JPH07231138A - Surface light-emitting semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a surface light-emitting semiconductor laser which can fix the polarising surface in the desired direction and has the stabilized polarizing surface not influenced by an application current level by providing, in the path of the oscillated light beam, a metal material grating which is continuous in the predetermined first direction but is dispersive in the second direction perpendicular to the first direction. CONSTITUTION:In a surface light emitting semiconductor laser in such a constitution that a resonator which is perpendicular to the substrate surface is provided and the upper and lower sides of the active layer 20 is held by reflection mirrors, a metal material grating 24 which is continuous in the predetermined first direction but is dispersive in the second direction which is perpendicular to the first direction is provided in the light path of the oscillated beam. For instance, a semiconductor multilayer reflecting mirror 19 consisting of InP and InGaAsP is formed on a semiconductor substrate 18 of Ink, and a light- emitting layer 20 consisting of InGaAsP, a clad layer 21 of InP and a contact layer 22 of InGaAsP are formed thereon. Moreover, a grating pattern 24 of metal film and a multilayer film reflecting mirror 25 consisting of two kinds of dielectric materials having different refraction indices are provided thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polarization plane control of a surface emitting semiconductor laser which emits light in a direction perpendicular to a substrate. The surface emitting semiconductor laser of the present invention ensures stable polarization planes. It becomes possible to provide a light source.

[0002]

2. Description of the Related Art As is well known, surface-emitting lasers operate at low threshold values, are capable of high-speed modulation and large-scale two-dimensional integration, and are expected as devices constituting optical communication and optical information processing systems. Has been done.

FIG. 6 shows a schematic sectional structure of a conventional surface emitting laser. 6A shows the case where the semiconductor multilayer film is used as the reflection film, FIG. 6B shows the case where the dielectric multilayer film is used as the reflection film, and FIG. 6C shows the case where the metal film is used as the reflection mirror. In each case, it shows. That is,
The structure shown in FIG. 6A is a structure in which the active layer 2 is sandwiched between the semiconductor multilayer films 1 and 3. In the structure shown in FIG. 6B, the dielectric multilayer films 4 and 10 sandwich the upper and lower layers of the contact layer 5, the cladding layer 6, the active layer 7, the cladding layer 8 and the InGaAsP layer 9 in this order from the top. It is a structure. Further, similarly to the structure shown in FIG. 6C, the contact layer 12, the cladding layer 13, the active layer 14, and the
It has a structure in which metal films 11 and 17 sandwich the upper and lower sides of a stack of a clad layer 15 and an InGaAsP layer 16. In addition, there are surface emitting lasers configured by combining these reflecting mirrors.

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

[0005]

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

[0006]

In order to solve the above-mentioned problems, the present invention has a surface emitting device having a resonator having a vertical direction with respect to a substrate surface, and a structure in which an active layer is sandwiched between reflecting mirrors. In the semiconductor laser, it is continuous in one or both of the reflection mirrors, between the reflection mirror and the active layer, and outside the reflection mirror in a predetermined first direction. , And has a discrete grid-shaped metal film in the second direction perpendicular thereto.

That is, the surface emitting semiconductor laser according to claim 1 of the present invention is a surface emitting semiconductor laser having a structure in which a resonator is provided in a direction perpendicular to the substrate surface, and an active layer is sandwiched by reflecting mirrors. A lattice-shaped metal body that is continuous in a predetermined first direction but is discrete in a second direction perpendicular to the first direction is arranged in the optical path of the oscillated light. And

The surface emitting semiconductor laser according to claim 2 is
It is characterized in that the metal body is arranged outside the reflecting mirror.

A surface emitting semiconductor laser according to a third aspect of the present invention is characterized in that the metal body is disposed inside the reflecting mirror.

A surface emitting semiconductor laser according to a fourth aspect is characterized in that the metal body is disposed between the reflecting mirror and the active layer.

In the surface emitting semiconductor laser according to a fifth aspect of the present invention, in each of the above constitutions, the metal body is a lattice-shaped metal thin film.

According to a sixth aspect of the present invention, in the surface emitting semiconductor laser according to the first to fourth aspects, the top of the convex portion and the lower portion of the concave portion in the concavo-convex shape in which the metal body has grooves arranged on a desired layer are provided. It is characterized by being a deposited metal thin film.

A surface emitting semiconductor laser according to a seventh aspect of the present invention is characterized in that, in the structure according to the fifth aspect, the width and interval of the lattice-shaped metal thin film are about the emission wavelength or smaller.

The surface emitting semiconductor laser of claim 8 is characterized in that, in the structure of claim 6, the width, depth and interval of the groove are smaller than the emission wavelength.

[0015]

In the surface emitting semiconductor laser of the present invention, as described above, the emission wavelength is smaller than or equal to the emission wavelength inside the one or both reflecting mirrors, between the reflecting mirror and the active layer, or outside the reflecting mirror. It has a grid-like metal body with width and spacing. 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 waves having an electric field perpendicular to the lattice are neither absorbed nor reflected. In other words, since the reflectivity in the lattice direction is different from that in other directions,
The polarization plane is determined by the direction of the lattice-shaped metal body.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the 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 is a semiconductor substrate of single crystal InP, reference numeral 19 is 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, then λ / (4 · n). Also, reference numeral 20
Is a single crystal InG having an emission wavelength peak of 1.55 μm
Reference numeral 21 is a light emitting layer made of aAsP, 21 is a clad 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. Further, reference numeral 24 is a grid pattern of a metal film formed by an electron beam exposure apparatus, and 25 is a multilayer film reflecting mirror made of two kinds of dielectrics having different refractive indexes. Further, reference numeral 23 is a metal for forming an ohmic electrode on the contact layer 22, and reference numerals 27 and 28 are current blocking layers made of p-type and n-type InP for confining the current.

FIG. 1B is a top view of this element,
In this figure, the dielectric multilayer film 25 is omitted. In the figure, reference numeral 29 indicates a light emitting region.

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

On the n-type InP substrate 18, n-type InGaAsP (thickness 0.112 μm) and n-type InP (thickness 0.122 μm) corresponding to a forbidden band width of 1.4 μm in wavelength.
34 pairs are laminated to form a semiconductor multilayer film reflecting mirror 19. Next, InGaAsP, which is the light emitting layer 20, is laminated with a thickness of two wavelengths (about 0.875 μm) at the optical wavelength, and the p-type InP clad layer 21 is formed for 9/4 times the optical wavelength (about 1. 1 μm) in thickness. Contact layer 2
2 is a p-type InGaAsP contact layer whose forbidden band width corresponds to 1.4 μm in wavelength. Contact layer 22
The ohmic electrode 23 is formed using a metal such as Au, Zn, or Ni in a portion avoiding the upper light emitting region 29. A gold grid pattern 24 having a width of 100 nm, an interval of 100 nm, and a thickness of 30 nm is formed thereon by using an electron beam exposure apparatus. Then, the 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, 6 pairs are laminated to give a reflectance equal to or lower than the reflectance required for oscillation. The bottom layer in contact with the contact layer is SiO ₂ having a low refractive index, and the top layer is TiO ₂ . The thickness of SiO ₂ is about 0.26 μm, and the thickness of TiO ₂ is about 0.16 μm. Current is p-type contact layer 2
2 and the ohmic electrode 26 formed on the n-type substrate. In this case, light having an electric field in the direction perpendicular to the lattice is not reflected by the lattice-shaped metal film 24, and thus 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. Since the metal film is thin, the light that has not been reflected is transmitted without being strongly absorbed by the metal film. The transmitted light is reflected by the dielectric multilayer film 25 thereon. Therefore,
Light having an electric field in the lattice direction will have a higher reflectance 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 reflecting mirror on the substrate side is also a multilayer film reflecting mirror 25 composed of the lattice-shaped metal film 24 and two kinds of dielectrics having different refractive indexes. In this case, the thickness of the n-type InP clad layer 30 is 9 optical wavelengths.
/ 4 times (about 1.1 μm), and this cladding layer 30
The lower layer 31 is an n-type InGaAsP layer whose forbidden band width corresponds to 1.4 μm in wavelength. In the structure of this element, the InP substrate 18 is etched with an etchant having a selectivity to expose the surface of the InGaAsP layer 31, and a metal film having a gold lattice pattern with a width of 100 nm, a distance 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 laminated thereon. InGaAsP layer 3
The one that is in contact with 1 is SiO ₂ having a low refractive index, and the bottom layer is TiO ₂ .

In the first and second embodiments,
The lattice-like metal film 24 is formed into a tungsten lattice-like pattern having a width of 400 nm and an interval of 300 nm, and its thickness is determined from the thickness (skin depth) at which the electric field amplitude is 1 / e (e is the base of natural logarithm). If the thickness is 200 nm and the light having the electric field in the lattice direction is hardly transmitted, the light having the electric field in the lattice direction suffers 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-shaped metal film 24, and thus is reflected with a large reflectance provided by the dielectric multilayer film. Therefore, oscillation occurs in the direction perpendicular to this lattice. In this case, it goes without saying that the dielectric multi-layer film must be provided with the reflectance necessary for oscillation.

(Embodiment 3) FIG. 3 is a sectional view showing a third embodiment of the present invention. On the n-type InP substrate 18, an n-type InGaA having a forbidden band width of 1.4 μm in wavelength.
sP (thickness 0.112 μm) and n-type InP (thickness 0.1
22 μm) and 34 pairs are laminated to form a semiconductor multilayer film 19 (reflecting mirror). Next, InGa that is the light emitting layer 20
As is formed with a thickness of two wavelengths (about 0.875 μm) at the optical wavelength. Furthermore, p-type InP (thickness: 0.
122 μm) and p-type InGaAsP (thickness 0.112 μm) corresponding to a forbidden band width of 1.4 μm in wavelength.
A semiconductor multilayer film (reflecting mirror) 32 is formed by stacking five pairs. An ohmic electrode 23 is formed using a metal such as Au, Zn, or Ni in a portion of the multilayer film 32 that is located on the final p-type InGaAsP layer except for the light emitting region. Further, a gold grid pattern having a width of 100 nm, an interval of 100 nm, and a thickness of 30 nm is formed thereon by using an electron beam exposure apparatus.

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

In the above embodiment, the grid-like metal film is formed between the contact layer and the reflecting mirror or outside the reflecting mirror.
A grid-shaped metal film may be formed inside the reflecting mirror.

In the first to third embodiments, the light emitting layer is a long wavelength InGaAsP bulk, but other material systems, quantum well structures, strained structures, etc. are also applicable. Further, in the above-described first to third embodiments, the current confinement is performed by the embedded structure of the semiconductor, but the current confinement may be performed by ion implantation or the like, or the current confinement structure may not be formed.
A similar effect can be expected with a material that can obtain a high reflectance such as silver or aluminum other than gold as the lattice-shaped metal film. On the other hand, even if a material with high absorption loss such as nickel or platinum other than tungsten, metal such as platinum, or alloy is used,
It is possible to control the plane of polarization. Further, the width and the interval of the grid of the grid-shaped metal are most effective when the width and the spacing are sufficiently smaller than the wavelength, but the same effect can be expected even when the wavelength is about the wavelength.

(Embodiment 4) FIG. 4A is a sectional view of a basic structure showing a fourth embodiment of the surface emitting semiconductor laser according to the present invention. In the figure, reference numeral 18 is a semiconductor substrate of single crystal InP, 19 is a semiconductor multi-layered film reflecting mirror made of single crystal InP and single crystal InGaAsP formed on the semiconductor substrate 18, and its thickness is When the ratio is represented by n and the oscillation wavelength is represented by λ, it is λ / (4 · n). Reference numeral 20 is a semiconductor multilayer film reflecting mirror made of single crystal InP and single crystal InGaAsP having an emission wavelength peak of 1.55 μm. Reference numeral 22 is an InGaAsP crystal having irregularities on the top of the light emitting region, 23 is a metal for forming an ohmic electrode, and 24 is a metal film. Also,
Reference numerals 27 and 28 are current blocking layers made of p-type and n-type InP for confining the current.

Next, each part of the element having the above-mentioned structure will be described in detail.

On the n-type InP substrate 18, the n-type InGaAsP (0 ..
112 μm) and 34 pairs of n-type InP (0.122 μm) are laminated. Then, InGa which is a light emitting layer of the active layer 20
AsP is laminated for two wavelengths (about 0.875 μm) at an optical wavelength, and p-type InP (0.112 μm) and P-type InGa corresponding to a forbidden band width of 1.4 μm are further stacked thereon.
20 pairs of AsP (0.112 μm) are laminated. InG
Au, Z is formed in a portion of the aAsP layer 22 which is not in the light emitting region.
The ohmic electrode 23 is formed using a metal such as n or Ni. Then, using an electron beam exposure apparatus, a width of 100n
An m resist pattern is formed. Then, the InGaAsP layer is etched using a sulfuric acid-based etchant, and then the resist is removed. Then, the laser structure is completed by depositing gold on the entire surface. A current is passed through the ohmic electrode 23 and the ohmic electrode 26 formed on the n-type substrate 18. FIG. 4B is an enlarged view of the groove portion of the unevenness on the InGaAsP contact layer 22. Light having an electric field in a direction perpendicular to the depth direction of the uneven groove 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 uneven groove is reflected by the semiconductor multilayer film, reflected by the metal film on the concave portion forming the groove, and further 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 feels a higher reflectance than light having an electric field in the direction perpendicular to the groove. Therefore, oscillation occurs in this direction.

(Embodiment 5) FIG. 5 shows a fifth embodiment of the present invention. In the above embodiment, the active layer 2 is used.
The upper reflecting mirror is a multilayer film reflecting mirror 25 made of two kinds of dielectrics having different refractive indexes. In this case, the thickness of the p-type InP clad layer 21 is 9/4 times the optical wavelength (about 1.1 μm), and the layer 2 on the clad layer 21 is
2 is a p-type I with a forbidden band width of 1.4 μm
It is an nGaAsP layer (about 0.3 μm). An ohmic electrode 23 is formed using a metal such as Au, Zn, or Ni in a portion other than the light emitting region, and 6 pairs of dielectric multilayer films 25 made of SiO ₂ and TiO ₂ are laminated on the entire surface. InGaAsP
The lower layer is SiO ₂ with a lower refractive index and the final layer is T
iO ₂ . The dielectric multilayer film is left so as to cover the upper part of the light emitting region, and etching is performed using a fluorine-based gas so that the ohmic electrode is exposed. Then, a width of 100 nm and an interval of 10 are formed on the dielectric multilayer film remaining on the light emitting region.
A 0 nm resist pattern is formed, and the TiO ₂ film on the surface is etched using a fluorine-based gas. After that, the resist is removed in oxygen plasma, and gold is deposited on the entire surface with 30
nm vapor deposition.

In Examples 4 and 5 above, the unevenness was formed on the upper layer of the reflecting mirror, and the metal on the bottom surface of the concave portion and the upper surface of the convex portion were deposited. However, the unevenness was formed inside the reflecting mirror to form the metal. It may be deposited, or unevenness may be formed between the contact layer and the reflecting mirror to deposit the metal.

In the fourth and fifth embodiments, the light emitting layer is a bulk of long-wavelength InGaAsP, but other material systems, quantum well structures, strained structures, etc. are also applicable. further,
In the above-mentioned embodiment, the current confinement is performed by the embedded structure of the semiconductor, but the current confinement by ion implantation or the like is also possible.
The current constriction structure does not have to be formed. Further, as a metal to be deposited on the uneven portion, a material other than gold, such as silver or aluminum, which can obtain a high reflectance, can be expected to have the same effect.

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

[0034]

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

[Brief description of drawings]

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 second embodiment of the surface emitting semiconductor laser according to the present invention.

FIG. 3 is a sectional structural view of a surface emitting semiconductor laser according to a third embodiment of the present invention.

4A and 4B show a fourth embodiment of the surface emitting semiconductor laser according to the present invention, wherein FIG. 4A is a sectional structural view, and FIG. 4B is an enlarged view of an uneven groove portion in FIG. 4A.

FIG. 5 is a sectional structural view of a surface emitting semiconductor laser according to a fifth embodiment of the present invention.

6A and 6B show a cross-sectional structure of a conventional surface-emitting semiconductor laser, wherein FIG. 6A is a cross-sectional structural view of a surface-emitting semiconductor laser using a semiconductor multilayer film as a reflecting mirror, and FIG. 6B is a dielectric multilayer film. Is a sectional structure diagram of a surface emitting semiconductor laser using as a reflecting mirror, and FIG. 7C is a sectional structure diagram of a surface emitting semiconductor laser using a metal film as a reflecting mirror.

[Explanation of symbols]

 1 semiconductor multilayer film 2 active layer 3 semiconductor multilayer film 4 dielectric multilayer film 5 contact layer 6 clad layer 7 active layer 8 clad layer 9 InGaAsP layer 10 dielectric multilayer film 11 metal film 12 contact layer 13 clad layer 14 active layer 15 clad 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 Buried Layer 28 n-InP Buried Layer 29 Light Emitting Area 30 Cladding Layer 31 InGaAsP Layer 32 Semiconductor Multilayer Film

Claims (8)

[Claims] 1. A resonator having a vertical direction with respect to a substrate surface,
In a surface emitting semiconductor laser having a structure in which an upper and lower sides of an active layer are sandwiched by reflecting mirrors, a grating is continuous in a predetermined first direction but discrete in a second direction perpendicular to the first direction. A surface-emitting semiconductor laser, wherein the metal body is arranged in the optical path of oscillation light. 2. The surface emitting semiconductor laser according to claim 1, wherein the metal body is arranged outside the reflecting mirror. 3. The surface emitting semiconductor laser according to claim 1, wherein the metal body is arranged inside the reflecting mirror. 4. The surface emitting semiconductor laser according to claim 1, wherein the metal body is arranged between the reflecting mirror and the active layer. 5. The surface emitting semiconductor laser according to claim 1, wherein the metal body is a lattice-shaped metal thin film. 6. The metal thin film, which is a metal thin film deposited on the top of a convex portion and the bottom of a concave portion in an uneven shape formed by arranging grooves on a desired layer.
5. The surface emitting semiconductor laser according to any one of 1. 7. The surface emitting semiconductor laser according to claim 5, wherein the width and the interval of the lattice-shaped metal thin film are about the emission wavelength or smaller. 8. The surface emitting semiconductor laser according to claim 6, wherein the width, the depth, and the interval of the groove are smaller than the emission wavelength.