JPH05102613A - Multiple wave length semiconductor laser device - Google Patents

Abstract

PURPOSE:To offer a multiple wave length semiconductor laser device having different luminous wave length in a plurality of active regions without using heat treatment process causing deterioration of the reliability in a semiconductor laser. CONSTITUTION:In a semiconductor laser device having a plurality of active regions consisting of an active layer 13 having quantum well structure, a plurality of active layers 16, 17 have the mutually different electronic transition energy quantum levels due to control of optical gain. Control of optical gain is performed by adjusting the length of a resonator to be formed by an edge of a laser or reflectivity in a reflection film forming an outgoing loss of light on a laser edge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device which emits a plurality of light beams having different wavelengths in optical communication using wavelength division multiplexing.

[0002]

2. Description of the Related Art Conventionally, as a multi-wavelength laser, a multi-wavelength semiconductor laser by mixed crystal as shown in FIG. 10 has been proposed. The structure of the laser shown in FIG.
1 μm of n-type Si-doped Al _0.4 Ga _0.6 As cladding layer 32, five layers of GaAs / Al _0.2 Ga _0.8 As quantum well layer 33, and _0.8 μm of p-type Be-doped Al _0.4 Ga _0.6.
As clad layer 34, 0.1 μm p-type Be-doped Ga
As cap layer 35, 0.1 μm SiNx layer 36, p
The ohmic electrode 37 and the n-type ohmic electrode 38 are formed.

In this structure, the quantum well layer 33 is a semiconductor layer having a quantum well structure in which a quantum well layer 33a having a narrow forbidden band is sandwiched by barrier layers (= optical waveguide layers) 33b having a wide forbidden band. The quantum well layer 33 is sandwiched between the cladding layers 32 and 34 for confining light.

In this semiconductor laser device, the p-type Be-doped GaAs cap layer 35 is provided with p-type Be-doped Al _0.2 G.
a _0.8 As After heat treatment protective layer (not shown) is deposited,
SiNx is formed in a mixed crystal region (also referred to as a mutual diffusion region).
After depositing a layer (not shown), 100 ° C. in a heat treatment furnace
It is rapidly heated to 950 ° C. at a heating rate of / s and cooled immediately after reaching 950 ° C. By repeating this operation, the quantum well layer 33a and the barrier layer 33b are formed in the quantum well active layer 33 in the region covered with the SiNx layer (not shown).
Mutual diffusion of the constituent elements occurs between them, resulting in mixed crystal and increase in electron transition energy.

After that, the SiNx layer and Al _0.2 Ga _{0.8 are formed.}
The As heat treatment protective layer is removed, and the GaAs cap layer 35 is etched leaving a 10 μm wide stripe. Next, deposit a 0.1 μm SiNx layer 36 shown in FIG.
Open a 10 μm wide window. Then n-type ohmic electrode 3
8 and the p-type ohmic electrode 37 are formed, and end faces are formed by cleavage to form a semiconductor laser.

Thus, the semiconductor laser formed from the mixed crystal active region 39 emits light having a larger transition energy, that is, light of a shorter wavelength than the semiconductor laser formed from the non-mixed crystal active region 40.

The term "mixed crystallization" as used herein means to mutually diffuse constituent elements between semiconductor layers having different compositions. In the case of quantum wells, if mixed crystals occur between a well layer formed with a composition with a small forbidden band and a barrier layer formed with a composition with a large forbidden band, the composition of the well layer increases the bandgap. And the transition energy increases.

[0008]

In the fabrication of the conventional multi-wavelength laser device, when an insulating film is deposited on the semiconductor layer for the purpose of mixed crystal and a rapid heat treatment is performed, the semiconductor layer and the insulating film are There is a problem in the reliability of the semiconductor laser because the stress caused by the difference in the coefficient of thermal expansion between the two causes a transition in the semiconductor layer and silicon, which is an n-type dopant, diffuses into the quantum well active layer.

Therefore, an object of the present invention is to provide a multi-wavelength semiconductor laser device capable of emitting light of different wavelengths in a plurality of active regions without using a heat treatment step of lowering the reliability of the semiconductor laser.

[0010]

The above object of the present invention can be achieved by the following constitutions. That is, in a multi-wavelength semiconductor laser device having a plurality of active regions composed of an active layer having a quantum well structure, the plurality of active regions have multi-wavelength semiconductor laser devices having different electronic transition energy quantum levels by controlling optical gain. Is.

The control of the optical gain in each of the active regions is performed by adjusting the length of the resonator formed by the cleaved end face of the laser, or by making the light emission loss in the reflection film formed on the end face of the laser. This can be done by adjusting the reflectance.

[0012]

The semiconductor laser device is an optical amplifier that amplifies light in the resonator. Therefore, the longer the resonator length, the longer the amplification distance, and the larger the reflectance at the cleaved end face, the more reflected light into the resonator, that is, the amplified light, and the optical gain increases. To increase.

Further, in the semiconductor laser device having the quantum well active layer, since the density of states changes stepwise with respect to energy (FIG. 8), the gain at each quantum level is limited and high. A large gain is obtained by the transition at the energy level. Therefore, by adjusting the cavity length and the reflectance at the end face, it is possible to determine the quantum level at which the gain required for laser oscillation can be obtained.

In a semiconductor laser device having an ordinary quantum well active layer, laser oscillation occurs at the transition 24 between the first quantum levels, but when the optical gain in the semiconductor laser device decreases,
The laser does not oscillate between the first quantum levels having a small gain, but oscillates at the transition 25 between the second quantum levels having a large gain.
Therefore, it is possible to form a two-wavelength semiconductor laser device that oscillates between the first quantum level and the second quantum level by changing the optical gain in the adjacent active regions. In addition, it is possible to form a semiconductor laser device having more wavelengths by the same method.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 FIG. 1 is a sectional view showing a first example in which two semiconductor laser devices having different cavity lengths are arranged in parallel. The procedure for manufacturing the semiconductor laser device shown in FIG. 1 will be described below.

First, as shown in FIG. 2A, n-type GaA is used.
Se-doped Al _0.6 Ga _0.4 on the (100) surface of the substrate 1
1 μm thick glad layer 11 made of As, undoped A
Optical waveguide layer 1 made of _0.3 Ga _0.7 As and having a thickness of 0.1 μm 1
2. Quantum well active layer 13 made of non-doped GaAs and having a thickness of 0.01 μm, optical waveguide layer 12 made of non-doped Al _0.3 Ga _0.7 As and having a thickness of 0.1 μm, Mg-doped Al _0.6 G
The cladding layer 14 made of a _0.4 As and having a thickness of 1 μm and the cap layer 15 made of Mg-doped GaAs and having a thickness of 0.1 μm are sequentially laminated by the MOCVD method.

After that, a SiNx film 6 is deposited to a thickness of 0.2 μm, a stripe-shaped window having a width of 5 μm is opened by photolithography, and a p-type electrode metal 7 is vapor-deposited as shown in FIG. 2B. ..

Then, as shown in FIG. 3, a photoresist 1 is formed on the p-type electrode metal 7 by photolithography.
8 is patterned. First, the p-type electrode metal 7 and the SiNx film 6 are etched using the photoresist 18 as a mask.

Next, as shown in FIG. 4, a groove 26 for separating the active regions from each other and one end surface 19 of the short cavity laser a are formed by chlorine-based dry etching using the photoresist 18 as a mask. Then, the photoresist 18
After peeling off, the GaAs substrate 1 side is polished to a thickness of 100 μm, the n-type electrode metal 8 is vapor-deposited as shown in FIG. 1, and both ends 20 of the long cavity laser b are cleaved by cleavage.
One end face 20 of the short cavity laser a is formed.

On the side of the long cavity laser b, by making the cavity length of the laser 300 μm or more, laser oscillation (wavelength 850 nm) at the first quantum level occurs in the active region 16. On the side of the short cavity laser a, if the cavity length of the laser is 200 μm or less, the optical gain is reduced because the distance over which light is amplified is shortened, and laser oscillation occurs at the first quantum level with a small gain. Does not occur and laser oscillation (wavelength 800 nm) at the second quantum level with a large gain is generated in the active region 1
Occurs at 7.

Embodiment 2 Next, FIG. 5 shows an embodiment in which two semiconductor lasers having reflecting films having different reflectances are arranged in parallel on the end face of the semiconductor laser according to the present invention. The steps up to FIGS. 2A and 2B in the manufacturing procedure of the semiconductor laser device of the present embodiment are exactly the same as those of the first embodiment. SiNx film 6 on the semiconductor layer
To a thickness of 0.2 μm and a 5 μm wide stripe-shaped window is opened by photolithography, and a p-type electrode metal 7 is deposited. The p-type electrode metal 7 is etched using the photoresist 18 as a mask in the same manner as shown in FIG. 3 to separate the electrode 7. Thereafter, as shown in FIG. 5, the photoresist 18 is peeled off, and the GaAs substrate 1 side is exposed to 100%.
After polishing to a thickness of μm, the n-type electrode metal 8 is deposited.

Next, a method of forming a reflective film having different reflectances on the end surface of the semiconductor laser device will be described with reference to FIGS. An end face is formed by cleaving with a cavity length of 300 μm, and a SiO ₂ layer 21 is formed on the end face of the front surface which is the light emitting side by λ.
/ 2 (λ: wavelength of laser light) is deposited (Fig. 6)
(A)). 6 and 7 are views seen from above in FIG.

A photoresist 18 is formed and dipped on the SiO ₂ layer 21 in one active region (long wavelength side b) of the end face of the front surface by photolithography (FIG. 6B), and the other is used as a mask. The SiO ₂ layer 21 in the active region (short wavelength side a) is etched to a desired thickness with a hydrofluoric acid-based etchant (FIG. 7A).

Since the film thickness of the SiO ₂ layer 21 and the reflectance on the end face have the relationship shown in FIG. 9, when the thickness of the SiO ₂ layer 21 changes from 0 to λ / 4, the reflection on the end face is reflected. Rate 32
% To 7%, the reflectance is 2 on the short wavelength side a.
The thickness is set to be a low reflection film 21a of 0% or less. Further, a λ / 2 SiO ₂ layer protective film (not shown) is formed on either end of the rear end facet.

In the active region on the high reflection film 21b side, laser oscillation (wavelength 850n
The reflectivity of the rear end face and the cavity length are set so that m) is possible. On the other hand, in the active region where the low-reflection film 21a is formed, the light emission loss from the front end face increases, so that the optical gain decreases. Then, the optical gain necessary for the laser oscillation cannot be obtained in the first quantum level with the small gain, and the laser oscillation (wavelength 8
00 nm) will be generated. In this way, it becomes possible to emit light with different wavelengths from each active region.

The present invention may have a composition other than the semiconductor composition of the above-mentioned embodiment, for example, GaInAlP mixed crystal system, GaInAsP.
It is also possible to use materials such as mixed crystal system and AlInAsP mixed crystal system.

[0027]

According to the present invention, in a semiconductor laser device having a plurality of active regions, the optical gain is controlled by changing the cavity length in each active region and the reflectivity at the end face to control the electron gain. Change the transitional quantum level,
A highly reliable multi-wavelength semiconductor laser can be formed without using a heat treatment step.

[Brief description of drawings]

FIG. 1 is a perspective view showing a semiconductor laser device of a first embodiment according to the present invention.

FIG. 2 is a cross-sectional view showing a part of the manufacturing process of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 is a perspective view showing a part of the manufacturing process of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing a semiconductor laser device according to a first embodiment of the present invention.

FIG. 5 is a perspective view showing a semiconductor laser device according to a second embodiment of the present invention.

FIG. 6 is a manufacturing process diagram of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 7 is a manufacturing process diagram of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram showing the relationship between energy and state density of a multiwavelength semiconductor laser.

FIG. 9 is a diagram showing the relationship between the film thickness of a SiO ₂ protective layer and the reflectance of laser light.

FIG. 10 is a perspective view of a conventional multiwavelength semiconductor laser.

[Explanation of symbols]

1, 31 ... N-type GaAs substrate, 6, 36 ... SiNx
Film, 7, 37 ... p-type ohmic electrode, 8, 38 ... n-type ohmic electrode, 11 ... n active Se-doped Al _0.6 Ga
_0.4 As clad layer, 12 ... Non-doped Al _0.3 Ga _0.7
As optical waveguide layer, 13 ... GaAs quantum well active layer, 14 ...
Mg-doped Al _0.3 Ga _0.4 As clad layer, 15 ... Mg
Doped GaAs cap layer, 16 ... Active region of long resonator, 17 ... Active region of short resonator, 18 ... Photoresist, 19 ... End face formed by etching, 20 ...
End faces formed by cleavage, 21 ... SiO ₂ film, 2
1a ... Active region coated with low reflection film, 21b ... λ /
2 active region coated with a protective film, 24 ... transition between first quantum level of electron and hole, 25 ... transition between second quantum level of electron and hole, 26 ... groove, 32 ... n-type Si-doped Al _0.4
Ga _0.6 As clad layer, 33 ... Five layers of GaAs / Al
_0.2 Ga _0.8 As quantum well layer, 34 ... p-type Be-doped Al
_0.4 Ga _0.6 As clad layer, 35 ... p-type Be-doped Ga
As cap layer, 39 ... Mixed crystal active region, 40 ... Non-crystallized active region,

Claims (3)

[Claims] 1. A multi-wavelength semiconductor laser device having a plurality of active regions formed of active layers having a quantum well structure, wherein the plurality of active regions have different electron transition energy quantum levels by controlling optical gain. Characteristic multi-wavelength semiconductor laser device. 2. The multiwavelength semiconductor laser device according to claim 1, wherein the control of the optical gain in each of the active regions is performed by adjusting the length of the resonator formed by the cleaved end face of the laser. .. 3. The control of the optical gain in each of the active regions is performed by adjusting the output loss of light by adjusting the reflectance of a reflection film formed on the cleaved end face of the laser. Multi-wavelength semiconductor laser device.