JP2013077744A - Semiconductor laser and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser having a stable oscillation wavelength and a high output by forming a distributed Bragg reflection region in high accuracy in a distributed Bragg reflection (DBR) semiconductor laser having an AlGaInP-based clad layer and an AlGaAs-based active layer.SOLUTION: A semiconductor laser includes an AlGaAs-based diffraction grating layer in an AlGaInP-based clad layer. The diffraction grating layer in a distributed Bragg reflection region is formed to have unevenness so that the diffraction grating layer remains in a thickness direction, and an uneven part is buried by a thin AlGaAs-based diffraction grating buried layer.

Description

  The present invention relates to a semiconductor laser used for an optical disc, optical communication, a sensor, etc., and more particularly to a distributed Bragg reflection type semiconductor laser.

  2. Description of the Related Art Semiconductor lasers (LD: Laser Diode) have been put into practical use as light sources for optical disc recording / playback and optical communications, and their application range has been expanded to processing, medical, display, and sensor applications. In these applications, the sensitivity of the Si photodiode is high, it oscillates in the infrared wavelength band (830 nm band) invisible to the human eye, the oscillation wavelength is stable, the high output and the long life. It may be required at the same time.

  As a semiconductor laser having a stable oscillation wavelength in the infrared wavelength band, an AlGaAs distributed reflection type laser is known (for example, Patent Document 1). In this example, after epitaxially growing all the layers, a region for forming a distributed Bragg reflector (DBR) is exposed by etching, and after forming a diffraction grating, epitaxial growth is performed again.

JP-A-7-263802 (paragraphs 0013 to 0018, FIG. 1)

  However, with conventional AlGaAs semiconductor lasers, it has been difficult to obtain devices with sufficiently high output and long life for new applications. One of the reasons why high output cannot be obtained is overflow from the AlGaAs-based active layer to the AlGaAs-based cladding layer. In order to suppress overflow, it is conceivable to use AlGaInP having a band gap larger than that of AlGaAs for the cladding layer. However, when this material system is used, it is difficult to accurately form the distributed Bragg reflection region.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and to form a distributed Bragg reflection region with high accuracy in a distributed Bragg reflection semiconductor laser having an AlGaInP-based cladding layer and an AlGaAs-based active layer.

  The semiconductor laser of the present invention is a semiconductor laser having a laser oscillation region and a distributed Bragg reflection region for adjusting the oscillation wavelength, and the laser oscillation region is a first conductivity type AlGaInP system formed on a semiconductor substrate. A first cladding layer, an AlGaAs-based active layer formed on the first cladding layer, a second conductivity type AlGaInP-based second cladding layer formed on the active layer, and a second cladding layer And a second conductivity type AlGaAs-based diffraction grating layer formed on the diffraction grating layer, and a second conductivity type AlGaInP-based third cladding layer formed on the diffraction grating layer, and the distributed Bragg reflection region is The laser oscillation region and the first cladding layer, the active layer, the second cladding layer, and the diffraction grating layer are shared, and the diffraction grating layer in the distributed Bragg reflection region is uneven so that the diffraction grating layer remains in the thickness direction. With the concavo-convex portion is buried by the diffraction grating buried layer an AlGaAs, on the diffraction grating buried layer, a fourth cladding layer of AlGaInP system.

  In the semiconductor laser of the present invention, since the distributed Bragg reflection region can be formed with high accuracy, a semiconductor laser having a stable oscillation wavelength and a high output can be obtained.

It is sectional drawing which shows the semiconductor laser in Embodiment 1 of this invention. It is sectional drawing which shows the semiconductor laser in Embodiment 2 of this invention. It is a figure which shows the manufacturing method of the semiconductor laser in Embodiment 1 of this invention. It is a top view of the semiconductor laser in Embodiment 1 of this invention.

Embodiment 1
FIG. 1 is a cross-sectional view showing a semiconductor laser according to Embodiment 1 of the present invention. In FIG. 1, 1 is an n-type GaAs substrate, 2 is an n-type (Al _0.2 Ga _0.8 ) _0.51 In _0.49 P-n cladding layer, 3 is an Al _0.4 Ga _0.6 As-SCH layer (separated confinement heterostructure), 4 Is a GaAs quantum well (QW) layer, 5 is an Al _0.4 Ga _0.6 As-SCH layer, 6 is a p-type (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P-lower p-clad layer, and 7 is a p-type Al _0.6 Ga layer. _0.4 As diffraction grating layer, 8 and 22 are p-type (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P-upper p-clad layer, 9 and 23 are p-type GaAs contact layers, and 21 is p-type Al _0.4 Ga _0.6 As. It is a diffraction grating buried layer.

  The semiconductor laser 101 includes a laser oscillation region 102 without a diffraction grating and a distributed Bragg reflection region 103 with a diffraction grating. An n-electrode 10 is formed on the back side of the GaAs substrate 1, and a p-electrode 11 is formed on the GaAs contact layer 9 in the laser oscillation region 102 without a diffraction grating.

  Next, a manufacturing method of the semiconductor laser 101 according to the embodiment of the present invention will be described with reference to FIG. First, as shown in FIG. 3A, an n cladding layer 2, an SCH layer 3, a quantum well layer 4, an SCH layer 5, a lower p cladding layer 6, a diffraction grating layer 7, and an upper p cladding are formed on a GaAs substrate 1. The layer 8 and the contact layer 9 are epitaxially grown in this order.

Next, as shown in FIG. 3B, in the distributed Bragg reflection region 103, the diffraction grating layer 7 is exposed by accurately etching the diffraction grating layer 7. In the present embodiment, the group V element of the Al _0.6 Ga _0.4 As diffraction grating layer 7 is As, and the group V element of the (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P-upper p-cladding layer 8 is P. is there. Since the V group elements of the two layers are different, only the upper p-cladding layer 8 whose V group is P can be selectively etched by wet etching with hydrochloric acid without forming an etching stop layer. The diffraction grating layer 7 can be exposed flatly.

  Subsequently, as shown in FIG. 3C, unevenness of the diffraction grating is formed on the diffraction grating layer 7 in the distributed Bragg reflection region 103 by electron beam drawing and etching. A diffraction grating pattern may be formed using an interference exposure method instead of electron beam drawing. Then, as shown in FIG. 1, the diffraction grating buried layer 21, the upper p-cladding layer 22, and the contact layer 23 are epitaxially grown in the distributed Bragg reflection region 103. In the above example, the second growth layer is p-doped, but it is not necessary to dope.

In this example, the Al _0.6 Ga _0.4 As diffraction grating layer 7 was etched so that the diffraction grating layer remained in the thickness direction to form irregularities. Thereafter, a thin Al _0.4 Ga _0.6 As diffraction grating buried layer 21 was epitaxially grown so as to cover it, and then a thick (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P-upper p-clad layer 22 was grown.
This is because the second epitaxial growth is a buried growth in an uneven layer and it is difficult to grow with a good surface state. Group V can grow relatively easily on the As layer. Group V grows AsGaAs, so that the surface state of the interface is improved, and the crystallinity of the subsequently grown upper p-cladding layer 22 is improved. A favorable distributed Bragg reflection region 103 can be obtained. Furthermore, the surface state of the interface can be further improved by making the Al composition of the diffraction grating buried layer 21 smaller than that of the diffraction grating layer 7.

[Comparative Example] In Patent Document 1 described above, a thick AlGaAs cladding layer is formed on the diffraction grating layer of the GaInP layer. When this configuration is applied, the upper p-cladding layer 22 is directly formed thick on the diffraction grating layer 7. Compared to this configuration, in the configuration of the first embodiment, the crystallinity of the upper p-cladding layer 22 is improved, and a good distributed Bragg reflection region 103 can be obtained.

The difference in refractive index necessary for the diffraction grating is that the refractive index of the diffraction grating embedded layer 21 is made larger than that of the diffraction grating layer 7, that is, the Al _0.4 Ga _0.6 As layer having a lowered Al composition is used. Obtained by adopting as.

The p-side electrode 11 is formed on the front side of the semiconductor wafer processed as described above, and then the back side is ground and polished so that the wafer has a predetermined thickness, thereby forming the n-side electrode 10. Thereafter, a laser bar is formed from the wafer by cleavage, and a coating film is formed on the cleavage surface by electron beam evaporation. FIG. 4 is a view of the semiconductor laser 101 as viewed from above. In this example, an anti-reflection (AR) coating film 104 is formed on the cleavage surface on the distributed Bragg reflection region 103 side, and a high reflection (HR) coating film 105 is formed on the laser oscillation region 102 side without the diffraction grating. The method for forming the coating film may be sputtering, for example, instead of electron beam evaporation.
Thereafter, the laser stripe portion is cut out as a laser chip, die-bonded to an AlN submount using AuSn solder, and mounted on a Φ5.6 CAN package to complete the semiconductor laser 101.

  When a voltage is applied in the forward direction between the p-electrode 11 and the n-electrode 10 of the semiconductor laser 101 fabricated as described above and a current is passed through the laser oscillation region 102, light emission occurs in this region. A part of the light is reflected by the distributed Bragg reflection region 103 having a diffraction grating, and is returned to the laser oscillation region 102 to be amplified to cause laser oscillation. Since the diffraction grating reflects only light of a single wavelength, the oscillation wavelength of the laser light is constant and is emitted from the end face on which the antireflection coating 104 is applied.

  In this embodiment, the group V element of the diffraction grating layer is As, and the group V element of the cladding layer thereon is P, so that the cladding layer is selectively etched to form the diffraction grating layer accurately and flatly. Exposed. The exposed diffraction grating layer is etched so that the diffraction grating layer remains in the thickness direction, and a diffraction grating buried layer is grown so as to cover it, and then an upper cladding layer is formed. Thereby, a distributed Bragg reflection region can be accurately formed in a semiconductor laser having an AlGaInP-based clad layer and an AlGaAs-based active layer, and there is an effect that a semiconductor laser having a stable oscillation wavelength and a high output can be obtained.

Embodiment 2
As described in Embodiment 1, the refractive index of AlGaAs increases as the Al composition decreases. On the other hand, since the laser oscillation light propagating along the laser stripe propagates back and forth between the laser oscillation region 102 and the distributed Bragg reflection region 103, the electric field distribution in the laser oscillation mode is preferably close to the same shape in both regions. Thereby, reflection at the coupling portion is eliminated, and single mode oscillation is stably obtained.
FIG. 2 is a diagram showing a structure of a semiconductor laser in which the electric field distribution of the laser oscillation region 202 and the distributed Bragg reflection region 203 is brought close to the same shape. In the laser oscillation region 202, a p-type (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P buffer layer 32 and a p-type Ga _0.51 In _0.49 P electric field matching layer 33 are _disposed between the diffraction grating layer 7 and the upper p-cladding layer 8. Form. The thickness and position of the Ga _0.51 In _0.49 P electric field matching layer 33 are set so that the electric field distribution in the laser oscillation mode is more matched between the distributed Bragg reflection region 203 and the laser oscillation region 202. Other configurations are the same as those of the first embodiment shown in FIG.

  In order to manufacture the semiconductor laser 201 of the second embodiment, the n-cladding layer 2 is 3500 nm, the SCH layer 3 is 20 nm, the quantum well layer 4 is 8 nm, and the SCH layer 5 is formed on the GaAs substrate 1 as in the first embodiment. 20 nm, the lower p-cladding layer 6 is 100 nm, the diffraction grating layer 7 is 50 nm, the buffer layer 32 is 10 nm, the electric field matching layer 33 is 80 nm, the upper p-cladding layer 8 is 1500 nm, and the contact layer 9 is 200 nm in this order.

Next, in the distributed Bragg reflection region 103, etching is performed accurately up to the top of the diffraction grating layer 7 to expose the diffraction grating layer 7. The diffraction grating layer 7 is Al _0.6 Ga _0.4 As, and the buffer layer 32 / electric field matching layer 33 / upper p-cladding layer 8 is (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P / Ga _0.51 In _0.49 P / (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P, and the combination of the V group As layer and the V group P layer is the same as in the first embodiment, and only the V group P layer is selectively etched. The diffraction grating layer 7 can be exposed accurately and flatly.

Subsequently, unevenness of a diffraction grating having a depth of 35 nm is formed on the diffraction grating layer 7 in the distributed Bragg reflection region 103 by electron beam drawing and etching. Then, in the distributed Bragg reflection region 103, the diffraction grating buried layer 21 is epitaxially grown by 40 nm, the upper p-cladding layer 22 is 1568 nm, and the contact layer 23 is 200 nm.
Subsequent steps are performed in the same manner as in Embodiment Mode 1, and the semiconductor laser 201 can be manufactured.

  In the second embodiment, reflection at the coupling portion between the laser oscillation region 202 and the distributed Bragg reflection region 203 is reduced, and there is an effect that single mode oscillation can be stably obtained.

In the above example, the cladding layer and the electric field matching layer are (Al _0.2 Ga _0.8 ) _0.51 In _0.49 P or the like, but if it is an AlGaInP system, the composition can be selected according to the purpose. Here, the AlGaInP system means (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1) lattice-matched with the GaAs substrate.
In addition, although the quantum well is GaAs and the SCH layer is Al _0.4 Ga _0.6 As, if it is an AlGaAs system, the composition can be selected according to the purpose, such as the oscillation wavelength and optical confinement. It can also be a quantum well. Here, the AlGaAs system means Al _x Ga _1-x As (0 ≦ x ≦ 1).
Further, although the diffraction grating layer is Al _0.6 Ga _0.4 As and the diffraction grating buried layer is Al _0.4 Ga _0.6 As, in the case of AlGaAs, in consideration of selective etching, selective growth, refractive index as a diffraction grating, etc. The composition can be selected according to the purpose.
In FIGS. 1-3, although the rectangular thing was shown as the unevenness | corrugation of a diffraction grating, the shape of a triangular saw and smooth wave shape may be sufficient.

1 GaAs substrate
2 (Al _0.2 Ga _0.8 ) _0.51 In _0.49 P-n cladding layer,
3 Al _0.4 Ga _0.6 As-SCH layer 4 GaAs quantum well (QW) layer 5 Al _0.4 Ga _0.6 As-SCH layer 6 (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P-lower p-clad layer,
7 Al _0.6 Ga _0.4 As diffraction grating layer,
8, 22 (Al _0.25 Ga _0.75 ) _0.51 In _0.49 P-upper p-clad layer,
9, 23 GaAs contact layer,
10 n electrode 21 Al _0.4 Ga _0.6 As diffraction grating buried layer
11 p-electrode 101 semiconductor laser 102 laser oscillation region 103 distributed Bragg reflection region

Claims (5)

On the semiconductor substrate, a laser oscillation region and a distributed Bragg reflection region for adjusting the oscillation wavelength,
A semiconductor laser comprising:
The laser oscillation region has a first conductivity type formed on the semiconductor substrate.
A first cladding layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1);
An active layer of Al _x Ga _1-x As (0 ≦ x ≦ 1) formed on the first cladding layer;
A second conductivity type formed on the active layer;
A second cladding layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1);
A diffraction grating layer of Al _x Ga _1-x As (0 ≦ x ≦ 1) of the second conductivity type formed on the second cladding layer;
A second conductivity type formed on the diffraction grating layer;
A third cladding layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1);
Have
The distributed Bragg reflection region shares the first cladding layer, the active layer, the second cladding layer, and the diffraction grating layer,
The diffraction grating layer in the distributed Bragg reflection region is formed with unevenness so that the diffraction grating layer remains in the thickness direction, and the uneven part is embedded in the diffraction grating of Al _x Ga _1-x As (0 ≦ x ≦ 1). Embedded by layer,
On the diffraction grating buried layer,
A semiconductor laser having a fourth cladding layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1). 2. The semiconductor laser according to claim 1, wherein an Al composition of the diffraction grating layer is larger than an Al composition of the diffraction grating buried layer. In the laser oscillation region, between the diffraction grating layer and the third cladding layer,
The semiconductor laser according to claim 1, further comprising an electric field matching layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1). On the semiconductor substrate, a laser oscillation region and a distributed Bragg reflection region for adjusting the oscillation wavelength,
A method of manufacturing a semiconductor laser comprising:
On the semiconductor substrate,
A first cladding layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1) of the first conductivity type;
An active layer of Al _x Ga _1-x As (0 ≦ x ≦ 1),
A second cladding layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1) of the second conductivity type,
A diffraction grating layer of Al _x Ga _1-x As (0 ≦ x ≦ 1) of the second conductivity type,
Forming a third clad layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1) of the second conductivity type in this order;
The third cladding layer in the distributed Bragg reflection region;
Etching and removing until reaching the diffraction grating layer;
Etching the diffraction grating layer so that the diffraction grating layer remains in the thickness direction to form irregularities;
A step of embedding the diffraction grating layer in which the irregularities are formed with a diffraction grating embedding layer of Al _x Ga _1-x As (0 ≦ x ≦ 1);
On the diffraction grating buried layer
Forming a fourth cladding layer of (Al _x Ga _1-x ) _0.51 In _0.49 P (0 ≦ x ≦ 1);
A method for manufacturing a semiconductor laser comprising: 5. The semiconductor laser according to claim 4, wherein an Al composition of the diffraction grating layer is larger than an Al composition of the diffraction grating buried layer.

Images