JP2006019470A - Surface emitting semiconductor laser and optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface emitting semiconductor laser which can reduce intrinsic noise and return light noise, and to provide an optical module using this surface emitting semiconductor laser as a light source. <P>SOLUTION: The surface emitting semiconductor laser includes an n-type DBR layer 12, an active layer 14, a p-type DBR layer 17, a p-type contact layer 18, and a p-type side electrode 20 on an n-type semiconductor substrate 11 to retrieve output light through an opening 20a of the p-type side electrode 20. An optical absorption layer 21 is formed on a p-type contact layer 18 in the opening 20a of the p-type side electrode 20, in which, when an absorption coefficient to a luminescense wavelength is α (cm<SP>-1</SP>), and the thickness is t, an equation 0.1≤αt≤1 is satisfied when the luminescence wavelength is shorter than 850 nm, and an equation 0.4≤αt≤1 is satisfied when the luminescence wavelength is 850 nm or longer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface emitting semiconductor laser and an optical module using the surface emitting semiconductor laser as a light source.

ただし、Ｓ₀ は内部光密度、∂ｇ_t ／∂ｎは微分利得係数、τ_p は光子の寿命時間を示している。
半導体レーザ［基礎と応用］伊藤良一・中村道治共編、培風館、ｐ．１５５ In the characteristics of a semiconductor laser, fluctuation of emission intensity amplitude, that is, relative noise intensity (RIN) is a characteristic having a very high influence on application. This RIN is classified into two types, one is “inherent noise” that occurs when there is no return light, and the other is “return light noise” that is added when there is return light. Among these, it is known that the intrinsic noise has a strong correlation with the output light output as shown in FIG. That is, it has a peak at a specific frequency ( _fr : relaxation oscillation frequency), monotonically decreases on the low frequency side, and becomes a constant value below 10 MHz. RIN As further increase of the semiconductor laser output (P _out) is lowered as a whole, f _r increases. Here, the decrease in RIN with the output of the semiconductor laser is essentially a phenomenon seen when _fr increases. Here, _fr is represented by the following formula (for example, Non-Patent Document 1).

Where S ₀ is the internal light density, ∂g _t / ∂n is the differential gain coefficient, and τ _p is the photon lifetime.
Semiconductor Laser [Basics and Applications] edited by Ryoichi Ito and Michiharu Nakamura, Baifukan, p. 155

there is high-speed modulation of a specific performance of the semiconductor laser affected by f _r. That is, for example, communication semiconductor lasers require high-speed modulation, but at this time, as one factor for determining the upper limit frequency of direct modulation of semiconductor lasers, stimulated emission may not be able to follow the change in the number of carriers. . This phenomenon is remarkable at frequencies above f _r, f _r gives laser inherent frequency limitations. Another factor is that the applied current is not effectively injected into the active layer in the high frequency region due to the entire laser or the parasitic impedance of the package.
Therefore, increasing the f _r is a large capacity and high speed transmission of several Gbps or the like in recent years in implementing using light, which is one of the important characteristics required for the semiconductor laser.

Conventionally, the following countermeasures (a) to (c) have been studied in order to solve the problem of frequency limitation due to the fact that stimulated emission cannot follow the change in the number of carriers.
(A) In order to reduce the photon lifetime τ _p , the cavity length is shortened to about 100 μm in a Fabry-Perot resonator semiconductor laser (Non-patent Document 2).
IEEE J. Quantum Electron., QE-21, 121, 1985

(B) In order to increase the differential gain (活性 g _t / ダ ブ ル n), a p-type impurity is added to the active layer of the double heterojunction (DH) laser (Non-Patent Document 3).
Appl. Phys. Lett., 45, 1302, 1984 Further, a high-concentration p-type impurity is modulated and added only to the barrier layer in the multiple quantum well (MQW) structure (Non-patent Document 4). European Conference on Optical Communication 2 (invited) 29 in Helsinki 1987 Moreover, the well layer in MQW is made into a multilayer (nonpatent literature 5). Jpn. J. Appl. Phys. 24, L539, 1985 (c) Regarding the increase of the photon density S0, the photon density of the Fabry-Perot resonator type semiconductor laser depends on the occurrence of end face breakdown (AlGaAs system) or thermal saturation (GaInAsP system). ), The end face is made transparent to the laser beam in order to increase the end face breaking photon density (Non-patent Document 6). IEEE J. Quantum Electron., QE-21, 121, 1985

However, in recent years, vertical cavity surface emitting laser (VCSEL), which is a novel device form, has attracted attention as a form of laser for optical communication. As shown in FIG. 25, in this device configuration, the resonator length is effectively the optical guide layer (lower clad layer and upper clad layer) disposed above and below the active layer and the distributed Bragg reflector (DBR). The thickness of the light guide layer is generally considered to be a λ resonator length, and is limited to the same wavelength (or an integer multiple thereof) including the thickness of the active layer portion. Yes. Therefore, with respect to (a) above, the resonator length cannot be effectively reduced to λ or less. Further, regarding (b), in the Fabry-Perot resonator type semiconductor laser, it is common to increase the total number of MQW well layers as described above, but the active layer has a lattice mismatch such as GaInNAs in particular. When using a material, increasing the number of wells is not generally an appropriate means from the relationship with the critical film thickness. Therefore, it is considered effective to increase the internal light density in (c). However, in applications such as communication, the light output is generally limited due to the safety of laser light and the like. It is that to many simply increase the S ₀ can not cope.

  Further, as described above, the laser noise also includes “return light noise” that is generated because the emitted light is reflected by an external optical system and returns to the laser itself. Although this phenomenon has various factors, it is understood that this phenomenon is a competition between the external resonance mode depending on the external cavity length and the longitudinal mode (internal mode) of the laser itself. In this case, the cause is essentially the presence of return light, and noise can be reduced by solving this.

In surface-emitting lasers and the like, it is known that the reflectivity of DBR is close to 99%, and the distribution of light density of standing waves is almost concentrated in the active layer region and is low near the exit end face. (FIG. 25) (Non-patent Document 6).
IEEE Journal of Quantum Electronics 27 p.1332 (1998)

Patent Document 1 discloses a surface emitting laser having a protective film on a GaAs contact layer in a laser light emission opening portion. The thickness of the GaAs contact layer is the light emitted from the GaAs contact layer with respect to the emission wavelength. In addition to being described as thinning to suppress absorption, the protective film is selected from a SiO ₂ film, a SiO _x N _y film, a SiN _x film, and an In _x Sn _y O _z film. It is described that a transparent medium that transmits laser light is desirable. Therefore, the technical idea of Patent Document 1 is greatly different from the present invention in which a light absorption layer is provided at the laser light emission opening and the light absorption layer actively absorbs light to reduce laser noise. Is.
JP 2002-9393 A

As a result of intensive studies to simultaneously reduce the above-described intrinsic noise and return light noise, the present inventors have a sufficiently large absorption capacity in the emission wavelength region near the emission emission end face of the surface emitting laser compared to the conventional one. It has been found that it is effective to provide a light absorption layer. Absorbing This is because the light absorption layer is present, the internal light density necessary to obtain any emission output result f _r increases to increase, and the return light from the outside to the light absorbing layer Thus, it is considered that the fact that the active layer is not reached contributes greatly. The film used as the light absorption layer may be a semiconductor film, a dielectric film, or a metal, and may have a sufficiently large absorption capability in the emission wavelength region.

  Here, in the conventional end surface emitting type semiconductor laser, the end surface reflectance is usually 70 to 80% at the highest, and the light emitting end surface and the light emitting portion are the same, so a light absorption layer is provided near the end surface. The use of this has been a problem because it causes deterioration of the end face, but particularly in a surface emitting laser (Non-Patent Document 7), the reflectance of DBR is close to 99%, and the distribution of light density of standing waves is almost active. It is concentrated in the layer region and is low in the vicinity of the emission end face (FIG. 24). Therefore, even if the light absorption layer is formed in the vicinity of the emission end face, it does not cause deterioration.

Therefore, the problem to be solved by the present invention is to increase the relaxation oscillation frequency and reduce the relative noise intensity by artificially increasing the internal light density for obtaining an arbitrary emission intensity, It is an object of the present invention to provide a surface emitting semiconductor laser capable of reducing intrinsic noise and return light noise and an optical module using the surface emitting semiconductor laser as a light source.
The above problems and other problems will become apparent from the description of this specification.

In order to solve the above problem, the first invention is:
A first reflective layer;
An active layer on the first reflective layer;
A second reflective layer on the active layer;
An electrode having an opening on the second reflective layer;
In a surface emitting semiconductor laser that extracts output light having a wavelength shorter than 850 nm from the second reflective layer through the opening of the electrode,
On the second reflective layer inside the opening of the electrode, light of 0.1 ≦ αt ≦ 1, where α (cm ⁻¹ ) is the absorption coefficient with respect to the emission wavelength, and t (cm) is the thickness. It has an absorption layer.

Here, the lower limit of αt is set to 0.1. In a surface emitting semiconductor laser having an emission wavelength shorter than 850 nm (780 nm band, etc.), the light absorption layer sufficiently absorbs light if it is 0.1 or more. As a result of the pseudo increase in the internal light density required to obtain an arbitrary light output, the relaxation oscillation frequency is sufficiently increased, and the return light from the outside is sufficiently absorbed by the light absorption layer. This is because the intrinsic noise and the return light noise can be sufficiently reduced by not reaching the active layer. The upper limit of αt is set to 1 to sufficiently reduce the intrinsic noise and the return light noise. This is because an excessive decrease in the intensity of the laser beam emitted outside the laser is suppressed and an increase in operating current is suppressed. From the viewpoint of further reducing the inherent noise and the return light noise, 0.2 ≦ αt ≦ 1 is preferably satisfied.
When the light absorption layer has an n-layer multilayer structure, αt = α ₁ t ₁ + α ₂ t ₂ +... + Α, where α _{i is} the absorption coefficient of the i layer and t _i (i = 1 to n) is the thickness. Consider _n-1 t _n-1 + α _n t _n .

  Any material can be used for the light absorption layer as long as it has a sufficiently large absorption coefficient with respect to the emission wavelength, and examples thereof include metals and insulators. As the metal, for example, at least one selected from the group consisting of Ti, Pt, Au, AuGe, Ni, Pd, Cr and Hf is used, and these single metals or alloys are used. Either a film or a multilayer metal film may be used. Thus, when forming a light absorption layer with a metal, the thickness is generally 2 nm or more and 12 nm or less. As the insulator, a semiconductor can be used. For example, in addition to amorphous Si, there are GaInAs, GNAAs, GaInNAs, GaAs, AlGaAs, and the like, and the most suitable one according to the emission wavelength. To be elected. If necessary, a laminated film of a metal film and an insulating film may be used as the light absorption layer, and as the metal film and the insulating film, for example, those described above can be used.

For the purpose of improving the adhesion of the light absorbing layer to the base and protecting the surface, if necessary, an absorption coefficient near the emission wavelength on the light absorbing layer or between the second reflective layer and the light absorbing layer. An insulating film that does not have a thickness may be provided. As such an insulating film, for example, SiO _x (x is, for example, near 2), SiN _x (x is, for example, around 4/3), SiN _x O _y , Al ₂ O ₃ , TiO _x (where x is, for example, around 2). ) And ZrO _x (x is, for example, near 2), and at least one selected from the group consisting of ZrO _x can be used.

  The light absorption layer may have a uniform thickness or a thickness distribution according to the purpose. Specifically, the thickness of the outer peripheral portion of the light absorption layer may be larger than the thickness of the central portion. In this case, light absorption at the outer peripheral portion is increased, which is suitable for obtaining a unimodal beam as output light. Contrary to the above, the thickness of the outer peripheral portion may be smaller than the thickness of the central portion. In this case, light absorption at the central portion is increased, which is suitable for obtaining a bimodal beam as output light. Yes.

Typically, the light absorption layer is provided on the second reflective layer via the contact layer. More specifically, for example, the contact layer has a recess in a portion corresponding to the opening of the electrode, and a light absorption layer is provided on the contact layer of the recess. In another example, a light absorption layer is provided on the second reflective layer, a contact layer having an opening corresponding to the opening of the electrode is provided on the light absorption layer, and an electrode is provided on the contact layer. It is done. Alternatively, a light absorption layer is provided on the second reflection layer, a contact layer having a recess in a portion corresponding to the opening of the electrode is provided on the light absorption layer, and the electrode is provided on the contact layer. The light absorption layer may be provided at a depth in the middle of the contact layer. That is, the light absorption layer may be provided in the form of being inserted in the middle of the contact layer. When a material having an absorption coefficient that cannot be ignored with respect to the emission wavelength, for example, GaAs, is used as the contact layer material, the entire αt of the light absorption layer and the contact layer is included in the above range. . The light absorption layer may be provided directly on the second reflective layer.
The light absorption layer may be provided so as to bridge the opening of the electrode. Furthermore, a light absorbing layer may be provided in the transparent window portion of the package that accommodates the surface emitting semiconductor laser.
The electrode openings, contact layer openings or recesses are typically circular.

  The first reflective layer and the second reflective layer are typically made of a semiconductor multilayer film (DBR), one of which is n-type and the other is p-type. Specifically, the semiconductor multilayer film is, for example, one in which AlGaAs layers having different Al compositions are alternately stacked, or one in which AlGaInP layers having different Al compositions and Ga compositions are alternately stacked. The active layer and the second reflective layer typically have a cylindrical shape, that is, a mesa post structure. Also, typically, a current confinement layer is provided on the upper or lower portion of the active layer. This current confinement layer is typically formed by oxidation confinement. AlGaAs is used as the material of the active layer, and the active layer has a single quantum well structure or a multiple quantum well structure.

The second invention is
A first reflective layer;
An active layer on the first reflective layer;
A second reflective layer on the active layer;
An electrode having an opening on the second reflective layer;
In a surface emitting semiconductor laser that extracts output light having a wavelength of 850 nm or more from the second reflective layer through the opening of the electrode,
On the second reflective layer inside the opening of the electrode, when the absorption coefficient with respect to the emission wavelength is α (cm ⁻¹ ) and the thickness is t (cm), light of 0.4 ≦ αt ≦ 1 It has an absorption layer.

Here, the lower limit of αt is set to 0.4. In the surface-emitting semiconductor laser having an emission wavelength of 850 nm or more, if the light emission wavelength is 0.4 or more, the light absorption layer sufficiently absorbs light and emits any light. As a result of the pseudo increase of the internal light density necessary to obtain the output, the relaxation oscillation frequency is sufficiently increased, and the return light from the outside is sufficiently absorbed by the light absorption layer to reach the active layer. This is because the intrinsic noise and the return light noise can be sufficiently reduced by not reaching, and the upper limit of αt is set to 1 while the intrinsic noise and the return light noise are sufficiently reduced, This is for suppressing an excessive decrease in the intensity of the emitted laser light and suppressing an increase in operating current. From the viewpoint of further reducing the inherent noise and the return light noise, 0.6 ≦ αt ≦ 1 is preferably satisfied.
The material of the active layer is, for example, GaAs, AlGaAs, GaInNAs, GaInAsP, or the like.
In the second invention, what has been described in relation to the first invention is valid as long as it is not against the nature thereof.

The third invention is
A first reflective layer;
An active layer on the first reflective layer;
A second reflective layer on the active layer;
An electrode having an opening on the second reflective layer;
Output light having a wavelength shorter than 850 nm is extracted from the second reflective layer through the opening of the electrode,
On the second reflective layer inside the opening of the electrode, light of 0.1 ≦ αt ≦ 1, where α (cm ⁻¹ ) is the absorption coefficient with respect to the emission wavelength, and t (cm) is the thickness. An optical module comprising a surface emitting semiconductor laser having an absorption layer as a light source.
Here, the use and configuration of the optical module are not limited. For example, the optical module is a communication optical module.
In the third invention, what has been described in relation to the first invention is valid as long as it is not contrary to the nature thereof.

The fourth invention is:
A first reflective layer;
An active layer on the first reflective layer;
A second reflective layer on the active layer;
An electrode having an opening on the second reflective layer;
Output light having a wavelength of 850 nm or more is extracted from the second reflective layer through the opening of the electrode,
On the second reflective layer inside the opening of the electrode, when the absorption coefficient with respect to the emission wavelength is α (cm ⁻¹ ) and the thickness is t (cm), light of 0.4 ≦ αt ≦ 1 An optical module comprising a surface emitting semiconductor laser having an absorption layer as a light source.
In the fourth invention, what has been described in relation to the first and third inventions is valid as long as it is not contrary to the nature thereof.

FIG. 1 shows the correlation between the thickness t (nm) of the light absorption layer and the amount of absorption (%) with respect to various absorption coefficients. The absorption coefficient is 1 × 10 ⁻² (cm in order from the bottom to the top curve. ⁻¹ ), 1 × 10 ⁻¹ (cm ⁻¹ ), 1 × 10 ⁰ (cm ⁻¹ ), 1 × 10 ¹ (cm ⁻¹ ), 1 × 10 ² (cm ⁻¹ ), 1 × 10 ³ ( cm ⁻¹ ), 1 × 10 ⁴ (cm ⁻¹ ), 1 × 10 ⁵ (cm ⁻¹ ), and 1 × 10 ⁶ (cm ⁻¹ ). FIG. 2 shows the correlation between the absorption coefficient and the absorption amount (%) with respect to the thickness t (nm) of various light absorption layers, and the thicknesses are 1 nm, 10 nm, 100 nm, and 1000 nm in order from the bottom to the top curve. It is. FIG. 3 shows the wavelengths of the absorption coefficients of AlGaAs, GaAs, and GaInAs. For AlGaAs, the Al composition is 0.3023, 0.3624, 0.4199, 0.4682, and GaInAs in order from the right to the left curve. The In composition is 0.18, 0.30, 0.40, 0.44, and 0.53 in order from the left to the right curve. FIG. 4 shows the absorption coefficients of AlGaAs, GaAs, and GaInAs for various emission wavelengths. In FIG. 4, n and k are the real part and the imaginary part of the complex refractive index, respectively. FIG. 5 shows absorption coefficients of Al ₂ O ₃ , a-Si, and SiN as examples of insulators. FIG. 6 shows absorption coefficients of Ti, Pt, and Au as examples of metals.

  In the present invention configured as described above, the light absorption layer provided on the second reflection layer inside the opening of the electrode can absorb light sufficiently with respect to the emission wavelength. As a result of the pseudo-enough increase in the internal light density necessary to obtain the light emission output of the active layer, the relaxation oscillation frequency increases, and the return light from the outside is sufficiently absorbed by the light absorption layer. You can avoid reaching up to.

  According to the present invention, the internal light density necessary for obtaining an arbitrary light output is sufficiently increased in a pseudo manner. As a result, the relaxation oscillation frequency is increased and the return light from the outside is sufficiently supplied to the light absorption layer. By being absorbed, it is possible to prevent the active layer from reaching the active layer, thereby reducing intrinsic noise and return light noise. This surface emitting semiconductor laser is suitable for use as a light source for communication, for example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are denoted by the same reference numerals.
FIG. 7 is a sectional view showing a vertical cavity surface emitting semiconductor laser according to the first embodiment of the present invention.

  As shown in FIG. 1, in this surface emitting semiconductor laser, an n-type DBR layer 12, a lower cladding layer 13, an active layer 14 as a light-emitting layer, on an n-type semiconductor substrate 11 such as an n-type GaAs substrate, The upper cladding layer 15, the current confinement layer 16, the p-type DBR layer 17, and the p-type contact layer 18 are sequentially stacked.

The n-type DBR layer 12 is composed of a semiconductor multilayer film in which n-type AlAs layers 12a and n-type GaAs layers 12b are alternately stacked. For example, the n-type DBR layer 12 has a total thickness of about 4 μm in which 35 layers of these layers are stacked. The lower cladding layer 13 is made of, for example, Al _x Ga _1-x As, for example, x = 0.3. The active layer 14 is composed of a semiconductor corresponding to the emission wavelength, and as the semiconductor, for example, one selected from those already mentioned can be used. The upper cladding layer 15 is made of, for example, Al _y Ga _1-y As, for example, y = 0.3. The current confinement layer 16 has a structure in which the circumference of the circular p-type AlAs layer 16a is surrounded by a ring-shaped Al oxide layer 16b, and the p-type AlAs layer 16a is a portion through which current flows. The diameter of the p-type AlAs layer 16a is, for example, about 12 μm. The thicknesses of the p-type AlAs layer 16a and the Al oxide layer 16b are, for example, about 30 nm. The p-type DBR layer 17 is formed by alternately stacking p-type Al _z Ga _1-z As layers 17a and p-type Al _w Ga _1-w As layers 17b (where z> w, 0 <z, w <1). For example, these layers have a total thickness of about 3 μm obtained by laminating 25 layers of these layers. For example, z = 0.9 and w = 0.1. The current confinement layer 16 is provided in place of the lowermost p-type Al _z Ga _{1 -z} As layer 17a of the p-type DBR layer 17. The p-type contact layer 18 is made of, for example, p-type GaAs having an impurity concentration of 5 × 10 ¹⁸ cm ⁻³ .

  The uppermost n-type AlAs layer 12b, lower cladding layer 13, active layer 14, upper cladding layer 15, current confinement layer 16, p-type DBR layer 17 and p-type contact layer 18 of the n-type DBR layer 12 are cylindrical as a whole. And has a post-type mesa structure. The diameter of the mesa portion is, for example, about 30 to 40 μm. The p-type contact layer 18 has a circular recess 18a at the center, and has a ring shape. The diameter of the recess 18a is, for example, about 20 μm.

An insulating film 19 such as a SiO ₂ film or a SiN _x film is provided so as to cover the surface of the n-type DBR layer 12 in the mesa portion and a portion other than the mesa portion. The insulating film 19 has a thickness of about 300 nm, for example. The insulating film 19 is provided with an opening 19a. A p-side electrode 20 is provided in ohmic contact with the p-type contact layer 18 through the opening 19a. The p-side electrode 20 is made of, for example, a Ti / Pt / Au laminated film and has a total thickness of about 500 nm. The p-side electrode 20 has a circular opening 20a having the same diameter as the diameter of the recess 18a of the p-type contact layer 18 at the center thereof.

A light absorption layer 21 is provided inside the recess 18 a of the p-type contact layer 18. As the light absorption layer 21, a metal film (single-layer metal film or multilayer metal film) or an insulating film is used. As the metal film and the insulating film, for example, those already mentioned can be used. In this case, the entire αt of the light absorption layer 21 and the p-type contact layer 18 thereunder is 0.1 ≦ αt ≦ 1, preferably 0.2 ≦ αt ≦ 1, in the emission wavelength band of 780 nm. The material and the thickness of the light absorption layer 21 and the p-type contact layer 18 thereunder are selected so that 0.4 ≦ αt ≦ 1, preferably 0.6 ≦ αt ≦ 1, at 850 nm or more. . For example, when the emission wavelength is in the 780 nm band, when the light absorption layer 21 is made of a Ti film having a thickness of 5 nm and the p-type contact layer 18 of the recess 18a is made of GaAs having a thickness of 30 nm, the absorption coefficient of Ti is 5 from FIG. .35 × 10 ⁵ cm ⁻¹ , and the absorption coefficient of GaAs is 1.63 × 10 ⁴ cm ^{−1 according} to FIG. 4, so αt = (5.35 × 10 ⁵ ) × 5 × 10 ⁻⁷ + (1. 63 × 10 ⁴ ) × 30 × 10 ⁻⁷ = 0.32. Alternatively, when the light absorption layer 21 is made of an a-Si film having a thickness of 300 nm and the p-type contact layer 18 of the recess 18a is made of GaAs having a thickness of 30 nm, the absorption coefficient of a-Si is 5.59 × from FIG. Since the absorption coefficient of 10 ³ cm ⁻¹ and GaAs is 1.63 × 10 ⁴ cm ⁻¹ from FIG. 4, αt = (5.59 × 10 ³ ) × 300 × 10 ⁻⁷ + (1.63 × 10 ⁴ ) × 30 × 10 ⁻⁷ = 0.22. When the emission wavelength is 850 nm or more, when the light absorption layer 21 is made of a Ti film having a thickness of 12 nm and the p-type contact layer 18 of the recess 18a is made of GaAs having a thickness of 100 nm, the absorption coefficient of Ti is 4.86 from FIG. × 10 ⁵ cm ^-1, the absorption coefficient of GaAs is a 4 than ^{1.05 × 10 4 cm -1, αt} = (4.86 × 10 5) × 12 × 10 -7 + (1.05 × 10 ⁴ ) × 100 × 10 ⁻⁷ = 0.69.
On the other hand, an n-side electrode 22 is provided in ohmic contact with the back surface of the n-type semiconductor substrate 11. The n-side electrode 22 is made of, for example, an AuGe / Ni / Au laminated film.

Next, a method for manufacturing the surface emitting semiconductor laser configured as described above will be described.
As shown in FIG. 8, first, an n-type DBR layer 12, a lower cladding layer 13, an active layer 14, an upper cladding layer 15, and the like are formed on an n-type semiconductor substrate 11 by, for example, a metal organic chemical vapor deposition (MOCVD) method. A p-type AlAs layer 23, a p-type DBR layer 17, and a p-type contact layer 18 are grown sequentially.

Next, for example, a SiN _x film (not shown) is formed on the p-type contact layer 18 by, for example, plasma CVD, and a circular resist pattern (not shown) is further formed thereon by lithography. The SiN _x film is etched by a reactive ion etching (RIE) method using, for example, CF ₄ as an etching gas using the pattern as a mask. Thus, a circular SiN _x film is formed.

Next, using the circular SiN _x film thus formed as an etching mask, the substrate is formed up to the uppermost n-type AlAs layer 12b of the n-type DBR layer 12 by RIE using, for example, a chlorine-based gas as an etching gas. Anisotropic etching is performed in a direction perpendicular to the surface. As a result, as shown in FIG. 9, the uppermost n-type AlAs layer 12 b, lower clad layer 13, active layer 14, upper clad layer 15, p-type AlAs layer 23, and p-type DBR layer 17 of the n-type DBR layer 12. The p-type contact layer 18 is processed into a post-type mesa shape.

Next, the mesa portion thus formed is heated in a water vapor atmosphere at a temperature of, for example, 400 ° C. for about 25 minutes to selectively oxidize only the outer peripheral portion of the p-type AlAs layer 23 in a ring shape. As a result, as shown in FIG. 10, a current confinement layer 16 in which a circular p-type AlAs layer 16a is surrounded by a ring-shaped Al oxide layer 16b is formed.
Next, after the SiN _x film used as an etching mask is removed by etching, for example, by RIE, as shown in FIG. 11, for example, plasma is formed on the surface of the n-type DBR layer 12 in the mesa portion and portions other than the mesa portion. An insulating film 19 made of, for example, a SiO ₂ film or a SiN _x film is formed by CVD. Next, the central portion of the upper surface of the mesa post portion of the insulating film 19 is removed by etching to form a circular opening 19a. Next, a Ti / Pt / Au laminated film is formed on the entire surface by vacuum deposition or the like to form the p-side electrode 20, and then the p-side electrode 20 is patterned into a predetermined shape by etching to form an opening 20a. Next, using this p-side electrode 20 as a mask, the p-type contact layer 18 is etched to a predetermined depth by, for example, the RIE method to form a recess 18a.

Next, as shown in FIG. 7, after a metal film or an insulating film is formed on the entire surface by a vacuum deposition method (heating deposition method, electron beam deposition method), CVD method, sputtering method, etc., this is etched into a predetermined shape. Then, the light absorption layer 21 is formed in the recess 18 a of the p-type contact layer 18.
Next, if necessary, the n-type semiconductor substrate 11 is polished to a predetermined thickness from the back surface side, and then an AuGe / Ni / Au laminated film is formed on the back surface of the n-type semiconductor substrate 11 by vacuum deposition or the like. Thus, the n-side electrode 22 is formed.
Thereafter, the laser wafer obtained as described above is made into chips.
As described above, the target surface emitting semiconductor laser is manufactured.

As described above, according to the first embodiment, the light absorption layer 21 is provided in the recess 18a of the p-type contact layer 18, and the entire αt of the light absorption layer 21 and the p-type contact layer 18 below the light absorption layer 21 is provided. However, when the emission wavelength is 780 nm, 0.1 ≦ αt ≦ 1, preferably 0.2 ≦ αt ≦ 1, and when the emission wavelength is 850 nm or more, 0.4 ≦ αt ≦ 1, preferably 0.6 ≦ αt ≦. By selecting the material and thickness of the light absorption layer 21 and the p-type contact layer 18 thereunder so as to be 1, sufficient light absorption can be performed with respect to the emission wavelength. For this reason, the internal light density necessary to obtain an arbitrary light output is increased sufficiently in a pseudo manner, so that the relaxation oscillation frequency is sufficiently increased and the return light from the outside is sufficiently absorbed by the light absorption layer. As a result, the active layer 14 can be hardly reached. As a result, it is possible to significantly reduce inherent noise and return light noise. Also, the high frequency characteristics can be improved.
Further, when a metal film is used as the light absorption layer 21 and an electrical pseudo-ohmic junction is formed between the metal film and the p-type contact layer 18, a p-type contact is formed by the p-side electrode 20 and the metal film. The ohmic contact can be made with respect to the entire layer 18, and the contact area increases as compared with the case where no metal film is formed as the light absorption layer 21. For this reason, the contact resistance R _c of the p-side electrode 20 is effectively reduced. Further, since the ohmic contact can be made with respect to the entire p-type contact layer 18 by the metal film as the p-side electrode 20 and the light absorption layer 21, the metal film as the p-side electrode 20 and the light absorption layer 21 during laser operation. When a voltage is applied between the n-side electrode 22 and the n-side electrode 22, a current flows from the entire metal film as the p-side electrode 20 and the light absorption layer 21. For this reason, the area of the current path is greatly increased, and the sheet resistance of the p-type DBR layer 17 and the n-type DBR layer 12 is also effectively reduced. As a result, the series resistance R _s (meaning differential resistance of current-voltage characteristics) of the surface emitting semiconductor laser is greatly reduced. In addition to the reduction of the contact resistance R _c , the operating current can be reduced.
The surface emitting semiconductor laser according to the first embodiment is suitable for use as a light source for communication, for example.

Next explained is a surface emitting semiconductor laser according to the second embodiment of the invention.
As shown in FIG. 12, in this surface-emitting semiconductor laser, the light absorption layer 21 provided inside the recess 18a of the p-type contact layer 18 is a stacked layer of a first layer 21a and a second layer 21b. It has a structure. One of the first layer 21a and the second layer 21b is made of a metal film, and the other is made of an insulating film. As these metal films and insulating films, for example, those already mentioned can be used.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the second embodiment, the same advantages as those of the first embodiment can be obtained.

Next explained is a surface emitting semiconductor laser according to the third embodiment of the invention.
As shown in FIG. 13, in this surface-emitting semiconductor laser, the light absorption layer 21 provided in the recess 18a of the p-type contact layer 18 includes the first layer 21a and the first layer 21a as in the second embodiment. In this case, the second layer 21b is provided only on the outer peripheral portion of the recess 18a. The light absorption layer 21 is made of a metal film or an insulating film. As these metal films and insulating films, for example, those already mentioned can be used.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.

  According to the third embodiment, the same advantages as those of the first embodiment can be obtained, and the following advantages can also be obtained. That is, since the outer peripheral portion of the light absorption layer 21 is thicker than the central portion, and thus the outer portion absorbs more light, the outer peripheral portion is selectively absorbed in the intensity distribution of the laser light extracted from the p-type DBR layer 17. As a result, it is possible to easily realize laser oscillation with a single transverse beam like a single transverse mode. Laser oscillation with a single-peak beam like a single transverse mode can be realized by reducing the current confinement diameter to 4 μm or less, for example. However, according to the third embodiment, it is not necessary to reduce the current confinement diameter. Therefore, the manufacturing yield of the surface emitting semiconductor laser is high.

Next explained is a surface emitting semiconductor laser according to the fourth embodiment of the invention.
As shown in FIG. 14, in this surface emitting semiconductor laser, the light absorption layer 21 provided inside the recess 18a of the p-type contact layer 18 is formed of a single-layer metal film or insulating film. The thickness of the light absorption layer 21 is different between the outer peripheral portion and the central portion, and the ring-shaped outer peripheral portion is thicker. As the metal film and the insulating film, for example, those already mentioned can be used.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the fourth embodiment, the same advantages as those of the first and third embodiments can be obtained.

Next explained is a surface emitting semiconductor laser according to the fifth embodiment of the invention.
As shown in FIG. 15, in this surface emitting semiconductor laser, a light absorption layer 21 made of a p-type semiconductor is laminated on a p-type DBR layer 17, and a p-type contact layer 18 is laminated thereon. The p-type contact layer 18 is provided with a circular opening 18b. As a semiconductor which comprises the light absorption layer 21, a suitable thing can be used according to a use etc. from what was already mentioned, for example. For example, when the active layer 14 is made of AlGaAs or GaAs, the light absorption layer 21 is made of GaInAs, and when the active layer 14 is made of AlGaAs, GaAs, GaInNAs, GaInAsP, or AlGaAsP, the light absorption layer 21 is made of GNAs. When the active layer 14 is made of Al _x Ga _1-x As, the light absorption layer 21 is made of Al _y Ga _1-y As (1>x>y> 0). As a specific example, when the light absorption layer 21 is made of a GaInAs film having a thickness of 100 nm and an In composition of 0.18 at an emission wavelength band of 780 nm, the absorption coefficient of this GaInAs is 2.76 × 10 5 from FIG. ^{Since 4} cm ⁻¹ , αt = 2.76 × 10 ⁴ × 100 × 10 ⁻⁷ = 0.28. When the light emission wavelength is 850 nm or more, when the light absorption layer 21 is made of a GaInAs film having a thickness of 300 nm and an In composition of 0.18, the absorption coefficient of GaInAs is 1.95 × 10 ⁴ cm ⁻¹ from FIG. Therefore, αt = 1.95 × 10 ⁴ × 300 × 10 ⁻⁷ = 0.59.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the fifth embodiment, advantages similar to those of the first embodiment can be obtained.

Next explained is a surface emitting semiconductor laser according to the sixth embodiment of the invention.
As shown in FIG. 16, in this surface emitting semiconductor laser, a light absorption layer 21 made of a p-type semiconductor is laminated on a p-type DBR layer 17, and a p-type contact layer 18 is laminated thereon. The p-type contact layer 18 is provided with a circular recess 18a. As a semiconductor which comprises the light absorption layer 21, a suitable thing can be used according to a use etc. from what was already mentioned, for example. For example, when the emission wavelength is in the 780 nm band, when the light absorption layer 21 is made of a GaInAs film having a thickness of 100 nm and an In composition of 0.18, and the p-type contact layer 18 of the recess 18a is made of GaAs having a thickness of 30 nm, Since the absorption coefficient of GaInAs having the above composition is 2.76 × 10 ⁴ cm ⁻¹ from FIG. 4 and the absorption coefficient of GaAs is 1.63 × 10 ⁴ cm ⁻¹ from FIG. 4, αt = (2.76 × 10 ⁴ ) × 100 × 10 ⁻⁷ + (1.63 × 10 ⁴ ) × 30 × 10 ⁻⁷ = 0.33. When the emission wavelength is 850 nm or more, the light absorption layer 21 is made of a GaInAs film having a thickness of 300 nm and an In composition of 0.18, and the p-type contact layer 18 of the recess 18a is made of GaAs having a thickness of 30 nm. Since the absorption coefficient of GaInAs is 1.95 × 10 ⁴ cm ⁻¹ from FIG. 4 and the absorption coefficient of GaAs is 1.05 × 10 ⁴ cm ⁻¹ from FIG. 4, αt = (1.95 × 10 ⁴ ). × 300 × 10 ⁻⁷ + (1.05 × 10 ⁴ ) × 30 × 10 ⁻⁷ = 0.62.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the sixth embodiment, the same advantages as those of the first embodiment can be obtained.

Next explained is a surface emitting semiconductor laser according to the seventh embodiment of the invention.
As shown in FIG. 17, in this surface emitting semiconductor laser, a light absorption layer 21 made of a p-type semiconductor is laminated on a p-type DBR layer 17, and a p-type contact layer 18 is laminated thereon. The p-type contact layer 18 is provided with a circular opening 18b. As a semiconductor which comprises the light absorption layer 21, a suitable thing can be used according to a use etc. from what was already mentioned, for example. The thickness of the light absorption layer 21 is different between the outer peripheral portion and the central portion, and the ring-shaped outer peripheral portion is thicker.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the seventh embodiment, the same advantages as those of the first and third embodiments can be obtained.

Next explained is a surface emitting semiconductor laser according to the eighth embodiment of the invention.
As shown in FIG. 18, in this surface emitting semiconductor laser, the light absorption layer 21 has a laminated structure of a first layer 21a made of a p-type semiconductor and a second layer 21b made of a metal or an insulator. The first layer 21 a is inserted between the p-type DBR layer 17 and the p-type contact layer 18, and the second layer 21 b is provided inside the opening 18 b of the p-type contact layer 18. As the p-type semiconductor, the metal film, and the insulating film, for example, those already mentioned can be used.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the eighth embodiment, the same advantages as those of the first embodiment can be obtained.

Next explained is a surface emitting semiconductor laser according to the ninth embodiment of the invention.
As shown in FIG. 19, in this surface emitting semiconductor laser, a light absorption layer 21 is provided so as to cover the opening 20a so as to bridge the opening 20a of the p-side electrode 20. In other words, the light absorption layer 21 is provided in the shape of an air bridge above the recess 18 a of the p-type contact layer 18. As the light absorbing layer 21, a metal film or an insulating film can be used.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment. In this case, the light absorption layer 21 is formed, for example, by forming an opening 20 a in the p-side electrode 20, forming a recess 18 a in the p-type contact layer 18, and then applying a resist (not shown) over the entire surface of the p-side electrode 20. The resist is embedded in the openings 20a and the recesses 18a, and the resist is exposed and cured, and then a metal film or an insulating film is formed on the resist and patterned by etching. Can be formed.
According to the ninth embodiment, the same advantages as those of the first embodiment can be obtained.

Next explained is a surface emitting semiconductor laser according to the tenth embodiment of the invention.
As shown in FIG. 20, in this surface emitting semiconductor laser, the surface emitting semiconductor laser according to the first embodiment, in which the light absorption layer 21 is omitted, is housed in a package 24. In the package 24, a transparent window portion 25 is provided in a portion above the opening 20 a of the p-side electrode 20, and a light absorption layer 21 is provided on the transparent window portion 25. As the light absorbing layer 21, a metal film or an insulating film can be used.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the tenth embodiment, the same advantages as those of the first embodiment can be obtained.

Next explained is a surface emitting semiconductor laser according to the eleventh embodiment of the invention.
As shown in FIG. 21, in this surface-emitting semiconductor laser, the light absorption layer 21 provided in the recess 18a of the p-type contact layer 18 has the same structure as the first layer 21a and the first layer 21a as in the second embodiment. In this case, the second layer 21b is provided only on the outer peripheral portion of the recess 18a. The light absorption layer 21 is made of a metal film or an insulating film. As these metal films and insulating films, for example, those already mentioned can be used. Further, the n-side electrode 22 is provided not on the back surface of the n-type semiconductor substrate 11 but on the lower cladding layer 13 around the mesa post portion.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the eleventh embodiment, the same advantages as those of the first and third embodiments can be obtained.

Next explained is a surface emitting semiconductor laser according to the twelfth embodiment of the invention.
As shown in FIG. 22, in this surface emitting semiconductor laser, the light absorption layer 21 has a laminated structure of a first layer 21a made of a p-type semiconductor and a second layer 21b made of a metal or an insulator. The first layer 21a is provided so as to be inserted in the middle of the p-type contact layer 18, and the second layer 21b is a double ring on the first layer 21a inside the opening 18b of the p-type contact layer 18. It is provided in the shape. As the metal film and the insulating film, for example, those already mentioned can be used.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the twelfth embodiment, the same advantages as those of the first embodiment can be obtained.

Next explained is a surface emitting semiconductor laser according to the thirteenth embodiment of the invention.
As shown in FIG. 23, in this surface emitting semiconductor laser, the light absorption layer 21 provided in the recess 18a of the p-type contact layer 18 is formed of a single-layer metal film or insulating film. The thickness of the light absorption layer 21 is different between the outer peripheral portion and the central portion, and the circular central portion is thicker. As the metal film and the insulating film, for example, those already mentioned can be used.
Other than the above are the same as in the first embodiment.
The method for manufacturing the surface emitting semiconductor laser is the same as that in the first embodiment.
According to the thirteenth embodiment, the same advantages as those of the first embodiment can be obtained, and the following advantages can also be obtained. That is, since the light absorption layer 21 has a thicker central portion than the outer peripheral portion, and therefore has a large amount of light absorption in the central portion, the central portion is selectively absorbed in the intensity distribution of the laser light extracted from the p-type DBR layer 17. As a result, laser oscillation with a multimode-like bimodal beam can be easily realized.

As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.
For example, the numerical values, materials, structures, shapes, substrates, processes, and the like given in the above-described embodiments are merely examples, and different numerical values, materials, structures, shapes, substrates, processes, etc. are used as necessary. May be.

For example, although the MOCVD method is used as the semiconductor layer growth method in the above-described embodiment, other growth methods such as a molecular beam epitaxy (MBE) method and a chemical beam epitaxy (CBE) method may be used.
In the above-described embodiment, the current confinement layer 16 is provided above the active layer 14. However, the current confinement layer 16 may be provided below the active layer 14.
In the above-described embodiment, the laser light is extracted from the side opposite to the n-type semiconductor substrate 11. However, when the laser light is extracted through the n-type semiconductor substrate 11, the n-type semiconductor substrate 11 and the n-type semiconductor substrate 11 are extracted. A light absorption layer 21 is provided between the DBR layer 12.
Furthermore, two or more of the above-described embodiments may be combined as necessary.

It is a basic diagram which shows the correlation with the thickness of a light absorption layer, and the amount of absorption. It is a basic diagram which shows the correlation with the absorption coefficient and absorption amount of a light absorption layer. It is a basic diagram which shows the absorption coefficient of AlGaAs, GaAs, and GaInAs. It is a basic diagram which shows the absorption coefficient of AlGaAs, GaAs, and GaInAs. It is a basic diagram which shows the absorption coefficient of an insulator. It is a basic diagram which shows the absorption coefficient of a metal. 1 is a cross-sectional view showing a surface emitting semiconductor laser according to a first embodiment of the present invention. It is sectional drawing for demonstrating the manufacturing method of the surface emitting semiconductor laser by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the surface emitting semiconductor laser by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the surface emitting semiconductor laser by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the surface emitting semiconductor laser by 1st Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 2nd Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 3rd Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 4th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 5th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 6th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 7th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 8th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 9th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 10th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 11th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 12th Embodiment of this invention. It is sectional drawing which shows the surface emitting semiconductor laser by 13th Embodiment of this invention. It is a basic diagram which shows the correlation of a modulation frequency and RIN. It is sectional drawing which shows the conventional vertical cavity surface emitting laser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... n-type semiconductor substrate, 12 ... n-type DBR layer, 13 ... Lower clad layer, 14 ... Active layer, 15 ... Upper clad layer, 16 ... Current confinement layer, 17 ... P-type DBR layer, 18 ... P-type contact layer , 18a ... opening, 19 ... insulating film, 20 ... p-side electrode, 20a ... opening, 21 ... light absorption layer, 22 ... n-side electrode

Claims (30)

A first reflective layer;
An active layer on the first reflective layer;
A second reflective layer on the active layer;
An electrode having an opening on the second reflective layer;
In a surface emitting semiconductor laser that extracts output light having a wavelength shorter than 850 nm from the second reflective layer through the opening of the electrode,
On the second reflective layer inside the opening of the electrode, light of 0.1 ≦ αt ≦ 1, where α (cm ⁻¹ ) is the absorption coefficient with respect to the emission wavelength, and t (cm) is the thickness. A surface emitting semiconductor laser comprising an absorption layer.   2. The surface emitting semiconductor laser according to claim 1, wherein 0.2 ≦ αt ≦ 1.   2. The surface emitting semiconductor laser according to claim 1, wherein the light absorption layer is made of a metal.   4. The surface emitting semiconductor laser according to claim 3, wherein the metal is at least one selected from the group consisting of Ti, Pt, Au, AuGe, Ni, Pd, Cr, and Hf.   4. The light absorbing layer is formed of a single layer metal film or a multilayer metal film made of at least one selected from the group consisting of Ti, Pt, Au, AuGe, Ni, Pd, Cr and Hf. The surface emitting semiconductor laser described.   4. The surface emitting semiconductor laser according to claim 3, wherein the thickness of the light absorption layer is 2 nm or more and 12 nm or less.   2. The surface emitting semiconductor laser according to claim 1, wherein the light absorption layer is made of an insulator.   8. The surface emitting semiconductor laser according to claim 7, wherein the insulator is a semiconductor.   9. The surface emitting semiconductor laser according to claim 8, wherein the semiconductor is amorphous Si.   9. The surface emitting semiconductor laser according to claim 8, wherein the semiconductor is GaInAs, GaNAs, GaInNAs, GaAs or AlGaAs.   2. The surface emitting semiconductor laser according to claim 1, wherein the light absorption layer is a laminated film of a metal film and an insulating film.   2. The surface emitting semiconductor laser according to claim 1, further comprising an insulating film having no absorption coefficient near an emission wavelength, on the light absorption layer or between the second reflection layer and the light absorption layer. . The insulating film having no absorption coefficient near the emission wavelength is characterized by comprising at least one selected from the group consisting of SiO _x , SiN _x , SiN _x O _y , Al ₂ O ₃ , TiO _x and ZrO _x. The surface emitting semiconductor laser according to claim 12.   2. The surface emitting semiconductor laser according to claim 1, wherein the thickness of the outer peripheral portion of the light absorbing layer is larger than the thickness of the central portion.   2. The surface emitting semiconductor laser according to claim 1, wherein the thickness of the outer peripheral portion of the light absorption layer is smaller than the thickness of the central portion.   2. The surface emitting semiconductor laser according to claim 1, wherein the light absorption layer is provided on the second reflective layer via a contact layer.   7. The surface emitting semiconductor laser according to claim 6, wherein the contact layer has a recess in a portion corresponding to the opening of the electrode, and the light absorption layer is provided on the contact layer of the recess. .   The light absorbing layer is provided on the second reflective layer, a contact layer having an opening corresponding to the opening of the electrode is provided on the light absorbing layer, and the electrode is provided on the contact layer. 2. The surface emitting semiconductor laser according to claim 1, wherein the surface emitting semiconductor laser is formed.   The light absorbing layer is provided on the second reflective layer, a contact layer having a recess in a portion corresponding to the opening of the electrode is provided on the light absorbing layer, and the electrode is provided on the contact layer. 2. The surface emitting semiconductor laser according to claim 1, wherein the surface emitting semiconductor laser is formed.   2. The surface emitting semiconductor laser according to claim 1, wherein the light absorption layer is provided at a depth in the middle of the contact layer.   2. The surface emitting semiconductor laser according to claim 1, wherein the light absorption layer is provided directly on the second reflective layer.   2. The surface emitting semiconductor laser according to claim 1, wherein the light absorption layer is provided so as to bridge the opening of the electrode.   2. The surface emitting semiconductor laser according to claim 1, wherein the light absorbing layer is provided in a transparent window portion of a package for housing the surface emitting semiconductor laser.   2. The surface emitting semiconductor laser according to claim 1, wherein the first reflective layer and the second reflective layer are made of a semiconductor multilayer film.   2. The surface emitting semiconductor laser according to claim 1, wherein the active layer and the second reflective layer have a cylindrical shape.   2. The surface emitting semiconductor laser according to claim 1, further comprising a current confinement layer on an upper side or a lower side of the active layer. A first reflective layer;
An active layer on the first reflective layer;
A second reflective layer on the active layer;
An electrode having an opening on the second reflective layer;
In a surface emitting semiconductor laser that extracts output light having a wavelength of 850 nm or more from the second reflective layer through the opening of the electrode,
On the second reflective layer inside the opening of the electrode, when the absorption coefficient with respect to the emission wavelength is α (cm ⁻¹ ) and the thickness is t (cm), light of 0.4 ≦ αt ≦ 1 A surface emitting semiconductor laser comprising an absorption layer.   28. The surface emitting semiconductor laser according to claim 27, wherein 0.6 ≦ αt ≦ 1. A first reflective layer;
An active layer on the first reflective layer;
A second reflective layer on the active layer;
An electrode having an opening on the second reflective layer;
Output light having a wavelength shorter than 850 nm is extracted from the second reflective layer through the opening of the electrode,
On the second reflective layer inside the opening of the electrode, light of 0.1 ≦ αt ≦ 1, where α (cm ⁻¹ ) is the absorption coefficient with respect to the emission wavelength, and t (cm) is the thickness. An optical module comprising a surface emitting semiconductor laser having an absorption layer as a light source. A first reflective layer;
An active layer on the first reflective layer;
A second reflective layer on the active layer;
An electrode having an opening on the second reflective layer;
Output light having a wavelength of 850 nm or more is extracted from the second reflective layer through the opening of the electrode,
On the second reflective layer inside the opening of the electrode, when the absorption coefficient with respect to the emission wavelength is α (cm ⁻¹ ) and the thickness is t (cm), light of 0.4 ≦ αt ≦ 1 An optical module comprising a surface emitting semiconductor laser having an absorption layer as a light source.

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