JP4531955B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device and a method for manufacturing the same, and more particularly, a semiconductor laser device having an internal current confinement structure on a GaAs substrate by a combination of an AlAs (N) layer and an Al (As) N layer, in particular, light emission. The present invention relates to a semiconductor laser element that is optimal as a semiconductor laser element having a wavelength range of 0.6 μm to 1.65 μm and a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, in the field of a narrow stripe type semiconductor laser device having an emission wavelength of 980 nm band formed on a GaAs substrate, a ridge waveguide type semiconductor laser device having a current injection region in a stripe ridge formed on an active layer is manufactured. Is typically used because it is easy to operate and has high operational reliability.
[0003]
[Problems to be solved by the invention]
However, the ridge waveguide type semiconductor laser device has a problem that the threshold current is higher than that of a buried stripe semiconductor laser device, that is, a semiconductor laser device having an internal current confinement structure.
The reason why the threshold current of the ridge waveguide type semiconductor laser device becomes higher than that of the buried stripe semiconductor laser device is that the position of the active layer is usually obtained even if the width of the lower portion of the ridge is as narrow as 2 to 3 μm. In this case, the current injected from the current injection region above the ridge is diffused, and the width of the current injection region is expanded from about 3 μm to about 5 μm, which is about 1.5 times that of the bottom of the ridge.
Here, the buried stripe semiconductor laser element refers to a semiconductor laser having a structure in which a double heterostructure having an active layer is formed in a mesa shape by etching, and then both sides of the mesa are buried with a current confinement layer. In particular, a semiconductor laser element having an internal current confinement structure embedded with a compound semiconductor layer having a low refractive index is classified as a refractive index waveguide type semiconductor laser element, and can maintain stable single mode transverse mode oscillation. Therefore, it is considered optimal as a light source in the field of optical communication.
[0004]
Accordingly, an object of the present invention is to provide a GaAs semiconductor laser element having a narrow stripe type internal current confinement structure with a low threshold current in view of such a situation.
[0005]
[Means for Solving the Problems]
The present inventor has found that the AlAsN layer has a phenomenon that the electrical insulation increases as the N content increases, and “GaInNAs / GaAs” published in 29p-T-6 of the 1999 Spring Applied Physics Society Proceedings. Attention was paid to research on the effect of substrate off-angle in MOVPE growth of quantum well structures.
According to the 1999 Spring Applied Physics Society Proceedings 29p-T-6, when the substrate surface of the GaAs substrate is turned off in the A direction, the PL wavelength of the GaInNAs layer grown on the substrate surface increases as the off angle increases. The wavelength shifts, that is, the N content of the GaInNAs layer increases.
Therefore, when a GaNAs layer containing N or an AlAsN layer is grown on a GaAs substrate, it is usually grown on the (100) plane of the GaAs substrate. By using a GaAs substrate having a surface inclined in the A-plane direction, the amount of N incorporation is changed, and an AlAs (N) layer having a low N content, a high As content, and a low electrical insulating property is obtained. The idea is to form a current confinement structure by forming an Al (As) N layer having a high N content, a low As content, and a high electrical insulation on the (111) A surface. did.
And this inventor confirmed this idea experimentally and came to invent this invention.
[0006]
In order to achieve the above object, a semiconductor laser device according to the present invention includes a (100) plane provided as a bottom surface, and (N11) A plane (N A GaAs substrate formed as a stepped substrate having a recess formed on the (100) plane;
An AlAs (N) layer formed on the (100) plane of the GaAs substrate via a compound semiconductor layer directly on the GaAs substrate or an AlAs (N) layer formed on the (N11) A plane. And an AlAsN current confinement structure including an Al (As) N layer having a higher N content and a lower As content.
[0007]
Practically, N on the (N11) A plane (N; integer) is 1, an AlAs (N) layer is formed on the (100) plane, and on the (111) A plane of the stepped substrate. An Al (As) N layer is formed.
[0008]
In a preferred embodiment of the present invention, the active layer of the semiconductor laser element is formed of any one of GaInP, AlGaInP, AlGaAs, GaAs, GaInAs, GaInAsSb, GaInNAs, and GaInNAsSb, so that the emission wavelength is 0.6 μm to 1.65 μm. A semiconductor laser device of the band can be manufactured.
[0009]
In the semiconductor laser device according to the present invention, since a low electrical insulating AlAsN layer having a low N content is formed on the (100) surface of the recess, the injected current flows through the (100) surface, On the (N11) A plane, for example, the (111) A plane, a highly electrically insulating AlN (As) layer having a high N content and a low As content is formed, so that the injection current is (111) A It is blocked by the surface and does not flow.
As a result, the combination of a narrow (for example, 2 μm wide) flat (100) plane region and (111) A plane region constitutes an internal current confinement structure, so that the active layer is disposed close to the internal current confinement structure. As a result, current flows only in the (100) plane region, and excess leakage current does not flow outside the (100) plane region, so that the threshold current becomes as small as that of the buried hetero stripe semiconductor laser element.
In other words, in the present invention, the width of the (100) plane of the recess corresponds to the width of the current injection region, and the width of the (100) plane of the recess is reduced to form a narrow stripe type semiconductor laser device. The threshold current can be reduced.
Preferably, the width of the (100) plane of the recess is 2 μm or less, and the height difference between the lower end and the upper end of the (N11) A plane is 2 μm or more.
[0010]
In addition, AlN has a larger band gap and a lower refractive index than AlAs. A GaInAs active layer is formed on a GaAs substrate having a recess along the recess, and the GaInAs active layer existing in the recess is surrounded by an AlAs (N) layer, thereby forming a GaInAs active layer having a low refractive index. A refractive index waveguide type semiconductor laser device surrounded by. This realizes a semiconductor laser element that oscillates the transverse mode in a stable single mode.
[0011]
A method of manufacturing a semiconductor laser according to the present invention is a method of manufacturing a semiconductor laser element having a current confinement structure by a combination of an AlAs (N) layer and an Al (As) N layer,
A concave portion is formed on the (100) surface of the GaAs substrate, which includes a (100) surface provided as a bottom surface and a (N11) A surface (N; integer) heading obliquely upward from both edges of the (100) surface. And a process of
While irradiating cracked AH ₃ directly on the GaAs substrate or via the compound semiconductor layer on the GaAs substrate, simultaneously irradiating radical nitrogen and aluminum atoms, an AlAs (N) layer is formed on the (100) plane. And forming an Al (As) N layer having a higher N content and a lower As content on the (N11) A surface than the AlAs (N) layer.
[0012]
In the method of manufacturing a semiconductor laser device according to the method of the present invention, the active layer is exposed to the atmosphere by etching the active layer during the manufacturing process of the semiconductor laser device, as in the case of a buried hetero semiconductor laser device. Therefore, there is a merit that the active layer is not oxidized, and a highly reliable semiconductor laser device can be realized.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below specifically and in detail with reference to the accompanying drawings.
Embodiment of Semiconductor Laser Element This embodiment is an example of an embodiment of a semiconductor laser element according to the present invention, and FIG. 1 is a cross-sectional view showing the configuration of the semiconductor laser element of this embodiment. It is.
The semiconductor laser device 10 of the present embodiment is a semiconductor laser device having an emission wavelength of 980 nm band, and the (100) surface 14a provided as the bottom surface as the semiconductor substrate 12 and both edges of the (100) surface 14a, respectively. A GaAs substrate having a plate thickness of about 80 μm is provided on the (100) plane with the concave portion 14 formed of a (111) A surface 14b obliquely upward as a side surface.
The width of the (100) surface 14a is 2 μm, the height difference between the lower end and the upper end of the (111) A surface 14b is 2 μm, and the pitch of the recesses is 250 μm.
[0014]
The semiconductor laser element 10 includes an n-GaAs buffer layer 16 having a film thickness of 0.3 μm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ along a recess 14 on a GaAs substrate 12 and a film thickness of 1.5 μm. The n-Al _0.3 Ga _0.7 As cladding layer 18 has a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ .
In addition, the semiconductor laser element 10 is formed on the (100) plane of the n-AlGaAs cladding layer 18 as a current confinement structure, and has a 20 nm thick AlAs (N) layer 20 containing almost no N, and a (111) A plane. And an AlN (As) layer 22 having a high N content and a low As content. The AlN (As) layer 22 selectively takes in N, and as a result, hardly contains As.
[0015]
The semiconductor laser element 10 further includes a GaAs optical confinement layer having a thickness of 0.1 μm, a Ga _0.8 In _0.2 As quantum well active layer, and a thickness of 0 along the AlAs (N) layer 20 and the AlN (As) layer 22. SCH-MQW 24 comprising a 1 μm GaAs optical confinement layer, p-Al _0.3 Ga _0.7 As clad layer 26 having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ and a film thickness of 1.5 μm, and a recess of p-AlGaAs clad layer 26 A p-GaAs contact layer 28 having a width of 2 μm and a carrier concentration of 3 × 10 ¹⁹ cm ⁻³ and a film thickness of 0.2 μm is provided along the bottom surface (100).
In the semiconductor laser device 10, a laminated metal film of Ti / Pt / Au is used as the p-side electrode 30 on the p-GaAs contact layer 28 and the p-AlGaAs cladding layer 26, and the back surface of the GaAs substrate 12 is used as the n-type electrode 32. Are provided with a laminated metal film of AuGeNi / Au.
The cavity length of the semiconductor laser element 10 is 300 μm, the laser front end face is as-cleaved, and the laser rear end face is HR coated by PCVD.
[0016]
Since the AlAs (N) layer 20 having a low electrical insulation property is formed on the (100) surface of the recess of the n-AlGaAs cladding layer 18, an injection current flows, whereas the (111) A surface has an electrical insulation property. Since the high Al (As) N layer 22 is formed, no current flows. As a result, in the SCH-MQW 24 formed on the AlAs (N) layer 20 and the AlN (As) layer 22, current flows only in the flat active layer region having a width of 2 μm at the bottom of the recess, and in other regions. Excessive leakage current will not flow. Therefore, the threshold current becomes as low as that of the embedded narrow stripe semiconductor laser element.
Moreover, since AlN has a larger band gap than AlAs, the refractive index of AlN is also smaller. In the semiconductor laser device 10 having the configuration as shown in FIG. 1, since the GaInAs active layer in the recess is surrounded by the AlN (As) layer 22 having a low refractive index, the active layer is surrounded by a layer having a low refractive index. It becomes a waveguide type semiconductor laser element. Thereby, a stable single mode can be obtained.
[0017]
Embodiment of Method for Manufacturing Semiconductor Laser Device This embodiment is an example of an embodiment in which the method for manufacturing a semiconductor laser device according to the present invention is applied to the manufacturing of the semiconductor laser device 10 described above. 2 (a) to 2 (c) and FIGS. 3 (d) to 3 (e) are cross-sectional views for each process in fabricating a semiconductor laser device according to the method of this embodiment.
First, the n-GaAs substrate 12 is subjected to a photolithography process and an etching process, and as shown in FIG. 2 (a), the bottom surface is obliquely upward from both edges of the (100) surface 14a and the (100) surface 14a. A concave portion 14 composed of the (111) A surface 14b is formed on the (100) surface as the side surface to face.
The pitch of the recesses is 250 μm in the longitudinal direction, the width of the (100) surface 14a that is the flat bottom surface of the recess is 2 μm, and the difference in height between the recesses, that is, the difference between the lower end and the upper end of the (111) A surface 14b is 2 μm.
[0018]
Next, the GaAs substrate 12 is carried into a gas source MBE growth apparatus, and epitaxial growth is performed after thermal cleaning.
First, as shown in FIG. 2 (b), the n-GaAs buffer layer 16 having a carrier concentration of 1 × 10 ¹⁸ cm ^-3 with a thickness of 0.3 [mu] m, followed by a carrier concentration of 1 × 10 ¹⁸ cm ^-3 The n-Al _0.3 Ga _0.7 As cladding layer 18 is grown to a thickness of 1.5 μm.
[0019]
Next, under the following growth process conditions, radical nitrogen and aluminum atoms are irradiated at the same time while irradiating cracked AsH ₃ along the recess formed in the n-AlGaAs cladding layer 18, as shown in FIG. ), An AlAs (N) layer 20 containing almost no N is formed on the (100) plane, and N is selectively taken into the (111) A slope, and as a result, contains almost no As. An AlN (As) layer 22 is formed.
The growth process conditions are controlled so that the film thickness of the AlAs (N) layer containing almost no N formed on the flat bottom surface is 3 nm to 200 nm, for example, 20 nm.
[0020]
Growth process condition Growth method: Gas source MBE method AsH ₃ partial pressure: 5 × 10 ⁻⁵ Torr
Radical nitrogen partial pressure: 6 × 10 ⁻⁶ Torr
Partial pressure of aluminum atom 4 × 10 ^-7 Torr
Growth temperature 450 ° C
[0021]
Subsequently, as shown in FIG. 3D, on the AlAs (N) layer 20 and the Al (As) N layer 22, a GaAs optical confinement layer having a film thickness of 0.1 μm, a Ga _0.8 In _0.2 As quantum well active layer. SCH-MQW24 composed of a GaAs optical confinement layer with a thickness of 0.1 μm, a p-Al _0.3 Ga _0.7 As cladding layer 26 with a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ and a thickness of 1.5 μm, and a carrier concentration of A p-GaAs contact layer 28 having a thickness of 3 × 10 ¹⁹ cm ⁻³ and a thickness of 0.2 μm is sequentially grown.
Next, as shown in FIG. 3E, the p-GaAs contact layer 28 is left only on the 2 μm-wide flat bottom surface of the recess of the p-AlGaAs cladding layer 26 by photolithography and etching.
Next, as shown in FIG. 1, a laminated metal film of Ti / Pt / Au is deposited on the p-GaAs contact layer 28 and the p-AlGaAs cladding layer 26 to form a p-side electrode 30. Furthermore, after the back surface of the GaAs substrate 12 is polished and adjusted to a plate thickness of about 80 μm, an AuGeNi / Au laminated metal film is deposited to form the n-side electrode 32.
[0022]
The resonator length in the stripe direction is, for example, 300 μm, the laser front end face is as-cleaved, and the laser rear end face is HR coated by PCVD. Thereafter, the semiconductor laser element can be manufactured by cutting out the semiconductor laser chip with a pitch of 250 μm around the concave portion.
[0023]
Since the AlAs (N) layer containing almost no N is formed on the (100) plane, the injected current flows through the (100) plane, while the (111) A plane has a highly electrically insulating Al. Since the (As) N layer 22 is formed, no current flows through the (111) A plane.
Therefore, in the semiconductor laser device manufactured by the method of this embodiment, current flows only in the flat active layer region having a width of 2 μm, and excess leakage current does not flow, so the threshold current is small.
[0024]
In addition, since AlN has a larger band gap than AlAs, the refractive index of AlN is smaller. Therefore, the semiconductor laser device 10 manufactured by the method of this embodiment is a refractive index waveguide type semiconductor laser device in which the GaInAs active layer in the recess is surrounded by the Al (As) N layer 22 having a low refractive index. A stable single mode can be obtained. As described above, according to the method of this embodiment, a refractive index waveguide type / internal current confinement type semiconductor laser element can be easily fabricated on a GaAs substrate.
Furthermore, in the method of manufacturing the semiconductor laser device of this embodiment, the active layer is exposed to the atmosphere by etching the active layer during the manufacturing process of the semiconductor laser device, as in the case of the buried hetero semiconductor laser device. Therefore, there is a merit that the active layer is not oxidized, and a highly reliable semiconductor laser device can be realized.
[0025]
In the embodiment, an example of a 980 nm band laser is shown. However, the material of the active layer is GaInP, AlGaInP, GaAs, AlGaAs, GaInAs, GaInAsSb, GaInNAs, and GaInNAsSb, and the cladding layer and the optical confinement layer are adapted to each active layer. By using this material, it is possible to cover the wavelength range of 600 to 1650 nm. At this time, the AlAsN current confinement technique can be used in the same manner as in the embodiment.
In this embodiment, an example of growth by the gas source MBE method is shown, but MBE, CBE, or MOCVD method may be used.
[0026]
【The invention's effect】
The semiconductor laser device of the present invention is formed on a conductive AlAs (N) layer formed on the (100) surface of a GaAs substrate and an (N11) A surface, and has a higher N content than the AlAs (N) layer. Therefore, the AlAsN current confinement structure including the Al (As) N layer having high electrical insulation is provided.
In the present invention, by narrowing the width of the (100) surface of the recess, the spread of the injection current can be prevented and the threshold current can be lowered. A GaAs semiconductor laser element having an internal current confinement structure is realized.
In addition, since the semiconductor laser device according to the present invention has the same configuration as that of the refractive index waveguide type semiconductor laser device by surrounding the GaInAs active layer of the recess with the Al (As) N layer 22 having a low refractive index, A stable single mode can be obtained in the transverse mode.
According to the method of the present invention, a refractive index waveguide type / internal current confinement type semiconductor laser device can be easily fabricated on a GaAs substrate, and a semiconductor laser as in the case of a buried hetero semiconductor laser device. Since the active layer is not exposed to the atmosphere by etching the active layer during the device manufacturing process, there is a merit that the active layer is not oxidized, and high operation reliability can be realized.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a semiconductor laser device according to an embodiment.
FIGS. 2A to 2C are cross-sectional views for each step in fabricating a semiconductor laser device according to the method of the embodiment.
FIGS. 3D to 3E are cross-sectional views for each process in manufacturing a semiconductor laser device according to the method of the embodiment, following FIG. 2C. FIGS.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Semiconductor laser element 12 Example GaAs substrate 14 Recess 14a (100) surface 14b (111) A surface 16 n-GaAs buffer layer 18 n-Al _0.3 Ga _0.7 As cladding layer 20 AlAs (N) layer 22 AlN (As ) Layer 24 SCH-MQW
26 p-Al _0.3 Ga _0.7 As cladding layer 28 p-GaAs contact layer 30 p-side electrode 32 n-type electrode

Claims (5)

As a stepped substrate having a recess on the (100) plane, which has a (100) plane provided as a bottom surface and a (N11) A plane (N; integer) heading diagonally upward from both edges of the (100) plane. A formed GaAs substrate;
An AlAs (N) layer formed on the (100) plane of the GaAs substrate via a compound semiconductor layer directly on the GaAs substrate or on the (N11) A plane, and AlAs (N) A semiconductor laser device comprising: an AlAsN current confinement structure including an Al (As) N layer having a higher N content and a lower As content than the layers. (N11) N of the A plane (N; integer) is 1, an AlAs (N) layer is formed on the (100) plane, and Al (As) N is formed on the (111) A plane of the stepped substrate. 2. The semiconductor laser device according to claim 1, wherein a layer is formed. 3. The semiconductor laser device according to claim 1, wherein a width of the (100) plane of the recess is 2 μm or less, and a height difference between a lower end and an upper end of the (N11) A plane is 2 μm or more. 2. The semiconductor laser device according to claim 1, wherein the active layer of the semiconductor laser device is formed of any one of GaInP, AlGaInP, AlGaAs, GaAs, GaInAs, GaInAsSb, GaInNAs, and GaInNAsSb. A method of manufacturing a semiconductor laser device having a current confinement structure by a combination of an AlAs (N) layer and an Al (As) N layer,
A concave portion is formed on the (100) surface of the GaAs substrate, which includes a (100) surface provided as a bottom surface and a (N11) A surface (N; integer) heading obliquely upward from both edges of the (100) surface. And the process of
While irradiating cracked AH ₃ directly on the GaAs substrate or via the compound semiconductor layer on the GaAs substrate, simultaneously irradiating radical nitrogen and aluminum atoms, an AlAs (N) layer is formed on the (100) plane. And a step of forming an Al (As) N layer having a higher N content and a lower As content on the (N11) A surface than the AlAs (N) layer. A method for manufacturing a laser element.

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