JP3422365B2 - Ridge stripe type semiconductor laser device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ridge stripe type semiconductor laser device and a method for manufacturing the same, and more particularly, it is used as a light source required for an electronic device such as a light source for pickup of an optical disk device, an information processing device and a communication device. The present invention relates to a ridge stripe type semiconductor laser device and a method for manufacturing the same.

[0002]

2. Description of the Related Art As an ordinary ridge stripe type semiconductor laser device, a structure shown in FIG. 7 is known. This is described in IEE, Journal of Quantum Electronics, Vol. 29, page 1853. Mesa in the same structure is formed by wet etching using the SiO ₂ film as a mask. This technology is a refractive index waveguide structure in which after the formation of a mesa, the side of the mesa has a smaller refractive index than the cladding layer or is embedded with a medium that absorbs the oscillation wavelength to confine the light horizontally and horizontally. And a single horizontal transverse mode laser oscillation can be obtained.

The following two examples are known in which the mesa is formed by dry etching instead of wet etching. The first example is written by Yoshikawa et al. In Electronics Letters, Vol. 30, page 2035. The sectional structure is shown in FIG. This is because the mesa is formed by dry etching, and the same operational reliability as that obtained by forming the mesa by wet etching is obtained. The second example is Kidoguchi et al.
Vol. 36, page 1892, Journal of Applied Physics. The structure is almost the same as that of Yoshikawa et al., And the operation reliability at an optical output of 25 mW is obtained by forming a mesa by dry etching.

The problem with such a technique is that the operating current value of the semiconductor laser increases. Considering application to optical disks, it is better that the operating current is smaller. If the operating current is small, the laser diode will
It is generally known that it operates stably. The reason that the operating current becomes large is that the lateral leakage current to the side of the mesa is large. This is shown in FIG. In the ridge stripe laser, an n-type block layer 102 is buried beside the mesa 101 and a thin p-type cladding layer 103 is left at the side of the mesa 101 to prevent current from being injected into the active layer from portions other than the mesa portion. A current block structure that forms a reverse bias is formed. At this time, most of the current flows into just below the mesa as indicated by the solid arrow in the figure, but part of it spreads out laterally, and the dotted arrow 105 in the figure
Flow as indicated by. This spread current is the active layer 1
Even if it is injected into 04, it does not give a sufficient carrier density to obtain a gain, so that it becomes a reactive current that does not contribute to laser oscillation. This not only unnecessarily increases the laser operating current, but deteriorates the reliability of the laser, and is also inconvenient for reducing the power consumption of the optical disk device and the like. If h is made too small in order to suppress the current spread, a sufficient breakdown voltage cannot be obtained, and a current as indicated by a broken line 106 in the drawing will flow. Therefore, making h small cannot be said to be an effective means for suppressing the spreading current to the side of the mesa. In the experiment by the inventor, it was confirmed that in the case of the structure shown in the first conventional example, the current blocking cannot be performed when h is 0.15 μm or less.

It is desirable to reduce the operating current value by suppressing the reactive current due to current spreading.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ridge stripe type semiconductor laser device having a small operating current value by suppressing a reactive current due to current spreading, and a manufacturing method thereof.

[0007]

Means for solving the problem Means for solving the problem are expressed as follows. In the expression, the technical matters corresponding to the claims are enclosed in parentheses (), and numbers, symbols, etc. are added. The number, symbol, etc. are at least one of the technical matters corresponding to the claim and a plurality of modes of implementation.
Although the correspondence and correspondence with the technical matters of the two forms are clarified, it is not intended to show that the technical matters of the claims are limited to the technical matters of the embodiments.

A ridge stripe type semiconductor laser device according to the present invention comprises a substrate (2) and a double heterostructure layer formed on the surface of the substrate (2), and the double heterostructure layer is a p-type cladding layer. (7) and an n-type cladding layer (3), and an active layer (4) sandwiched between the p-type cladding layer (7) and the n-type cladding layer (3). A mesa (21) for horizontally confining light is formed in either one of the mold cladding layers (3), and the cladding layer on the side where the mesa (21) is formed ( In 7), the thickness of the portion near the side of the mesa (21) is formed smaller (22) than the thickness of the portion far from the side.

Due to the shape structure of the mesa (21), the reactive current is suppressed and the operating current value is reduced.

The portion near the side of the mesa is the active layer (4).
Has a shape (22) that is not carved, or
That portion near the side of the mesa has a sculpted shape (22) that has just reached the active layer (4) or slightly beyond the active layer (4).

A method for manufacturing a ridge stripe type semiconductor laser device according to the present invention comprises etching a semiconductor by a dry etching method and forming a mesa by etching (2
This can be easily realized by a method of manufacturing a ridge stripe type semiconductor laser device, which comprises increasing the physical etching property when performing 1). Increasing the physical etching property is to positively adjust the gas pressure of the etching gas used for etching in association with the acceleration voltage of positive ions existing in the plasma of the etching gas. As compared with the conventional case, the gas pressure of the etching gas is controlled to be lower, and the acceleration voltage of the positive ions existing in the plasma of the etching gas is simultaneously set to be higher and controlled. Such physical conditions can easily form a hollow beside the mesa.

If the semiconductor is an AlGaInP semiconductor,
It is preferable that the substrate temperature is 200 ° C. or lower, the etching gas pressure is 5 × (10 −4) torr or lower, and the effective accelerating voltage of positive ions is 600 V or higher. The substrate is a semiconductor substrate or a dielectric substrate.

[0013]

DETAILED DESCRIPTION OF THE INVENTION FIG.
The embodiment of the Leip type semiconductor laser device is
It is shown as an Ip type, and is
FIG. 2 to 5 show a ridge according to the present invention.
Embodiment of Manufacturing Method of Striped Semiconductor Laser Device
Is shown. As shown in FIG.
Of n-type GaAs substrate 2 by crystal growth (MOVPE) method
N type (Al_0.7Ga _0.3)_0.5In
_0.5P first clad layer (thickness 1.5 μm) 3 is formed
To be done. On the upper surface of the first cladding layer 3, a 4 quantum well active layer
4 is formed. The quadruple quantum well active layer 4 is made of GaInP.
(Thickness 7 nm) layer, and (Al_0.7Ga_0.3)_{0
． 5}In_0.5Formed with a P (4 nm thick) layer
There is.

Next, as shown in FIG. 2, p-type (Al
_0.7 Ga _0.3 ) _0.5 In _{0. A 5} P second clad layer (thickness: 1.5 μm) 7 is formed. Further, a p-type GaInP hetero buffer layer (thickness: 20 nm) 8 is formed on the upper surface of the second cladding layer 7. Further, a p-type GaAs cap layer (thickness: 0.3 μm) 9 is laminated on the upper surface of the hetero buffer layer 8, and thereafter, a SiO ₂ film is formed on the entire surface of the substrate by a thermal CVD method, and then by a photolithography method. SiO ₂ stripes 12 having a width of about 5 μm are formed.

Next, as shown in FIG. 3, the SiO ₂ stripe 12 is used as a mask and a RIBE apparatus is used to obtain a substrate temperature of 200 ° C. and a gas pressure of 1 × 10 minus 4 tor.
Under the conditions of r and accelerating voltage of 1000 V, chlorine plasma left over the surface of the active layer 4 to a thickness of 0.3 μm
The second clad layer 7 is dry-etched so that the clad layer 7'is left, and the mesa 21 is formed. As a result of this formation, a cut 22 is formed in the remaining second cladding layer 7'on the side of the mesa where the side surface of the mesa and the upper surface of the quadruple quantum well active layer 4 intersect. The minimum thickness h2, which is the shortest distance between the notch 22 and the upper surface of the quadruple quantum well active layer 4, is shown in FIG.
, 0.1 μm.

Next, as shown in FIG. 4, the mesa 22 is formed by the MOVPE method using the SiO ₂ stripe 12 as a mask.
Beside the upper surface of the second clad layer 7 and the side surface of the mesa 22 selectively on the first block layer of n-type AlInP (thickness 0.3 μm).
m) 5 is formed. Further, on the upper surface and the side surface of the first block layer 5, a second block layer of n-type GaAs (having a thickness of 0.5 μm) is formed.
m) 6 is formed. By this formation, the first block layer 5 is embedded in the second block layer 6.

Next, the SiO ₂ stripes 12 are removed with buffered hydrofluoric acid, and as shown in FIG.
The p-type GaAs contact layer 10 is laminated on the entire upper surface of the substrate by the OVPE method. Further, the p-side electrode 11 is formed on the upper surface of the contact layer 10 by the vapor deposition method, and the n-type GaA is formed.
The n-side electrode 1 is formed on the lower surface of the s substrate 2.

Finally, the laser substrate is cleaved into individual chips each having a stripe width of 300 μm and a cavity length of 600 μm so that the waveguide stripe becomes the center line, and the structure shown in FIG. Complete. When the characteristics of the semiconductor laser manufactured in this manner were evaluated, when the stripe width was 5 μm, the optical output during continuous oscillation was 15 mW, and the operating current value was 55 mA.
The semiconductor laser of the comparison target (having the structure shown in FIG. 7) having the same substrate, layer structure, and stripe width but having a mesa formed by wet etching has an operating current value of 60 mA during continuous oscillation of 15 mW. Met.

FIG. 8 is a sectional view showing another embodiment of the ridge stripe type semiconductor laser device according to the present invention as a ridge stripe type, as seen from a direction perpendicular to the waveguide stripe. 9 to 12 show another embodiment according to the present invention. As shown in FIG. 9, n-type (Al _0.7 Ga _0.3 ) _0.5 I was formed on the upper surface of the n-type GaAs substrate 2 by the vapor phase organic metal crystal growth (MOVPE) method.
A first cladding layer (thickness: 1.5 μm) 3 of n _0.5 P is formed. The quadruple quantum well active layer 4 is formed on the upper surface of the first cladding layer 3. The quadruple quantum well active layer 4 is made of GaIn.
A layer of P (thickness 7 nm), and (Al _0.7 Ga _0.3 ).
_And a layer of _0.5 In _0.5 P (thickness 4 nm). These steps are the same as those in the above-described embodiment.

Next, as shown in FIG. 9, p-type (Al
_0.7 Ga _0.3 ) _0.5 In _{0. A 5} P second clad layer (thickness: 1.5 μm) 7 is formed. Further, a p-type GaInP hetero buffer layer (thickness: 20 nm) 8 is formed on the upper surface of the second cladding layer 7. Further, a p-type GaAs cap layer (thickness: 0.3 μm) 9 is laminated on the upper surface of the hetero buffer layer 8, and thereafter, a SiO ₂ film is formed on the entire surface of the substrate by a thermal CVD method, and then by a photolithography method. SiO ₂ stripes 12 having a width of about 5 μm are formed. These steps are the same as those in the above-described embodiment.

Next, as shown in FIG. 10, using the RIBE apparatus with the SiO ₂ stripe 12 as a mask,
Substrate temperature 200 ° C, gas pressure 1 × 10 minus 5 to
Under the conditions of rr and an acceleration voltage of 1000 V, chlorine plasma is used to dry-etch the second clad layer 7 so as to leave a residual second clad layer 7 ′ having a thickness of 0.3 μm above the active layer 4, The mesa 21 is formed.

By this formation, a cut 22 is formed in the remaining second cladding layer 7'at the side of the mesa where the side surface of the mesa and the upper surface of the quadruple quantum well active layer 4 intersect. The minimum distance h2 in FIG. 6, which is the shortest distance between the notch 22 and the upper surface of the quadruple quantum well active layer 4, is as shown in FIG.
It became 0.0 μm. The only difference in these steps from the above-described embodiment is that the gas pressure is 10 −5 torr.

Next, by the MOVPE method, using the SiO ₂ stripes 12 as a mask, as shown in FIG.
Aside from 2, the first block layer (thickness: 0.3) selectively formed on the upper surface of the second cladding layer 7 and the side surface of the mesa 22.
μm) 5 is formed. Further, on the upper surface and the side surface of the first block layer 5, a second block layer of n-type GaAs (thickness 0.5
μm) 6 is formed. By this formation, the first block layer 5 is embedded in the second block layer 6.

Next, the SiO ₂ stripes 12 are removed with buffered hydrofluoric acid, and as shown in FIG.
A p-type GaAs contact layer 10 is laminated on the entire upper surface of the substrate by the MOVPE method. Further, the p-side electrode 11 is formed on the upper surface of the contact layer 10 by the vapor deposition method, and the n-type Ga is formed.
The n-side electrode 1 is formed on the lower surface of the As substrate 2.

Finally, the laser substrate is cleaved into individual chips each having a stripe width of 300 μm and a cavity length of 600 μm so that the waveguide stripe becomes the center line, and the structure shown in FIG. Complete. When the characteristics of the semiconductor laser manufactured in this manner were evaluated, when the stripe width was 5 μm, the optical output during continuous oscillation was 15 mW, and the operating current value was 55 mA.
In this way, the gas pressure is 1 × 10 minus the fourth power torr.
Was changed from 1 × 10 to minus 5th power torr,
The laser operating performance did not change.

FIG. 13 is a sectional view showing another embodiment of the ridge stripe type semiconductor laser device according to the present invention as a ridge stripe type, as seen from a direction perpendicular to the waveguide stripe. 14 to 17 show another embodiment of the present invention. As shown in FIG. 14, n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 was formed on the upper surface of the n-type GaAs substrate 2 by the vapor phase metal organic crystal growth method.
A P first clad layer (thickness: 2.5 μm) 3 is formed. The quadruple quantum well active layer 4 is formed on the upper surface of the first cladding layer 3.

The quadruple quantum well active layer 4 is made of n-type Al _0.3.
A Ga _0.7 As clad layer (thickness: 2.5 μm),
(A guide layer of Al _0.2 Ga _0.8 As (thickness: 20 n
m), GaAs barrier layer (thickness 5 nm) and In _0.2 G
a _0.9 As layer. The layer formation and material of the quadruple quantum well active layer 4 are different from those in the above-described embodiments.

Next, as shown in FIG. 15, p-type (A
l _0.3 Ga _0.7 ) As second cladding layer (thickness 2.
5 μm) 7 is formed. Further, a p-type GaAs cap layer (thickness 0.5 μm) 9 is formed on the upper surface of the second cladding layer 7. After that, a SiO ₂ film is formed on the entire surface of the substrate by a thermal CVD method, and then a SiO ₂ stripe 12 having a width of about 3 μm is formed by a photolithography method.

Next, as shown in FIG. 15, the SiO ₂ stripe 12 is used as a mask and a RIBE apparatus is used.
Substrate temperature 200 ° C, gas pressure 1 × 10 minus 5 to
Under the conditions of rr and an acceleration voltage of 1000 V, chlorine plasma is used to dry-etch the second clad layer 7 so as to leave a residual second clad layer 7 ′ having a thickness of 0.3 μm above the active layer 4, The mesa 21 is formed.

By this formation, a cut 22 is formed in the remaining second cladding layer 7'at the side of the mesa where the side surface of the mesa and the upper surface of the quantum well active layer 4 intersect. Notch 2
The minimum distance h2 in FIG. 6, which is the shortest distance between the upper surface of the 2 and 4 quantum well active layer 4, is as shown in FIG.
It became 0.1 μm. The difference between these steps and the above-described embodiment is that the thickness of each layer, the layered structure of layers, and the layer forming material are different.

Next, as shown in FIG. 16, the mesa 2 is formed by the MOVPE method using the SiO ₂ stripe 12 as a mask.
On the side of No. 2, the first block layer 5 (thickness 0.8 μm) 5 of n-type Al _0.55 Ga _0.45 As is selectively formed on the upper surface of the second cladding layer 7 ′ and the side surface of the mesa 22. . Further, a second block layer 6 (thickness 0.7 μm) 6 of n-type GaAs is formed on the upper surface and the side surface of the first block layer 5. By this formation, the first block layer 5 is embedded in the second block layer 6.

Next, the SiO ₂ stripe 12 is removed with buffered hydrofluoric acid, and as shown in FIG.
A p-type GaAs contact layer 10 is laminated on the entire upper surface of the substrate by the MOVPE method. Further, the p-side electrode 11 is formed on the upper surface of the contact layer 10 by the vapor deposition method, and the n-type Ga is formed.
The n-side electrode 1 is formed on the lower surface of the As substrate 2.

Finally, the laser substrate is cleaved into individual chips each having a stripe width of 300 μm and a cavity length of 900 μm so that the waveguide stripe becomes the center line, and the structure shown in FIG. 13 is obtained. Complete. The resonator length of 900 μm is different from the two embodiments described above.

When the characteristics of the semiconductor laser manufactured as described above were evaluated, when the stripe width was 3 μm, the operating current value when the optical output during continuous oscillation was 30 mW was 85 mA. The operating current value of the semiconductor laser of the comparison object having the same substrate, layer structure, and stripe width but having the mesa formed by wet etching during continuous oscillation of 30 mW was 91 mA.

In these embodiments, AlGaInP is used.
Although the semiconductor lasers of AlGaAs and AlGaAs are described, it is effective for all semiconductor lasers such as InP long-wave laser used for communication and GaN blue laser of shorter wavelength as long as it is a ridge buried type. . Also,
In any case, the structure according to the present invention can be realized by performing dry etching under appropriate conditions that enhance the physical etching property.

Physical operation: Generally, in a ridge-embedded semiconductor laser, current spreads to the side of the mesa as shown by a dotted arrow 105 in FIG. Even if the spread current is injected into the active layer 104, sufficient carriers cannot be supplied, so that the gain cannot be generated.
The reactive current does not contribute to laser oscillation. In order to reduce the reactive current, the mesa side remaining thickness h in FIG. 19 may be reduced. However, if h is extremely reduced,
A through current as indicated by a broken line arrow 106 in the drawing flows.
In the ridge-embedded semiconductor laser, the reverse bias structure of the n-type current block layer and the p-type cladding layer on the side of the mesa blocks the current flowing through the side of the mesa, but if h is small, a sufficient breakdown voltage cannot be obtained, Current flows even at a relatively low voltage. Therefore, reducing h is not an effective means for suppressing the spreading current to the side of the mesa. In an experiment conducted by the inventor, it was confirmed that current blocking cannot be performed when h is 0.15 μm or less.

In the constricted structure according to the present invention, as shown in FIG. 6, only a part of the side of the mesa is made thinner than the other part, so that the function of the current block is not impaired, and it is indicated by a solid arrow in the figure. Such spreading current to the side of the mesa is suppressed. Also in this case, the breakdown voltage of the thin portion is low, but the current injection cross-sectional area is smaller than that of the mesa portion, so the current resistance is large, and as a result, the current hardly flows in the thin portion.
Further, when the mesa formation is performed by wet etching, FIG.
As shown in FIG. 6, the mesa side becomes flat, but if the dry etching is performed under an appropriate condition in which the physical etching property is increased, a shape as shown in FIG. be able to.

[0038]

The ridge stripe type semiconductor laser device and the method of manufacturing the same according to the present invention operate by suppressing the reactive current that does not contribute to laser oscillation by forming a shape in the cladding layer that suppresses the current spreading to the side of the mesa. The current value can be kept low. Such a shape can be easily formed by changing physical conditions.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a ridge stripe type semiconductor laser device according to the present invention.

FIG. 2 is a sectional view showing an embodiment of a method for manufacturing a ridge stripe type semiconductor laser device according to the present invention.

FIG. 3 is a cross-sectional view showing a step subsequent to FIG.

FIG. 4 is a cross-sectional view showing a step subsequent to that of FIG.

FIG. 5 is a sectional view showing a step subsequent to that of FIG.

FIG. 6 is a cross-sectional view showing optical confinement of operation according to the present invention.

FIG. 7 is a sectional view showing a semiconductor laser device for comparison.

FIG. 8 is a sectional view showing another embodiment of the ridge stripe type semiconductor laser device according to the present invention.

FIG. 9 is a cross-sectional view showing another embodiment of the method for manufacturing a ridge stripe type semiconductor laser device according to the present invention.

FIG. 10 is a sectional view showing a step subsequent to FIG. 9.

FIG. 11 is a sectional view showing a step subsequent to that of FIG. 10.

FIG. 12 is a sectional view showing a step subsequent to that of FIG. 11.

FIG. 13 is a sectional view showing still another embodiment of a method for manufacturing a ridge stripe type semiconductor laser device according to the present invention.

FIG. 14 is a sectional view showing still another embodiment of the present invention.

FIG. 15 is a cross-sectional view showing the next step of FIG.

16 is a sectional view showing a step subsequent to that of FIG. 15. FIG.

17 is a sectional view showing a step subsequent to that of FIG. 16. FIG.

FIG. 18 is a sectional view showing a structure of a known semiconductor laser device.

FIG. 19 is a sectional view showing an operation of a known semiconductor laser device.

[Explanation of symbols]

2 ... Substrate 3 ... n-type clad layer 4 ... Active layer 7 ... p-type clad layer 21 ... Mesa 22 ... Shape

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-5-327110 (JP, A) JP-A-5-327113 (JP, A) JP-A-2001-44567 (JP, A) JP-A-4-167489 (JP, A) JP-A-5-343791 (JP, A) Jpn. J. Appl. Phys. Part 1, Vol. 31 No. 12B (1992), p. 4381-4386 Jpn. J. Appl. Phys. Part 1, Vol. 34 No. 2B (1995), p. 1273-1278 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 JISST file (JOIS)

Claims (3)

(57) [Claims] 1. A substrate, A double heterostructure layer formed on the substrate surface.
, The double heterostructure layer includes a first cladding layer and a second cladding layer.
Pad layer, the first clad layer and the second clad layer
With an active layer sandwiched between Either the first clad layer or the second clad layer
One lateral cladding layer is used to confine the light horizontally.
A mesa is formed, The clad layer on the side where the mesa is formed is
The thickness of the part near the side of the mesa is the thickness of the part far from the side.
Formed smaller thanAnd, beside the mesa
Formed in a constricted shape, where the thickness of the part far from the
And The constricted shape is such that the clad layer is dry-etched.
Formed by Ridge stripe type semiconductor laser device
Place 2. The ridge stripe type semiconductor laser device according to claim 1, wherein the portion near the side of the mesa has a shape that is scooped so as not to reach the active layer. 3. The ridge according to claim 1, wherein the portion near the side of the mesa has a scooped shape that reaches just the active layer or slightly beyond the active layer. Striped semiconductor laser device.