JPH05283796A - Surface emission type semiconductor laser - Google Patents

Abstract

PURPOSE:To enable a surface emission type high-power semiconductor laser having low thermal resistance, which is provided with a vertical resonator structure possessed of a multilayered reflecting mirror, by providing at least one electrode which is possessed of a heat sink function and kept in contact with the laminate side face of the multilayered film reflecting mirror traversing the side face. CONSTITUTION:An N-type first DBR reflecting mirror 11, an N-type GaAs first clad layer 15, an InGaAs active layer 16, a P-type GaAs second clad layer 17, and a P-type second DBR reflecting mirror 12 are epitaxially grown in succession on a semiconductor substrate 14 through the intermediary of an N-type buffer layer 15 of GaAs of the like. A part of the second clad layer 17 and the peripheral side face of the second reflecting mirror 12 are exposed, a high impurity concentration layer is formed, a P-type contact metal electrode 13 is evaporated on the whole surface, and a metal 26 excellent thermal conductivity and possessed of a heat sink function is formed on a part around the metal electrode 13 which is not covered with a plating resist layer 25 to enhance the metal electrode 13 in heat dissipation effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting semiconductor laser, that is, a semiconductor laser having a vertical cavity structure for emitting laser light in a vertical direction.

[0002]

2. Description of the Related Art A vertical cavity surface emitting semiconductor laser has been rapidly developed in recent years, and its excellent low threshold characteristics, high frequency characteristics, etc. have attracted attention, and light sources for next-generation OEIC Is expected to be applied.

A typical structure thereof is, as shown in FIG. 7, a buffer layer 2, a first multilayer reflective film 3, a first cladding layer 4, an active layer 5 and a second cladding layer 6 on a substrate 1. , The second multilayer reflective film 7 is successively epitaxially grown, and the peripheral portion thereof is removed by etching, leaving a central portion, for example, in a cylindrical shape at a depth from the second multilayer reflective film 7 to the first multilayer reflective film 3. The insulating flattening film 8 is in contact with the peripheral side surface of the columnar portion so as to surround it, that is, so as to fill the columnar portion.
For example, a configuration may be adopted in which polyimide is applied, and one electrode 9 is ohmicly deposited on the second multilayer reflective film 7 by coating the same.

Now, InGaAs strained quantum well (oscillation wavelength λ
≈1 μm) A vertical cavity surface emitting semiconductor laser will be described. The substrate 1 is made of, for example, n-type GaAs substrate, and similarly the buffer layer 2 is made of n-type GaA.
s, and the first multilayer reflective film 3 is made of n-type Al.
A repeating laminated film of an As film and a GaAs film is formed as a multilayer film structure of λ / 4 period.

The first cladding layer 4 is made of n-type GaAs, the active layer is made of In _0.2 Ga _0.8 As, and the second
The clad layer 6 is made of p-type GaAs, and the second multilayer reflective film 7 can be formed by a multilayer film of λ / 4 period like a repeated laminated film of p-type AlAs and GaAs.

The electrode 9 is composed of, for example, an AuZn metal electrode.

In this way, a vertical resonator is formed between the first and second multilayer reflective films 3 and 7, and the electrode 9 and the substrate 1 are formed.
By connecting the operating power supply V between them, a current is injected into the active layer 5 through the first and second multilayer reflective films 3 and 7, and a laser beam having a wavelength determined by the vertical cavity length is oscillated. It is done like this.

In the surface emitting semiconductor laser having the vertical resonance structure having such a structure, since the mirror having an extremely high reflectance is formed by using the multilayer reflection film, the light confinement coefficient can be increased and the resonance can be achieved. By making the device length equivalent to the wavelength, it is possible to achieve an extremely low threshold value and reduce the lifetime of light. In addition, a multilayer film reflecting mirror (hereinafter D
BR Reflective Mirror
Since the emission condition of light is limited to the light satisfying the Bragg reflection condition and the oscillation light of a predetermined wavelength can be obtained only in the direction perpendicular to the multilayer reflection film, An angular, single mode semiconductor laser is constructed.

In the surface emitting semiconductor laser having the vertical cavity structure of this kind, since the electric current is supplied through the DBR reflecting mirror and the light is led out through one of the two, the multilayer reflective film is formed by the above-mentioned semiconductor. The DBR reflecting mirror formed by stacking is used. This DBR reflecting mirror has a problem that the series resistance increases especially in the p-side DBR where the carrier mobility is low.

That is, since the mobility of holes is 1/10 or less of that of electrons, the DBR on the p-side is
In the reflecting mirror, in the above example, the series resistance on the side of the second multilayer reflective film 7 becomes a problem, which causes an increase in thermal resistance.

This resistance can be lowered to some extent by high-concentration doping. In this case, however, light absorption by free carriers (plasmon absorption) becomes a hindrance to efficient oscillation, so that it is usually 5 × 10 ¹⁰ cm ^−. Impurity doping of ³ or more is avoidable, so this p
On the other hand, it is not possible to sufficiently reduce the on-resistance, which causes an increase in thermal resistance during high current injection, which makes it difficult to achieve high output.

[0012]

SUMMARY OF THE INVENTION As described above, the present invention increases the thermal resistance at the time of high current injection and increases the output, especially due to the increase of the on-resistance in the vertical cavity surface emitting semiconductor laser using the semiconductor multilayer film reflecting mirror. It solves the problem of inhibition.

[0013]

The present invention is shown in FIG. 1 which is an enlarged schematic cross-sectional view of one example thereof, and in FIG. 2 which is a schematic plan view thereof, a multilayer film reflecting mirror (DBR reflecting mirror). ) In a surface emitting semiconductor laser having a vertical cavity structure having 11 and 12, at least one electrode 13 is provided on the multilayer film reflecting mirror 12 on the side to which the multilayer film stacking side face of the multilayer film reflecting mirror 12 is crossed. It is an electrode having a heat sink function to be in contact with.

[0014]

As described above, in the present invention, at least one of the multilayer film reflecting mirrors is covered with the electrode having the heat sink effect, so that the resistance thermal resistance which is a problem in the semiconductor multilayer film reflecting mirror is reduced. It is possible to increase the output by peeling off.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a surface-emitting type semiconductor laser according to the present invention will be described with reference to the drawings. To facilitate understanding, referring to FIGS. explain.

As shown in FIG. 3A, for example, n-type GaA
MOC is formed on the semiconductor substrate 14 made of s-substrate.
If necessary, n-type G may be formed by VD (metalorganic chemical vapor deposition) or MBE (molecular beam epitaxy).
n-type first DB through the buffer layer 15 such as aAs
R reflector 11, first cladding layer 15 made of n-type GaAs, active layer 16 made of InGaAs, p-type Ga
Second clad layer 17 made of As, second p-type DB
The R reflector 12 is sequentially epitaxially grown.

First and second DBR reflectors 11 and 12
Are, for example, n-type and p-type AlAs and GaAs, respectively.
And the reflectance with respect to the wavelength of the emitted laser light is R ₁ and R _2, and {(R ₁ + R ₂ ) / 2}> 9
At 0%, for example, R ₂ <R ₁ . Then the second DB
On the R reflecting mirror layer 12, for example, a SiO ₂ mask layer 18 and S
A mask layer 20 having a two-layer structure of the i ₃ N ₄ mask layer 19 is formed by, for example, a plasma CVD method.

Then, a photoresist layer 21 by well-known photography is formed on this in a portion where the vertical resonator is finally formed, for example, in a circular pattern.

Next, as shown in FIG. 3B, using the photoresist layer 21 as a mask, first, the portions of the upper Si ₃ N ₄ mask layer 19 other than the adhered portion of the etching resist layer 21 are removed by etching. The SiO ₂ mask layer 18 below this is etched as a mask. The mask 20 formed by the mask layers 18 and 19 is used as an etching mask, and the second DBR reflecting mirror 12, the cladding layer 17, and the active layer 16 are left below the pillar 20 as a columnar portion 22.
RIE (reactive ion etching) using a halogen-based gas such as Cl ₂ or E
Vertically anisotropic dry etching such as CR-RIE (electron cyclotron resonance-RIE) is performed to remove the periphery of the columnar portion 22 by etching. After that, the remaining photoresist layer 21 is removed by ashing or the like.

As shown in FIG. 3C, an insulating layer 23 such as a Si ₃ N ₄ film is deposited by plasma CVD on the entire surface including the peripheral surface of the columnar portion 22 left by the etching.

As shown in FIG. 4A, a coating type insulating material 24 such as polyimide or SOG (spin on glass (low melting point glass)) is applied to the column portion 22 so as to embed the base portion side of the column portion 22. The portion of the layer 16 facing the peripheral end face is coated and covered.

Next, as shown in FIG. 4B, the insulating layer 2 around the upper portion of the columnar portion 22 not covered with the insulating material 24 as an etching mask by isotropic etching is used.
3 is etched back to form a part of the second cladding layer 17 and the second cladding layer 17.
The peripheral side surface of the DBR reflecting mirror 12 is exposed. Then Z
The second cladding layer 17 such as n and the second DBR reflector 1
A p-type dopant having the same conductivity type as that of No. 2 is diffused on the peripheral surface exposed to the outside of the cylindrical portion 22 to form the high impurity concentration layer 25.

As shown in FIG. 4C, the high impurity concentration layer 25
A metal electrode 13 for p-type contact such as Au / Zn / Au is vapor-deposited over the entire surface including.

Next, as shown in FIG. 5A, a plating resist layer 25 made of, for example, photoresist is further added to the cylindrical portion 2.
2 form a ring, for example, with a required gap
A on the part not covered by the plating resist layer 25
A metal portion 26 having a heat sink function having good thermal conductivity such as u plating is plated.

Next, as shown in FIG. 5B, the mask layer 20 and the like on the second DBR reflecting mirror 12 are removed, a coating type planarizing film 27 of polyimide or the like is applied over the entire surface, and then etch back is performed. And flatten it.

Next, an electrode window is opened in a part of the flattening film 27 made of polyimide or the like, and as shown in FIGS. 1 and 2, the other electrode 28 of Au / Ge or the like is formed on the first cladding layer. Ohmic contact with. 13A and 2
8A indicates a contact portion such as an external lead connection provided extending from the electrodes 13 and 28.

Then, an operating power source is connected between the electrodes 13 and 28, and the first and second DBR reflecting mirrors 11 and 12 are connected.
Oscillation is caused in the cavity portion between them, and the laser light is extracted through the second DBR reflection film 12 side in the figure.

In the illustrated example, the columnar portion 22 has a cylindrical shape, but it may have an arbitrary pattern such as a prismatic shape.

Further, in the illustrated example, when the etching depth in the step of FIG. 3B is stopped at the position of the p-type second cladding layer 15, as described above, the resistance of the p-type is particularly problematic. Since the electrode 13 is provided across the side surface of the second DBR film 12, that is, the laminating direction of the multilayer film,
Since the problem of resistance is improved and the metal portion 26 having a heat sink effect is provided, the heat dissipation effect is excellent and the thermal resistance can be improved.

However, as shown in FIG. 6, the etching depth explained in FIG. 4B is set to the first DBR reflecting mirror 11.
The metal portion 26 is formed in the vicinity of the insulating layer 2 as a depth across the
The thermal resistance in the first DBR reflecting mirror 11 can be reduced by entering the through-hole 3.
6, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and duplicate description will be omitted.

Further, in the above-mentioned example, the laser light is guided from the second DBR reflecting mirror 12 side, but the first DBR reflecting mirror 11 side of the substrate 14 is etched to form a window. It may be formed (not shown), and R ₁ <R ₂ may be set so that the laser light is derived therefrom.

Further, the conductivity type of each part can be selected to be the conductivity type opposite to that shown in the drawing, and various modifications can be made without being limited to the above example.

Further, according to the above-mentioned structure, the outer periphery of the columnar portion 22 constituting the vertical resonator is the metal portion 26 and the flattening film 27.
Since it is embedded by means of the like and is formed flat as a whole, it is advantageous for application to OEIC.

[0034]

As described above, in the present invention, since the electrode having the heat sink effect by the metal portion 26 is attached to the side surface of at least one of the multilayer film reflecting mirrors, there is a problem in the semiconductor multilayer film reflecting mirror. It is possible to increase the output by reducing the resistance and thermal resistance.

[Brief description of drawings]

FIG. 1 is an enlarged schematic cross-sectional view of an example of a surface emitting semiconductor laser according to the present invention.

FIG. 2 is an enlarged schematic plan view of a surface emitting semiconductor laser according to the present invention.

FIG. 3 is a manufacturing process diagram (1) of an example of the surface emitting semiconductor laser according to the present invention.

FIG. 4 is a manufacturing process diagram (2) of an example of the surface emitting semiconductor laser according to the present invention.

FIG. 5 is a manufacturing process diagram (3) of an example of the surface emitting semiconductor laser according to the present invention.

FIG. 6 is a schematic cross-sectional view of another example of the present invention.

FIG. 7 is a schematic cross-sectional view of a conventional surface emitting semiconductor laser.

[Explanation of symbols]

 11 First Multilayer Reflector 15 First Cladding Layer 16 Active Layer 17 Second Cladding Layer 12 Second Multilayer Reflector

Claims (1)

[Claims] 1. A surface-emitting type semiconductor laser having a vertical cavity structure having a multi-layered film reflecting mirror, wherein at least one electrode is provided on the side of the multi-layered film laminated mirror of the multi-layered film reflecting mirror with respect to the corresponding multi-layered film reflecting mirror. A surface-emitting type semiconductor laser characterized in that it is an electrode having a heat sink function which is in contact with and across the surface.