JP3911342B2 - Manufacturing method of semiconductor laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device and a manufacturing method thereof.
[0002]
[Prior art]
Generally, when a semiconductor laser diode and an optical fiber are coupled, a lens is provided between the semiconductor laser diode and the optical fiber. Recently, a semiconductor laser diode with a waveguide lens in which a semiconductor laser diode and a waveguide lens are integrally formed has been manufactured, and has been used as a small and inexpensive module.
[0003]
This waveguide lens is composed of a quantum well layer which is continuous with the active layer and gradually becomes thinner as the barrier layer and the well layer are separated from the active layer. For example, the selective growth mask 51 shown in FIG. Then, by growing the active layer, it is formed continuously with the active layer. In other words, the selective growth mask 51 is formed so as to have a relatively wide constant width in the laser portion where the active layer is grown and formed so that the width is gradually narrowed in the lens portion where the waveguide lens is formed. Has been. When the selective growth mask 51 is formed in the above-described shape and the material gas is supplied from above using the MOCVD method to grow the barrier layer and the well layer, the selective growth is performed as shown in FIG. Since the epitaxial layer does not grow on the mask 51 and the material gas does not decrease, the concentration of the material gas increases.
[0004]
As a result, since the selective growth mask 51 is wide in the laser portion, the concentration of the material gas in the laser portion increases as the high concentration region of the material gas on both sides increases, and the lens portion is selected as the distance from the laser portion increases. The amount of material gas flowing from above the growth mask 51 is reduced, and the material gas concentration is lowered. As a result, as shown in FIG. 14B, a laser oscillation active layer for lasing with a substantially constant film thickness is formed in the laser portion corresponding to the material gas concentration, and in the lens portion, A waveguide lens having a waveguide layer whose film thickness decreases with distance from the active layer is formed.
[0005]
A waveguide lens can also be formed by forming an active layer using the selective growth mask disclosed in JP-A-6-181363 and shown in FIG. In JP-A-6-181363, an n-type AlGaAs lower cladding layer 102, a quantum well active layer 103, a p-type AlGaAs are formed on an n-type GaAs substrate 101 using a selective growth mask 110 shown in FIG. After growing the upper cladding layer 104 and the pGaAs contact layer 105, the p-side electrode 107 is formed. As described above, by growing the active layer using the selective growth mask 110 shown in FIG. 15A, the waveguide lens 108 whose thickness gradually decreases at both ends of the active layer as the distance from the active layer increases. 109 is formed. An n-side electrode 106 is formed on the lower surface of the n-type GaAs substrate 101. In JP-A-6-181363, the waveguide lenses 108 and 109 formed on both ends of the active layer are used to relax the light concentrated on the end of the laser diode and prevent temperature rise at the end, Laser diode destruction is prevented.
[0006]
[Problems to be solved by the invention]
However, the waveguide layer of the waveguide lens formed as described above has a problem that the threshold current increases in the waveguide laser integrated with a conventional semiconductor laser diode because the light absorption is relatively large. there were.
[0007]
Accordingly, an object of the present invention is to provide a method of manufacturing a semiconductor laser device in which a waveguide lens is integrally formed, which can lower the threshold current as compared with the conventional example.
[0008]
[Means for Solving the Problems]
In order to solve the conventional problems, the present invention shortens a waveguide lens, particularly a waveguide layer portion having a relatively large loss, thereby reducing a threshold current .
[0011]
Furthermore, the method of manufacturing a semiconductor laser device according to the present invention includes a quantum well layer having a predetermined width and a predetermined length between the p-type cladding layer and the n-type cladding layer, and the quantum well layer is substantially A laser oscillation active layer formed to have a constant thickness and a waveguide layer formed so that the thickness gradually decreases from the boundary with the laser oscillation active layer toward the emission end. A method of manufacturing a semiconductor laser device integrated with a waveguide lens,
The manufacturing method includes a step of forming the quantum well layer by forming a selective growth mask facing each other with a portion for growing the quantum well layer interposed therebetween and selectively growing the mask using a MOCVD method.
In the process,
Each of the selective growth masks has a first portion provided corresponding to the lasing active layer, and a width that is continuous with the first portion on the waveguide layer side and wider than the width of the first portion. By forming the second portion so that the second portion is separated from the end of the waveguide lens , the material gas concentration becomes uniform in the region where the laser oscillation active layer is formed, and In the region where the waveguide layer is formed, control is performed so as to decrease at a constant rate from the laser oscillation active layer toward the emission end.
According to this method, in the waveguide layer, the length of the first waveguide layer having a thickness of 70% or more of the thickness of the laser oscillation active layer is set to 70% of the thickness of the laser oscillation active layer. It can be made shorter than the length of the second waveguide layer having the following thickness.
[0012]
Further, in the method of manufacturing the semiconductor laser device, the waveguide layer that gradually decreases the width of the first portion and the width of the second portion from the boundary with the laser oscillation active layer toward the emission end. It can be set based on the thickness reduction rate and the growth pressure.
In the method of manufacturing a semiconductor laser device, it is preferable that the interval between the second portions is narrower than the interval between the first portions.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below.
The semiconductor laser diode according to the embodiment of the present invention is a waveguide lens integrated semiconductor laser diode in which the laser oscillation section 15 and the waveguide lens section 16 are integrally formed, and has the following characteristics.
That is, the semiconductor laser diode of the present embodiment uses the unique selective growth mask, and the laser oscillation active layer of the laser oscillation unit 15 and the waveguide layer of the waveguide lens unit 16 formed continuously on the active layer. As a result, the length of the waveguide lens portion 16 is shortened as a whole as compared with the conventional example, and the length of the relatively thick film portion having a large light absorption loss in the waveguide layer is reduced. Characterized by shortening. With this configuration, the semiconductor laser diode of the present embodiment can reduce the light absorption loss in the waveguide lens unit 16, and therefore has a threshold value as compared with the conventional waveguide lens integrated semiconductor laser diode. The current can be lowered.
[0014]
More specifically, in the semiconductor laser diode of the present embodiment, the laser oscillation unit 15 and the waveguide lens unit 16 are respectively formed on the p-type InP substrate 21 and the p-type InP clad layer 22 shown in FIGS. (Thickness 1 μm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), InGaAsP active layer 23, n-type InP cladding layer 24 (thickness 0.5 μm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), n-type InP layer 28 The n-type InGaAs contact layer 29 and the n-type electrode (Au / Ge / Ni / Au) 31 are sequentially formed. In this embodiment, the SiO ₂ insulating film 30 is formed on the n-type InGaAs contact layer 29, and the n-type electrode 31 is connected to the n-type InGaAs via the opening formed in the SiO ₂ insulating film. A p-type electrode 32 (Ti / Pt / Au) is formed on the lower surface of the p-type InP substrate 21 so as to be in contact with the contact layer 29.
[0015]
Further, in the semiconductor laser diode of the embodiment, as shown in FIGS. 1 and 3, resonance occurs in the upper part of the p-type InP substrate 21, the p-type InP clad layer 22, the InGaAsP active layer 23, and the n-type InP clad layer 24. A mesa portion having a sufficiently long length in the direction is formed, and a p-type InP layer 25, an n-type InP current blocking layer 26, and a p-type InP layer 27 are formed on both sides of the mesa portion. In the present embodiment, the InGaAsP active layer 23 includes an InGaAsP well layer 11 and an InGaAsP barrier layer 12 alternately between the InGaAsP light confinement layer 13 and the InGaAsP light confinement layer 14 as shown in FIG. It consists of stacked quantum well layers. In the waveguide lens portion 16, the thickness of each of the InGaAsP light confinement layers 13, 14, the InGaAsP well layer 11 and the InGaAsP barrier layer 12 decreases from the connection portion with the laser oscillation portion 15 toward the emission end. In the formed waveguide lens portion 16, the laser beam is transmitted so that the laser beam spreads at the emission end, and is output from the emission end. As a result, the spread of the emitted light can be suppressed. In the embodiment, the thickness of the active layer of the laser oscillation unit 15 is set to 200 nm, for example, and the thickness of the active layer at the emission end is set to 50 nm, for example. In this specification, the quantum well layer of the waveguide lens unit 16 is referred to as a waveguide layer, and the quantum well layer of the laser oscillation unit 15 is referred to as a laser oscillation active layer.
[0016]
Next, a method for manufacturing the semiconductor laser diode of the present embodiment will be described. In this manufacturing method, after forming a SiO ₂ insulating film on the upper surface of the p-type InP substrate 21, the selective growth mask 1 is formed by patterning into the shape shown in FIG. Here, the selective growth mask 1 includes a first portion 1 a provided corresponding to the laser oscillation portion 15 and a second portion 1 b provided corresponding to the waveguide lens portion 16. The width of the portion 1b is formed so as to be wider than that of the first portion 1b. When the following layers are grown by the metal organic chemical vapor deposition method (MOCVD method) using the selective growth mask 1 having such a shape, the material gas in the region 2 where each layer of the laser oscillation unit 16 is to be formed is grown. Concentration can be made uniform, and in the region 3 where each layer of the waveguide lens 16 is to be formed, the concentration of the material gas is decreased at a constant rate from the boundary 4 with the region 2 toward the emission end 3a of the region 3. Can be distributed. As a result, in the region 2 where each layer of the laser oscillation unit 16 is to be formed, each layer to be grown can be formed with a constant film thickness, and in the region 3 where each layer of the waveguide lens 16 is to be formed, each layer to be grown is It can be formed so that the film thickness decreases at a constant rate toward 3a.
[0017]
When the above-described semiconductor layers are formed by the MOCVD method using the selective growth mask 1 of FIG. 5, the rate of decrease in film thickness from the boundary 4 toward the emission end 3a is closely related to the growth pressure Pg. There is. That is, when setting a specific reduction rate, it is necessary to increase the area of the second portion 1b of the selective growth mask 1 as the growth pressure Pg is lower, and the dimensions indicated by a and b in the figure are increased. There is a need. When the growth pressure Pg is set high, it is necessary to reduce the area of the second portion 1b, and it is necessary to reduce the dimensions indicated by a and b in the figure. In other words, in the present embodiment, by combining various dimensions of a and b of the selective growth mask 1, not only can the film thickness be reduced at a constant rate, but also the reduction rate can be set arbitrarily.
[0018]
Next, TMI (trimethyl indium), TEG (triethyl gallium), DEZn (diethyl zinc), PH ₃ (phosphine), AsH ₃ (arsine) and H ₂ S are used as material gases by metal organic chemical vapor deposition. The p-type InP clad layer 22, the InGaAsP active layer 23, and the n-type InP clad layer 24 are grown.
Then, after removing the selective growth mask as shown in FIG. 6, a SiO 2 insulating film 33 is formed on the n-type InP cladding layer 24. ,
Next, the mesa structure shown in FIG. 7 is formed by etching using the SiO ₂ insulating film 33 as a mask. The mesa width is set to about 1 μm.
[0019]
Next, as shown in FIG. 8, using the SiO ₂ insulating film 33 as a selective growth mask and using TMI, TEG or the like as a material gas, the P-type InP layer 25 and the n-type InP current blocking are performed by metal organic vapor phase epitaxy. A layer 26 and a p-type InP layer 27 are grown and formed.
Next, after removing the SiO ₂ insulating film 33, an n-type InP layer 28 and an n-type InGaAs contact layer 29 are grown on the n-type InP cladding layer 24 and the p-type InP layer 27 as shown in FIG. Form. Finally, the SiO ₂ insulating film 30, the n-type electrode 31, and the p-type electrode 32 are formed. As described above, the semiconductor laser diode with the waveguide lens of the embodiment shown in FIG. 1 is manufactured.
[0020]
In the semiconductor laser diode of the embodiment manufactured as described above, the active layer or the like is grown using the selective growth mask 1 described above, and therefore, the waveguide lens for the laser oscillation unit 15 is compared with the conventional example. The length of the part 16 can be shortened. As a result, the loss due to light absorption in the waveguide lens portion 16 can be reduced, so that the threshold current for laser oscillation can be lowered.
In particular, in the present invention, as will be described in detail in the following embodiments, the waveguide layer in the waveguide lens portion 16 has a relatively large absorption portion (a film of the laser oscillation active layer). The shortening of the length of the portion (hereinafter referred to as the first waveguide layer) having a film thickness of 70% or more of the thickness greatly contributes to the reduction of light absorption in the waveguide lens portion 16. In this specification, the waveguide lens part corresponding to the first waveguide layer is referred to as a first lens part, and the waveguide lens part corresponding to the waveguide layer excluding the first waveguide layer is referred to as a second lens part.
According to our study, the first waveguide layer in the waveguide lens unit 16 has a band cap corresponding to a wavelength 3 nm to 50 nm smaller than the wavelength of the laser oscillation light.
[0021]
【Example】
Examples according to the present invention will be described below.
Example 1.
Example 1 is an example of a semiconductor laser diode manufactured according to the manufacturing method described in the above embodiment using the selective growth mask shown in FIG.
FIG. 10A shows a film thickness distribution in a longitudinal section parallel to the longitudinal direction (resonance direction) of the active layer (quantum well layer) grown using this selective growth mask. In FIG. 10A, the vertical axis represents the relative film thickness when 50 nm is 1.
As shown in FIG. 10A, in Example 1, the length of the laser oscillation active layer of the laser oscillation unit 16 can be set to 220 μm, and the length of the waveguide layer of the waveguide lens unit 16 can be set to 230 μm. The length of the first waveguide layer having a relatively large absorption loss in the waveguide layer could be 100 μm. Here, the laser oscillation active layer is a portion that substantially contributes to laser oscillation and has a thickness of 95% or more with respect to the flat region (the same applies to Example 2 and the comparative example). In FIG. 10A, the target value for setting the film thickness of the quantum well layer is indicated by a dotted line.
[0022]
On the other hand, in the comparative example using the selective growth mask of the conventional example of FIG. 11B, the length of the laser oscillation active layer is 160 μm and the length of the waveguide layer as shown in FIG. The length of the first waveguide layer having a relatively large absorption loss was 185 μm.
Thus, in Example 1, since the length of the waveguide layer can be made shorter than that of the comparative example, and the length of the first waveguide layer can be made shorter, the threshold current at 85 ° C., which was 23 mA in the comparative example, is It was reduced to 19 mA.
[0023]
Example 2
Example 2 is an example of a semiconductor laser diode manufactured according to the manufacturing method described in the above embodiment using the selective growth mask shown in FIG.
That is, in Example 2, the selective growth mask is formed so that the width of the region 3 sandwiched between the second portions of the selective growth mask is narrower than the width of the region 2.
FIG. 12A shows the film thickness distribution in a longitudinal section parallel to the longitudinal direction (resonance direction) of the active layer grown using this selective growth mask. In FIG. 12A, as in FIG. 10A, the vertical axis represents the relative film thickness when 50 nm is 1.
As shown in FIG. 12A, in Example 2, the length of the active layer of the laser oscillation part can be 260 μm, the length of the waveguide layer can be 190 μm, and the lens part has a relatively large absorption loss. The length of the first waveguide layer could be 60 μm. Further, as apparent from FIG. 12A, in Example 2, the film thickness of the quantum well layer can be set to a value very close to the target value.
[0024]
As described above, in Example 2, the selective growth mask was formed so that the width of the region 3 sandwiched between the second portions of the selective growth mask was narrower than the width of the region 2, thereby increasing the length of the waveguide layer. Further, the length of the first waveguide layer can be made shorter than that of the first embodiment. Thereby, in the semiconductor laser diode of Example 2, the threshold current at 85 ° C. could be set to 18 mA, which is lower than that of Example 1.
In the second embodiment, as indicated by the reference numeral 5 in FIG. 12B, the width of the second portion is increased inward at a certain angle near the boundary between the region 2 and the region 3. ing. Thus, in the second embodiment, the disturbance of the material gas concentration is prevented near the boundary between the region 2 and the region 3, and a portion having a non-uniform film thickness is prevented near the boundary.
[0025]
The graph of FIG. 13 shows the photoluminescence wavelength with respect to the position of the quantum well layer in the semiconductor laser diodes of Examples 1 and 2 and the comparative example.
As is apparent from the graph of FIG. 13, it can be seen that the distribution of the photoluminescence wavelength almost uniquely corresponds to the above-described film thickness distribution.
From the graph of FIG. 3, it can also be seen that Examples 1 and 2 can make the length of the waveguide layer shorter than that of the comparative example, and can make the length of the first waveguide layer shorter.
[0026]
It goes without saying that the waveguide lenses in the embodiments and examples described above are not limited to lenses when connected to optical fibers. The present invention can also be applied to a lens for preventing breakage of an end face described in the conventional example, a waveguide lens formed between a semiconductor laser diode and another waveguide in an optical integrated circuit or the like.
[0027]
【The invention's effect】
As described in detail above, the semiconductor laser device according to the present invention includes a quantum well layer composed of the lasing active layer and the waveguide layer between the p-type cladding layer and the n-type cladding layer, In the waveguide layer, the length of the first waveguide layer having a thickness of 70% or more of the thickness of the laser oscillation active layer is 70% or less of the thickness of the laser oscillation active layer. It is shorter than the length of the second waveguide layer.
Thus, the semiconductor laser device according to the present invention can reduce the absorption loss of light in the first waveguide layer having a relatively large absorption loss of the waveguide lens portion. The threshold current can be lowered compared to.
[0028]
In the semiconductor laser device according to the present invention, the threshold current can be further lowered by setting the length of the waveguide layer to 100 μm or more and 250 μm or less.
[0029]
In the semiconductor laser device of the present invention, the threshold current can be further reduced by setting the length of the waveguide layer to 160 μm or more and 220 μm or less.
[0030]
Furthermore, in the method of manufacturing a semiconductor laser device according to the present invention, a quantum well layer composed of a laser oscillation active layer and a waveguide layer is formed between a p-type cladding layer and an n-type cladding layer using a selective growth mask. Each of the selective growth masks is provided corresponding to the laser oscillation active layer, the first portion is provided corresponding to the waveguide layer, and the first growth mask is formed. The waveguide layer is formed such that the thickness gradually decreases from the boundary with the laser oscillation active layer toward the emission end. To be. Accordingly, in the waveguide layer, the length of the first waveguide layer having a thickness of 70% or more of the thickness of the laser oscillation active layer is reduced to a thickness of 70% or less of the thickness of the laser oscillation active layer. A semiconductor laser device in which a waveguide lens is integrally formed can be manufactured, which can be formed shorter than the length of the second waveguide layer having a thickness, and can reduce the threshold current as compared with the conventional example. Can do.
[0031]
In the method of manufacturing the semiconductor laser device, a semiconductor laser device having a lower threshold current can be obtained by narrowing the interval between the second portions as compared with the interval between the first portions in the selective growth mask. Can be manufactured.
[Brief description of the drawings]
FIG. 1 is a partially broken perspective view showing a configuration of a semiconductor laser diode according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a configuration of the semiconductor laser diode of the embodiment in a cross section parallel to the light guiding direction.
FIG. 3 is a cross-sectional view showing a configuration of the semiconductor laser diode of the embodiment in a cross section perpendicular to a light guiding direction;
FIG. 4 is a schematic cross-sectional view showing a configuration of a quantum well layer in the semiconductor laser diode of the embodiment.
FIG. 5 is a plan view showing a selective growth mask used for manufacturing the semiconductor laser diode of the embodiment.
FIG. 6 is a cross-sectional view after selective growth in the method of manufacturing a semiconductor laser diode according to the embodiment.
FIG. 7 is a cross-sectional view after mesa etching in the manufacturing method of the semiconductor laser diode of the embodiment.
FIG. 8 is a cross-sectional view after the burying growth in the semiconductor laser diode manufacturing method of the embodiment.
FIG. 9 is a cross-sectional view after forming a contact layer in the manufacturing method of the semiconductor laser diode of the embodiment.
10A is a graph showing a film thickness distribution of the semiconductor laser diode of Example 1 according to the present invention, and FIG. 10B is a selective growth mask used for manufacturing the semiconductor laser diode of Example 1. FIG. FIG.
FIG. 11 is a graph showing a film thickness distribution of a semiconductor laser diode of a comparative example, and FIG. 11B is a plan view showing a selective growth mask used for manufacturing the semiconductor laser diode of the comparative example.
12A is a graph showing a film thickness distribution of the semiconductor laser diode of Example 2 according to the present invention, and FIG. 12B is a selective growth mask used for manufacturing the semiconductor laser diode of Example 2. FIG. FIG.
FIG. 13 is a graph showing PL wavelength distributions with respect to positions in each quantum well layer of Examples 1 and 2 and a comparative example.
14A is a plan view showing a selective growth mask used for manufacturing a conventional semiconductor laser diode, and FIG. 14B is a view of a layer A formed using the selective growth mask of FIG. It is a graph which shows the film thickness distribution in sectional drawing of -A ', (c) is a figure which shows typically the flow of the growth seed | species (material gas) at the time of film formation (during growth).
15 (a) is a perspective view showing a selective growth mask used for manufacturing another conventional semiconductor laser diode, and FIG. 15 (b) is a semiconductor formed using the selective growth mask of FIG. 15 (a). It is sectional drawing of a laser diode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Selective growth mask, 1b 1st part, 1b 2nd part, 11 InGaAsP well layer, 12 InGaAsP barrier layer, 13 InGaAsP light confinement layer, 14 InGaAsP light confinement layer, 15 Laser oscillation part, 16 Waveguide lens part, 21 p-type InP substrate 21, 22 p-type InP clad layer, 23 InGaAsP active layer, 24 n-type InP clad layer, 25 p-type InP layer, 26n-type InP current blocking layer, 27 p-type InP layer, 28 n-type InP layer 29 n-type InGaAs contact layer, 30 SiO ₂ insulating film, 31 n-type electrode, 32 p-type electrode.

Claims (3)

A laser oscillation comprising a quantum well layer having a predetermined width and a predetermined length between a p-type cladding layer and an n-type cladding layer, wherein the quantum well layer has a substantially constant thickness. A method of manufacturing a semiconductor laser device integrated with a waveguide lens comprising an active layer and a waveguide layer formed so that the thickness gradually decreases from the boundary between the laser oscillation active layer and the emission end. And
The manufacturing method includes a step of forming the quantum well layer by forming a selective growth mask facing each other with a portion for growing the quantum well layer interposed therebetween and selectively growing the mask using a MOCVD method.
In the process,
Each of the selective growth masks has a first portion provided corresponding to the lasing active layer, and a width that is continuous with the first portion on the waveguide layer side and wider than the width of the first portion. By forming the second portion so that the second portion is separated from the end of the waveguide lens , the material gas concentration becomes uniform in the region where the laser oscillation active layer is formed, and A method of manufacturing a semiconductor laser device, comprising: controlling so as to decrease at a constant rate from the laser oscillation active layer toward an emission end in a region where the waveguide layer is formed.   The width of the first portion and the width of the second portion are reduced to the growth rate and the thickness reduction rate of the waveguide layer that gradually decreases from the boundary with the laser oscillation active layer toward the emission end. 2. The method of manufacturing a semiconductor laser device according to claim 1, wherein the semiconductor laser device is set based on the setting.   3. The method of manufacturing a semiconductor laser device according to claim 1, wherein in the manufacturing method of the semiconductor laser device, the interval between the second portions is narrower than the interval between the first portions.

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