JP2001015861A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser device which is provided with a stripe structure, prevented from degradation on of device characteristics due to the fact that the stripe structure is damaged when a bonding operation is performed onto a heat sink or the like, and capable of outputting stably. SOLUTION: An N-type GaAs buffer layer, an N-type InGaP clad layer, an InGaAsP barrier layer, an InGaAs active layer, an InGaAsP barrier layer, a P-type InGaP clad layer, a P-type InGaAsP etching stop layer, a P-type InGaP clad layer, and a P-type GaAs contact layer are successively laminated on an N-type GaAs substrate. Thereafter, the contact layer and a clad layer 19 located thereunder are etched, and a ridge is formed deviatedly from the center in a widthwise direction. At the same time, a pickup trapezoidal part of a height same as the ridge is formed at the center of a chip. A dielectric film 22 is formed thereon, and a P-side electrode 23 and a N-side electrode 24 are formed. When the P-side electrode 23 is formed, an electrode is formed also on the pickup trapezoidal part at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device, and more particularly, to a semiconductor laser device having a stripe structure.

[0002]

2. Description of the Related Art Conventionally, there has been known a semiconductor laser device having a stripe structure for controlling a transverse mode in order to obtain a single fundamental mode oscillation. Usually, these semiconductor laser elements are bonded to a heat sink or the like by using solder when they are mounted. The bonding method includes a junction up method and a junction down method. The junction up method is a method of bonding a surface far from the active layer out of two surfaces parallel to the active layer to a heat sink, and the junction down method is a method of bonding a surface near the active layer to a heat sink. In particular, the junction up method
Since distortion of the bonding surface with the heat sink is hardly transmitted to the active layer, there is an advantage that an output with less noise can be obtained.

In bonding by a junction-up method, a capillary or the like is fixed to the center of a semiconductor laser element and bonded onto a heat sink. Particularly, in a semiconductor laser device having a ridge waveguide type stripe structure, the capillary or the like is used. There is a problem that the ridge portion is damaged by the fixing device, and good output cannot be obtained. US Pat. No. 5,305,340 discloses a method for protecting a ridge portion of a semiconductor laser device having this ridge structure.
The issue states that the ridge has walls higher than the ridge on both sides of the ridge.

However, the above method has the following problems. That is, the height of the ridge is usually 1.5 to
Since the thickness is about 2 μm, for example, when a wall is formed using gold, it is necessary to use a method such as gold plating to increase the height. However, when the plating thickness is large, problems such as peeling of the film occur due to the stress of the gold film. In order to prevent this, after the thickness of the gold plating is about 1 μm, annealing is performed at an appropriate temperature, for example, about 300 ° C., and gold plating is applied again about 1 μm. Thus, film peeling can be prevented, but there is a problem that productivity is not good and cost is increased because the number of steps is increased.

[0005]

As described above, in a semiconductor laser device having a stripe structure, in the assembly step of bonding elements to a heat sink or the like by using a solder or the like by a junction-up method, the stripe portion may be damaged. And when the stripe portion is damaged, there is a problem that the element characteristics deteriorate. For example, there are problems such as an increase in oscillation threshold current, a decrease in luminous efficiency, and a decrease in reliability over time.

Therefore, it is important for a semiconductor laser device having a stripe structure to have an element structure that does not damage the stripe portion during assembly.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a low-cost semiconductor laser device with good productivity which prevents a ridge portion from being damaged when a semiconductor laser device is bonded to a heat sink or the like and reduces device characteristics. It is intended to provide.

[0008]

According to a semiconductor laser device of the present invention, at least a lower clad layer, an active layer, an upper clad layer, a partially removed dielectric film and electrodes are laminated in this order on a substrate. And a semiconductor laser device having a stripe structure in which carriers are injected from a part of the dielectric film from which the part is removed, wherein one of two end faces parallel to the active layer, which is far from the active layer, is placed on a heat sink. In the semiconductor laser device bonded to the semiconductor laser device, the stripe structure is formed at a position shifted from the center in the width direction of the semiconductor laser element, and the stripe is formed on one of the two end surfaces near the active layer. A metal pad electrically connected to the active layer is formed at a position away from the structure.

Further, in the semiconductor laser device of the present invention, the stripe structure is a ridge type, and the height of the metal pad is equal to or greater than the height of the ridge portion. May be used.

[0010]

As described above, when bonding a semiconductor laser device to a heat sink or the like, the upper portion of the stripe portion, which is the light emitting region, has been fixed by a capillary or the like, so that the stripe portion may be damaged. However, according to the semiconductor laser device of the present invention, the semiconductor laser device having the stripe structure has two end faces parallel to the active layer. Among them, in a semiconductor laser device having an end face remote from an active layer adhered on a heat sink, a stripe structure is formed at a position shifted from a center in a width direction of the semiconductor laser element, and the two end faces are separated from each other. Of these, a metal pad electrically connected to the active layer is formed at a position on the end face near the active layer and away from the stripe structure. By doing so, the metal pad can be fixed on the heat sink with a capillary or the like, so that the stripes can be prevented from being damaged by the equipment to be fixed. Obtainable.

Further, since the metal pad portion is electrically connected to the active layer, wire bonding is performed on the metal pad portion in the assembling process. Even if it is applied to the pad, the light does not propagate to the light emitting region of the element, so that it is possible to prevent the light emitting region from being damaged by the distortion, so that high temporal reliability can be obtained.

Also, in a semiconductor laser device having a ridge type stripe structure, the ridge portion is formed at a position shifted from the center in the width direction of the semiconductor laser device, and of the two end faces parallel to the active layer, By forming a metal pad electrically connected to the active layer on the end face close to the ridge and away from the ridge, it is possible to prevent the ridge part from being damaged by equipment when bonding to the heat sink. Further, by setting the height of the metal pad to be equal to or higher than the height of the ridge portion, there is an advantage that the ridge portion near the active layer is less likely to be damaged, and a stable output can be obtained.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view of a ridge waveguide type semiconductor laser device having a lasing wavelength of 950 nm up to a contact layer in a laminating direction according to a first embodiment of the present invention.

As shown in FIG. 1, a semiconductor crystal is formed on an n-type GaAs (carrier concentration: 7 to 20 × 10 ¹⁷ cm ⁻³ ) substrate 11 by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). ) Depending on the method
N-type GaAs of about 600 nm (carrier concentration of 7 to 20)
× 10 ¹⁷ cm -3) buffer layer 12, 2 μm thick n-type In
GaP (carrier concentration: 5 to 15 × 10 ¹⁷ cm ⁻³ ) cladding layer 13, In _1-x Ga _x As _1-y P _y (x = 0.78) having a thickness of 45 nm
8, y = 0.43, undoped) barrier layer 14, 9 nm thick I
nGaAs (non-doped) active layer 15, 45 nm thick I
n _1-x Ga _x As _1-y P _y (non-doped) barrier layer 16, p-type InGaP having a thickness of 400 nm (carrier concentration 5 to 20 ×
10 ¹⁷ cm ^-3) cladding layer 17, a thickness of approximately 4 to 10 nm p-type InGaAsP (carrier concentration 5 to 15 × 10 ¹⁷ cm
^-3 ) Etching stop layer 18, 1.6 μm thick p-type I
nGaP (carrier concentration: 5 to 20 × 10 ¹⁷ cm ⁻³ ) cladding layer 19, p-type GaAs having a thickness of about 150 to 500 nm
(Carrier concentration 5-30 × 10 ¹⁸ cm ^-3 ) Contact layer
20 are sequentially laminated to form a semiconductor crystal.

Next, a description will be given of the above-described process of forming a semiconductor crystal into an element. FIG. 2 shows a perspective view of the completed semiconductor laser device, and FIG. 3 shows a manufacturing process of the semiconductor laser device in the AA ′ section of FIG.

As shown in FIG. 3A, a resist pattern 21 for ridge etching is formed on the sample after crystal growth by a usual photolithography process. At this time, when the crystal surface is the (100) plane, the ridge stripe direction is (01-1) in order to obtain a mesa-shaped ridge.
It is formed in a direction perpendicular to the plane.

Next, as shown in FIG.
The p-type GaAs contact layer 20 is removed by etching with a hydrogen peroxide-based etchant, and then the p-type InGaP clad layer 19 is etched with a hydrochloric acid-based etchant. At this time, p
Since the etching rate of the InGaAsP etching stop layer 18 is much lower than that of the p-type InGaP cladding layer 19, the etching is performed at an appropriate etching time so that the etching is performed near the upper portion of the etching stopper layer 18. Stop and easily obtain the desired shape. After that, the resist pattern 21 is removed.

Next, as shown in FIG. 3C, a dielectric film 22 such as SiO ₂ or Si ₃ N _{4 is} deposited to a thickness of about 100 to 200 nm by a method such as plasma CVD. FIG.
As shown in d, in order to open a window for electrode contact on the top of the ridge, by the photolithography process described above,
The resist is patterned and the dielectric film is formed by a method such as reactive ion etching using a fluorine-based gas.
22 is removed by etching. After that, remove the resist,
As shown in FIG. 3e, in order to pattern the p-side electrode, the resist is patterned by a photolithography process, and the electrons are formed in the order of, for example, Ti / Pt / Au (each film thickness is, for example, 50 nm / 80 nm / 300 nm). The p-side electrode 23 is deposited by a beam evaporation method or the like and patterned by lift-off.

Next, the sample is polished to a thickness of about 120 to 150 μm in order to facilitate formation of the resonator surface by cleavage. As shown in FIG. 3F, the n-side electrode 24 is formed by combining an AuGe /
In the order of Ni / Au, for example, the film thickness is 50 nm, 30 nm, 30 nm.
Deposit about 0 nm. Thereafter, in order to obtain ohmic contact between the electrodes, the electrodes are reacted at about 400 ° C. for about 1 minute.

By forming as described above, a metal pad having the same composition as the p-side electrode is formed substantially at the center of the surface on which the p-side electrode is formed.

Next, as shown in FIG. 4, at a predetermined position,
Cleavage is performed at predetermined intervals, for example, at 750 μm intervals in a bar shape. The bar-shaped sample 41 has 8 semiconductor laser elements.
They are connected.

Next, as shown in FIG. 5A, coating of each cleaved end face with a dielectric film is performed as follows. A dielectric film 51 is formed on the end face on the emission side where the bar is cleaved so that the reflectance with respect to the oscillation wavelength of 950 nm of the semiconductor laser device is, for example, about 10%, and on the end face on the opposite side to the emission end face. Has an oscillation wavelength of 950 n
The dielectric multilayer film 59 is formed so that the reflectance with respect to m is 80% or more.

FIG. 5B is an enlarged view of one semiconductor laser device of the bar-shaped sample in FIG. 5A. FIG.
As shown in FIG. 5, alumina (Al ₂ O ₃ ) is formed on the light emitting end face of the semiconductor laser element 50 as a dielectric film 51 with a predetermined thickness.
For example, it is deposited by an ion assisted electron beam evaporation method. Furthermore, using the same method for the rear end face,
The first layer 52 of Al ₂ O _{3 is made} of titanium oxide (T) so that the reflectance for an oscillation wavelength of 950 nm is, for example, 80% or more.
The second layer 53 of iO _2), third silicon dioxide (SiO ₂₎
A dielectric multilayer film 5 comprising a layer 54, a fourth layer 55 of titanium oxide (TiO ₂ ), and a fifth layer 56 of silicon dioxide (hereinafter SiO ₂ ).
9 is deposited to a predetermined thickness. Thereafter, the bar-shaped sample 41 is cleaved at a predetermined position to form an element. After that, each element is subjected to electrical evaluation and sorting, and the semiconductor laser element 50 is replaced with tin, silver, copper, bismuth (Sn / Ag / Cu / Bi)
Solder to a ceramic heat sink with metallized upper and lower surfaces using lead-free solder.

At this time, if the ridge is located at the center as in the prior art, the chip may be damaged when the chip is lifted by using a vacuum, which may affect the output. However, as shown in FIG. 6, the capillary 61 can be lifted in the vicinity of the center of the chip without having to touch the ridge portion and with a good weight balance. It is important to have the vicinity of the center of the chip for the following reasons. In order to increase the adhesion to the solder when adhering to the stem, it is possible to raise the temperature of the heat sink and to solder while holding down the chip with an appropriate load while keeping the chip parallel and as much as possible without tilting the chip significantly. Therefore, a highly reliable semiconductor laser device that has good solder coatability, high bond strength between the chip and the heat sink, and does not cause a problem such as a position shift with the passage of time can be easily manufactured.

Thereafter, as shown in FIG. 7, the heat sink 71 to which the semiconductor laser element 50 is adhered is placed on a copper header.
Adhere to 72 by soldering. After that, the copper header 72 is connected to the ceramic 74 such as alumina which has been metallized on the upper surface electrically insulated and the plus side and the minus side of the element by a gold wire 73 by heating and ultrasonic bonding, respectively, Complete the semiconductor laser device.

As shown in FIG. 7, since the trapezoidal portion for pickup at the center of the element is electrically connected to the electrode on the top of the ridge, wire bonding is performed on this portion. As a result, since wire bonding is performed on a portion of the semiconductor laser device away from the light emitting portion, even if distortion during wire bonding is applied, it does not extend to the light emitting region of the device, that is, the ridge portion. Since damage at the time of assembling can be prevented from reaching the vicinity of the light emitting region of the element, high temporal reliability can be obtained.

Next, the fact that the lower layer of the trapezoidal portion for pickup has a trapezoidal shape when viewed from above will be described. This is a trapezoid in which the main material to be etched in this embodiment, that is, the cladding layer is InGaP, which is etched with hydrochloric acid. This corresponds to the direction of the ridge stripe, that is, the crystal plane (01-
In the 1) direction, the etching shape becomes a so-called mesa shape, but on the same surface, in the direction perpendicular to the (01-1) direction,
Since it has an inverted mesa shape, depending on the performance of the p-CVD apparatus, SiO ₂ or Si ₃ formed between the electrode and the crystal layer may be used.
This is to prevent the formation of gaps due to failure of coating of the derivative film such as N ₄ . That is, in the crystal direction of the oblique side of the trapezoid, a mesa shape that is slightly vertical is obtained without forming an inverted mesa shape.

However, for example, the cladding layer is made of AlGaAs.
When a crystal or the like is used, a mesa shape can be obtained with a tartaric acid-based etching solution regardless of the crystal orientation, so that the coverage of a dielectric film such as SiO ₂ or Si ₃ N ₄ is not reduced. There is no problem if the shape is not limited to a trapezoid but may be a rectangle or the like.

Next, the shape of the cleavage region of the semiconductor laser device will be described. The edge of the long side when the chip is viewed from above, that is, the region where the chip is cleaved after coating the dielectric film on the end face of the bar-shaped semiconductor laser device, is subjected to scribe cleavage after etching the cladding layer. Even if an attempt is made to insert, the ridge etching of the cleaved portion, that is, the etching of the cladding layer is not performed because it is difficult to enter. Further, if a p-electrode is present in the cleavage region, cleavage damage is unlikely to occur, and the yield of chip cleavage is reduced. Therefore, the cladding layer in the cleavage region is not etched, and the upper dielectric film is exposed, as shown in FIG. It is desirable to have a simple structure.

Alternatively, when the dielectric film is removed only in the cleavage region and the structure in which the final formation surface of the clad layer is exposed is obtained, the cleavage property is further improved, and the yield is improved.

In the embodiment of the present invention, the metal pad portion is formed substantially at the center of the chip. However, the metal pad portion is not limited to the center, but may be located rearward from the center of the resonator length (rearward with respect to the light emitting surface). It may be formed. In particular, when the curvature of the light emitting surface side of the heat sink to be bonded is large, there is an advantage that the semiconductor laser device can be easily fixed at the time of soldering because the metal pad portion is located behind the center.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure in a stacking direction of a semiconductor laser device according to a first embodiment of the present invention;

FIG. 2 is a perspective view showing the semiconductor laser device according to the first embodiment of the present invention;

FIG. 3 is a diagram showing a manufacturing process of the semiconductor laser device in an AA ′ section of FIG. 2;

FIG. 4 is a perspective view showing a bar-shaped sample before being made into a semiconductor laser device according to the first embodiment of the present invention;

FIG. 5 is a view showing a semiconductor laser device according to a first embodiment of the present invention in which a dielectric film is formed on an end face;

FIG. 6 is a diagram when the semiconductor laser device according to the first embodiment of the present invention is lifted by a capillary.

FIG. 7 is a diagram in which the semiconductor laser device according to the first embodiment of the present invention is mounted on a heat sink or the like.

[Explanation of symbols]

11 Substrate 18 Etch stop layer 19 P-type clad layer 20 Contact layer 22 Dielectric film 23 P-side electrode 24 N-side electrode 50 Semiconductor laser element 51 Al ₂ O ₃ film 61 Capillary 71 Heat sink

Claims (4)

[Claims] At least a lower clad layer, an active layer, an upper clad layer, a partially removed dielectric film and an electrode are laminated on a substrate in this order, and a part of the dielectric film is removed. A semiconductor laser device having a stripe structure in which carriers are injected from a part of a film, wherein a semiconductor laser element having two end faces parallel to the active layer, the end face far from the active layer adhered to a heat sink, The stripe structure is formed at a position deviated from the center in the width direction of the semiconductor laser device, and, of the two end surfaces, on an end surface close to the active layer, at a position away from the stripe structure, A semiconductor laser device, wherein a metal pad electrically connected to the active layer is formed. 2. The method according to claim 1, wherein the stripe structure is of a ridge type, and a height of the metal pad is equal to or greater than a height of the ridge portion.
13. The semiconductor laser device according to claim 1. 3. In a chip cleavage portion in a cavity length direction,
3. The semiconductor laser device according to claim 1, wherein the electrode is removed, and the dielectric film is exposed. 4. In a chip cleavage portion in a resonator length direction,
3. The semiconductor laser device according to claim 1, wherein the electrode and the dielectric are removed, and a final film forming surface of the upper clad layer is exposed.