JPH0722697A - Semiconductor laser element and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser element having high reliability by suppressing inner diffusion of an impurity added in a crystal for constituting the element. CONSTITUTION:An end face grown layer 4 made of a crystal having a larger band gap than that of a crystal for constituting an active layer 3 is formed on a light emitting end face 2 of a resonator formed of a crystal containing Al and having the layer 3. The layer 4 is grown at a growing temperature of 500 deg.C or lower by an organic metal vapor growing method or a molecular beam epitaxial growing method.

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 and its manufacturing method.

[0002]

2. Description of the Related Art In the above-mentioned semiconductor laser device, at the light emitting end face of a resonator, oxygen in the atmosphere adheres to and bonds with the crystal surface to increase the surface level. Therefore, the band gap on the light emitting end face is narrower than that inside the device, and the band gap on the light emitting end face of the active layer is also narrower than inside the device. Generally, the laser oscillation wavelength (energy) of a semiconductor laser device is determined by the bandgap of the active layer, but the bandgap at the light emitting end face of the active layer is narrower than that inside the device as described above. In addition, the laser light oscillated inside the element is absorbed by the light emitting end face. Therefore, heat is generated due to the absorption of the laser light at the light emitting end face, and the heat generation further narrows the bandgap at the light emitting end face of the active layer, resulting in a vicious cycle in which the absorption of the laser light is further increased. Due to this vicious circle, the crystal that constitutes the light emitting end face is finally destroyed and melted due to the high temperature, and the element is deteriorated. Even when crystal destruction does not occur, defects and dislocations in the crystal grow due to the temperature rise due to the heat generation.
This causes the growth of the device, which leads to deterioration of the device. The breakage of the crystal due to the absorption of laser light at the light emitting end face is a factor that hinders the reliability of the semiconductor laser device.

Conventionally, semiconductor laser devices having various structures have been proposed in order to prevent deterioration of the device due to absorption of laser light at the light emitting end face. For example, Matsumoto et al., At the 51st Annual Meeting of Applied Physics, Autumn 1990: 28p-R-5 ~ 6), proposed a window-type structure in which an edge growth layer with less absorption of lasing laser light was provided at the light emitting edge. We propose a semiconductor laser device. FIG. 4 shows a semiconductor laser device having the above window structure. The internal structure 40 of this semiconductor laser device is S. Yamamo
to et. al; Appl. Phys. Lett. 40 (1982) 372. VSIS (V- using a GaAlAs-based mixed crystal as shown in
channel substrate inner stripe) structure,
An end face growth layer 43 having a band gap larger than that of the active layer 41 is formed on the light emitting end face 42. In this figure, 45 is a p-side electrode, 46 is an n-side electrode, and 47 is a dielectric film.

For example, VSIS having an oscillation wavelength of 780 nm
-Type semiconductor laser device, Al mixed crystal ratio x of active layer 41
Is 0.14, whereas A is used as the end face growth layer 43.
A Ga _1-t Al _t As crystal having a mixed crystal ratio t of 0.14 or more can be used. In this case, the bandgap of the end face growth layer 43 is larger than that of the active layer 41, and becomes a layer that absorbs less oscillated laser light. Therefore, the characteristics at the time of particularly high output are improved, and a semiconductor laser device having excellent long-term reliability can be realized.

The window type semiconductor laser device is manufactured as follows. First, as shown in FIG.
The VSIS structure as the internal structure 40 is formed by the liquid phase epitaxial growth (LPE) method.

Next, as shown in FIG. 5B, VSIS
The structure-formed wafer 50 is cleaved into bars 51. The cleaved surface 42 of the bar 51 serves as a cavity end surface which is a light emitting end surface of the semiconductor laser device.

After that, as shown in FIG.
1 is lined up on a jig 53 made of carbon, and this is MOCVD
It is installed on the susceptor 54 in the (organic metal vapor phase growth) type growth apparatus. The growth of the end surface growth layer 43 is performed by heating the susceptor 54 with high frequency while flowing, for example, AsH ₃ gas, TMA (trimethylaluminum), TMG (trimethylgallium) as the source gas 55. The growth temperature at this time is set to about 800 ° C.

Since the entire surface of the bar 51 is a good crystal plane, the growth of the end face growth layer is performed on the entire surface as shown in FIG. 5 (d). Since the portion 43a of the grown end face growth layer is the portion where the p-side electrode 46 is formed, the element resistance of the semiconductor laser element increases if left unremoved. Therefore, after the growth is completed, the end face growth layer 43 on the light emitting end face is formed.
A dielectric film 47 for suppressing oxidation is vapor-deposited thereon, and the unnecessary portion 43a is removed by etching using this as a mask as shown in FIG. 5 (e).

Thereafter, as shown in FIG. 5 (f), the p-side electrode 45 and the n-side electrode 46 are formed in the bar state and divided into chips. A window type semiconductor laser device is obtained as described above.

[0010]

Since the end face growth layer 43 is formed in the window type semiconductor laser device, it is necessary to suppress light absorption at the light emitting end face 42 and improve the device characteristics at high output. You can However, since the end face growth layer 43 is formed in a high temperature atmosphere of about 800 ° C., the following problems occur.

In order to control the conductivity type, a small amount of Zn, Be, Mg or the like is added to the crystal forming the semiconductor laser element, and Te, Se, Si or the like is added to the n-type as impurities. Has been done. However, these impurities are diffused inside the semiconductor laser device by being placed at a high temperature when the end face growth layer 43 is formed, and the formed pn junction position is moved, or the impurities are moved between crystals having different compositions. For example, the impurity concentration distribution inside the semiconductor laser element is changed. As a result, the electrical characteristics and optical characteristics of the semiconductor laser device are deteriorated, and the reliability of the semiconductor laser device is adversely affected.

The present invention solves the above problems,
It is an object of the present invention to provide a semiconductor laser device having high reliability by suppressing the internal diffusion of impurities added to the crystal forming the semiconductor laser device.

[0013]

A semiconductor laser device of the present invention is made of a crystal containing Al, and has a bandgap larger than that of a crystal forming the active layer on a light emitting end face of a resonator including an active layer. In a semiconductor laser device in which an edge growth layer made of crystal is formed, the edge growth layer is grown at a growth temperature of 500 ° C. or lower by a metal organic chemical vapor deposition method or a molecular beam epitaxial growth method,
Thereby, the above object is achieved.

The method of manufacturing a semiconductor laser device according to the present invention comprises:
In a method of manufacturing a semiconductor laser device, wherein an end face growth layer made of a crystal having a band gap larger than that of a crystal forming the active layer is formed on a light emitting end face of a resonator including an active layer The end face growth layer is grown at a growth temperature of 500 ° C. or lower by a metal organic chemical vapor deposition method or a molecular beam epitaxial growth method, whereby the above object is achieved.

[0015]

In the present invention, the end face growth layer is grown at a low temperature of 500 ° C. or lower by the metal organic vapor phase epitaxial growth method or the molecular beam epitaxial growth method. Therefore, it is possible to suppress the internal diffusion of the impurities added to the crystal.

[0016]

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

Example 1 FIG. 1A is a perspective view showing a semiconductor laser device of Example 1. This semiconductor laser device has a VSIS structure. A stripe-shaped V groove 13 is formed on a p-type GaAs substrate 11 on which an n-type GaAs current confinement layer 12 is formed, and a p _- type Ga _1-y A is formed thereon.
_{l y As (0 <y ≦} 1) cladding layer 14, p-type Ga _1-x A
l _x As (0 ≦ x <1) active layer 3, n-type Ga _{1 -z} Al _z A
The s (0 <z ≦ 1) cladding layer 16 and the n-type GaAs contact layer 17 are sequentially stacked. The end face of this VSIS internal structure 1 is made into a laser light emitting end face 2 by cleavage. On the light emitting facet 2, Ga _1-t Al _t As (x having an Al mixed crystal ratio t larger than the Al mixed crystal ratio x of the active layer 3 is formed.
<T ≦ 1) The end face growth layer 4 is formed. This Al mixed crystal ratio t can be set as t> 0.14 in the case of a semiconductor laser device having an oscillation wavelength of 780 nm. In this embodiment, t = 0.6 is set to have a sufficiently large band gap with respect to the active layer inside the device. The edge growth layer 3 is grown at a growth temperature of 500 ° C. or lower. Further, the dielectric film 8 is formed on the end face growth layer 4, and the substrate 11 side and the contact layer 17 are formed.
On the side, a p-side electrode electrode 6 and an n-side electrode 7 are formed, respectively.

This semiconductor laser device can be manufactured, for example, as follows. First, as shown in FIG. 2A, the internal structure 1 of the semiconductor laser device is formed. An n-type GaAs current confinement layer 12 having a thickness of 0.8 μm is laminated on the p-GaAs substrate 11 by the LPE method, and a stripe-shaped V groove 13 having a width of 3 μm and a depth of 1.0 μm is formed by chemical etching. After that, in the second growth process by the LPE method, a p-Ga _0.55 Al _0.45 As clad layer 14 having a thickness of 0.8 μm (a portion other than the V groove 13) and a p-Ga _0.86 Al _0.14 As active layer having a thickness of 0.06 μm are formed. 3. An n-Ga _0.55 Al _0.45 As cladding layer 16 having a thickness of 1 μm and an n-GaAs contact layer 17 having a thickness of 2 μm are successively laminated.

The wafer 20 on which the laminated structure is formed as described above is cleaved to the resonator length to form a laser bar 21 as shown in FIG. 2 (b). The cleavage plane of this laser bar 21 is
It becomes the light emitting end face 2 of the semiconductor laser device.

Next, as shown in FIG. 2C, the MOCV
According to the D method, Ga _0.6 having a thickness of 0.1 μm was formed on the light emitting end face 2.
The Al _0.4 As end face growth layer 4 is grown. The growth temperature at this time was set to 500 ° C. or lower, and the V / III ratio was set to 45 for growth. As described above, at the low temperature growth temperature of 500 ° C. or less, diffusion of impurities added to the n-type or p-type crystal can be reduced.

The growth of the end face growth layer 4 is also performed on a portion other than the light emitting end face 2 as shown in FIG. 2 (c). Since the element resistance of the semiconductor laser element increases if the portion 4a of the grown end face growth layer is left, it is removed after the growth. A dielectric film 8 for suppressing oxidation is vapor-deposited on the end face growth layer 4 of the light emitting end face, and this is used as a mask.
As shown in (d), the unnecessary portion 4a is removed by etching.

Next, the p-side electrode 6 and the n-side electrode 7 are formed on the laser bar 21 in this state. AuZn, Au, Mo, and Au are sequentially deposited as the metal for the p-side electrode 6, and AuGe, Ni, Mo, and Au are sequentially deposited as the metal for the n-side electrode 7, and 4
A good ohmic contact can be obtained by alloying the vapor-deposited metal with the crystals constituting the semiconductor laser device in a nitrogen atmosphere at 00 ° C. After that, the laser bar 21 is divided into chips to obtain a window type semiconductor laser device as shown in FIG.

In the above semiconductor laser device, since the growth of the end face growth layer 4 is performed at a low temperature of 500 ° C. or less, it is possible to suppress the internal diffusion of the impurities added to the crystal forming the semiconductor laser device. . Therefore, it is possible to prevent the deterioration of the characteristics of the semiconductor laser device after the end face growth layer 4 is formed.

In order to suppress the oxidation of the light emitting end face, a dielectric film 8 is vapor-deposited on the end face growth layer 4 and assembled into a heat dissipation package, and the package has a temperature of 60 ° C. and an optical output of 40.
A long-term running test was conducted under a constant light output drive condition of mW. As a result, as shown in FIG. 2E, an increase in the drive current IOP was suppressed as compared with the conventional semiconductor laser device, and the reliability could be improved.

(Second Embodiment) FIG. 1B is a perspective view showing a semiconductor laser device according to a second embodiment. In the semiconductor laser device of this embodiment, the light emitting end face 5 is formed by etching.

This semiconductor laser device is manufactured as follows. First, the VSIS internal structure 1 is formed in the same manner as in the first embodiment. Next, as shown in FIG.
The resist 20 covers the wafer 20 excluding the portion where the light emitting end face 5 is to be formed by photolithography.

After that, as shown in FIG.
A crystal surface to be the light emitting end surface 5 is formed by dry etching such as E (reactive ion beam etching).

Next, as shown in FIG. 3C, the first embodiment
The end face growth layer 4 is grown by the MOCVD method using the same conditions as above, and the unnecessary growth portion 4a is removed.

The wafer on which the end face growth layer 4 is formed as described above is cleaved to the laser bar 21, and as shown in FIG. 3D, a dielectric for suppressing oxidation is formed on the end face growth layer 4 of the light emitting end face 5. The film 8 is vapor-deposited, and the unnecessary portion 4a is removed by etching using this as a mask.

Next, the p-side electrode 6 and the n-side electrode 7 are formed on the laser bar 21 in this state in the same manner as in Example 1, and the laser bar 21 is divided into chips, as shown in FIG. 1 (b). A window type semiconductor laser device.

Also in the semiconductor laser device of this embodiment, since the growth of the end face growth layer 4 is carried out at a low temperature of 500 ° C. or less as in the first embodiment, the characteristics of the semiconductor laser device after the formation of the end face growth layer 4 are shown. It can prevent the deterioration.

In Examples 1 and 2 above, AlGaA
Although the s-based semiconductor laser device is shown, other compounds or mixed crystal system may be used.
It can also be applied to an AlP-based semiconductor laser device.

Although the semiconductor laser device having the VSIS structure has been described, the present invention can be applied to the semiconductor laser devices having other structures. Furthermore, for the sake of simplicity, a semiconductor laser device having a double hetero structure is shown.
(Separated Confinement Heterostructure) type and GR
It can also be applied to an IN (Graded Index) -SCH type semiconductor laser device. MO is used as a method for growing the edge growth layer.
Although the CVD method is used, the same effect can be obtained by using the MBE method.

[0034]

As is apparent from the above description, in the present invention, since the end face growth layer grown on the light emitting end face of the resonator is grown at a low temperature of 500 ° C. or less, a semiconductor laser device is constructed. The internal diffusion of impurities contained in the crystal can be suppressed. Therefore, it is possible to suppress the deterioration of the characteristics of the semiconductor laser device and improve the reliability.

[Brief description of drawings]

FIG. 1A is a perspective view showing a semiconductor laser device according to a first embodiment, and FIG. 1B is a perspective view showing a semiconductor laser device according to a second embodiment.

2 (a) to 2 (d) are diagrams showing a manufacturing process of the semiconductor laser device of Example 1, and FIG. 2 (e) is a diagram showing a running time and a driving current in Example 1 and a conventional semiconductor laser device. It is a graph which shows the relationship of.

3 (a) to 3 (e) are diagrams showing a manufacturing process of the semiconductor laser device of Example 2. FIG.

FIG. 4 is a perspective view showing a conventional semiconductor laser device.

5 (a) to 5 (f) are views showing a manufacturing process of a conventional semiconductor laser device.

[Explanation of symbols]

 1 Internal Structure 2, 5 Light Emitting Edge 3 Active Layer 4 Edge Growth Layer 6 p-side Electrode 7 n-side Electrode 8 Dielectric Film 11 Substrate 12 Current Constriction Layer 13 Striped V-groove 14, 16 Cladding Layer 17 Contact Layer 20 Wafer 21 Laser bar

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Hayashi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (2)

[Claims] 1. A semiconductor laser comprising an Al-containing crystal, and an end face growth layer made of a crystal having a bandgap larger than that of the crystal forming the active layer is formed on a light emitting end face of a resonator including an active layer. A semiconductor laser device in which the end face growth layer is grown at a growth temperature of 500 ° C. or lower by a metal organic chemical vapor deposition method or a molecular beam epitaxial growth method. 2. A semiconductor laser comprising an Al-containing crystal, and an end face growth layer made of a crystal having a bandgap larger than that of the crystal forming the active layer is formed on a light emitting end face of a resonator including an active layer. A method of manufacturing a semiconductor laser device, wherein the end face growth layer is grown at a growth temperature of 500 ° C. or lower by a metal organic chemical vapor deposition method or a molecular beam epitaxial growth method.