JP2001024277A - Surface emitting semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser wherein a transversal mode is stable, optical output is large, and manufacture of high reproducibility is enabled with a simple process. SOLUTION: In a surface emitting semiconductor laser in which a first electrode 10, a semiconductor substrate 1, a first multilayer reflecting film 2, an active layer 4 and a second muitilayer reflecting film 6 are laminated in order, current injection into the active layer 4 through a part where a contact layer 8 is formed is made possible by a second electrode 9 and a cap layer 7 in which the contact layer 8 is formed in a part corresponding to a light outputting region 11, and current injection into the active layer 4 through a part where the contact layer 8 is not formed is made impossible. By adjusting an optical thickness of the second electrode 9 and an optical thickness of the contact layer 8, the reflectivity of the peripheral part of a part where the contact layer 8 is formed is made lower than the reflectivity of a part where the contact layer 8 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-emitting type semiconductor laser and a method for manufacturing the same, and more particularly, it is used as a light source for optical information processing and communication, a light source for an image processing apparatus and a copying apparatus, and has a lateral mode. The present invention relates to a surface-emitting type semiconductor laser which is stable, has a low threshold current, and has a high output, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, surface-emitting type semiconductor lasers have attracted attention in technical fields such as optical communication and optical interconnection because two-dimensional arraying is easy.
It is said that a surface-emitting type semiconductor laser can reduce the threshold current relatively easily and reduce power consumption, but it is difficult to achieve high output.

At present, low-cost multimode optical fibers are used for optical communication.
Since it is possible to dramatically increase the number of lines, it is expected that a single mode optical fiber will be used in the future. It is assumed that the laser provided to the single mode optical fiber is a laser that oscillates in a stable single mode (0-order fundamental transverse mode).

On the other hand, if the stability of the transverse mode is required in the surface-emitting type semiconductor laser, there is a trade-off that the threshold current increases and the response characteristic deteriorates or it is difficult to increase the output. It is difficult to obtain a device that satisfies at the same time.

For example, in a proton injection type surface emitting laser having a gain waveguide structure, a slight difference in refractive index occurs between a current passing region and a surrounding region due to a thermal lens effect. As a result, a weak light confinement is created. Therefore, it is known that a stable transverse mode can be obtained even if the diameter of the non-proton injection region (current path) is increased to about 10 μm. However, since the light confinement itself is weak, it is not possible to expect a great improvement in the luminous efficiency, and since the heat generation is large, the threshold current is high and the responsiveness is poor when no bias is applied.

On the other hand, a selective oxidation type surface emitting semiconductor laser having a refractive index waveguide structure selectively oxidizes a part of a multilayer reflective film near an active layer to perform current confinement and reduce refractive index conduction. Since it has a wave path and has a strong light confinement effect, the threshold current is low and the response is fast. However, the light confinement effect is so strong that the diameter of the light emitting region is typically 5 μm to stabilize the transverse mode.
In the following, it is necessary to make it considerably narrower than the above-described proton injection method, and therefore, there is a disadvantage that the volume of the light emitting region is reduced and high output cannot be expected.

As described above, it is difficult to solve the relative problems of securing the stability of the transverse mode and increasing the output. As an attempt to achieve both the stability of the transverse mode and the increase in output, there is, for example, a surface-emitting type semiconductor laser disclosed in Japanese Patent Application Laid-Open No. Hei 6-112587. As shown in FIG. 11, the surface-emitting type semiconductor laser 125 has a parallel mirror stack 1 on a substrate 130 on which electrodes 147 are formed.
32, an active layer and a spacer layer 135, and a parallel mirror stack 138 are sequentially stacked to form a mesa 140. On the parallel mirror stack 138, a contact window 142 is provided. A dielectric layer 144 having an opening in the light emitting region is provided on 142. A contact layer 146 made of an optically transparent conductive material such as ITO is provided so as to cover the opening and the dielectric layer 144, and a part of the contact layer is made in contact with the electrode, and the current distribution 149 is controlled. Then, the dielectric layer 144 and the contact layer 146
Controls an optical mode 148 that is located on the surface of the mesa 140 with an optical thickness that provides a predetermined mirror reflectivity and is independent of the edge of the mesa 140. As mentioned above,
It is possible to control current and optical mode separately,
It is stated that this makes it possible to achieve good overlap between the current and optical modes and high output.

In this surface-emitting type semiconductor laser, a contact layer 146 embedded in the opening of the dielectric layer 144 is provided in the opening of the dielectric layer 144. An element having characteristics cannot be manufactured with good reproducibility. That is, the mirror reflectance is controlled by the optical thickness of each of the dielectric layer 144 and the contact layer 146. If the alignment of the two is not perfect, the distribution of the mirror reflectance may be uneven. As a result, the transverse mode becomes unstable.

Further, in order to manufacture the present element, in addition to the laminating step of sequentially laminating the respective semiconductor layers, two laminating steps of a laminating step of the contact window 142 and a laminating step of the dielectric layer 144 are performed. Step of laminating contact layer 146 on opening of dielectric layer 144 and step of laminating dielectric layer 14
And a contact layer lamination step of laminating the contact layer 146 on the contact layer 4 twice, and the manufacturing process is complicated.

As described above, JP-A-6-11258
The surface emitting semiconductor laser disclosed in Japanese Patent Application Laid-Open No. 7-1995 has a problem that the characteristics are liable to vary easily, in spite of requiring an advanced semiconductor process.

[0011]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a surface-emitting type semiconductor laser which has a stable transverse mode, a large light output, and can be manufactured with good reproducibility by a simple process. It is in.

[0012]

In order to achieve the above object, a surface-emitting type semiconductor laser according to the present invention comprises a first electrode provided on a semiconductor substrate and a first electrode provided on a side of the semiconductor substrate opposite to the first electrode. A first multilayer reflective film provided on the surface, a second multilayer reflective film provided opposite to the first multilayer reflective film with the active layer interposed therebetween, and optically transparent to laser oscillation light A second electrode for injecting a current into the active layer together with the first electrode; and a second electrode provided between the second electrode and the second multilayer reflective film, and optically coupled to laser-oscillated light. A transparent contact layer is formed in a portion corresponding to the light emitting region, and current can be injected into the active layer through the portion where the contact layer is formed, and a portion where the contact layer is not formed Layer that disables current injection into active layer By adjusting the optical thickness of the second electrode and the optical thickness of the contact layer, the reflectance of the peripheral portion of the portion where the contact layer is formed can be adjusted by the contact layer. It is characterized by lowering the reflectance than the portion.

It is preferable that the cap layer is made of a material that is optically transparent to laser-oscillated light and that is lattice-matched with the second multilayer reflective film. The contact layer is preferably formed of a material that is lattice-matched with the cap layer, is capable of heterojunction with the cap layer, and is capable of making ohmic contact with the second electrode.

Further, the surface emitting semiconductor laser of the present invention comprises:
The active layer is preferably made of an AlGaAs-based semiconductor. When the active layer is made of an AlGaAs-based semiconductor, the cap layer is preferably made of an AlGaInP-based semiconductor or a GaInP-based semiconductor. , AlGaAs-based semiconductor or GaAs-based semiconductor.

Cadmium-tin oxide or indium-tin oxide can be used as the material of the second electrode.

Further, according to the method of manufacturing a surface emitting semiconductor laser of the present invention, a first multilayer reflective film, an active layer,
A laminating step of sequentially laminating a second multilayer reflective film, a cap layer, and a contact layer; an etching step of etching the contact layer while leaving a portion corresponding to a light emitting region; An electrode laminating step of forming the second electrode so as to cover the peripheral portion.

In the etching step, the cap layer is preferably used as an etch stopper when the contact layer is etched, and each layer is etched so that the etching selectivity of the contact layer with respect to the cap layer is larger than 10 times. It is more preferable to select the material and the etchant. In addition, it is preferable that, after the cap layer is laminated by crystal growth of a semiconductor, the contact layer is continuously laminated by crystal growth of a semiconductor.

The surface-emitting type semiconductor laser of the present invention can be applied not only to a planar type but also to a post type. The side surface of the reflection film may be oxidized from the surroundings to partially form an insulating region.

In the surface-emitting type semiconductor laser of the present invention, the optical thickness of the contact layer formed at the portion corresponding to the light emitting region and the second electrode formed so as to cover the contact layer and its peripheral portion are formed. Since the optical thickness is adjusted so that the reflectance of the peripheral portion of the portion corresponding to the light emitting region is relatively reduced with respect to the reflectance of the portion corresponding to the light emitting region, the light emitting region Only in this case, laser oscillation in the Fabry-Perot mode occurs efficiently. In addition, since the layer structure is different between the portion where the contact layer is formed and the peripheral portion, an effective refractive index difference is also generated, and an optical waveguide is formed. As described above, the surface emitting semiconductor laser of the present invention can control the optical mode,
Basic transverse mode oscillation can be easily obtained.

The contact layer electrically connects the cap layer and the second electrode. Since the contact layer is formed only in the portion corresponding to the light emitting region, the contact layer is formed in the portion where the contact layer is formed. , The current can be injected into the active layer, and the current cannot be injected into the active layer through the portion where the contact layer is not formed. Therefore, the injected current flows perpendicularly to the light emitting region toward the active layer, and a current path is formed at the center of the device in a plane horizontal to the semiconductor substrate. This means that the gain region (gain region) is limited to this vicinity,
The overlap between the gain region and the basic lateral mode is maximized, and the selectivity of the basic lateral mode is improved.

As described above, in the surface emitting semiconductor laser of the present invention, the threshold current can be reduced by the current confinement effect of the contact layer and the basic lateral mode selectivity.
Because it is possible to enlarge the area of the light emission area,
High output can be achieved in the basic lateral mode.

Further, in the surface emitting semiconductor laser of the present invention, except for a laminating step of sequentially laminating a first multilayer reflective film, an active layer, a second multilayer reflective film, a cap layer, and a contact layer on a semiconductor substrate. The manufacturing process can be performed by a single etching step of etching the contact layer and a single electrode laminating step of forming the second electrode without requiring a complicated process. In particular, when the cap layer is used as an etch stopper, it is easy to control the etching depth when forming the contact layer, to prevent a decrease in mirror reflectance in the light emitting region, to prevent variations in element characteristics,
Also, it is effective for improving the yield of the device.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of a surface emitting semiconductor laser according to the present invention will be described in detail with reference to the drawings. (First Embodiment) The structure of a surface emitting semiconductor laser according to a first embodiment of the present invention shown in FIG.

As shown in FIG. 2, an n-type Al _0.9 Ga _0.1 As layer and an n-type Al _0.9 Ga _0.1 As layer are formed on the (100) plane of the n-type GaAs substrate 1 by metal organic chemical vapor deposition (MOCVD). first made of multi-layer stacks of the Al _{0. 3} Ga _0.7 as layer
A multilayer reflective film 2, a first spacer layer 3 made of undoped Al _0.5 Ga _0.5 As, and an undoped Al _0.11 Ga
_0.89 As quantum well layer and undoped Al _0.3 G
a quantum well active layer 4 composed of a laminate of a _0.7 As barrier layer; a second spacer layer 5 composed of undoped Al _0.5 Ga _0.5 As; a p-type Al _0.9 Ga _0.1 As layer and a p-type Al _0.9 Ga _0.1 As layer.
Multi-layer reflective film 6 composed of a multilayered structure of Al _0.3 Ga _0.7 As layer of p-type, cap layer 7 of p-type Ga _0.5 In _0.5 P, and contact layer 8 of p-type GaAs
Are sequentially formed.

Here, the first multilayer reflection film 2 is made of n-type Al.
_It consists of a multilayer structure of a _0.9 Ga _0.1 As layer and an n-type Al _0.3 Ga _0.7 As layer, and each layer has a thickness of λ / 4n _r (where λ is the laser oscillation wavelength and n _r is the structure of each layer). And a layer having a different mixed crystal ratio.
They are stacked for 0.5 cycle. The carrier concentration after doping with silicon, which is an n-type impurity, is 3 × 10 ¹⁸ cm ⁻³ .

The second multilayer reflective film 6 is made of p-type Al.
_This is a laminate of a _0.9 Ga _0.1 As layer and a p-type Al _0.3 Ga _0.7 As layer.
/ 4n is _r, are 30-period stacking layers of different mixed crystal ratios alternately. The carrier concentration after doping with carbon, which is a p-type impurity, is 5 × 10 ¹⁸ cm ⁻³ .

The number of periods (the number of layers) of the second multilayer reflection film 6 is set to the first
The reason for making the number smaller than the number of layers of the multilayer reflective film 2 is to take out the emitted light from the upper surface of the substrate by providing a difference in reflectance.
Although not described in detail, in order to reduce the series resistance of the device, the second multilayer reflective film 6 includes an intermediate part between the Al _0.9 Ga _0.1 As layer and the Al _0.3 Ga _0.7 As layer between these layers. A plurality of so-called intermediate layers having an aluminum mixed crystal ratio are interposed.

The quantum well active layer 4 has a laminated structure in which quantum well layers of undoped Al _0.11 Ga _0.89 As having a thickness of 8 nm and barrier layers of undoped Al _0.3 Ga _0.7 As having a thickness of 5 nm are alternately laminated. It is. The number of quantum well layers is appropriately determined according to desired characteristics. Typically, the number of quantum well layers is three, and the outer layers of the quantum well layers are all barrier layers.
The number of barrier layers is four, one more than the quantum well layer. This oscillates light in the 780 nm wavelength band.

The film thickness from the lower surface of the first spacer layer 3 to the upper surface of the second spacer layer 5 is an integral multiple of λ / _{nr as} a whole so that a standing wave stands between them. It is designed so that the “belly” portion comes to the position of the quantum well active layer 4.

Cap layer 7 made of p-type GaInP
Is a thin layer having a thickness of 0.1 μm, and has a carrier concentration of 1 × 10 ¹⁸ after doping with zinc which is a p-type impurity.
cm ^-3 . The carrier concentration of the cap layer 7 is set to a level at which current injection is not easily performed by the Schottky barrier even if the second electrode 9 made of a semiconductor material described later is formed directly on this layer.

GaInP has an optical energy band gap of about 1.9 eV and is transparent to laser-oscillated light in the 780 nm band, so that unnecessary light absorption does not occur.

The carrier concentration of the contact layer 8 made of p-type GaAs after doping zinc, which is a p-type impurity, is 5 × 10 ¹⁹ cm ⁻³ . The carrier concentration of the contact layer 8 is set to a concentration sufficient to form an ohmic contact when the contact layer 8 contacts the second electrode 9.

By adjusting the optical thickness of the contact layer 8 together with the optical thickness of the second electrode 9, the phase in the Fabry-Perot mode with respect to the light emitted from the active layer is adjusted. Can be. The optical thickness of the contact layer 8 and the second electrode 9 will be described later.

As described above, the cap layer 7 and the second electrode 9 cannot make ohmic contact due to the Schottky barrier, and current cannot be injected into the cap layer 7. On the other hand, between the cap layer 7 and the contact layer 8 is a heterojunction of the same conductivity type, and since the contact layer 8 and the second electrode 9 are in ohmic contact, the contact layer 8 is formed. The current injection into the cap layer 7 can be performed in the portion where it has been set. As described above, the carrier concentration of the cap layer 7 is set to a level at which current is not easily injected due to the Schottky barrier.
Is very thin and does not hinder current injection.

Next, the substrate is taken out of the growth chamber, and as shown in FIG. 3, an etching mask (photoresist) 21 having a diameter of 5 to 10 .mu.m is formed in the light emitting area forming area by using a photolithography technique. Using a mixture of sulfuric acid, hydrogen peroxide and water as an etchant, only the portion corresponding to the light emitting region of the contact layer 8 is left, and the other portion is removed by etching.

In the present embodiment, the p-type GaAs forming the contact layer 8 is replaced by the p-type G
Since the etching selectivity is 10 times or more that of aInP, the etching can be easily stopped at the interface between the contact layer 8 and the cap layer 7.

Here, the p-type Ga remaining after the etching
The shape (planar shape) of the contact layer 8 made of As in the direction horizontal to the substrate plane is rectangular,
It can be any shape such as an ellipse or a diamond. However, the planar shape of the contact layer 8 affects the reflectance distribution. For example, if the contact layer 8 has a two-fold symmetry (a geometric shape that returns to the original shape when rotated by 180 °) such as a rectangle, an ellipse, or a diamond, the shape of the laser light The plane of polarization tends to be aligned in a certain direction according to its shape. By utilizing this property, the plane of the contact layer 8 can be made elliptical, elliptical, rhombic, or the like to control the polarization plane of the laser light.

As shown in FIG. 4, after removing the etching mask 21 made of a photoresist, indium tin oxide is used to cover the exposed portion of the cap layer 7 and the contact layer 8 by using an RF sputtering method. Things (IT
A second electrode 9 made of O) is deposited. In order to make the contact between the contact layer 8 and the second electrode 9 an ohmic contact,
Annealing is performed in a temperature range of 300 to 600 ° C. The annealing temperature may be appropriately determined from this temperature range in consideration of the balance with other steps.

The layer configuration around the portion corresponding to the light emitting region 11 is, from the bottom, the first multilayer reflective film 2, the first spacer layer 3, the quantum well active layer 4, the second spacer layer 5, and the second multilayer. Although the reflective layer 6, the cap layer 7, and the second electrode 9 are sequentially laminated, the layer configuration corresponding to the light emitting region 11 is such that a contact layer is provided between the cap layer 7 and the second electrode 9. This is a layer configuration in which 8 is added.

By adjusting the optical thickness of the contact layer 8 and the optical thickness of the second electrode 9, FIG.
As shown in (B), the reflectance of the peripheral portion of the portion corresponding to the light emitting region is configured to be relatively lower than the reflectance of the portion corresponding to the light emitting region.

The optical thickness of the layer added to the resonator formed by the first multilayer reflection film 2 and the second multilayer reflection film 6 is
When it is equal to an integral multiple of a half wavelength of the oscillation wavelength λ of the laser oscillation light, the Q of the resonator increases, and when it is equal to an odd multiple of a quarter wavelength, the Q of the resonator decreases.

In this embodiment, the sum of the optical thickness of the contact layer 8 and the optical thickness of the second electrode 9 is made equal to an integral multiple of a half wavelength of the oscillation wavelength λ of the laser oscillation light. Thereby, the Q of the resonator is increased in a portion corresponding to the light emitting region 11, and the optical thickness of the second electrode 9 is reduced.
By making the wavelength equal to an odd multiple of the quarter wavelength, the Q of the resonator is reduced in the peripheral portion of the portion corresponding to the light emitting region 11.

Since the purpose is to provide a difference in reflectance between the portion corresponding to the light emitting region 11 and the peripheral portion, the reflectance of the peripheral portion of the portion corresponding to the light emitting region 11 is reduced. It is not necessary to make the optical thickness exactly an odd multiple of a quarter wavelength or an integral multiple of a half wavelength if the reflectance is relatively lower than the reflectance of the portion corresponding to.

As described above, since the optical thickness of the contact layer 8 and the optical thickness of the second electrode 9 cause a difference in mirror loss, by controlling the optical thickness of these layers, the mirror thickness can be reduced. The optical mode can be controlled by changing the reflectance spatially. That is, if a high reflectivity region is defined and its diameter is made equal to the mode size of the operation mode of the lowest order, it is possible to easily obtain a single-peak fundamental transverse mode oscillation.

Further, since the gain region where the amount of current injected from the contact layer 8 is large coincides with the light emitting region 11, as shown in FIG. Since the overlap becomes maximum and the overlap between the higher-order optical mode and the gain region becomes smaller, the oscillation in the higher-order mode is suppressed.
It oscillates in the basic mode. By providing a difference in reflectance between the portion corresponding to the light emitting region 11 and the peripheral portion in this manner, conditions advantageous for the oscillation of the zero-order fundamental transverse mode are set, and an effect that a desired mode is selected is obtained. be able to.

The contact layer 8 has a function of preventing the spread of the injected current. That is, current confinement is performed by the contact layer 8, and as shown in FIG.
The carriers injected into the cap layer 7 made of GaInP of the type spread through the current path 22 into the device. At this time, the current density is high in the portion corresponding to the light emitting region 11 and has a distribution that attenuates as the distance from the region increases, so that the laser oscillation itself is not hindered.

The threshold current can be reduced by the synergistic effect of the current confinement effect and the mode selection effect.
Further, since the degree of light confinement is smaller than that of the conventional refractive index waveguide type, the transverse mode is stable even when the diameter of the aperture is increased to about 10 μm, and the maximum light output in the fundamental transverse mode is dramatically increased. Can be improved.

Finally, on the back surface of the n-type GaAs substrate 1, A
By forming the first electrode 10 made of a uGe / Ni / Au layer, a surface emitting semiconductor laser having the configuration shown in FIG. 1 and oscillating at a wavelength of λ to 780 nm can be obtained.

In the first embodiment, the carrier concentration of the cap layer 7 can be easily controlled by the Schottky barrier even if the second electrode 9 made of a semiconductor material described later is formed directly on this layer. By setting the concentration at such a level that injection is not performed, ohmic contact between the cap layer 7 and the second electrode 9 is not obtained, and the current injection portion is limited to the portion where the contact layer 8 is formed. However, for example, by interposing a silicon insulating film between the cap layer 7 and the contact layer 8, the insulating property between the cap layer 7 and the second electrode 9 is further increased, so that an ineffective current is reduced. It is also possible to devise it not to flow to.

However, the optical thickness of the second electrode 9 is set so that the reflectance of the peripheral portion of the portion corresponding to the light emitting region 11 is relatively lower than the reflectance of the portion corresponding to the light emitting region 11. In addition, it is necessary to adjust the optical thickness of the silicon insulating film.

In the first embodiment described above, by selecting the material of the cap layer 7 and the contact layer 8, the cap layer 7 and the second electrode 9 are not brought into ohmic contact, and the contact layer 8 and the second electrode 9 are not contacted. Although the current confinement is performed by making ohmic contact with 9, another current confinement (current confinement) means can be used in order to more efficiently inject current into the active layer.

For example, in the same manner as in the first embodiment except that the cap layer 7 is formed of undoped or n-type GaInP, a first multilayer reflective film 2, a first spacer layer 3, a quantum well The active layer 4, the second spacer layer 5, the second multilayer reflective film 6, and the cap layer 7 are sequentially laminated, and FIG.
As shown in the figure, by etching using the mask 21,
After the contact layer 8 made of undoped or p-type GaAs is formed only in the portion corresponding to the light emitting region, as shown in FIG. 7A, except for the region where the contact layer 8 is formed, the silicon-based insulating layer is formed. An impurity diffusion mask 23 made of a film is formed. As shown in FIG. 7 (B), by performing vapor phase diffusion of zinc using the mask 23, zinc is diffused into the contact layer 8 and the cap layer 7 thereunder, thereby forming the contact layer 8 and the cap layer 7a. A zinc diffusion region 24 is formed. Since both the cap layer 7 and the contact layer 8 are thin, diffusion reaching the cap layer 7 is relatively easy. Although not particularly shown in the drawing, after removing the mask 23, the second electrode 9 is formed, and the phase adjustment is performed so that the portion corresponding to the light emitting region 11 and the peripheral portion have different reflectances. .

Since zinc works as a p-type dopant,
A pn junction 25 is formed at the interface between the cap layer 7 made of n-type GaInP and the cap layer 7a in which zinc is diffused. The carriers injected into the cap layer 7a flow toward the second multilayer reflective film 6 while avoiding the junction 25,
The effect of current constriction can be obtained. Also, even when the cap layer 7 is undoped, the carriers injected into the cap layer 7a cannot pass through the undoped GaInP layer having a high resistivity like the cap layer 7, and
It will flow toward the second multilayer reflective film 6.

When the conductivity type of the laminated film is reversed and the conductivity type of the second multilayer reflective film 6 is n-type, silicon or germanium acting as an n-type dopant is used as a diffusion source instead of zinc. Can also.

Further, for example, similarly to the first embodiment, the first multilayer reflective film 2, the first spacer layer 3, the quantum well active layer 4, the second spacer layer 5, the second multilayer reflective film 6, and The substrate on which the cap layer 7 is sequentially laminated is taken out of the growth chamber,
As shown in FIG. 3, after a contact layer 8 made of p-type GaAs is formed only in a portion corresponding to the light emitting region 11 by etching, a silicon-based layer is formed on the contact layer 8 as shown in FIG. A mask 26 made of an insulating film or a photoresist is formed, and proton implantation is performed on a portion of the cap layer 7 around a portion corresponding to the light emitting region 11, thereby increasing the resistance as shown in FIG. The formed proton injection region 27 is formed. Although not particularly shown in the drawing, after removing the mask 26, the second electrode 9 is formed, and phase adjustment is performed so that a portion corresponding to the light emitting region 11 and a peripheral portion thereof have different reflectances. .

The proton injection region 27 prevents carriers from spreading in the cap layer 7 in the lateral direction.
The effect of current constriction can be obtained. (Second Embodiment) A surface emitting semiconductor laser according to a second embodiment is similar to the first embodiment except that it is formed in a pillar (post) shape as shown in FIG. The configuration is the same as that of the surface emitting semiconductor laser. By forming the pillars (posts), a further current confinement effect can be obtained.

A method of manufacturing the surface emitting semiconductor laser will be briefly described.

In the same manner as in the first embodiment, the first multilayer reflection film 2, the first spacer layer 3, the quantum well active layer 4, the second spacer layer 5, the second multilayer reflection film 6, and the cap layer 7 are formed. The sequentially laminated substrates are taken out of the growth chamber, and as shown in FIG. 3, a contact layer 8 made of p-type GaAs is formed only in a portion corresponding to the light emitting region 11 by etching.

Thereafter, the cap layer 7 and the second multilayer reflection film 6 are removed by a dry etching technique while leaving the outer peripheral portion of the light emitting region 11 in an annular shape.
To form

After removing the etching mask, a second electrode 9 made of indium tin oxide (ITO) is deposited using an RF sputtering method so as to cover the exposed portion of the cap layer 7 and the contact layer 8. Film. In order to make the contact between the contact layer 8 and the second electrode 9 into ohmic contact, annealing is performed in a temperature range of 300 to 600C.
The annealing temperature may be appropriately determined from this temperature range in consideration of the balance with other steps.

After covering the side surface of the exposed post 31 with the silicon-based insulating film 28, an upper electrode 29 made of Cr / Au is formed so as to make contact with the second electrode 9. Lastly, the AuGe / Ni / Au
By forming the first electrode 10 having the configuration shown in FIG. 9, a surface emitting semiconductor laser oscillating at a wavelength of λ to 780 nm can be obtained.

In the surface-emitting type semiconductor laser of this embodiment, the area through which the current can pass is limited to a slightly larger area than the contact layer 8, so that the current spread below the contact layer is small, and Since the number of ineffective injected carriers that do not contribute to the reduction is reduced, the threshold value or the efficiency can be further reduced. (Third Embodiment) A surface emitting semiconductor laser according to a third embodiment is a modification of the surface emitting semiconductor laser according to the second embodiment, and as shown in FIG. The lowermost layer of the multilayer reflective film 6 is replaced with Al _0.9 Ga _0.1 As and AlA
s, and except that its peripheral portion was oxidized into an insulating region.
The configuration is the same as that of the surface emitting semiconductor laser according to the second embodiment. As described above, by selectively oxidizing a part of the AlAs layer, a stronger current confinement effect can be obtained.

A method for manufacturing this surface emitting semiconductor laser will be briefly described.

As in the second embodiment, the first multilayer reflective film 2, the first spacer layer 3, the quantum well active layer 4, the second spacer layer 5, the second multilayer reflective film 6, and the cap layer 7 are formed. The sequentially laminated substrates are taken out of the growth chamber, and as shown in FIG. 3, a contact layer 8 made of p-type GaAs is formed only on a portion corresponding to the light emitting region 11 by etching.
The cap layer 7 and the second multilayer reflective film 6 are removed using a dry etching technique while leaving the outer peripheral portion of the light emitting region 11 in a ring shape, and a so-called post 31 is formed.

After that, it is indirectly applied to steam at 400 ° C. for about 10 minutes.
By performing so-called wet oxidation by touching
2. The AlAs layer in the multilayer reflection film 6 is oxidized from the peripheral portion.
Al _TwoO_ThreeAnd a part of the post 31 has an insulating region 30 (selected).
Selective oxidation layer) is formed.

After removing the etching mask, a second electrode 9 made of indium tin oxide (ITO) is deposited by RF sputtering so as to cover the exposed portion of the cap layer 7 and the contact layer 8. Film. In order to make the contact between the contact layer 8 and the second electrode 9 into ohmic contact, annealing is performed in a temperature range of 300 to 600C.
The annealing temperature may be appropriately determined from this temperature range in consideration of the balance with other steps.

After the exposed side surface of the post 31 is covered with the silicon-based insulating film 28, an upper electrode 29 made of Cr / Au is formed so that the second electrode 9 can be contacted. Lastly, the AuGe / Ni / Au
By forming the first electrode 10 having the configuration shown in FIG. 10, a surface emitting semiconductor laser oscillating at a wavelength of λ to 780 nm can be obtained.

In the surface emitting semiconductor laser of this embodiment,
The selective oxidation layer 30 provided as a current confinement layer also functions as a light confinement, while the current confinement function is shared by the contact layer 8. Accordingly, the threshold current is further reduced, and the stability of the transverse mode is further improved and the output is increased.

In the third embodiment, the lowermost layer of the second multilayer reflective film 6 is made of AlAs instead of Al _0.9 Ga _0.1 As, but the position and material of the layer subjected to selective oxidation are not limited to this. By forming a part of the second multilayer reflective film 6 as an AlGaAs layer having an aluminum composition ratio of 90% or more, preferably 98% or more, and the other as an AlGaAs layer having a lower aluminum composition ratio, a part of the semiconductor layer is formed. Can be selectively oxidized.

In the third embodiment, Al
In the selective oxidation of the As layer, the heating temperature is set to 400 ° C., but is not limited to this, and may be set to a temperature that can control the final size of the current path to a desired value. Increasing the heating temperature increases the oxidation rate and allows a desired oxidation region to be formed in a short time. However, it is preferable that the oxidation distance be about 400 ° C. because the oxidation distance is most easily controlled.

In the first to third embodiments, the material of the second electrode 9 is indium tin oxide (IT
O) was used, but is not limited to this material.

The material of the second electrode 9 may be any material that is optically transparent to light having a wavelength of laser oscillation and has high conductivity. More specifically, even when laminated with a thickness of 100 to 300 nm, the layer exhibits a conductivity in the range of 1 × 10 ^{3 to} 1 × 10 ⁵ Ω ^-1 cm ^-1 which is sufficient to make contact with the electrode. In addition, a semiconductor material having a transmittance of 80% or more and an absorptivity of 10% or less for light in a wavelength range of 500 to 900 nm can be selected.

[0073] Such materials, in addition to indium tin oxide (ITO), cadmium tin oxide (CTO), _{etc., Cd 2-x Sn x O} 4 in x 0.2 to 0. 4, In _2-y SnO _4, where y is 0.01 to 0.5.
Compounds in the range of 2 satisfy the above conditions.
These materials usually have a refractive index of about 2,
At the time of phase adjustment, it is necessary to control the optical thickness in consideration of the refractive index.

In the first to third embodiments, GaInP is used as the material of the cap layer 7.
It is not limited to this material. A so-called lattice-matching material having a lattice constant close to that of the semiconductor substrate and typically having a lattice mismatch rate of 0.1% or less, and a material that satisfies the requirement of transmitting laser-oscillated light. I just need. For example, GaAs / AlGa is used as a material for forming the active layer.
When an As-based semiconductor is used, (Al _X Ga _{1 -X} ) _0.5
An In _0.5 P-based material or a ZnS _x Se ₁ -x _- based material satisfies the above requirements for the material of the cap layer 7. It is preferable that the Al content is not too large in that the deterioration due to oxidation of the material is small.

When the cap layer 7 is used as an etch stopper, the material forming the contact layer 8 has an etching selectivity 10 times or more that of the material forming the cap layer 7. It is more preferable to select a material.

In each of the first to third embodiments, the second multilayer reflective film 7 is a p-type, and the first multilayer reflective film 4
Is n-type, but the present invention is not limited to this, and the conductivity type can be inverted. The conductivity type may be determined from a comprehensive point of view while taking into account the difference in element resistance depending on the light extraction direction and the conductivity type.

In general, the p-type layer is more concerned with an increase in element resistance due to the discontinuity of the forbidden band width than the n-type layer. Therefore, an increase in the number of p-type layers is a factor of deteriorating laser characteristics, and is therefore preferable. Absent. Further, in the above-described embodiment, the second multilayer reflective film has a smaller number of layers than the first multilayer reflective film because the emitted light is extracted from the upper surface of the substrate. For this reason, the conductivity type of the second multilayer reflective film is set to p-type.
Therefore, when taking out the emitted light from the back surface of the substrate,
It is conceivable that the number of layers of the second multilayer reflective film is larger than the number of layers of the first multilayer reflective film, and the conductivity type of the second multilayer reflective film is n-type.

Since the element resistance is inversely proportional to the area,
For example, in the case of the surface-emitting type semiconductor laser formed in a post shape as seen in the second and third embodiments, the second multilayer reflection film having a small area causes an increase in element resistance.
Therefore, it is more preferable that an n-type layer that can have a smaller element resistance than the p-type layer with the same area be used as the second multilayer reflective film.

In the first to third embodiments, the material constituting the quantum well active layer is GaAs / AlG
Although an aAs-based semiconductor was used, the invention is not limited to this. For example, GaAs / InGaAs may be used for the quantum well active layer.
It is also possible to use a GaInP / AlGaInP-based semiconductor. In the case of a GaAs / InGaAs-based semiconductor, since the emission wavelength from the quantum well layer is transparent to the GaAs substrate, it is easy to take out the emitted light from the back surface of the substrate, and there is also an advantage in the process.

In the first to third embodiments, the cap layer is provided separately from the second multilayer reflective film. However, the outermost layer of the second multilayer reflective film is an undoped layer, and this is used as a cap layer. You may.

In the first to third embodiments, the case where the MOCVD method is used as the crystal growth method has been described. However, the present invention is not limited to this. For example, the molecular beam epitaxy (MBE) method may be used. A similar semiconductor film can be obtained.

It should be noted that any of the embodiments should not be interpreted in a limited manner, and can be realized by other methods as long as the constituent features of the present invention are satisfied.

[0083]

As described above, the surface-emitting type semiconductor laser of the present invention can control the optical mode by adjusting the optical thickness of the layers to be laminated, and can easily perform the fundamental transverse mode oscillation. Is obtained.

Further, the surface emitting semiconductor laser of the present invention
It is possible to make contact with the electrode only at the portion corresponding to the light emitting region, and to simultaneously perform current confinement and improve the selectivity of the basic lateral mode, reduce the threshold current and reduce the light emitting region. Because it is possible to expand the area,
There is an effect that high output can be achieved in the basic lateral mode.

Further, the surface emitting semiconductor laser of the present invention has an effect that it can be manufactured with a simple process with good reproducibility.

[Brief description of the drawings]

FIG. 1A is a sectional view of a planar type surface emitting semiconductor laser according to a first embodiment of the present invention, and FIG. 1B is a reflectance distribution of the surface emitting type semiconductor laser shown in FIG. FIG.

FIG. 2 is a cross-sectional view in a manufacturing process of the planar surface emitting semiconductor laser according to the first embodiment of the present invention (lamination process).

FIG. 3 is a cross-sectional view in a manufacturing process of the planar surface emitting semiconductor laser according to the first embodiment of the present invention (etching process).

FIG. 4 is a cross-sectional view in a manufacturing step of the planar surface-emitting type semiconductor laser according to the first embodiment of the present invention (second electrode forming step).

FIG. 5 is a conceptual diagram showing an overlap between a gain region and an optical mode of the planar type surface emitting semiconductor laser according to the first embodiment of the present invention.

FIG. 6 is a conceptual diagram showing a current path of the planar type surface emitting semiconductor laser according to the first embodiment of the present invention.

FIGS. 7A and 7B are cross-sectional views of a first modified example in which the current injection method of the planar surface emitting semiconductor laser according to the first embodiment of the present invention is improved (Zn); FIGS. Diffusion method).

FIGS. 8A and 8B are cross-sectional views of a second modification in which the current injection method of the planar surface emitting semiconductor laser according to the first embodiment of the present invention is improved (proton). Injection method).

FIG. 9 is a sectional view of a surface emitting semiconductor laser according to a second embodiment of the present invention.

FIG. 10 is a sectional view of a surface emitting semiconductor laser according to a third embodiment of the present invention.

FIG. 11 is a cross-sectional view of a surface emitting semiconductor laser according to the related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 GaAs substrate 2 first multilayer reflective film 3 first spacer layer 4 quantum well active layer 5 second spacer layer 6 second multilayer reflective film 7 cap layer 8 contact layer 9 second electrode 10 first electrode 11 opening (light emission) Region) 21 resist mask 22 current path 23 insulating film mask 24 zinc diffusion region 25 pn junction 26 mask for proton injection 27 proton injection region 28 silicon-based insulating protective film 29 upper electrode 30 selective oxide layer (insulating region) 125 VCSEL 130 Substrate 132,138 Parallel mirror stack 135 Spacer layer 139 Trench 140 Mesa 142 Contact window 144 Dielectric layer 146 Contact layer 147 Electrode 148 Optical mode 149 Current distribution

Claims (10)

[Claims] A first electrode provided on a semiconductor substrate; a first multilayer reflection film provided on a surface of the semiconductor substrate opposite to the first electrode; and a first multilayer reflection film sandwiching an active layer. A second multilayer reflection film provided so as to face the film, a second electrode optically transparent to laser-oscillated light, and for injecting a current into the active layer together with the first electrode; Provided between the second electrode and the second multilayer reflective film,
A contact layer optically transparent to the laser oscillation light is formed at a portion corresponding to the light emitting region, and current can be injected into the active layer through the portion where the contact layer is formed. And a cap layer that disables current injection into the active layer through a portion where the contact layer is not formed, and adjusts an optical thickness of the second electrode and an optical thickness of the contact layer. Accordingly, the surface-emitting type semiconductor laser in which the reflectance of the peripheral portion of the portion where the contact layer is formed is lower than the reflectance of the portion where the contact layer is formed. 2. The surface emitting semiconductor according to claim 1, wherein the cap layer is optically transparent to laser-oscillated light, and is formed of a material lattice-matched with the second multilayer reflective film. laser. 3. The contact layer is formed of a material that is lattice-matched with the cap layer, is capable of heterojunction with the cap layer, and has ohmic contact with the second electrode. The surface emitting semiconductor laser according to claim 1. 4. A first electrode provided on a GaAs substrate of a first conductivity type, and a first multilayer reflection type AlGaAs-based first conductivity type provided on a surface of the substrate opposite to the first electrode. And a second conductive type Al provided to face the first multilayer reflective film with an undoped AlGaAs-based active layer interposed therebetween.
A second GaAs-based multilayer reflective film, a second electrode that is optically transparent to laser-oscillated light, and that injects a current into the active layer together with the first electrode; Provided between the second multilayer reflective film,
A contact layer that is optically transparent to the laser oscillation light is formed at a portion corresponding to the light emitting region, and current can be injected into the active layer through the portion where the contact layer is formed. And a cap layer that disables current injection into the active layer through a portion where the contact layer is not formed, wherein the optical thickness of the second electrode and the optical thickness of the contact layer are A surface-emitting type semiconductor laser in which the reflectivity of a portion around the portion where the contact layer is formed is made lower than the reflectivity of the portion where the contact layer is formed by adjusting. 5. The cap layer is made of an AlGaInP-based semiconductor or a GaInP-based semiconductor.
3. A surface emitting semiconductor laser according to claim 1. 6. The surface emitting semiconductor laser according to claim 4, wherein said contact layer is formed of an AlGaAs-based semiconductor or a GaAs-based semiconductor. 7. The surface emitting semiconductor laser according to claim 1, wherein the second electrode is formed of cadmium tin oxide or indium tin oxide. 8. A method for manufacturing the surface emitting semiconductor laser according to claim 1, wherein the first multilayer reflection film, the active layer, and the second multilayer are formed on a semiconductor substrate. A laminating step of sequentially laminating a reflective film, a cap layer, and a contact layer; an etching step of etching the contact layer while leaving a portion corresponding to a light emitting region; and a portion where the contact layer is formed and a peripheral portion thereof. An electrode laminating step of forming a second electrode so as to cover the surface of the semiconductor laser. 9. The method according to claim 8, wherein in the etching step, the cap layer is used as an etch stopper when etching the contact layer. 10. The method for manufacturing a surface-emitting type semiconductor laser according to claim 8, wherein the contact layer is formed by laminating the cap layer by crystal growth of a semiconductor and then continuously by crystal growth of a semiconductor. .