JP2001007440A - Semiconductor laser device and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To relatively easily suppress absorption of a laser beam by a beam size conversion unit. SOLUTION: An active layer in which quantum well layers and barrier layers made of a compound semiconductor material are alternately stacked is formed on a surface of a conductive semiconductor substrate. The portion of the active layer on the first region in the surface of the semiconductor substrate has a substantially constant thickness, and the portion on the second region adjacent to the first region is the first region. And gradually become thinner as the distance from the boundary increases. A cladding layer made of a semiconductor material of a second conductivity type opposite to the first conductivity type is formed on the active layer. Mixing of constituent atoms occurs in a portion of the active layer on the second region without causing mixing of constituent atoms in a portion on the first region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device and a method of manufacturing the same, and more particularly, to a semiconductor laser device having a beam spot size converter integrated therein and a method of manufacturing the same.

[0002]

2. Description of the Related Art In the field of optical communication, there is a demand for a technique for optically coupling a semiconductor laser device and an optical fiber with high efficiency. By integrating a laser beam spot size converter in a semiconductor laser device, high coupling efficiency can be realized without using a lens. In addition, since the positional accuracy margin is large, the optical coupling step can be simplified. The simplification of the optical coupling process makes it possible to reduce the cost of the optical communication device. In particular, there is a strong demand for a price reduction for the optical communication device of the subscriber system.

FIG. 6 is a sectional view of a conventional semiconductor laser device in which a spot size converter is integrated. An active layer 100 having a multiple quantum well structure is sandwiched between cladding layers 101 and 102. Electrodes 103 and 104 are formed outside the cladding layers 101 and 102, respectively. Electrode 1
Numerals 03 and 104 allow a current to flow through the active layer 100 and the cladding layers 101 and 102 in the thickness direction.

The active layer 100 includes a stimulated emission section 100b and a spot size conversion section 100a. The spot size conversion section 100a becomes gradually thinner as it goes away from the boundary with the stimulated emission section 100b. The stimulated emission section 100b and the spot size conversion section 100a constitute an optical resonator. The laser beam amplified by the stimulated emission section 100b is emitted to the outside from the end face of the spot size conversion section 100a.

[0005] The spot size of the laser beam propagating from the stimulated emission section 100b toward the emission end face increases as the spot size conversion section 100a becomes thinner.
Therefore, the spot size of the emitted laser beam can be increased.

[0006]

When the well layer becomes thin,
The transition energy between the first energy levels of the valence band and the conduction band (hereinafter, simply referred to as transition energy) increases. The transition energy can be specified by observing the wavelength of photoluminescence. Therefore, the portion of the spot size converter 100a near the relatively thin exit end face does not absorb the laser beam. However,
Since the transition energy near the boundary with the stimulated emission unit 100b is close to the transition energy of the well layer of the stimulated emission unit, it absorbs the laser beam. In order to suppress this absorption, a current is usually applied to a portion of the spot size conversion unit 100a near the boundary with the stimulated emission unit 100b.
That is, when viewed from the normal direction of the substrate, one of the electrodes 10
The electrodes are arranged so that a part 104a of the fourth part overlaps a part of the spot size conversion part 100a.

The current flowing through the spot size converter 100a does not contribute to laser oscillation. For this reason, the laser oscillation efficiency decreases.

In order to prevent the laser beam from being absorbed by the spot size converter 100a, a semiconductor laser device having a structure in which this portion is formed of a semiconductor material having a transition energy larger than that of the stimulated emission portion 100b has been proposed. I have. However, in order to adopt this structure, the spot size conversion unit 100a must be
The crystal must be grown in another step different from the crystal growth step of b. For this reason, the number of manufacturing steps increases, which is against the demand for cost reduction.

An object of the present invention is to provide a semiconductor laser device capable of relatively easily suppressing absorption of a laser beam by a beam size converter and a method of manufacturing the same.

[0010]

According to one aspect of the present invention, an active layer in which quantum well layers and barrier layers made of a compound semiconductor material are alternately stacked on a surface of a semiconductor substrate of a first conductivity type. Forming a portion on the first region in the surface of the semiconductor substrate, the thickness of which is substantially constant, and a portion on the second region adjacent to the first region, Forming the active layer such that the thickness gradually decreases as the distance from the boundary with the first region increases; and a semiconductor material of a second conductivity type opposite to the first conductivity type is formed on the active layer. Forming a cladding layer and causing a mixture of constituent atoms in a portion of the active layer on the second region without causing a mixture of constituent atoms in a portion of the active layer on the first region. Manufacturing method of semiconductor laser device having steps It is provided.

When the laser beam propagates over the second region, the beam spot size increases as the active layer becomes thinner. Therefore, optical coupling with another optical device can be easily performed. When the constituent atoms of the portion on the second region of the active layer are mixed, the transition energy of that portion becomes larger than the transition energy of the well layer. Therefore, the active layer on the second region does not absorb the laser beam.

According to another aspect of the present invention, a stimulated emission portion in which quantum well layers and barrier layers formed of a compound semiconductor material are alternately stacked, and the stimulated emission portion is provided at one end face of the stimulated emission portion. And a spot size conversion section which becomes thinner as the distance from the boundary with the stimulated emission section increases and forms an optical resonator together with the stimulated emission section, and whose composition is a mixture of atoms constituting the stimulated emission section. And a pair of cladding layers made of a semiconductor material having a lower refractive index than the stimulated emission portion and the spot size conversion portion, sandwiching the spot size conversion portion and the layer composed of the stimulated emission portion and the spot size conversion portion substantially equal to the composition. And a semiconductor laser device having the following.

When the laser beam propagates through the spot size converter, the beam spot size increases as the thickness decreases. Therefore, optical coupling with another optical device can be easily performed. Since the constituent atoms of the spot size converter are mixed, the transition energy of that part is higher than the transition energy of the well layer. For this reason,
The spot size converter does not absorb the laser beam.

[0014]

FIG. 1A is a sectional view of a semiconductor laser device according to an embodiment of the present invention. On a surface of a substrate 1 made of InP having n-type conductivity, SCH (Separa
ted Confinement Heterostructure) layer 2, active layer 3,
The SCH layer 4, the p-type cladding layers 5, 6, and the p ⁺ -type contact layer 7 are stacked in this order. One end face of this laminated structure becomes the emission end face 21, and the opposite end face becomes the reflection end face 22. The emission end face 21 and the reflection end face 22 function as reflecting mirrors at both ends of the optical resonator. The lamination from the SCH layer 2 to the p-type cladding layer 5 is processed into a mesa shape that is long in the laser propagation direction (lateral direction on the paper) in the optical resonator.

A boundary 20 is defined between the exit end face 21 and the reflection end face 22. In a region between the boundary 20 and the reflection end face 22, the thickness of each layer is substantially constant. In the region between the boundary 20 and the emission end face 21, the thickness of each layer from the SCH layer 2 to the p-type cladding layer 5 depends on the boundary 20.
It gradually becomes thinner as you move away from it. Outgoing end face 2
The thickness at 1 is about 1/3 of the thickness at boundary 20. Unless otherwise specified, the thickness of each layer corresponds to the boundary 2
It indicates the thickness of the portion between 0 and the reflection end face 22. The portion of the active layer 3 between the boundary 20 and the reflection end face 22 forms the stimulated emission section 31, and the boundary 20 and the emission end face 21
The area between the two forms a beam spot size conversion unit 30.

The SCH layers 2 and 4 are made of non-doped GaI
nAsP, whose lattice constant matches the lattice constant of the InP substrate, and whose transition energy has a wavelength of 1.1 μm
Energy. Its thickness is 100 nm.

FIG. 1B is a sectional view of the active layer 3.
The stimulated emission section 31 of the active layer 3 has a strained multilayer quantum well structure. That is, it has a multilayer structure in which the quantum well layers 3a and the barrier layers 3b are alternately stacked. The barrier layer 3b is made of I
It is a 10-nm-thick layer formed of non-doped GaInAsP lattice-matched to nP, and its transition energy corresponds to a wavelength of 1.1 μm. The quantum well layer 3a includes:
This is a layer having a thickness of 6 nm formed of non-doped GaInAsP having a compression strain of 0%, and its transition energy corresponds to a wavelength of 1.3 μm. The active layer 3 includes ten quantum well layers 3a.

The beam spot size converter 3 of the active layer 3
0 indicates that the constituent atoms of the stimulated emission section 31 are mixed (intermixin
g) having the composition As described later with reference to FIG. 3C, the mixing of the atoms can be caused by, for example, irradiating a focused ion beam.

The p-type cladding layer 5 has a Zn concentration of 5 × 10 ¹⁷
This is a 500 nm-thick layer formed of InP of cm ^-3 . The p-type cladding layer 6 has a Zn concentration of 5 × 10 ¹⁷ cm ^−3.
Is a layer having a thickness of 4000 nm formed by InP. The p ⁺ -type contact layer 7 has a Zn concentration of 1 × 10 ¹⁹ cm
^-3 GaInAs layer with a thickness of 500 nm.

On the upper surface of the p ⁺ -type contact layer 7, a region above the beam spot size converter 30 is a protective film 8.
Covered with. A p-side electrode 9 is formed on the surfaces of the p ⁺ -type contact layer 7 and the protective film 8. The p-side electrode 9 is
It has a structure in which Ti, Pt, and Au are stacked in this order from the p ⁺ type contact layer 7 side. The p-side electrode 9 contacts the contact layer 7 in an area overlapping the stimulated emission section 31 when viewed from the normal direction of the active layer 3, and contacts the contact layer 7 in an area overlapping the beam spot size conversion section 30. do not do.

An n-side electrode 10 is formed on the lower surface of the substrate 1. The n-side electrode 10 has a laminated structure of an AuGe layer and an Au layer.

FIG. 2 shows the in-plane distribution of the transition energy of the active layer 3. The horizontal axis represents the position in the laser propagation direction in the optical resonator, and the left end corresponds to the emission end face 21 and the right end corresponds to the reflection end face 22. The vertical axis represents the transition energy. In the stimulated emission section 31, the transition energy is substantially constant and corresponds to the transition energy of the quantum well layer 3a. Boundary 2
At the position of 0, a step is formed such that the transition energy on the side of the beam spot size converter 30 becomes higher. This step is formed because the constituent atoms of the beam spot size converter 30 are mixed. Therefore, the transition energy at the end of the beam spot size conversion unit 30 on the boundary 20 side is intermediate between the transition energy of the quantum well layer 3a and the transition energy of the barrier layer 3b.

The transition energy of the beam spot size converter 30 gradually increases as the distance from the boundary 20 increases. This is because the thickness of the active layer 3 gradually decreases. Since the transition energy of the beam spot size conversion unit 30 is larger than the transition energy of the stimulated emission unit 31,
The beam spot size converter 30 does not absorb the laser beam stimulated emitted by the stimulated emitter 31 and reciprocating in the optical resonator. Therefore, there is no need to supply a current to the beam spot size converter 30. More specifically, referring to FIG. 1A, the p-side electrode 9 injects a current into the stimulated emission section 31, but hardly injects a current into the beam spot size conversion section 30.

Next, a method of manufacturing the semiconductor laser device according to the embodiment will be described with reference to FIGS.

FIG. 3A is a plan view of a portion of the InP substrate 1 where one semiconductor laser device is to be formed. One semiconductor laser device has, for example, one side (FIG. 3A)
Is formed in a rectangular region having a length of 500 μm. The left side and the right side of FIG. 3A correspond to the emission end face 21 and the reflection end face 22 of FIG. 1A, respectively. Note that the emission end face 21, the reflection end face 22, and the end faces adjacent thereto are formed by cleaving the substrate after all the wafer processes are completed.

In the area between the boundary 20 and the reflection end face 22,
A band-shaped region 41 having a width of 20 μm extending in the horizontal direction of the drawing is defined. An SiO ₂ mask 40 having a thickness of about 300 nm covers both sides of the band-shaped region 41. The distance between the output end face 21 and the boundary 20 is about 200 μm,
Is about 300 μm.

FIG. 3B is a dashed line B3 of FIG.
This corresponds to a cross section at -B3. On the surface of the substrate 1 by reduced pressure metal organic chemical vapor deposition (LPMO-CVD)
The SCH layer 2, the active layer 3, the SCH layer 4, and the p-type clad layer 5 are formed. Trimethylindium, triethylgallium, arsine, and phosphine are used as raw materials for In, Ga, As, and P, respectively. Dimethyl zinc is used as a source of Zn which is a p-type impurity. The growth temperature is 600 to 620 ° C.

No GaInAsP layer is deposited on the mask pattern 40 shown in FIG. Further, the growth rate in the band-shaped region 41 sandwiched between the mask patterns 40 is:
It is faster than the growth rate in other regions. In the region between the boundary 20 and the emission end face 21, the growth rate gradually decreases as the distance from the boundary 20 increases. For this reason,
As shown in FIG. 3B, in a region between the boundary 20 and the emission end face 21, the thickness of each layer gradually decreases as the distance from the boundary 20 increases. In the case of the present embodiment, the film thickness at the emission end face 21 is about 1 / th of the film thickness at the boundary 20.
It was 3.

As shown in FIG. 3 (C), an ion beam 45 is applied to a portion of the region between the boundary 20 and the emission end face 21 which extends the strip region 41. Ion beam 45
For example, a focused beam of Ga ⁺ ions having a focus in the active layer 3 is used. The irradiation conditions are, for example, an acceleration energy of 100 keV and a dose of 1 × 10 ¹³ cm ⁻² . Note that P ⁺ ions and the like can be used in addition to Ga ⁺ ions.

By this ion irradiation, the constituent atoms of the active layer 3 are mixed, and the distinction between the quantum well layer 3a and the barrier layer 3b shown in FIG. 1B becomes unclear. For this reason, the active layer 3
The transition energy of the portion irradiated with the ion beam 45 shifts to the higher energy side. In this way, a step of the transition energy is formed at the position of the boundary 20 as shown in FIG. In the case of this embodiment, this step is about 40 meV
Met.

FIGS. 4 and 5 show a dashed line A in FIG.
This corresponds to a cross-sectional view taken along 4-A4.

As shown in FIG. 4 (A), the laminated structure of the SCH layer 2 to the p-type cladding layer 5, SiO ₂ mask 1
1 to leave a mesa-shaped structure 12. These layers can be etched by, for example, dry etching using CH ₄ , H ₂ , and O ₂ . 3A, the mesa structure 12 extends in the length direction of the band-shaped region 41 and extends from the reflection end face 22 to the emission end face 21.

As shown in FIG. 4B, the mesa structure 1
2 are buried with a current block layer 13 made of p-type InP. On the surface of the current block layer 13, n-type InP
A current blocking layer 14 of 500 nm in thickness is deposited. The deposition of the current blocking layers 13 and 14 is performed by LPMO-
The CVD is performed under conditions that do not grow on the SiO ₂ mask 11. As the n-type impurity, for example, Si can be used. After depositing the current blocking layer 14, Si
The O ₂ mask 11 is removed.

As shown in FIG. 5A, a 4000 nm-thick cladding layer 6 made of p-type InP is deposited so as to cover the current blocking layer 14 and the p-type cladding layer 5. On the cladding layer 6, a contact layer 7 made of p ⁺ -type GaInAs is deposited. The Zn concentration of the contact layer 7 is, eg, 1 × 10 ¹⁹ cm ⁻³ .

As shown in FIG. 5B, the mesa structure 1
On both sides of 2, grooves 15 reaching the surface layer of substrate 1 are formed. The groove 15 is formed by wet etching using a bromo-based etchant.

The surface of the substrate is covered with a protective film 8 made of SiO ₂ . In a portion of the protective film 8 above the mesa structure 12,
An opening 8a for electrode contact is formed. Note that in a cross section taken along dashed-dotted line B3-B3 in FIG.
As shown in (A), the protective film 8 remains above the beam spot size converter 30.

A p-side electrode 9 is formed so as to cover the protection film 8. The p-side electrode 9 contacts the contact layer 7 at the bottom of the opening 8a. An n-side electrode 10 is formed on the back surface of the substrate 1. After the electrodes are formed, the substrate 10 is cleaved along the reflection end face 22, the emission end face 21, and the groove 15 shown in FIG.

According to the above embodiment, by irradiating an ion beam in the step shown in FIG.
The transition energy of the beam spot size converter 30 shown in FIG. Therefore, the transition energy of the beam spot size conversion unit 30 can be relatively easily increased as compared with the case where the stimulated emission unit 31 and the beam spot size conversion unit 30 are deposited in different processes.

In the above embodiment, the case where an InGaAsP-based semiconductor laser device is manufactured has been described as an example.
The above embodiment is also applicable to other semiconductor laser devices having a multiple quantum well structure. For example, the present invention can be applied to a semiconductor laser device in which the well layer and the barrier layer are formed of AlGaInAs, the active layer side of the cladding layer is formed of AlInAs, and the outside is formed of InP.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0041]

As described above, according to the present invention,
The transition energy of the beam spot size conversion unit is larger than the energy of the stimulated emission laser light. For this reason,
It is possible to prevent laser beam absorption in the beam spot size conversion unit.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment.

FIG. 2 is a graph showing a transition energy distribution of an active layer of a semiconductor laser device according to an example.

FIG. 3 is a plan view, a sectional view, and a perspective view of a substrate for describing a method of manufacturing a semiconductor laser device according to an embodiment.

FIG. 4 is a cross-sectional view of a substrate for describing a method of manufacturing the semiconductor laser device according to the embodiment.

FIG. 5 is a sectional view of a substrate for describing a method of manufacturing a semiconductor laser device according to an embodiment.

FIG. 6 is a sectional view of a conventional semiconductor laser device.

[Explanation of symbols]

1 substrate 2, 4 SCH layer 3 an active layer 5, 6 p-type cladding layer 7 p ⁺ -type contact layer 8 protective film 9 p-side electrode 10 n-side electrode 11 SiO ₂ mask 12 mesa structure 13 p-type InP current blocking layer Reference Signs List 14 n-type InP current blocking layer 15 groove 20 boundary 21 emission end face 22 reflection end face 30 beam spot size conversion section 31 stimulated emission section 40 mask pattern 41 band-shaped area 45 ion beam

Claims (4)

[Claims] 1. A step of forming, on a surface of a semiconductor substrate of a first conductivity type, an active layer in which quantum well layers and barrier layers made of a compound semiconductor material are alternately stacked, wherein the surface of the semiconductor substrate is The portion on the first region has a substantially constant thickness, and the portion on the second region adjacent to the first region gradually increases as the distance from the boundary with the first region increases. Forming the active layer so as to be thinner; forming a cladding layer made of a semiconductor material of a second conductivity type opposite to the first conductivity type on the active layer; Producing a mixture of constituent atoms in a portion of the active layer on the second region without causing a mixture of constituent atoms in a portion on the first region. 2. The method according to claim 1, wherein the step of causing the mixing includes the step of irradiating a portion of the active layer on the second region with an ion beam. 3. A stimulated emission portion in which quantum well layers and barrier layers formed of a compound semiconductor material are alternately stacked, and one end face of the stimulated emission portion is continuous with the stimulated emission portion, and the stimulated emission portion is provided. A spot size conversion section which becomes thinner as the distance from the boundary with the section increases and forms an optical resonator together with the stimulated emission section, wherein the spot has a composition substantially equal to a composition obtained by mixing atoms constituting the stimulated emission section. A semiconductor laser device comprising: a size conversion section; and a pair of cladding layers made of a semiconductor material having a lower refractive index than the stimulated emission section and the spot size conversion section, sandwiching a layer including the stimulated emission section and the spot size conversion section. 4. A pair of electrodes disposed outside the pair of cladding layers and for passing a current in the thickness direction to the cladding layer and the stimulated emission portion, wherein a surface normal of the stimulated emission portion is provided. When viewed from the direction, at least one electrode is
4. The semiconductor laser device according to claim 3, wherein a current flows in a region overlapping the stimulated emission unit, and no current flows in a region overlapping the spot size conversion unit. 5.