JP3097938B2 - Surface emitting semiconductor laser - Google Patents

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.

[0002]

2. Description of the Related Art Since a surface emitting semiconductor laser is a device capable of low threshold current operation, high-density two-dimensional integrated light source or dynamic single operation, it is used for optical information processing, optical communication,
Or, it is expected as a light source for optical interconnection. Also, with the increase in communication capacity, it is very promising to form a surface emitting semiconductor laser on a Si substrate that can be highly integrated with an electronic device.

In such a surface emitting semiconductor laser, a light reflecting layer having an extremely high reflectivity is required for laser oscillation. Conventionally, on Si substrate, InP substrate, or GaAs
The light-reflecting layer of the surface emitting semiconductor laser on the s substrate has two quarters of a semiconductor multilayer film having a film thickness of 1/4 of the optical wavelength and lattice-matched on each of the substrates, for example, I on an InP substrate
nP, InGaAsP (composition of 1.3 μm) is formed by epitaxial growth, or two types of dielectrics (for example, a-
DBR (distributed Bra) in which Si / SiO ₂ ) are alternately stacked at a film thickness of １ ／ of the optical wavelength.
gg reflector).

However, in a semiconductor multilayer film constituting a surface emitting semiconductor laser, II which is lattice-matched to a substrate is used.
The difference in the refractive index between the two types of semiconductors, ie, IV group compound semiconductors, cannot be large. In particular, in the case of a semiconductor lattice-matched to InP, the refractive index difference Δn between the two kinds of semiconductors, for example, InP, I
Δn of nGaAsP (1.3 μm composition) is a low value of about 0.25.

Therefore, it is necessary to increase the logarithm of the semiconductor multilayer film in order to obtain a high reflectivity, and the total film thickness of the surface emitting semiconductor laser is limited to a short wavelength band (oscillation wavelength of 800 to 1000).
(about 10 nm) and about 20 μm in a long wavelength band, the growth time is prolonged, and the film thickness fluctuates in the growth direction, so that a desired high reflectivity is hardly obtained.

In a surface emitting semiconductor laser, the first
When the light reflection layer and the second light reflection layer are composed of only a dielectric multilayer film having a high reflectivity (99% or more), a short cavity length where a quantum size effect occurs is formed, and current can be uniformly injected. Super lattice structure (MQW: multi quantum well) with a large number of wells (about 20 wells or less)
1) It is possible to form an active layer, and a remarkable decrease in threshold current density is expected. However, in this case, the total thickness of the semiconductor constituting the cavity is about 0.5
μm, it is difficult to ensure reproducibility and reliability,
In addition, since the electrodes are close to the active layer, it is difficult to inject a spatially uniform current into the active layer.

On the other hand, conventionally, when a surface emitting semiconductor laser is formed on a Si substrate, there are the following two problems. First, since the lattice constants of the Si substrate and InP are different, high-density dislocations occur in the semiconductor film constituting the surface emitting semiconductor laser, the threshold current increases, and stable operation is hardly obtained. In addition, cracks occur when the film thickness becomes about 15 μm due to the difference in thermal expansion coefficient between the Si substrate and InP. For this reason, it was difficult to form both the first light reflection layer and the second light reflection layer with a semiconductor multilayer film.

Further, it has been difficult to fabricate a surface emitting semiconductor laser on a substrate other than a GaAs substrate, an InP substrate or a Si substrate.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface emitting semiconductor laser which can oscillate a laser even at a low threshold current and can easily oscillate continuously at room temperature.

[0010]

In order to achieve the above-mentioned object, a first aspect of the present invention is a first semiconductor multi-layer having a thickness of 1/4 of an optical wavelength, wherein two types of semiconductor layers are alternately laminated. Of the optical wavelength obtained by alternately laminating a film and two types of dielectric layers.
A first light reflection layer having a first dielectric multilayer film having a thickness of 4; an n-type cladding layer, an active layer and a p-type cladding layer sequentially provided on the first light reflection layer; A second semiconductor multilayer film provided on the p-type cladding layer and having a film thickness of 1/4 of the optical wavelength and formed by alternately laminating two types of semiconductor layers, and two types of dielectric layers are alternately formed. A second dielectric multilayer film having a film thickness of 1/4 of the optical wavelength laminated on the first dielectric multilayer film of the first light reflective layer. The film is characterized by being fused to a dielectric film of a substrate having a dielectric film on the surface.

According to a second aspect of the present invention, there is provided a first semiconductor multi-layer film having a thickness of 1/4 of an optical wavelength and two types of dielectric layers formed by alternately laminating a metal part and two types of semiconductor layers. And a first light reflection layer having a first dielectric multilayer film having a thickness of 1/4 of the optical wavelength, which is obtained by alternately laminating the first light reflection layer, and n provided sequentially on the first light reflection layer. A type cladding layer, an active layer, a p-type cladding layer, and 1/1 of the optical wavelength provided on the p-type cladding layer and formed by alternately laminating two types of semiconductor layers.
A second reflection layer having a second semiconductor multilayer film having a thickness of 1/4 of an optical wavelength and a second semiconductor multilayer film having a thickness of 4 and a dielectric layer of two types alternately laminated; And wherein the first
Wherein the metal portion of the light reflection layer is fused to the metal film of a substrate having a metal film on the surface.

[0012]

According to the present invention, a long-wavelength surface emitting semiconductor laser having a short cavity length at which a quantum size effect occurs and having a light reflection layer with high reflectivity is held in the cavity direction with high reliability. It can be manufactured. For this reason, the superlattice structure (MQW) can be used within the uniform range of current injection (about 20 wells or less) in the active layer of the surface emitting semiconductor laser of the present invention, and the threshold current of laser oscillation can be reduced. Reduction is achieved and continuous oscillation at room temperature is facilitated.

The surface emitting semiconductor laser of the present invention is
When fabricated on a substrate, an n-type cladding layer, an active layer, and a p-type cladding layer, which are lattice-matched on another substrate in advance, can reduce the dislocation density of the semiconductor film and achieve a low threshold current. It is possible to significantly increase the lifetime of a semiconductor laser.

In a short wavelength band surface emitting semiconductor laser,
By greatly shortening the epitaxial growth time according to the present invention, it is easy to suppress the fluctuation of the film thickness, and the yield can be improved.

Further, GaAs, InP,
Although it was difficult to form a surface emitting semiconductor laser having a high-quality crystal other than a Si substrate, according to the present invention,
A surface-emitting semiconductor laser can be manufactured using a substrate other than a single crystal.

[0016]

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

(Embodiment 1) FIGS. 1 to 5 show a method of manufacturing a long-wavelength surface emitting semiconductor laser according to an embodiment of the present invention in the order of steps.

First, as shown in FIG. 1, an InP buffer layer 2 and an InGaAsP layer (1.3 μm
Composition) and the InP layer are alternately composed of 4.5 pairs, the second semiconductor multilayer film (DBR layer) 3, I having a thickness of 1/4 of the optical wavelength.
n-type cladding layer 4 made of nP, InGaAsP (1.
1 μm) between the barrier layer (3 μm composition) and the well layer of InGaAs.
An MQW active layer 5 composed of 0 pairs and a p-type cladding layer 6 composed of InP constitute a λ cavity, and the InGaAsP
Layers (1.3 μm composition) and InP layers are alternately formed into 4.5 pairs of first semiconductor multilayer films (D
(BR layer) 7 is continuously epitaxially grown.

Next, as shown in FIG. 2, an SiO ₂ layer and a TiO ₂ layer are alternately formed on the first semiconductor multilayer film 7.
Two pairs are deposited to form a first dielectric multilayer film 8 having a thickness of 1/4 of the optical wavelength.

Next, as shown in FIG. 3, a SiO ₂ dielectric film 9 is formed on the surface of the substrate by depositing SiO ₂ on the surface thereof in advance, as shown in FIG. The upper end surfaces of the first dielectric multilayer film 8 are brought into close contact with each other, and they are fused together at an annealing temperature of 450 ° C. while being evacuated.

Next, as shown in FIG. 4, after polishing the InP substrate 1 to a thickness of about 100 μm, the second semiconductor multilayer film 3 is mixed with a mixed solution of HCl and H ₃ PO _4.
Etching is performed until the InGaAsP layer of No. 1 appears, and thereafter, 12 pairs of SiO ₂ layers and TiO ₂ layers are alternately deposited to form a second dielectric multilayer film 11. Here, as shown in FIG. 4, the first semiconductor multilayer film 7 and the first dielectric multilayer film 8 constitute a first light reflecting layer 12, and the second semiconductor multilayer film 3 and the second The dielectric multilayer film 11 constitutes the second light reflection layer 13.

Next, as shown in FIG. 5, the first light reflection layer 12 is etched in a columnar shape with a diameter of 50 μm up to the InGaAsP layer of the first semiconductor multilayer film 7 and made of polyimide for element isolation. After planarization by the insulating film 14, the second semiconductor multilayer film 3 of the second light reflection layer 13 is formed of InGaAs of a donut shape having an outer diameter of 48 μm and an inner diameter of 40 μm.
Etching is performed up to the upper part of the sP layer, and finally, both electrodes 15 and 16 are patterned to form a target surface emitting semiconductor laser.

When the current-light output characteristics of the long-wavelength surface emitting semiconductor laser configured as described above were measured, laser oscillation having an oscillation wavelength of 1.55 μm was confirmed at a threshold current of 55 mA. In the life test, output 5
APC operation was performed under the condition of 00 μW, and laser oscillation was confirmed up to 1000 hours.

(Embodiment 2) FIGS. 6 to 10 show a method of manufacturing a surface emitting semiconductor laser according to another embodiment of the present invention in the order of steps.

First, as shown in FIG.
A GaAs buffer layer 32, an AlGaAs layer (Al mixed crystal ratio: 0.3) and an AlAs layer are alternately formed on the second semiconductor multilayer film (DBR) having a thickness of 1/4 of the optical wavelength and consisting of 4.5 pairs.
Layer) 33, an n-type clad layer 34, A made of AlGaAs (the mixed crystal ratio of Al is gradually changed from 1 to 0.3).
1GaAs (Al mixed crystal ratio: 0.3) barrier layer and GaAs
MQW active layer 35 composed of five pairs of s well layers, AlGa
A λ cavity is constituted by a p-type cladding layer 36 made of As (the mixed crystal ratio of Al is gradually changed to 0.3 to 1), and an AlAs layer and an AlGaAs layer (a mixed crystal ratio of Al of 0.1 are used).
3) The first semiconductor multilayer film (DBR layer) 37 having a thickness of 対 of the optical wavelength and consisting of five pairs is alternately grown continuously and epitaxially.

Next, as shown in FIG. 7, 12 pairs of SiO ₂ layers and TiO ₂ layers are alternately vapor-deposited on the first semiconductor multilayer film 37 to form a film having a thickness of １ ／ of the optical wavelength. A first dielectric multilayer film 38 is formed.

Next, as shown in FIG. 8, after etching to the upper end of the AlGaAs of the first semiconductor multilayer film 37 in a donut shape, gold is deposited to form a metal part 39. Thereafter, the upper end of the first dielectric multilayer film 38 is brought into close contact with the Si substrate 41 which is the second substrate on which the electrode 40 has been formed by depositing gold / tin in advance, and annealing is performed at 400 ° C. in an H ₂ atmosphere. Perform and fuse.

Next, as shown in FIG. 9, after the GaAs substrate 31 as the first substrate is polished to a thickness of about 100 μm, the second substrate is mixed with a mixed solution of H ₂ O ₂ and NH ₄ OH.
Etching is performed until the AlGaAs layer of the semiconductor multilayer film 33 appears, and then a second dielectric multilayer film 42 is formed by alternately depositing 12 pairs of SiO ₂ layers and TiO ₂ layers. Here, as shown in FIG. 9, the first semiconductor multilayer film 37 and the first dielectric multilayer film 38 constitute a first light reflecting layer 43, and the second semiconductor multilayer film 33 and the second The dielectric multilayer film 42 constitutes the second light reflection layer 44.

Next, as shown in FIG. 10, the first semiconductor multilayer film 37 of the first light reflection layer 43 is formed to form a waveguide.
Etching is performed in a cylindrical shape having a diameter of 20 μm to form a concave portion, and SiO ₂ is deposited in the concave portion for insulation to form an insulating film 45. After etching up to the upper portion of AlGaAs of the second semiconductor multilayer film 33 of the light reflection layer 44 and insulating between elements with polyimide, finally, the electrode 46 is patterned to form a target surface emitting semiconductor laser.

When the current-light output characteristics of the surface emitting semiconductor laser configured as described above were specified, laser oscillation at an oscillation wavelength of 850 nm was confirmed at a threshold current of 5 mA. In the life experiment, APC operation was performed under the condition of an output of 500 μW, and laser oscillation was confirmed up to 1000 hours.

In this embodiment, the surface-emitting semiconductor laser is formed of a semiconductor lattice-matched on the first substrate such as an InP substrate. However, one or more layers of a semiconductor composition having different lattice constants may be provided, or a light reflection layer may be formed. It goes without saying that the same effect can be obtained even if the semiconductor composition is gradually changed in order to lower the electric resistance, or if an intermediate layer is provided between the two kinds of semiconductor compositions.

[0032]

As described above, according to the present invention,
Even if the cavity length is short enough to cause the quantum size effect, a highly reliable long-wavelength surface emitting semiconductor laser can be manufactured. Therefore, the MQW (multi quantum well) having a superlattice structure is used for the active layer. And the threshold current of laser oscillation is reduced, and continuous oscillation at room temperature is facilitated.

In the short-wavelength band surface emitting semiconductor laser, the fluctuation of the film thickness can be easily suppressed and the yield can be improved by greatly shortening the epitaxial growth time.

When a Si substrate is used as the second substrate, the dislocation density of the semiconductor constituting the cladding layer and the active layer can be reduced as compared with a long wavelength band surface emitting laser formed on the Si substrate. A low threshold current is achieved and the lifetime of the semiconductor laser can be significantly increased. In addition, it becomes possible to manufacture a surface emitting semiconductor laser other than the GaAs, InP, and Si substrates.

The surface emitting semiconductor laser of the present invention is
By being highly integrated with an electronic device on a substrate, it can be used as a light source for optical switching, optical interconnection, or optical information processing.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one step of a manufacturing process of an embodiment of a semiconductor laser of the present invention.

FIG. 2 is a longitudinal sectional view showing a step subsequent to the step shown in FIG.

FIG. 3 is a longitudinal sectional view showing a step subsequent to the step shown in FIG. 2;

FIG. 4 is a longitudinal sectional view showing a step subsequent to the step shown in FIG. 3;

FIG. 5 is a longitudinal sectional view showing a step subsequent to the step shown in FIG. 4;

FIG. 6 is a longitudinal sectional view showing one step of a manufacturing process of another embodiment of the semiconductor laser of the present invention.

FIG. 7 is a longitudinal sectional view showing a step subsequent to the step shown in FIG. 6;

8 is a longitudinal sectional view showing a step subsequent to the step shown in FIG. 7;

FIG. 9 is a longitudinal sectional view showing a step subsequent to the step shown in FIG. 8;

FIG. 10 is a longitudinal sectional view showing a step subsequent to the step shown in FIG. 9;

[Explanation of symbols]

 Reference Signs List 1 InP substrate 2 InP buffer layer 3 Second semiconductor multilayer film 4 n-type cladding layer 5 MQW active layer 6 p-type cladding layer 7 first semiconductor multilayer film 8 first dielectric multilayer film 9 dielectric on Si substrate surface Film 10 Si substrate 11 second dielectric multilayer film 12 first light reflection layer 13 second light reflection layer 14 insulating film 15 electrode 16 electrode 31 GaAs substrate 32 GaAs buffer layer 33 second semiconductor multilayer film 34 n-type Clad layer 35 MQW active layer 36 p-type clad layer 37 first semiconductor multilayer film 38 first dielectric multilayer film 39 metal part 40 electrode 41 Si substrate 42 second dielectric multilayer film 43 first light reflection layer 44 Second light reflection layer 45 Insulating film 46 Electrode

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-229688 (JP, A) JP-A-2-302085 (JP, A) JP-A-2-306682 (JP, A) JP-A-3-302 263390 (JP, A) JP-A-2-54589 (JP, A) JP-A-4-263482 (JP, A) JP-A-4-340288 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) H01S 5/00-5/50

Claims (2)

(57) [Claims] 1. An optical wavelength of a first semiconductor multilayer film having a thickness of １ ／ of an optical wavelength obtained by alternately laminating two types of semiconductor layers and an optical wavelength obtained by alternately laminating two types of dielectric layers. A first light reflection layer having a first dielectric multilayer film having a thickness of 1/4, an n-type cladding layer, an active layer and a p-type cladding sequentially provided on the first light reflection layer A second layer having a film thickness of 1/4 of the optical wavelength, which is provided on the p-type cladding layer and is formed by alternately laminating two types of semiconductor layers.
A second reflective layer having a thickness of 1/4 of the optical wavelength and a second dielectric multilayer film formed by alternately laminating a semiconductor multilayer film of two types and two types of dielectric layers. The surface emitting semiconductor laser according to claim 1, wherein the first dielectric multilayer film of the first light reflection layer is fused to the dielectric film of a substrate having a dielectric film on the surface. 2. A semiconductor device comprising: a first semiconductor multilayer film having a film thickness of １ ／ of an optical wavelength formed by alternately laminating a metal portion and two types of semiconductor layers; and two types of dielectric layers alternately laminated. Optical wavelength 1
A first light reflecting layer having a first dielectric multilayer film having a thickness of ／, an n-type cladding layer, an active layer, and a p-type cladding layer sequentially provided on the first light reflecting layer And a second layer having a thickness of １ ／ of the optical wavelength, which is provided on the p-type cladding layer and is formed by alternately laminating two types of semiconductor layers.
A second reflective layer comprising a semiconductor multilayer film and a second dielectric multilayer film having a thickness of １ ／ of the optical wavelength obtained by alternately laminating two types of dielectric layers. The surface emitting semiconductor laser according to claim 1, wherein the metal part of the light reflection layer is fused to the metal film of a substrate having a metal film on the surface.