking layer
12 p-type Al _0.58 Ga _0.42 As upper third cladding layer
13 p-GaAs contact layer
14 n-side electrode
15 p-side electrode
18, 19 End face
20 Recess
25 Mesa Striped Ridge

Claims (5)

In a semiconductor light emitting device having a gain waveguide type and / or a refractive index waveguide type optical waveguide, wherein a plurality of semiconductor layers including a lower cladding layer, an active layer, and an upper cladding layer are laminated on a substrate.
Of the plurality of semiconductor layers, a concave portion having a slope with a plane orientation different from the plane orientation of the plane parallel to the plane of the substrate is formed on the laminated surface of the semiconductor layer on the substrate side of the active layer,
The active layer and the layer above the active layer are laminated above the lamination surface,
The optical waveguide is disposed so as to overlap a part including at least the slope of the concave part in a plan view and to have a part not overlapping the concave part in the plan view. Semiconductor light emitting device. The recess is striped,
2. The semiconductor light emitting element according to claim 1, wherein the optical waveguide is disposed so as to extend in a direction intersecting with the concave portion in the plan view. 3. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is a superluminescent diode. 3. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is an optical amplifier. A method of manufacturing a semiconductor light emitting device having a gain waveguide type and / or a refractive index waveguide type optical waveguide, wherein a plurality of semiconductor layers including a lower clad layer, an active layer, and an upper clad layer are laminated on a substrate. There,
Laminating a semiconductor layer below the active layer among the plurality of semiconductor layers on the substrate,
Forming a recess having a slope with a plane orientation different from the plane orientation of the plane parallel to the plane of the substrate on the lamination surface of the semiconductor layer;
The active layer and a layer above the active layer are stacked above the stacked surface on which the recess is formed, and so as to overlap with at least a part of the recess including the slope in a plan view. The method of manufacturing a semiconductor light-emitting element includes forming the optical waveguide so as to have a portion that does not overlap the concave portion in plan view.

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