JPH11204875A - Surface emitting laser, laser optical transmission module using it, and applied system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cheap applied system such as a laser optical transmission module, an optical interconnection, an optical fiber communication or the like where a surface emitting laser is used as a light source at a low cost by a method wherein the surface emitting laser excellent in characteristics is produced being kept high in yield and the surface emitting laser which is low in series resistance, excellent in characteristics, and capable of emitting a laser beam of long wavelengths band (1.2 to 1.6 μm). SOLUTION: A surface emitting laser is composed of an N-type GaAs substrate 1, an N-type semiconductor multilayer film reflective mirror 2, a first GaAs spacer layer 3, an active layer 4, a second GaAs spacer 5, a current constriction layer 6, a P-type GaAs current introduction layer, a regrowth interface 8, a P-type third GaAs spacer layer 9, and multilayer film reflective mirror 10. The current constriction layer 6 is formed of wide band gap semiconductor such as AlInP, AlGaInP or AlAs whose band gap is above 2e V, and an aperture layer is formed through a photolithography process and a regrowth process, whereby a surface emitting laser of this constitution can be markedly improved in yield.

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 more particularly to a surface-emitting type semiconductor laser having a so-called vertical resonator which oscillates a laser beam in a direction substantially perpendicular to a semiconductor layer constituting the device (hereinafter referred to as a vertical cavity). , Surface emitting lasers).

[0002]

2. Description of the Related Art A surface emitting laser emits laser light in a vertical direction from the surface of a substrate crystal, so that two-dimensional parallel integration is possible, and application to systems such as optical interconnection and parallel optical information processing, or optical fiber The application to communication is expected. Further, since the inspection of the element and the coupling with the optical fiber are easy, the system can be provided at low cost.
Further, by providing the current confinement layer, a current can be locally injected from a portion called an aperture, and laser oscillation can be caused in an active region with a small volume. Therefore, it is suitable for lower threshold current, that is, lower power consumption.

The use of an AlOx layer in which AlAs is selectively oxidized as a current confinement layer has recently been proposed, and a significant reduction in threshold current has been achieved. For details, see, for example, IEEE J. Select
ed Topics in Quantum Electronics, Volume 3, 893-904
Page, 1997.

[0004]

The AlOx current confinement layer is formed by etching an AlAs layer formed by a crystal growth method in a mesa shape and selectively oxidizing the AlAs layer from the periphery of the mesa to form an AlOx current confinement layer.
It is manufactured by changing into layers. The mesa central portion remaining without being oxidized in the AlAs layer becomes an aperture layer into which current is injected. In order to mass-produce a surface emitting laser with a low threshold current, it is necessary to reduce the size of the aperture layer to only a few μm and to precisely control the size. But,
The rate of oxidation of the AlAs layer is large and it is difficult to control the size of the aperture layer accurately, and a low yield is a problem in the practical use of a surface emitting laser having an AlOx current confinement layer. . Usually, GaAs layers are arranged above and below the AlAs aperture layer (and the AlOx current confinement layer). However, at the interface between the AlAs aperture layer and the GaAs layer, a hetero-barrier is generated, resulting in series resistance and deterioration of electrical characteristics.
Also, since AlOx as an insulator and GaAs as a semiconductor have a large difference in thermal expansion coefficient, physical delamination may occur at the interface between the AlOx current confinement layer and the GaAs layer, which reduces the yield of the device and the life of the device. There are problems such as shortening.

An object of the present invention is to produce a surface emitting laser having excellent characteristics at a high yield, and to provide an inexpensive laser light transmitting module and an optical interconnection using the laser as a light source, or an application system such as an optical fiber communication. It is to do. Another object is to provide a surface emitting laser having a low series resistance. As a further object, the long wavelength band (wavelength: 1.2 to 1.6μ) with excellent characteristics
m) is to provide a surface emitting laser.

[0006]

According to the present invention, there is provided an active layer for generating light on a substrate crystal, and a resonator structure in which upper and lower portions of the active layer are sandwiched between reflectors to obtain a laser beam from the light generated from the active layer. In a surface emitting laser that emits light perpendicular to the substrate crystal, a semiconductor having a band gap of 2 eV or more, such as AlInP, AlGaInP, or AlAs, a so-called wide gap semiconductor is used as a current confinement layer, The yield can be greatly improved by forming an aperture layer in the aperture (opening) provided in the current constriction layer by the opening formation) and the regrowth step (semiconductor crystal growth filling the opening). In the present specification, the term “wide-gap semiconductor” refers to a semiconductor material having a band gap (forbidden band width) of 2 eV or more, regardless of the type of the semiconductor material.
InP and AlGaInP are required to have a composition satisfying this band gap value.

On the other hand, the material of the aperture layer formed so as to fill the opening formed in the current confinement layer is, for example, a material having a smaller band gap than the current confinement layer.
GaAs or AlGaAs is preferred. Further, by forming a highly doped current introduction layer on the current confinement layer, the series resistance can be reduced. Furthermore, by using GaInNAs for the active layer, it can be applied to the 1.3 μm band or 1.55 μm band used in optical fiber communication (especially when the semiconductor layer other than the active layer is formed of GaAs, AlGaAs, AlAs, AlInP,
The active layer composition is desirable from the viewpoint of crystal growth).

With this configuration, it is possible to inject a current around the portion of the active layer facing the aperture layer, and the light generated by this is formed by a reflecting mirror facing the aperture layer through the aperture layer. Reciprocating in the resonator to generate stimulated emission light. Here, the term “reflector” refers to a film or a laminated structure of a plurality of films made of a substance having higher reflectivity than a layer (semiconductor layer) bonded to the active layer side,
The material is selected from a semiconductor or a dielectric. And
The reflectances of the reflector formed on the substrate side and the reflector formed on the opposite side of the substrate are set according to the specifications of the resonator.

The surface emitting laser of the present invention can be used in systems such as optical interconnection and optical fiber communication. In that case, it is preferable to use the surface emitting laser as a laser light transmission module packaged with an IC or an optical fiber component for driving the surface emitting laser.

The structure and manufacturing method of the surface emitting laser of the present invention,
The operation and the operation will be described with reference to FIG. In the figure, 1 is an n-type GaAs substrate, 2 is an n-type semiconductor multilayer film reflecting mirror, 3 is a first GaAs spacer layer, 4 is an active layer, and 5 is a 2G
aAs spacer layer, 6 is an AlInP current confinement layer, 7 is a p-type GaAs current introducing layer, 8 is a regrowth interface, 9 is a third GaAs spacer layer, 10 is a multilayer reflector, 11 is a p-side electrode, and 12 is an n-side. Electrodes. First, layers 2 to 7 are formed by a crystal growth method. Next, in order to form an aperture layer, a p-type GaAs current introduction layer 7, an AlInP current confinement layer 6, and a second GaAs spacer layer 5 are formed.
(A region including a portion provided for laser oscillation) is removed by etching as shown in FIG. 1 (this removes the current constriction layer from the optical axis for oscillating laser light). . Then, p
The third GaAs spacer layer 9 is produced by regrowing the type GaAs (in other words, the opening is filled with GaAs). 3rd GaAs
The portion of the spacer layer 9 sandwiched between the current confinement layers 6 becomes the aperture layer. The size of the aperture layer can be accurately controlled because it is produced by a photolithographic process. By setting the doping concentration of the aperture layer, that is, the third GaAs spacer layer 9 to about p = 1 × 10 ¹⁸ cm ⁻³ , sufficient conductivity can be obtained, and light loss with respect to laser light can be sufficiently reduced. Can be reduced to Finally, the multilayer reflector 10,
The p-side electrode 11 and the n-side electrode 12 are formed to complete the structure.

A current is injected from the p-side electrode 11 and the p-type 3G
The light is guided to the aperture layer through the aAs spacer layer 9 and the p-type GaAs current introducing layer 7. When the current flows in parallel with the current confinement layer 6, the p-type GaAs current introduction layer 7 has an extremely high resistance of p = 1 × 10 ²⁰ cm ^-3 and has a very low resistance, so that most of the current flows in this layer. Flows through. Also, the third GaAs spacer layer 9,
p-type GaAs current introduction layer 7, aperture layer, and second GaAs
Since the spacer layers 5 are all made of GaAs, no series resistance occurs due to the hetero barrier. Therefore, there is almost no voltage drop between the p-side electrode 11 and the active region immediately below the aperture. Further, since the series resistance of the n-type semiconductor multilayer mirror 2 is small, a surface emitting laser having a very low element resistance can be manufactured.

Here, the function of current confinement by AlInP will be described with reference to FIG. AlInP can be lattice-matched to a GaAs substrate and can provide high-quality crystals, so that optical deterioration such as scattering of laser light does not occur. Fig. 3 (a) shows n-type
FIG. 3B shows the band lineup of AlInP and p-type GaAs, and FIG. 3B shows the lineup of p-type AlInP and p-type GaAs. Even if holes indicated by + in the figure move from GaAs to AlInP, they cannot move due to a heterobarrier in the valence band (line drawn downward in the figure). That is, no current flows. The size of the hetero barrier is about 2 eV when AlInP is n-type, and is about 0.4 eV or more even when AlInP is p-type. In the structure of the present invention, as described above, almost no voltage drop occurs from the p-side electrode 11 to the active region immediately below the aperture.
Although the n-type is preferable, the p-type has a sufficiently large hetero-barrier even in the case of the p-type and functions as a current confinement layer for the p-type GaAs current introduction layer 7. As a material for the current confinement layer, the same effects as those of the present invention can be obtained as long as the band gap formed on the GaAs substrate is a wide gap semiconductor of 2 eV or more. For example, AlGaInP or AlAs may be used. The second GaAs spacer layer 5 is preferably a p-type or non-doped layer in order to prevent electrons from flowing into the AlInP current confinement layer 6.
In the present invention, since the current is constricted by the hetero barrier between the current introducing layer and the wide gap semiconductor, the surface emitting laser having a lower operating voltage is more suitable. That is, it is better that the active layer 4 has a small band gap and an oscillation wavelength longer than 0.85 μm. Specifically, GaInAs and GaInNAs are suitable as the material of the active layer. When the active layer is made of GaInNAs, a surface emitting laser having excellent characteristics in a long wavelength band can be manufactured. If the oscillation wavelength is shorter than 0.85μm,
The same effect can be obtained by replacing the GaAs layer with the AlGaAs layer in the above description.

Further, since the current confinement layer 6 is a semiconductor, it has substantially the same thermal expansion coefficient as the upper and lower GaAs layers, and has a feature that the element life is long without separation occurring at the hetero interface.

Therefore, the surface emitting laser of the present invention has excellent characteristics and a long life, and has a high yield.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to Examples 1 and 2 and FIGS.

<Embodiment 1> In the present embodiment, the emission wavelength is set to 0.
A 98 μm surface emitting laser was manufactured. FIG. 1 shows a structural sectional view. 1 is an n-type GaAs substrate (n = 1 × 10 ¹⁸ cm ⁻³ , thickness: d = 100μ)
m) and 2 are n-type GaAs / AlAs semiconductor multilayer mirrors (n = 1 × 10 ¹⁸
cm ^-3 ), 3 is an n-type first GaAs spacer layer (n = 1 × 10 ¹⁶ cm ^-3 , d == wavelength thickness in semiconductor), 4 is a non-doped GaInAs / GaAs strained quantum well active layer, 5 Is a p-type second GaAs spacer layer (p = 1 × 10 ¹⁶ cm
^-3 , d = 1/8 wavelength thickness in semiconductor), 6 is an n-type Al _0.5 In _0.5 P current confinement layer lattice-matched to the GaAs substrate (n = 1 × 10 ¹⁷ cm ^-3 , d = semiconductor 7 is a p-type GaAs current introduction layer (p = 1 × 10
²⁰ cm ^-3 , d = 1/2 wavelength thickness in semiconductor), 8 is the regrowth interface, 9
Is a p-type third GaAs spacer layer (p = 1 × 10 ¹⁸ cm ⁻³ ), 10 is a dielectric multilayer mirror, 11 is a p-side electrode, and 12 is an n-side electrode. As the active layer 4, a strained quantum well layer having an effective band gap of 1.27 eV (wavelength: 0.98 μm) was used in which three 7-nm-thick GaInAs well layers were separated by a 10-nm-thick GaAs barrier layer. The semiconductor multilayer reflector 2 was formed by alternately stacking a 屈折 wavelength-high refractive index GaAs layer in a semiconductor and a / 4 wavelength low refractive index AlAs layer in a semiconductor. To increase the reflectivity to 99.5% or more, the number of reflective mirror layers
0 pairs.

The semiconductor layer 2-7 was grown continuously in a high vacuum of 1 × 10 ⁻⁵ Torr using an actinic ray epitaxy apparatus. Metals such as aluminum, gallium and indium were used as group III raw materials, and phosphine and arsine were used as group V raw materials. Si, Be and CBr ₄ were used as dopant raw materials. The wafer is taken out, and a p-type GaAs current introducing layer 7 and a
The n-type AlInP current confinement layer 6 was selectively and sequentially etched with a sulfuric acid-based etching solution and a hydrochloric acid-based etching solution to form an aperture having a diameter of 3 μm. The wafer is returned to the actinic ray epitaxy apparatus, and a part of the p-type second GaAs spacer layer 5 is etched by 10 nm using tris-dimethylaminoarsine as shown in FIG. 1 to form a regrowth interface 8 having good crystallinity. did. Thereafter, the third GaAs spacer layer 9 was regrown. The portion of the third GaAs spacer layer 9 sandwiched between the current confinement layers 6 becomes an aperture layer. The aperture layer is
The size can be accurately controlled because it is produced by a photolithographic process. The thickness of the third GaAs spacer layer 9 is
The thickness of the spacer layer 5 was adjusted to 3 + 1/4 wavelength in the semiconductor, and finally a 3.5-wavelength resonator was formed together with the first GaAs spacer layer 3 (the growth rate of the third GaAs spacer layer 9 was:
It is the same on the regrowth interface 8 and the p-type GaAs current introduction layer 7). Since the portion outside the aperture layer is out of the resonance condition, laser oscillation does not occur, and a single transverse mode oscillation is obtained. Inner diameter 10μm outer diameter 15μ by lift-off method
After forming the ring-shaped p-side electrode 11 of m, the dielectric multilayer film reflecting mirror 10 was formed by the sputtering evaporation method. The dielectric multilayer mirror 10 is formed by alternately stacking a high-refractive-index amorphous Si layer having a quarter-wave thickness in a dielectric and a low-refractive-index SiO ₂ layer having a quarter-wave thickness in a dielectric. Produced. In order to make the reflectance 99% or more, the number of layers was set to 5 pairs. In the present embodiment, a material system of an amorphous Si layer and a SiO ₂ layer was used for the dielectric multilayer reflector of the surface emitting laser, but the dielectric multilayer reflector has high refractive index layers and low refractive index layers alternately laminated. SiN and SiO ₂ ,
Other material systems such as amorphous Si and SiN or TiO ₂ and SiO ₂ may be used. Thereafter, as shown in FIG. 1, the dielectric multilayer reflecting mirror 10 is formed by Cl-based reactive ion beam etching.
Was etched to expose the p-side electrode 11. Finally, an n-side electrode 12 was formed.

When a current was injected into the surface emitting laser,
Laser oscillation was performed at a threshold current of 10 μA. The laser light is emitted from the dielectric multilayer mirror and has an oscillation wavelength of 0.
It was 98 μm. The surface emitting laser has a long element life of 100,000 hours or more. Further, the yield on a 3-inch wafer was as high as 80% or more.

<Embodiment 2> In this embodiment, the emission wavelength is 1.
A 3 μm surface emitting laser was produced. FIG. 2 shows a cross-sectional view of the structure. 21 is an n-type GaAs substrate (n = 1 × 10 ¹⁸ cm ⁻³ , d = 300 μm),
22 is an n-type GaAs / AlInP semiconductor multilayer film reflecting mirror (n = 1 × 10 ¹⁸ c
m- ³ ), 23 is a non-doped first GaAs spacer layer (d = 1/2 wavelength thickness in a semiconductor), 24 is a non-doped GaInNAs / GaAs strained quantum well active layer, 25 is a non-doped second GaAs spacer layer (d = 26 is the p-type Al _0.3 lattice-matched to the GaAs substrate.
Ga _0.2 In _0.5 P current confinement layer (p = 1 × 10 ¹⁶ cm ⁻³ , d = 3/8 wavelength thickness in semiconductor), 27 is a p-type GaAs current introduction layer (p = 1 × 10 ¹⁹ c
m- ³ , d = one wavelength thickness in semiconductor), 28 is the regrowth interface, 29 is p
Type 3rd GaAs spacer layer (p = 1 × 10 ¹⁸ cm ^-3 ), 30 is non-doped
A GaAs / AlInP semiconductor multilayer film reflecting mirror, 31 is a p-side electrode, and 32 is an n-side electrode. The active layer 24 has an effective thickness of 0.95 eV (wavelength: 1.0 nm) in which one 7 nm thick GaInNAs well layer is sandwiched between 10 nm thick GaAs barrier layers.
A strained quantum well layer having a band gap of 3 μm) was used.
The semiconductor multilayer reflector 22 is composed of a high refractive index GaAs layer having a quarter wavelength thickness in the semiconductor and a low refractive index GaAs layer having a quarter wavelength thickness in the semiconductor.
Al _0.5 In _0.5 P layers lattice-matched to the substrate were alternately stacked.
In order to make the reflectivity 99.5% or more, the number of laminated reflective mirror layers was set to 20 pairs.

The semiconductor layers 22-27 were grown continuously in a vacuum of 50 Torr using a metal organic vapor phase epitaxy apparatus. Metals such as trimethylaluminum, trimethylgallium and trimethylindium were used as group III raw materials, and ヂ methylhydrazine, phosphine and arsine were used as group V raw materials. As a dopant material, ヂ silane and ヂ methylzinc were used. The wafer is taken out and subjected to a photolithographic process, as shown in FIG.
aAs current introduction layer 27, p-type AlInP current confinement layer 26, and second Ga
A part of the As spacer layer 25 was etched with a bromine-based etchant to form an aperture having a diameter of 5 μm. The wafer was returned to the metal organic vapor phase epitaxy apparatus, and a portion of the second GaAs spacer layer 25 was further etched by 10 nm using HCl to form a regrowth interface 28 having good crystallinity. After that, the third GaAs spacer layer 29 was regrown. The portion of the third GaAs spacer layer 29 interposed between the current confinement layers 26 becomes an aperture layer. The size of the aperture layer can be accurately controlled because it is produced by a photolithographic process. 3G
The thickness of the aAs spacer layer 29 was set to 3.5 wavelength in the semiconductor in accordance with the thickness of the first GaAs spacer layer 25, and finally a four-wavelength resonator was formed in combination with the GaAs spacer layer 23. Since the portion outside the aperture layer is out of the resonance condition, laser oscillation does not occur, and a single transverse mode oscillation is obtained. Subsequently, a non-doped GaAs / AlInP semiconductor multilayer mirror 30 was grown. The semiconductor multilayer mirror 30
A quarter-wavelength high-refractive-index GaAs layer and an AlInP layer lattice-matched with a quarter-wavelength low-refractive-index GaAs substrate in a semiconductor were alternately stacked. In order to make the reflectivity 99% or more, the number of laminated mirror layers was set to 15 pairs. Thereafter, as shown in FIG. 2, the outside of the semiconductor multilayer reflector 10 was etched to the second GaAs spacer layer 29 using a bromine-based etchant. Finally, a ring-shaped p-side electrode 31 and an n-side electrode 32 having an inner diameter of 7 μm and an outer diameter of 15 μm were formed.

When a current was injected into the surface emitting laser,
Laser oscillation was performed at a threshold current of 100 μA. The laser beam is emitted from the dielectric multilayer mirror, and the oscillation wavelength at room temperature is
1.3 μm. The surface emitting laser has a long element life of 100,000 hours or more. Further, the yield on a 3-inch wafer was as high as 70% or more. The above performance is very excellent as a long wavelength band surface emitting laser.

[0022]

According to the present invention, a wide gap semiconductor having a band gap of 2 eV or more, such as AlInP, AlGaInP, or AlAs, is used as a current confinement layer, and an aperture layer is formed by a photolithographic process and a regrowth process. Can be greatly improved, and a large number of surface emitting lasers having excellent characteristics and long life can be provided at low cost. Therefore, the surface emitting laser can be used in a laser light transmission module and an application system such as optical interconnection or optical fiber communication.

[Brief description of the drawings]

FIG. 1 is a sectional view of a surface emitting laser according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a surface emitting laser according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a band lineup of n-type AlInP and p-type GaAs (a) and a band lineup of p-type AlInP and p-type GaAs (b).

[Explanation of symbols]

1 ... n-type GaAs substrate, 2 ... n-type semiconductor multilayer mirror, 3 ... n-type
1 GaAs spacer layer, 4 ... active layer, 5 ... p-type second GaAs spacer layer, 6 ... AlInP current confinement layer, 7 ... p-type GaAs current introduction layer, 8 ...
Regrowth interface, 9 ... p-type third GaAs spacer layer, 10 ... multilayer reflector, 11 ... p-side electrode, 12 ... n-side electrode.

Claims (10)

[Claims] An active layer for generating light on a substrate crystal, and a resonator structure in which upper and lower portions of the active layer are sandwiched between reflecting mirrors to obtain a laser beam from the light generated from the active layer; A vertical cavity surface emitting laser that emits light perpendicularly to the surface emitting laser, comprising a current confinement layer made of a wide gap semiconductor having a band gap of 2 eV or more. 2. An active layer for generating light on a GaAs substrate crystal, and a resonator structure in which upper and lower portions of the active layer are sandwiched between reflectors to obtain a laser beam from the light generated from the active layer, A surface emitting laser that emits light perpendicular to a crystal, comprising: a current confinement layer made of a wide gap semiconductor having a band gap of 2 eV or more; and an aperture layer made of GaAs or AlGaAs. 3. The surface emitting laser according to claim 1, wherein a highly doped current introducing layer is formed on the current confining layer. . 4. The surface emitting laser according to claim 1, wherein said current confinement layer is one of a group selected from the group consisting of AlInP, AlGaInP and AlAs. laser. 5. The surface emitting laser according to claim 1, wherein said active layer is made of GaInAs or GaInNAs.
A surface emitting laser characterized in that a surface emitting laser is used. 6. The surface emitting laser according to claim 1, wherein a wavelength of the laser light is longer than 0.85 μm. 7. The surface emitting laser according to claim 1, wherein a wavelength of the laser light is 1.3 μm band or 1.55 μm used in optical fiber communication.
A surface emitting laser characterized by being in a band. 8. A laser light transmission module, wherein the surface emitting laser according to claim 1 is used as a light source. 9. An optical fiber communication system, wherein the surface emitting laser according to claim 1 is used as a light source. 10. An optical interconnection system, wherein the surface emitting laser according to claim 1 is used as a light source.