JPH053377A - Laser diode - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize a highly reliable laser diode by protecting the encapsulating resin layer with a layer having low absorptance of laser light and having heat resistance. In a laser diode in which a laser diode chip 1 having a light emitting end face a is resin-sealed with a sealing resin layer 9 such as an epoxy resin, a light absorption coefficient in the wavelength band of laser light is provided on the light emitting end face a. Low,
An end face fracture prevention layer 10 made of a silicon-based resin having high binding energy is formed. Here, the end surface destruction prevention layer 10 is a layer having a thickness of about 20 to 30 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode formed by sealing a laser diode chip with a resin, and more particularly to a technique for preventing resin destruction on a light emitting end face due to laser light emission.

[0002]

2. Description of the Related Art Conventionally, a laser diode is provided on an n-type GaAs substrate 2 as shown in FIG.
An n-type clad layer 3 made of AlGaAs (aluminum-gallium-arsenic), an active layer 4 made of GaAs (gallium-arsenic), a p-type clad layer 5, and a p-type cap layer 6 are laminated, and further a p-type cap layer 6 is formed. The electrode 7 is selectively deposited on the front surface side of the opening of the GaAs substrate 2, and the back electrode 8 is deposited on the back surface side of the GaAs substrate 2 to form the laser diode chip 1 having the DH structure (double heterojunction structure). At the same time, as shown in FIG. 7, it is known that this laser diode chip 1 is mounted on a heat dissipation plate 23a and the periphery thereof is sealed with a sealing resin layer 9 such as a transparent epoxy resin. Here, 20a is a lead frame, 21 is a gold wire used for wiring of each electrode, and 22 is a photodiode.

[0003]

In the conventional laser diode described above, the epoxy resin is directly applied to the end face a (hereinafter referred to as the light emitting end face a) from which the laser light is emitted from the light emitting region A of the laser diode chip 1. Since they are in contact with each other, when the laser diode is oscillated continuously,
There is a problem that the sealing resin layer 9 near the light emitting end face a generates heat and decomposes. Since the decomposition of this resin lowers the light emission efficiency of the laser diode, the heat generation is further increased and the decomposition progresses, and the sealing resin layer 9 in the vicinity of the light emitting end face a may be hollow.

For example, output 50 mW, oscillation wavelength 780
When a laser diode of nm is continuously oscillated in a state close to the maximum rating, after about 1000 hours, the sealing resin 9 on the light emitting end face a has a bottom face with a diameter of 5 μm on the light emitting end face a side and a height of 5 μm. It has been found that a conical fracture region of is formed.

When a laser diode having a maximum rating of 5 mW used for pickup from an optical recording medium is continuously used in an atmosphere having a temperature of about 60 ° C. and an operating current of about 55 mA, it takes about 40 to 60 hours. It is also known that the light energy of the laser light melts and destroys the sealing resin layer 9 in the vicinity of the light emitting end face a to generate perforations, which disturbs the light wave of the laser light.

In view of the above problems, the object of the present invention is to
By forming a layer having a low absorptance of laser light and having heat resistance on the light emitting end face, the sealing resin is protected from the laser light, and a highly reliable laser diode is realized.

[0007]

In order to solve the above problems, in a laser diode formed by resin-sealing a laser diode chip having at least one light emitting end face, the means taken by the present invention is: On the end face,
That is, the end face destruction prevention layer made of an organic resin having a low light absorption coefficient at least in the wavelength band of laser light and a dissociation energy of about 90 kcal / mol or more is formed to a thickness of about 5 μm or more. In the present invention, the dissociation energy is the energy for decomposing the atoms constituting the basic skeleton of the organic resin from the bonded state to the dissociated state, that is, the energy required for dissociation (dissociation energy), and the atoms of the polymer Corresponds to the binding energy of.

Here, for example, the end face destruction preventing layer is formed of
Dimethylpolysiloxane _{({(CH 3) 2 SiO} } n)
It is possible to use a silicon-based resin containing as a main component, or an acrylic-based resin such as a polymethylmethacrylate resin.

In the present invention, the end face destruction preventing layer is made of an inorganic material having a low light absorption coefficient at least in the wavelength band of laser light, instead of the organic resin material.
It is also possible to use one having a thickness of μm or more.

Here, for example, the end face breakage prevention layer is made of
Aluminum oxide or silicon oxide as a main component, low melting point glass as a main component, or the like can be used.

In the present invention, the thickness of the end face destruction preventing layer is set in the range of about 20 μm to about 30 μm, whereby the laser density of the laser beam passing through the sealing resin layer is regulated and the sealing resin layer is defined. It is preferable to further enhance the protection effect against

[0012]

According to such means, since the end face destruction preventing layer having a low absorption coefficient for the laser light is formed on the light emitting end face, the heat generation amount itself due to the absorption of the laser light at the interface portion is small, and the laser diode chip Even if there is heat conduction from the light emitting end face due to heat generation, the end face breakage prevention layer is made of a material having high heat resistance, so that destruction such as decomposition does not occur. Therefore, since the end face destruction prevention layer that does not deteriorate is formed in the part where the destruction is most likely to occur, the resin in the vicinity of the light emitting end face of the laser diode chip does not decompose and the emission characteristics of the laser diode are stabilized, and the life is long. Reliability can be improved.

Further, the thickness of the end face destruction preventing layer is about 20 μm.
To 30 μm, the laser light passes through the end face destruction prevention layer, so that the beam area of the laser light is expanded inside the end face destruction prevention layer. In this state, the laser light is sealed by the sealing resin. Pass through the layers. Therefore,
Since the laser light passes through the sealing resin layer with a low energy density, the sealing resin layer is less likely to be damaged.

[0014]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

[Embodiment 1] FIG. 1 is a sectional view of a laser diode chip used in a laser diode according to Embodiment 1 of the present invention, in which a DH structure (double heterojunction structure) made of GaAs (gallium-arsenic) is used. FIG. 3 is a cross-sectional view showing a state in which an end face destruction prevention layer made of a heat resistant organic resin layer is coated on the light emitting end face of the laser diode chip of FIG.

FIG. 2 (a) is a front view of the laser diode according to the first embodiment of the present invention, FIG. 2 (b) is a side view thereof, and FIG. 2 (c) is a plan view thereof.

Here, since the laser diode chip of this example has substantially the same structure as the diode chip 1 shown in FIG. 6, common parts are designated by the same reference numerals.

In these figures, the laser diode chip 1 is, for example, on an n-type GaAs substrate 2,
An n-type cladding layer 3 made of AlGaAs, an active layer 4 made of GaAs (gallium-arsenic), a p-type cladding layer 5,
And a p-type cap layer 6 are sequentially laminated, and an electrode 7 is selectively deposited on the front surface side of the opening of the p-type cap layer 6, and a back electrode 8 is formed on the back surface side of the GaAs substrate 2.
Is a laser diode chip having a DH structure coated with. The laser diode chip 1 is fixed to the front end side of the lead frame at the center of the three lead frames 20 via a silicon submount layer 23. The silicon submount layer 23 and the p-type cap layer 6 are connected to a gold wire. Bonding wires such as 6 are wired to each lead frame 20.

Further, the laser diode chip 1 is
The periphery thereof is sealed with a sealing resin 9 such as a transparent epoxy resin and used as a laser diode. In this example, the light emitting end face a of the diode chip 1 is used.
In addition, the absorption coefficient of light is low in the wavelength band of laser light,
The end face fracture prevention layer 10 made of an organic resin layer having a dissociation energy of about 90 kal / mol or more and a thickness of about 5 μm or more is formed.

Here, the end face breakage prevention layer 10 is made of a silicon-based resin composed of dimethyl polysiloxane ({(CH ₃ ) ₂ —Si—O} _n ). For example, dimethyl polysiloxane is formed on the light emitting end face a. And is cured at 150 ° C. for 4 hours to have a thickness of 5 μm or more. The step of applying dimethylpolysiloxane to the light emitting end surface a is performed in the state where the laser diode chip 1 is a single product or the lead frame 20.
It is carried out in the state where it was installed in. The bond energy of Si-O-Si of this dimethylpolysiloxane is about 108 kc.
Al / mol, which is sufficiently higher than that of a normal epoxy resin, and has no absorption band near the oscillation wavelength of 780 nm of a GaAs laser diode.

GaAs having a maximum rating of 5 mW in such a structure
FIG. 3 shows the relationship between the thickness of the end face breakdown prevention layer 10 and the life when the laser diode is continuously used at an operating current of about 55 mA in an atmosphere at a temperature of about 60 ° C. Here, the life time corresponds to the time until the sealing resin layer 6 (mold resin layer) is damaged and the laser output fluctuates.

In FIG. 3, the horizontal axis represents the end face destruction preventing layer 1.
The thickness of the dimethylpolysiloxane layer which is 0 and the beam area of the laser beam corresponding to this thickness are shown, and the vertical axis shows the life time. The laser light is emitted so that the beam area is expanded in the emission direction as shown by the chain line B in FIG. 4, and the beam area in FIG. 3 is the end surface destruction prevention layer 10 and the sealing resin layer 9. It is the beam area at the interface with.

As shown by the solid line C in FIG. 3, the life time of the laser diode extends as the thickness of the end face destruction prevention layer 10 increases. For example, when the end face fracture prevention layer 10 is not provided, the life time is 50 hours or less, whereas when the end face fracture prevention layer 10 has a thickness of about 5 μm, the life time is about 150 hours or more. Will be improved.
Furthermore, increase the thickness of the dimethylpolysiloxane layer,
When the thickness of the end face destruction prevention layer 10 is set to about 20 to about 30 μm, the life is extended to about 3800 hours to about 12000 hours, which is a life time which is sufficiently applicable as a laser diode for pickup of an optical recording medium. To be improved.

As described above, in the laser diode of this embodiment, it is not the sealing resin layer 9 such as epoxy resin that is in contact with the light emitting end face a, but the light absorption coefficient is low in the wavelength band of the laser light. The end face destruction prevention layer 10 is made of a silicon-based resin layer having high heat resistance, and the end face destruction prevention layer 10 is formed at a portion where the heat stress is most applied. Therefore, the encapsulating resin layer 9 does not directly receive heat conducted from the light emitting end face a or heat generated by absorption of laser light, so that decomposition or the like does not occur in the vicinity of the light emitting end face a and the emission characteristics of the laser diode are It is possible to achieve improvement in reliability such as stabilization and longer life.

Here, as plotted by the solid line C in FIG. 3, the relationship between the life time and the thickness of the surface breakdown preventing layer 10 is
The correlation is higher when the relationship between the lifetime and the beam area is considered. Therefore, the function of the surface breakage prevention layer 10 on the light emitting end face a on the sealing resin layer 9 is to directly disperse the energy of the laser light inside the sealing resin layer 9 in addition to the above-mentioned direct protection function from heat. It is also related to the effect of lowering the energy density. That is, as the laser light passes through the end face destruction preventing layer 10, the beam area of the laser light is expanded inside the end face destruction preventing layer 10, and the laser light passes through the sealing resin layer 9 in this state. Therefore, since the laser light passes through the sealing resin layer 9 in a state where the energy density is low, the sealing resin layer 9 is less likely to be damaged. Therefore, by prescribing the thickness of the end face damage prevention layer 10 to a predetermined thickness, the stress applied to the transparent mold resin layer can be relieved and the life can be extended. In this example, a laser diode is used for pickup of an optical recording medium, the thickness of the end face destruction preventing layer 10 is set to about 20 to 30 μm, and a target life time of about 3500 hours or more is cleared. .

In this example, the silicon-based resin composed of dimethylpolysiloxane was used as the end face destruction preventing layer 10 using the organic resin material, but the invention is not limited to this, and other silicon-based resin or An acrylic resin such as polymethylmethacrylate resin may be used.

Example 2 Next, as Example 2 of the present invention, an example in which an inorganic material is used for the end face fracture prevention layer will be described.

FIG. 5 is a sectional view of a laser diode chip used in a laser diode according to a second embodiment of the present invention, which is made of AlGaAs (aluminum-gallium-arsenic) having a DH structure shown in FIG. The light emitting end face a of the laser diode chip 1 is coated with an end face destruction prevention layer made of an inorganic material. In addition,
The configuration of the laser diode of this example has the same configuration as that of the laser diode of the first embodiment, and common parts are denoted by the same reference numerals and their description is omitted.

In FIG. 5, the inorganic layer 11 as an end face destruction preventing layer is made of Al ₂ O ₃ , SiO ₂ or Pb.
A powder of low melting point glass to which (lead), Zn (zinc) or the like is added is dispersed in alcohol in a solvent in the form of a slurry, which is applied on the light emitting end face a and then heated to about 450 ° C. It is a thing.

This inorganic layer 11 also has a wavelength of laser light of 7
Since it is almost transparent to 80 nm and has sufficiently high heat resistance, it is not destroyed by laser light, like the end face destruction prevention layer 10 using an organic resin (dimethylpolysiloxane) layer. The emission characteristics of the laser diode can be stabilized and the life can be extended. further,
When the thickness is about 20 to about 30 μm, in addition to the direct effect of the heat resistance, the inside of the encapsulating resin layer is expanded in the state where the beam diameter of the laser beam is expanded, as in Example 1. Acts to pass through and extends the life of the laser diode.

As described above, in any of the laser diodes of Examples 1 and 2, the formation of the surface destruction preventing layer protects the encapsulating resin layer from the laser beam and changes the quality of the encapsulating resin layer. Since the decomposition is suppressed, the emission characteristics of the laser diode can be stabilized and the life of the laser diode can be extended. Here, the shape of each laser diode chip and the material of each constituent part, the shape of the laser diode itself, etc. are not limited to the above-mentioned embodiment, and the optimum conditions are set according to the required laser light output, application, etc. It is of a nature to be set.

[0032]

As described above, according to the present invention, a laser diode formed by resin-sealing a laser diode chip has a low absorption coefficient for the laser light wavelength on the light emitting end face of the chip and is heat resistant. The feature is that an end face destruction prevention layer having high property is provided. Therefore, according to the present invention, the sealing resin layer is protected by the presence of the end face destruction prevention layer on the light emitting end face that does not deteriorate due to heat conduction due to heat generation of the chip and heat generation due to laser light absorption. Since it is prevented from disassembling,
It is possible to improve the reliability such as stabilization of the light emitting characteristics of the laser diode and extension of the life.

Particularly, the thickness of the end face destruction preventing layer is set to about 20 μm.
To 30 μm, the laser beam passes through the sealing resin layer in a state where the beam area is enlarged in the end face destruction prevention layer and the energy density is small. Therefore, the stress on the encapsulating resin layer is relieved, and a laser diode having a lifetime that can be sufficiently used as a pickup laser diode for an optical recording medium can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which a surface breakdown prevention layer is formed on a light emitting end surface of a laser diode chip used in a laser diode according to a first embodiment of the present invention.

2A is a schematic front view of a laser diode according to a first embodiment of the present invention, FIG. 2B is a schematic side view thereof, and FIG.
Is a plan view thereof.

FIG. 3 is a graph showing the relationship between the lifetime of the laser diode according to Example 1 of the present invention, the thickness of the surface breakdown prevention layer, and the beam area of laser light.

FIG. 4 is a perspective view showing a state where the laser diode according to the first embodiment of the present invention emits laser light.

FIG. 5 is a cross-sectional view showing a state in which an inorganic layer is formed on a light emitting end surface of a laser diode chip used in a laser diode according to a second embodiment of the present invention.

FIG. 6 is a perspective view showing a configuration of a laser diode chip.

FIG. 7 is a sectional view showing a structure of a conventional laser diode.

[Explanation of symbols]

1. Laser diode chip 2 ... GaAs substrate 3 ... n-type clad layer 4 ... Light emitting layer 5 ... p-type cladding layer 6 ... p-type cap layer 7 ... Electrode 8 ... Back electrode 9 ... Sealing resin layer 10 ... End face destruction prevention layer 11 ... Inorganic layer (end face destruction prevention layer) A: Light emitting area a ... Light emitting end face.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01L 23/31 (72) Inventor Katsue Nakata 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (8)

[Claims] 1. A laser diode formed by resin-sealing a laser diode chip having at least one light emitting end face, wherein the light emitting end face has a low light absorption coefficient at least in a wavelength band of laser light, and dissociates. A laser diode, wherein an end face destruction preventing layer made of an organic resin having an energy of about 90 kcal / mol or more is formed to a thickness of about 5 μm or more. 2. The laser diode according to claim 1, wherein the end face destruction preventing layer is made of an organic resin selected from the group consisting of a silicon resin and an acrylic resin. 3. The laser diode according to claim 2, wherein the silicon-based resin is mainly composed of dimethylpolysiloxane. 4. The laser diode according to claim 2, wherein the acrylic resin is polymethylmethacrylate resin. 5. A laser diode formed by resin-sealing a laser diode chip having at least one light emitting end face, wherein an inorganic material having a low light absorption coefficient at least in the wavelength band of laser light is provided on the light emitting end face. A laser diode in which an end face breakdown prevention layer made of is formed to a thickness of about 5 μm or more. 6. The laser diode according to claim 5, wherein the end face destruction preventing layer has a main component of one of aluminum oxide and silicon oxide. 7. The laser diode according to claim 5, wherein the end face destruction preventing layer has a low melting point glass as a main component. 8. The end face destruction preventing layer according to claim 1, wherein the end face destruction preventing layer has a thickness of about 20 μm.
A laser diode having a range of m to about 30 μm.