JP3243772B2 - 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 polarization control of a surface emitting semiconductor laser for emitting light in a direction perpendicular to a substrate. It is possible to provide a light source.

[0002]

2. Description of the Related Art As is well known, a surface emitting laser operates at a low threshold, is capable of high-speed modulation and large-scale two-dimensional integration, and is expected as a device constituting an optical communication and optical information processing system. Have been.

FIG. 6 shows a schematic sectional structure of a conventional surface emitting laser. 6A shows a case where a semiconductor multilayer film is used as a reflection film, FIG. 6B shows a case where a dielectric multilayer film is used as a reflection film, and FIG. 6C shows a case where a metal film is used as a reflection mirror. Are shown, respectively. That is,
The structure shown in FIG. 6A is a structure in which an active layer 2 is sandwiched between semiconductor multilayer films 1 and 3. In the structure shown in FIG. 6B, the dielectric multilayer films 4 and 10 sandwich the stack of the contact layer 5, the clad layer 6, the active layer 7, the clad layer 8, and the InGaAsP layer 9 in this order from the top. Structure. Further, the structure shown in FIG. 6C also has a contact layer 12, a cladding layer 13, an active layer 14,
It has a structure in which a metal film 11 and 17 sandwich the upper and lower portions of a stack composed of the cladding layer 15 and the InGaAsP layer 16. There is also a surface emitting laser composed of a combination of these reflecting mirrors.

However, these surface-emitting lasers have no structure for controlling the plane of polarization, and the plane of polarization has changed depending on the current injection level for each chip or even in the same chip. Therefore, it has been difficult to use it in a measurement system having polarization plane dependency and to use it in an array.

[0005]

SUMMARY OF THE INVENTION The present invention has been proposed in order to improve the above-mentioned drawbacks. It is an object of the present invention to fix a polarization plane in an arbitrary direction and to obtain a stable polarization without being influenced by an injection current level. An object of the present invention is to provide a surface emitting semiconductor laser having a polarization plane.

[0006]

In order to solve the above-mentioned problems, the present invention provides a surface emitting device having a structure in which a resonator is provided in a direction perpendicular to a substrate surface and an active layer is sandwiched between reflectors above and below an active layer. In the semiconductor laser, a position is continuous in a predetermined first direction inside one or both of the reflecting mirrors, between the reflecting mirror and the active layer, and at any position outside the reflecting mirror. And a discrete grid-like metal film in a second direction perpendicular thereto.

That is, a surface emitting semiconductor laser according to a first aspect of the present invention is a surface emitting semiconductor laser having a resonator perpendicular to a substrate surface and having a structure in which an active layer is sandwiched between upper and lower reflectors. A grid-like metal body that is continuous in a predetermined first direction but is discrete in a second direction perpendicular to the first direction is located inside the reflecting mirror located in the optical path of the oscillation light. Characterized by being arranged in

Further, the surface emitting semiconductor laser according to claim 2 is
A surface emitting semiconductor laser having a resonator perpendicular to a substrate surface and having a structure in which an active layer is sandwiched between reflectors above and below an active layer. The semiconductor laser is continuous in a predetermined first direction. And a lattice-shaped metal body that is discrete in a second direction perpendicular to the active layer is disposed between the reflector and the active layer located in the optical path of the oscillation light.

[0009]

[0010]

According to a third aspect of the present invention, in the above structure, the metal body is a lattice-shaped metal thin film.

According to a fourth aspect of the present invention, in the surface emitting semiconductor laser according to the first or second aspect, the metal body is deposited on the top of the convex portion and the bottom of the concave portion in the concavo-convex shape in which grooves are arranged on a desired layer. Characterized in that it is a metal thin film.

According to a fifth aspect of the present invention, there is provided the surface emitting semiconductor laser according to the third aspect, wherein the width and the interval of the lattice-shaped metal thin film are about the emission wavelength or smaller.

According to a sixth aspect of the present invention, in the surface emitting semiconductor laser according to the fourth aspect, the width, depth, and interval of the groove are about the emission wavelength or smaller.

[0015]

According to the surface emitting semiconductor laser of the present invention, as described above, the emission wavelength is about the emission wavelength or thinner inside the reflector on one or both sides, between the reflector and the active layer, or outside the reflector. It has a grid-like metal body with a width and an interval. Therefore, polarized waves having an electric field in the lattice direction of the lattice-shaped metal body are absorbed or reflected. On the other hand, polarized light having an electric field perpendicular to the grating is neither absorbed nor reflected. In other words, the reflectance in the grating direction is different from that in other directions,
The plane of polarization is determined by the direction of the lattice-shaped metal body.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

(Embodiment 1) FIG. 1A is a sectional view of a basic structure showing a first embodiment of a surface emitting semiconductor laser according to the present invention. In the figure, reference numeral 18 denotes a semiconductor substrate of single crystal InP, 19 denotes a semiconductor multilayer film reflecting mirror made of single crystal InP and single crystal InGaAsP formed on the semiconductor substrate 18, and its thickness has a refractive index. If n and the oscillation wavelength are represented by λ, it is λ / (4 · n). Also, reference numeral 20
Is a single crystal InG having an emission wavelength peak of 1.55 μm.
A light emitting layer made of aAsP, 21 is a cladding layer made of single crystal InP for confining carriers in the light emitting layer 20, and 22 is a contact layer made of single crystal InGaAsP. Reference numeral 24 denotes a lattice pattern of a metal film formed by an electron beam exposure apparatus, and reference numeral 25 denotes a multilayer film reflecting mirror made of two kinds of dielectric materials having different refractive indexes. Further, reference numeral 23 denotes a metal for forming an ohmic electrode on the contact layer 22, and reference numerals 27 and 28 denote current blocking layers made of p-type and n-type InP for constricting current.

FIG. 1B is a top view of the device.
In this figure, the dielectric multilayer film 25 is not shown. In the figure, reference numeral 29 indicates a light emitting area.

Next, each part of the device shown in the figure will be described in detail.

On the n-type InP substrate 18, n-type InGaAsP (0.112 μm thick) and n-type InP (0.122 μm thick) whose forbidden band width corresponds to 1.4 μm in wavelength are provided.
Are stacked to form a semiconductor multi-layer film reflecting mirror 19. Next, InGaAsP, which is the light emitting layer 20, is laminated with a thickness of two optical wavelengths (about 0.875 μm), and the p-type InP cladding layer 21 is 9/4 times the optical wavelength (about 1. (1 μm). Contact layer 2
Reference numeral 2 denotes a p-type InGaAsP contact layer whose forbidden bandwidth corresponds to a wavelength of 1.4 μm. Contact layer 22
An ohmic electrode 23 is formed using a metal such as Au, Zn, or Ni in a portion other than the upper light emitting region 29. A gold lattice pattern 24 having a width of 100 nm, an interval of 100 nm, and a thickness of 30 nm is formed thereon using an electron beam exposure apparatus. Then, a dielectric film S is formed on the light emitting region 29.
The dielectric multilayer film 25 is formed by alternately laminating iO ₂ and TiO _2. Here, six pairs for providing a reflectance equal to or lower than the reflectance required for oscillation are laminated. A SiO ₂ bottom layer of low refractive index in contact with the contact layer, the top layer becomes TiO _2. The thickness of SiO ₂ is about 0.26 μm, and the thickness of TiO ₂ is about 0.16 μm. The current is the p-type contact layer 2
2 and an ohmic electrode 26 formed on the n-type substrate. In this case, light having an electric field in a direction perpendicular to the lattice is not reflected by the lattice metal film 24, and is reflected only by the reflectance given by the dielectric multilayer film 25. On the other hand, most of the light having an electric field in the lattice direction is reflected by the metal film 24. The light not reflected passes through the metal film without being strongly absorbed by the metal film because the metal film is thin. The transmitted light is reflected by the dielectric multilayer film 25 thereon. Therefore,
Light having an electric field in the lattice direction will perceive a higher reflectivity than light having an electric field in the vertical direction. Therefore, oscillation occurs in this direction.

(Embodiment 2) FIG. 2 is a sectional view showing a second embodiment of the present invention. Unlike the above embodiment, the substrate-side reflecting mirror is also a multi-layered film reflecting mirror 25 made of a lattice-like metal film 24 and two kinds of dielectrics having different refractive indexes. In this case, the thickness of the n-type InP cladding layer 30 is 9 optical wavelengths.
/ 4 times (approximately 1.1 μm).
The lower layer 31 is an n-type InGaAsP layer whose band gap corresponds to a wavelength of 1.4 μm. In this device configuration, the InP substrate 18 is etched with a selective etching solution to expose the surface of the InGaAsP layer 31, and a metal film of a gold lattice pattern having a width of 100 nm, a spacing of 100 nm, and a thickness of 30 nm is formed thereon. 24 is formed using an electron beam exposure apparatus. Six pairs of dielectric multilayer films 25 made of SiO ₂ and TiO ₂ are stacked thereon. InGaAsP layer 3
The one in contact with 1 is SiO ₂ having a lower refractive index, and the lowermost layer is TiO ₂ .

In the first and second embodiments,
The lattice-shaped metal film 24 is a tungsten lattice pattern having a width of 400 nm and a spacing of 300 nm, and the thickness thereof is determined by the thickness (depth of the skin) at which the amplitude of the electric field is 1 / e (e is the base of natural logarithm). If the thickness is set to 200 nm and light having an electric field in the lattice direction is hardly transmitted, light having an electric field in the lattice direction receives a large absorption loss, and the reflectance does not increase. On the other hand, light in the direction perpendicular to the lattice is not absorbed by the lattice-like metal film 24, and is reflected at a large reflectance given by the dielectric multilayer film. Therefore, oscillation occurs in a direction perpendicular to the lattice. In this case, it is needless to say that the dielectric multilayer film must provide a reflectance necessary for oscillation.

(First Embodiment) FIG. 3 is a sectional view showing a first embodiment of the present invention. n
The band gap is 1.4 μm in wavelength on the InP substrate 18.
n-type InGaAsP (thickness: 0.112 μm)
m) and n-type InP (thickness: 0.122 μm) are stacked in 34 pairs to form a semiconductor multilayer film (reflection mirror) 19. Next, InGaAs, which is the light emitting layer 20, is formed with a thickness of two optical wavelengths (about 0.875 μm). Furthermore, on top of this, p-type InP (thickness: 0.122 μm) and a p-type InGaAsP whose band gap corresponds to a wavelength of 1.4 μm
(Thickness: 0.112 μm) are laminated to form a semiconductor multilayer film (reflecting mirror) 32. In a portion of the multilayer film 32 on the final p-type InGaAsP layer except for the light emitting region,
An ohmic electrode 2 made of a metal such as Au, Zn, Ni, etc.
Form 3 Further, a gold lattice pattern 24 having a width of 100 nm, an interval of 100 nm, and a thickness of 30 nm is formed thereon using an electron beam exposure apparatus.

In this case, light having an electric field perpendicular to the lattice is not reflected by the lattice metal film, and is reflected only by the reflectance given by the semiconductor multilayer film. Oscillation does not occur because the value of the reflectance is insufficient for oscillation. On the other hand, light having an electric field in the lattice direction receives both reflection by the semiconductor multilayer film and reflection by the metal film. Since the reflectance exceeds the reflectance required for oscillation, oscillation is possible. Therefore, only light having an electric field in the lattice direction selectively oscillates.

In the above embodiment, the lattice-like metal film is formed between the contact layer and the reflecting mirror, and in the reference example, the metal film is formed outside the reflecting mirror. A configuration in which a lattice-like metal film is formed inside a mirror is possible.

In the first or second embodiment, the light emitting layer is made of a long-wavelength InGaAsP bulk material. However, the present invention can be applied to other material systems, quantum well structures, strained structures and the like. Further, in the first or second embodiment, the current confinement is performed by the buried structure made of the semiconductor. However, the current confinement may be performed by ion implantation or the like, or the current confinement may not be performed.
In addition, similar effects can be expected with a material that can obtain a high reflectance, such as silver or aluminum, other than gold, as the lattice-like metal film. On the other hand, even if a material with a large absorption loss such as a metal or alloy such as nickel and platinum other than tungsten is used,
The polarization plane can be controlled. The effect is greatest when the width and interval of the lattice of the lattice-shaped metal are sufficiently narrower than the wavelength, but the same effect can be expected even when the width is about the wavelength.

(Embodiment 2) FIG. 4A is a sectional view of a basic structure showing a second embodiment of the present invention. In the figure, reference numeral 18 denotes a single crystal InP
Is a semiconductor multi-layer reflector made of single-crystal InP and single-crystal InGaAsP formed on the semiconductor substrate 18, and has a thickness of n, a refractive index of n,
When the oscillation wavelength is represented by λ, it is λ / (4 · n). Also,
Reference numeral 20 denotes an active layer composed of single-crystal InP and single-crystal InGaAsP having an emission wavelength peak of 1.55 μm. Reference numeral 22 denotes InGa with an unevenness on the upper part of the light emitting region.
23 is a metal for forming an ohmic electrode, and 24 is a metal film. Also, reference numeral 2
7 and 28 are p-type and n-type InPs for confining current.
It is a current block layer composed of:

Next, each part of the element having the above configuration will be described in detail.

On an n-type InP substrate 18, an n-type InGaAsP (0 .0) having a band gap corresponding to a wavelength of 1.4 μm is formed.
112 μm) and 34 pairs of n-type InP (0.122 μm). Next, InGa which is a light emitting layer of the active layer 20 is used.
AsP is laminated for two optical wavelengths (approximately 0.875 μm), and p-type InP (0.112 μm) and P-type InGa whose forbidden bandwidth corresponds to a wavelength of 1.4 μm are further formed thereon.
20 pairs of AsP (0.112 μm) are laminated. InG
Au and Z are formed on the portion of the aAsP layer 22 other than the light emitting region.
The ohmic electrode 23 is formed using a metal such as n or Ni. Thereafter, the width is 100 n using an electron beam exposure apparatus.
An m resist pattern is formed. Then, the InGaAsP layer is etched using a sulfuric acid-based etchant, and thereafter, the resist is removed. Then, a laser structure is completed by depositing gold on the entire surface. The current flows through the ohmic electrode 23 and the ohmic electrode 26 formed on the n-type substrate 18. FIG. 4B is an enlarged view of a groove portion having irregularities on the InGaAsP contact layer 22. Light having an electric field in a direction perpendicular to the depth direction of the concave and convex grooves is reflected only by the reflectance given by the semiconductor multilayer film. On the other hand, light having an electric field in the depth direction of the concave and convex grooves is reflected by the semiconductor multilayer film, reflected by the metal film on the concave portion forming the groove, and further reflected on the convex portion forming the groove. It is reflected by the metal film. Therefore, light having an electric field in the depth direction of the groove has a higher reflectivity than light having an electric field in the vertical direction. Therefore, oscillation occurs in this direction.

(Embodiment 3) FIG. 5 shows a third embodiment of the present invention. In the above-mentioned Embodiment 2, the reflecting mirror on the active layer 20 is replaced with two kinds of dielectric materials having different refractive indexes. This is a multi-layer reflecting mirror 25 made of a body. In this case, the thickness of the p-type InP cladding layer 21 is 9/4 times the optical wavelength (about 1.1 μm), and the layer 22 on this cladding layer 21 has a forbidden band width of 1.4 μm in wavelength. Is a p-type InGaAsP layer (about 0.3 μm). Au, in the part avoiding the light emitting area,
An ohmic electrode 23 is formed using a metal such as Zn or Ni, and a dielectric multilayer film 25 made of SiO2 and TiO2 is laminated in six pairs on the entire surface. The one that comes into contact with InGaAsP is SiO2 having a lower refractive index, and the final layer is TiO2.
This dielectric multilayer film is left so as to cover the upper part of the light emitting region,
Etching is performed using a fluorine-based gas so that the ohmic electrode is exposed. Then, a resist pattern having a width of 100 nm and an interval of 100 nm is formed on the dielectric multilayer film remaining on the light emitting region, and the surface of the resist is etched using a fluorine-based gas.
Etch the iO2 film. Thereafter, the resist is removed in oxygen plasma, and gold is deposited to a thickness of 30 nm on the entire surface.

In the above Reference Examples 2 and 3, irregularities are formed on the upper layer of the reflecting mirror, and the metal on the concave bottom surface and the convex upper surface is deposited. In the present invention, however, the irregularities are formed inside the reflecting mirror. To deposit the metal, or to form the unevenness between the contact layer and the reflector to deposit the metal.

In the above-mentioned Reference Examples 2 and 3, a metal is deposited by forming irregularities inside the reflecting mirror, or a metal is deposited by forming irregularities between the contact layer and the reflecting mirror. In the embodiment, the light emitting layer is made of a long wavelength system InGaAs.
Instead of using P bulk, another material system, a quantum well structure, a strain structure, or the like can be applied. Further, instead of performing the current confinement by the embedded structure of the semiconductor, the current may be confined by ion implantation or the like, or the current confinement may not be performed. Further, as a metal deposited on the concave and convex portions, a material other than gold, such as silver or aluminum, which can obtain a high reflectance, can expect the same effect.

The effect is greatest when the width, interval and depth of the unevenness are sufficiently narrower than the emission wavelength, but the same effect can be expected even when the emission wavelength is about the same.

[0034]

As described above, the surface emitting semiconductor laser of the present invention has a lattice-like metal body provided inside one or both reflecting mirrors, between the reflecting mirror and the active layer, or outside the reflecting mirror. Because of this, the plane of polarization is fixed parallel or perpendicular to the lattice direction depending on the properties of the metal body used, and the same plane of polarization is maintained even when the level of the injected current is changed.
Even if an array structure is formed, all oscillate on the same plane of polarization.

[Brief description of the drawings]

FIGS. 1A and 1B show a first embodiment of a surface emitting semiconductor laser according to the present invention, wherein FIG. 1A is a sectional structural view and FIG. 1B is a top view.

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

FIG. 3 is a sectional structural view of a first reference example of the present invention.

FIG. 4 shows a second reference example of the present invention;
(A) is a sectional structural view, and (b) is an enlarged view of the concave and convex groove portion of (a).

FIG. 5 is a sectional structural view of a third reference example of the present invention.

6A and 6B show a cross-sectional structure of a conventional surface-emitting semiconductor laser, in which FIG. 6A is a cross-sectional structure diagram of a surface-emitting semiconductor laser using a semiconductor multilayer film as a reflecting mirror, and FIG. Is a cross-sectional structure diagram of a surface-emitting semiconductor laser using as a reflecting mirror, and (c) is a cross-sectional structure diagram of a surface-emitting semiconductor laser using a metal film as a reflecting mirror.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor multilayer film 2 active layer 3 semiconductor multilayer film 4 dielectric multilayer film 5 contact layer 6 cladding layer 7 active layer 8 cladding layer 9 InGaAsP layer 10 dielectric multilayer film 11 metal film 12 contact layer 13 cladding layer 14 active layer 15 cladding Layer 16 InGaAsP layer 17 Metal film 18 InP semiconductor substrate 19 Semiconductor multilayer film 20 Active layer 21 Cladding layer 22 Contact layer 23 Ohmic electrode 24 Lattice metal 25 Dielectric multilayer film 26 Ohmic electrode 27 p-InP embedded layer 28 n-InP embedded Layer 29 light emitting region 30 cladding layer 31 InGaAsP layer 32 semiconductor multilayer film

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-21889 (JP, A) JP-A-5-21890 (JP, A) Table 8-8-503816 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) H01S 5/183

Claims (6)

(57) [Claims] 1. A resonator having a resonator perpendicular to a substrate surface,
In a surface emitting semiconductor laser having a structure in which a top and a bottom of an active layer are sandwiched between reflectors, a grating that is continuous in a predetermined first direction but is discrete in a second direction perpendicular to the first direction. A surface-emitting semiconductor laser, wherein a metal body in a shape of a circle is arranged inside the reflecting mirror located in the optical path of oscillation light. 2. A resonator having a resonator perpendicular to a substrate surface.
In a surface emitting semiconductor laser having a structure in which a top and a bottom of an active layer are sandwiched between reflectors, a grating that is continuous in a predetermined first direction but is discrete in a second direction perpendicular to the first direction. A surface-emitting semiconductor laser, comprising: a metal body disposed between the reflector and the active layer located in an optical path of oscillation light. 3. The surface emitting semiconductor laser according to claim 1, wherein said metal body is a lattice-shaped metal thin film. 4. The metal body according to claim 1, wherein the metal body is a metal thin film deposited on the top of the convex portion and the bottom of the concave portion in an uneven shape in which grooves are arranged on a desired layer.
4. The surface emitting semiconductor laser according to item 1. 5. The surface emitting semiconductor laser according to claim 3, wherein the width and the interval of the lattice-shaped metal thin film are about the emission wavelength or smaller. 6. The surface emitting semiconductor laser according to claim 4, wherein the width, depth, and interval of the groove are about the emission wavelength or smaller.