JPH08340146A - Surface emitting type semiconductor laser - Google Patents

Abstract

PURPOSE: To provide a long-wavelength band surface emitting type semiconductor laser, which oscillates in a continuous operation in a low threshold current and has a high reliability, by a method wherein a semiconductor multilayer reflecting mirror, which is high in reflectivity and does not contain Al elements, is realized. CONSTITUTION: A long-wavelength band laminated structure, which consists of an InGaAsP layer and an InP layer and has an active layer 5 which transmits a laser beam of a wavelength in the range of a wavelength of 1.25 to 1.65μm, and a semiconductor multilayer reflecting mirror 2 consisting of a combination of an InGaP layer and a GaAs layer or a combination of an InGaAsP layer and a GaAs layer are integrally constituted by a direct bonding system. Accordingly, a surface emitting type semiconductor laser, which has the semiconductor multilayer reflecting mirror which is high in reflectivity and does not contain chemically very active Al elements, and generates a laser beam of a wavelength of 1.25 to 1.65μm can be provided. As a result, the realization of the mirror 2 has an effect to the the improvement of the reliability of the long-wavelength band surface emitting type semiconductor laser, which oscillates in a continuous operation a low threshold current.

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 Regarding conventional long-wavelength surface emitting semiconductor lasers, IEE, Photonics Technology Letter, Vol. 6, No. 3, No. 31 (1994).
Pages 7 to 319 [IEEE Photonics Technology Lett
ers, vol. 6, No. 3 pp. 317-319 (1994)]. Uo
Mi et al., and a long-wavelength surface-emitting type semiconductor laser formed by direct bonding is described in Applied Physics Letters, vol. 64, No. 12 (1994), pages 1463 to 1465. . 64, No.
12 pp. 1463-1465 (1994)] J. J. Dudley et al.

[0003]

The 1.3 μm band and 1.55 μm band long-wavelength surface-emitting type semiconductor lasers of the prior art described above have the following problems. Up to now, room temperature (25 ° C) of long-wavelength surface emitting semiconductor lasers
No continuous operation has been obtained, and this is mainly due to the low reflectance of the multilayer-film reflective mirror forming the resonator. For example, in the 1.3 μm band, a candidate for a semiconductor multilayer film reflection mirror has been a combination of InP and InGaAsP so far, and an InGaAsP quaternary layer having a composition wavelength of 1.15 μm is used to reduce light absorption in the reflection mirror. Becomes However, the refractive indices of InP and InGaAsP at this time are 3.21 and 3.33, respectively, and the difference between the refractive indices is 0.1.
It is extremely small as 2, and it is necessary to form a semiconductor multilayer film of about 80 cycles in order to obtain a reflectance of 99% or more. However, the reflectance is 99 due to the increase of the optical absorption coefficient due to internal light absorption and scattered light loss due to the introduction of impurities into the semiconductor multilayer film.
You cannot increase to%.

On the other hand, as described in the above-mentioned first document, when the multilayer film reflecting mirror of the combination of dielectric / Si is used, it is necessary to remove the InP substrate of the surface emitting semiconductor laser section. , Not to mention the complexity of the manufacturing process,
Not suitable for two-dimensional integration.

On the other hand, as described in the above-mentioned second document, GaAs / A formed on a GaAs substrate.
A long wavelength band in which a semiconductor multilayer film reflecting mirror of 1As (refractive index difference: about 0.45) is integrated by a direct bonding method with an InGaAsP / InP laminated structure having a surface emitting active layer that emits light in a long wavelength band. Surface emitting semiconductor lasers have been reported. However, since AlAs is chemically very active and adversely affects the adhesion itself, there is a problem that the reliability of the element is lowered because it contains an Al element.

An object of the present invention is to realize a semiconductor multi-layer reflecting mirror having a high reflectivity and containing no Al element, so as to continuously oscillate at a low threshold current and to have a high reliability in a long wavelength band. An object is to provide a surface emitting semiconductor laser.

[0007]

The above object is to provide a laminated structure of InGaAsP / InP long wavelength band having an active layer in which the wavelength of laser light is in the range of 1.25 to 1.65 μm, and InGaP and GaAs. Combination or InGa
This is achieved by integrating a semiconductor multi-layered film reflecting mirror made of a combination of AsP and GaAs by a direct bonding method. In particular, the active layer is formed in a quantum well structure with a small number of co-layers, the semiconductor multilayer film reflecting mirror and the multilayer film reflecting mirror sandwiching the active layer are opposed to each other as a dielectric multilayer film reflecting mirror, and laser light is applied to a semiconductor This is achieved by emitting light from the substrate side. Further, the present object is achieved by a structure having at least a pair of electrodes for injecting a current into the active layer, in addition to the above-mentioned means, and in which a current does not pass directly through the bonding interface.

[0008]

The function of the present invention will be described below.

The refractive indices of InGaP and GaAs are about 3.1 and 3.4, respectively, in the long wavelength band, and the difference in the refractive index between them is 0.3, which is slightly smaller than that of the GaAs / AlAs system, but the number of periods 27, 30, and 35, the semiconductor multilayer film reflectances are 99.0%, 99.5%, and 99.7, respectively.
%, It was possible to obtain a high reflectance, so it worked effectively as a resonator for laser oscillation. Further, since it does not contain a chemically active Al element, the reliability of the device can be dramatically improved. Furthermore, the strength of the direct bonding itself was increased. In particular, by using a quantum well active layer structure, by using a dielectric multilayer mirror as the multilayer mirror on the other side, and by emitting laser light from the semiconductor substrate side, more reliable and flip A surface-emitting type semiconductor laser capable of two-dimensional integration by chip bonding can be realized. Further, by making the structure such that the current injected into the active layer does not pass through the adhesive interface, it is possible to reduce the influence of heat generation due to the voltage drop at the adhesive interface, which is further effective for higher reliability.

[0010]

EXAMPLES Examples of the present invention will be described below with reference to FIGS.

[Embodiment 1] FIG. 1 shows the present invention at 1.3 μm.
It is applied to a band-emission type semiconductor laser. n-G
An n-type semiconductor multilayer film reflection mirror having a periodic structure (35 periods) in which n-InGaP and n-GaAs are alternately laminated on an aAs substrate 1 at a thickness of 1/4 times the oscillation wavelength in each medium. 2 is formed by a metal organic chemical vapor deposition method. Next, on the n-InP substrate, the p-InGaAsP contact layer 3, the p-InP clad layer 4, and the film thickness of 0.1 μm.
InGaAsP active layer (composition wavelength: 1.3 μm) 5, n
The InP clad layer 6 is sequentially formed by the metal organic chemical vapor deposition method. After that, the semiconductor multilayer film reflecting mirror 2 and the n-InP
20 g /
A weight of about cm ² was put on and introduced into a thermal annealing furnace. In the furnace, while flowing hydrogen gas, the temperature was raised to 600 ° C. and left for 30 minutes for direct bonding. Next, n-InP
The substrate was removed by selective etching. After that, a convex light emitting region (diameter 10 μm) reaching the semiconductor multilayer film reflecting mirror 2 is formed by etching, flattened by the SiO 2 film 7 and the polyimide film 8, and then the ring-shaped p-side electrode 9,
Periodic structure in which TiO 2 films and SiO 2 films are alternately laminated with a thickness of ¼ times the oscillation wavelength in each medium (6
After forming the dielectric film multilayer mirror 10 having
The side electrode 11 was formed.

The prototype device is
The laser beam 12 oscillates with a threshold current of 2 mA and is emitted from the dielectric film multilayer film reflecting mirror 10 side. In addition, the adhesive strength is sufficient, and since the Al element is not included in the region where the laser light propagates, the reliability of the device is extremely high, and the temperature is 85 ° C. 2 mW.
In the constant light output life test, an estimated life of 100,000 hours or more was obtained.

[Embodiment 2] FIG. 2 is a view showing that the present invention is applied to a 1.55 μm surface-emitting type semiconductor laser having an active layer of a quantum well structure. n on the n-GaAs substrate 1
N-type semiconductor multilayer film reflecting mirror 13 having a periodic structure (30 periods) in which -InGaP and n-GaAs are alternately laminated with a thickness of about 1/4 times the oscillation wavelength in each medium.
Are formed by a metal organic chemical vapor deposition method. In this reflecting mirror, a film thickness of 10 is provided between n-InGaP and n-GaAs.
nm n-InGaAsP was inserted to reduce the electric resistance. Therefore, n-InGaP / n-InGaAs
The thickness is 1/2 times the oscillation wavelength in the medium in one period of P / n-GaAs. Next, an emission wavelength of 1 to 5 consisting of a p-InGaAsP contact layer 3, a p-InP cladding layer 4, an InGaAs quantum well layer with a thickness of 7 nm, and an InGaAsP barrier layer with a thickness of 10 nm is set on a p-InP substrate. Multiple quantum well active layer 1 of 0.55 μm band
4. The n-InP cladding layer 6 is sequentially formed by the metal organic chemical vapor deposition method. Then, the semiconductor multilayer film reflecting mirror 13 and n
-The surface of the InP clad layer 6 is face-to-face overlapped,
A weight of about 10 g / cm ² was put on and introduced into the thermal annealing furnace. In the furnace, while flowing hydrogen gas, the temperature was raised to 620 ° C. and left for 20 minutes for direct bonding. Then p-I
The nP substrate was removed by selective etching. Then, the semiconductor multilayer film reflecting mirror 13 is formed by reactive ion etching.
After forming a convex light emitting region (diameter: 7 μm) reaching to, and flattening with the polyimide film 8, the amorphous Si film and the SiO 2 film are 1 / th of the oscillation wavelength in each medium.
After forming the dielectric film multilayer mirror 15 and the p-side electrode 9 having a periodic structure (5 periods) in which quadruple thicknesses are alternately laminated, the window-side n-side electrode 11 is formed.

The prototype device is
With the introduction of the quantum well structure, the laser beam 12 oscillates with a threshold current of 0.5 mA, and the laser beam 12 is emitted from the n-GaAs substrate 1 side. Furthermore, since the element in which the laser light propagates does not contain an Al element, the reliability of the device is extremely high, and an estimated life of 100,000 hours or more was obtained in a constant light output life test of 85 ° C. and 4 mW.

[Embodiment 3] FIG. 3 is a diagram in which the present invention is applied to a 1.55 μm band surface emitting semiconductor laser having an active layer of a strained quantum well structure. On the p-GaAs substrate 16, p-InGaAsP (composition wavelength 0.75 μm) and p
−GaAs is 1/1 of the oscillation wavelength in each medium
A p-type semiconductor multilayer film reflecting mirror 17 having a periodic structure (35 periods) in which quadruple thicknesses are alternately laminated is formed by a metal organic chemical vapor deposition method. Then, n-In is formed on the p-InP substrate.
GaAs etch stop layer, n-InP clad layer 6,
InGaAs with a film thickness of 5 nm and a strain amount Δa / a of + 0.9%
A strained superlattice active layer 14 having a light emission wavelength of 1.55 μm and a p-InP clad layer 4 having a 5 to 30 periodic structure of a P strained quantum well layer and an InGaAsP barrier layer having a thickness of 10 nm, and a p-InP clad layer 4 are sequentially grown by metal organic chemical vapor deposition. Formed by. Thereafter, the semiconductor multilayer film reflecting mirror 17 and the surface of the p-InP clad layer 4 were placed face to face with each other, and a weight of about 10 g / cm ^{2 was} placed thereon, and they were introduced into the thermal annealing furnace. In the furnace, while flowing hydrogen gas, the temperature was raised to 630 ° C. and left for 40 minutes for direct bonding. Next, the p-InP substrate and the n-InGaAs etch stop layer were removed by selective etching. Further, on the n-GaAs substrate, the n-InGaP etch stop layer, the n-GaAs contact layer 18, and the n-InGaP are formed.
And n-GaAs with a thickness of 1/4 times the oscillation wavelength in each medium, stacked alternately (30 cycles)
The n-type semiconductor multilayer film reflecting mirror 13 made of is formed by a metal organic chemical vapor deposition method. After that, the semiconductor multilayer film reflecting mirror 1
The surface of 3 and the surface of the n-InP clad layer 6 were placed facing each other, and a weight of about 20 g / cm ² was placed thereon, and the surface was introduced into a thermal annealing furnace. While flowing hydrogen gas in the furnace, 63
The temperature was raised to 0 ° C. and the mixture was left for 40 minutes for direct bonding. Next, the n-GaAs substrate and the n-InGaP etch stop layer were removed by selective etching. Next, a p-type semiconductor multilayer film reflecting mirror 17 is formed by reactive ion beam etching.
Etching until the surface is reached, the convex light emitting area (5
μm × 5 μm), and then planarized by the polyimide film 8 to form an n-side electrode 11 and a window-opening p-side electrode 9.

The prototype device was tested at room temperature under continuous operation.
Threshold current of 0.08mA due to introduction of strained quantum well structure
The laser light 12 is emitted from the p-GaAs substrate 16 side. Furthermore, since the element in which laser light propagates does not contain Al element, the reliability of the device is extremely high, and
In the mW constant light output life test, an estimated life of 300,000 hours or more was obtained.

[Embodiment 4] FIG. 4 shows the present invention applied to a 1.3 μm band surface emitting semiconductor laser on a Si substrate. It has a periodic structure (35 periods) in which p-InGaAsP (composition wavelength 0.75 μm) and p-GaAs are alternately laminated on the p-GaAs substrate with a thickness of ¼ times the oscillation wavelength in each medium. The p-type semiconductor multilayer film reflecting mirror 17 is formed by a metal organic chemical vapor deposition method. After that, the semiconductor multilayer film reflecting mirror 17 and the surface of the Si substrate 19 were face-to-face overlapped with each other, and a weight of about 50 g / cm ² was placed thereon, and the resultant was introduced into the thermal annealing furnace. In the furnace, the temperature was raised to 680 ° C. while flowing hydrogen gas and phosphine gas, and left for 40 minutes for direct bonding. Next, the p-GaAs substrate was removed by selective etching. After that, a multilayer structure including the active layer 5 and the n-type semiconductor multilayer film reflecting mirror 13 is formed by the same steps as in Example 3, and then the surface of the p-type semiconductor multilayer film reflecting mirror 17 is formed by reactive ion beam etching. Etching until reaching, convex light emitting area (5μm × 8μm)
After the formation, a polyimide film 8 was used to flatten the film, and an n-side electrode 11 and a p-side electrode 9 were formed on the p-GaAs layer.

The prototype device is
It oscillates with a threshold current of 0.15 mA, and the laser light 12 is Si.
The light is emitted from the substrate 19 side. A in the area where the laser light propagates
Since the element is not included, the reliability of the device is extremely high.
In a constant light output life test at 5 ° C and 1 mW, 200,000
Got an estimated lifetime of over an hour.

Although only a single element is shown in the above embodiments, it can be applied to a one-dimensional array and a two-dimensional array, and an array element having uniform characteristics was obtained.

[0020]

According to the present invention, a semiconductor multi-layered film reflecting mirror made of a combination of InGaP and GaAs or a combination of InGaAsP and GaAs is integrated by a direct bonding method, so that a high reflectance and a very high chemical efficiency can be obtained. It is possible to provide a surface-emitting type semiconductor laser having a semiconductor multi-layer reflecting mirror that does not contain active Al element and the wavelength of laser light is 1.25 to 1.65 μm. As a result, it is effective for improving the reliability of the long-wavelength surface-emitting type semiconductor laser that continuously oscillates at a low threshold current.

[0021]

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of the present invention.

FIG. 2 is a structural diagram showing an embodiment of the present invention.

FIG. 3 is a structural diagram showing an embodiment of the present invention.

FIG. 4 is a structural diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... n-GaAs substrate 2,13 ... n-type semiconductor multilayer film reflecting mirror 4 ... p-InP clad layer 5,14 ... active layer 6 ... n-InP clad layer 8 ... polyimide film 10, 15 ... Dielectric film multilayer mirror 17 ... P-type semiconductor multilayer film mirror 19 ... Si substrate.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Misuzu Sagawa 1-280 Higashi Koikeku, Kokubunji City, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Kiyohisa Hiramoto 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory

Claims (9)

[Claims] 1. A resonator structure having at least an active layer for generating light and a semiconductor multilayer film reflecting mirror for obtaining laser light from the generated light on a semiconductor substrate, wherein the wavelength of the laser light is 1. In the surface-emitting type semiconductor laser having a range of 0.25 to 1.65 μm, the semiconductor multilayer film reflecting mirror is made of InGa.
Combination of P and GaAs, or InGaAsP and Ga
A surface-emitting type semiconductor laser characterized by being composed of a combination of As. 2. A surface having a resonator structure including, on a semiconductor substrate, at least an active layer for generating light, a clad layer for confining the light, and a semiconductor multilayer film reflecting mirror for obtaining laser light from the generated light. In the light emitting semiconductor laser, the active layer is made of an InGaAsP-based material, the cladding layer is InP, and the semiconductor multilayer film reflecting mirror is InG.
Combination of aP and GaAs, or InGaAsP and G
A surface-emitting type semiconductor laser comprising a combination of aAs. 3. The surface emitting semiconductor laser according to claim 1, wherein the surface emitting semiconductor laser has a direct adhesive interface between the semiconductor multilayer film reflecting mirror and the layer including the active layer. laser. 4. The surface emitting semiconductor laser according to claim 1, wherein the semiconductor substrate is GaAs.
A surface-emitting type semiconductor laser characterized by: 5. A surface-emitting type semiconductor laser according to claim 1, wherein the semiconductor substrate is Si. 6. A surface-emitting type semiconductor laser according to claim 1, wherein the active layer is formed of a quantum well structure having a small number of co-layers. 7. The surface-emitting type semiconductor laser according to claim 1, wherein the semiconductor multi-layered film reflecting mirror and the multi-layered film reflecting mirror facing the active layer are dielectric multi-layered film reflecting mirrors. A surface-emitting type semiconductor laser characterized by being present. 8. A surface-emitting type semiconductor laser according to claim 1, wherein the laser light is emitted from the semiconductor substrate side. 9. The surface emitting semiconductor laser according to claim 1, further comprising at least a pair of electrodes for injecting a current into the active layer, wherein no current passes through the direct bonding interface. A surface-emitting type semiconductor laser having a structure.