JP2010212606A - Surface emitting laser and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface emitting laser in which laser oscillation of a single-peak profile can be performed through low-resistance operation, and which is manufactured at low cost. <P>SOLUTION: The surface emitting laser includes a first multilayer reflecting film and a second multilayer reflecting film. The first reflecting film is composed of a plurality of pairs of low-refraction areas and high-refraction areas. The second multilayer reflecting film is composed of an active layer on a first multilayer reflecting film, a current confining structure on the active layer, a spacer layer on the current confining structure, and a plurality of pairs of low-refraction areas and high-refraction areas provided on the spacer layer. The current confining structure includes a first conduction type semiconductor layer, a second conduction type semiconductor layer on the first conduction type semiconductor layer, a tunnel junction area formed from the first conduction type semiconductor layer and the second conduction type semiconductor layer, and a current block layer provided between the first conduction type semiconductor layer and the second conduction type semiconductor layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface emitting laser suitable for optical interconnection and a method for manufacturing the same.

  In recent years, with the spread of the Internet, the amount of information that needs to be processed within and between computers has been increasing. As a device that exceeds the limit of electric signal transmission, a surface emitting laser capable of high-density mounting in a computer has attracted attention.

  In optical interconnection, in order to couple a surface emitting laser and a waveguide, direct coupling without using a lens is required for cost reduction. In order to couple with a waveguide with high coupling efficiency without a lens, it is desirable that the transverse mode has a unimodal optical profile. It is required to manufacture such an element with a high yield.

  This necessity is shown in FIG. 2B of Non-Patent Document 2. Compared with other higher-order modes, in the fundamental mode that is a single-peak optical profile, high coupling efficiency can be obtained even if the waveguide near-field image size Wf and the near-field image size Wl of the light emitting element are slightly different. For this reason, the degree of freedom in designing the waveguide is great.

  Among surface emitting lasers, those using tunnel junctions can reduce the resistance of the element, so that the IC drive voltage can be reduced and the effect of reducing the IC power consumption is great. Further, since the heat generation can be suppressed by reducing the resistance, a surface emitting laser having a long element life can be realized. As an example of such a surface emitting laser using a tunnel junction, Non-Patent Document 1 (FIG. 1) reports a buried tunnel junction surface emitting laser.

  As shown in FIG. 3 of this specification, the buried tunnel junction structure surface emitting laser includes a first multilayer reflective film 702, a first n-type spacer layer 703, and an active layer 704 on an n-type conductive semiconductor substrate 701. , P-type spacer layer 705, high-concentration p-type layer 706 that forms a tunnel junction, high-concentration n-type layer 707 that forms a tunnel junction, second n-type spacer layer 708, second multilayer reflective film 709, positive electrode 710 , And a negative electrode 711.

  As shown in FIGS. 4A to 4D of this specification, the buried tunnel junction structure surface emitting laser is manufactured as follows.

  First, as shown in FIG. 4A, a first multilayer reflective film 702 to a high-concentration n-type layer 707 that forms a tunnel junction are sequentially grown on an n-type substrate 701, and photolithography and etching are performed. The high-concentration p-type layer 706 and the high-concentration n-type layer 707 are processed by a technique to form a tunnel junction.

  Next, as shown in FIG. 4B, a second n-type spacer layer 708 is grown so as to embed the tunnel junction.

  Next, as shown in FIG. 4C, in order to take out the contact electrode on the substrate side from the surface side, the laminated film on the semiconductor substrate is etched until the first n-type spacer layer 703 is exposed to form a mesa.

Next, as shown in FIG. 4D, after the second multilayer reflective film 709 made of SiO ₂ / Si is formed, the dielectric in the contact portion is removed by etching, and then the positive electrode 710 and the negative electrode 711 are formed. The element is completed through the alloy. As a result, a low resistance surface emitting laser oscillating at a threshold current of 1 mA and a wavelength of 1090 nm and having an element resistance of 50Ω is obtained.

  In the manufacture of this surface emitting laser, the tunnel junction other than the light emitting region is removed by etching in order to form a current confinement structure.

  As an example of a surface emitting laser using another tunnel junction, a step generated by etching processing of a tunnel junction is embedded in a material having a different constituent element composition in Patent Document 1 (FIGS. 1, 2B, and 2C). A surface emitting laser having a flattened surface after being embedded has been reported.

  As another example of a surface emitting laser using a tunnel junction, Non-Patent Document 3 (FIG. 1A) reports a surface emitting laser in which a current constriction is formed by ion implantation in a tunnel junction. Yes.

JP 2008-103483 A

Kenichiro Yashiki et al., 22p-ZN-3 “Surface emitting laser with 1.1 μm buried tunnel junction structure”, Proceedings of the 53rd Joint Conference on Applied Physics, Spring 2006, p. 1223 J. Heinrich et al., "Butt-Coupling Efficiency of VCSEL's into Multimode Fibers", I Triple E Photonics E ), 1997, pp. 1555-1557 C. Starck et al., “1 mW CW RT 1.55 μm tunnel metallic VCSEL: thermal and electrical characteristics of GaAs / AlAs metamorphic mirrors (1 mW CW RT 1.55 μm tunnel metallic VCSEL). / AlAs metamorphic mirrors) ", CLEO Pacific Rim, 1999, pp. 196. 454-455 G. Ronald. Hadley et al., “Comprehensive Numerical Modeling of Electronics”, “Competitive Numerical Modeling of Lasers” (IEEE Journal of Quantum Electronics), 1996, pp. 607-616

  In the technique described in Non-Patent Document 1 described above, when the tunnel junction is etched, the second n-type spacer layer 708 and the second multilayer reflective film 709 are reflected to reflect the processed shape of the formed tunnel junction. Concavities and convexities occur at the interface 712.

The resonator length of this element is such that the interface between the first multilayer reflective film 702 and the first n-type spacer layer 703 and the interface between the second multilayer reflective film 709 and the second n-type spacer layer 708 are both interfaces. It is defined by the distance between. According to the relational expression (24) shown in Non-Patent Document 4, the resonance wavelength and effective refractive index of the convex resonator, which is the current injection region that emits light, are λ ₀ and n _eff , respectively, and the resonant wavelength and effective refractive index of the concave portion are When λ ₁ and n ₁ are set, and Δλ = λ ₀ −λ ₁ and Δn _eff = n _eff −n ₁ , the following formula (1):

The relationship exists. For example, for the sake of simplicity, if the uneven step is limited to an optical film thickness of λ / 4 or less, the cavity length is shorter in the recessed portion than in the protruding portion, and therefore, λ ₀ > λ ₁ . Therefore, n _eff > n ₁ , that is, the effective refractive index of the light emitting region is higher than the effective refractive index of the peripheral portion thereof, so that the refractive index is guided. For this reason, the degree of light confinement reflects the size of the uneven step. Here, the optical film thickness is a thickness defined for light having a known wavelength. When the actual thickness (physical film thickness) of the film is d and the refractive index of the material of the film is n with respect to the wavelength λ, the optical film thickness of the film is nd.

In order to realize high-speed operation, the resonator length is desirably short, and the second n-type spacer layer 708 which is a buried layer is desirably thin. A typical value of the etching step required for processing the tunnel junction is 30 nm or more, and the step due to the tunnel junction is maintained even after the buried layer is formed. This level difference is very large as Δn _eff / n _eff = 2 to 3% in terms of refractive index difference. As a result, the element easily oscillates in a multimode, the radiation angle is 40 degrees or more, and the coupling efficiency is low when coupled directly to the fiber.

  On the other hand, if the surface after embedding a processed tunnel junction is flattened as in the technique described in Patent Document 1, it is possible to oscillate with a single-peak optical profile. However, when producing this structure, high fabrication accuracy is required when processing the buried structure by photolithography according to the pattern of the tunnel junction. For this reason, the production yield decreases. Further, the cost increases due to the addition of an additional processing process.

  In the technique described in Non-Patent Document 3, when ion implantation is performed on a tunnel junction, the resonator length of the light emitting region becomes the same as the resonator length of the non-light emitting region, and if the influence of nonuniform current injection is small, it is simple. It becomes easy to oscillate with the optical profile of the peak. In this document, since the emission diameter is as large as 20 μm, the influence of nonuniform injection is large and the transverse mode is unstable due to the plasma effect. However, if the emission diameter is reduced and the influence of nonuniform injection is reduced, oscillation occurs with a single-peak optical profile. It becomes easy. In such a technique, when the ion-implanted layer is formed near the active layer, a part of ions easily reach the active layer. This becomes a cause of non-radiative recombination, and an increase in the threshold current causes an increase in element heat generation, resulting in a change in refractive index associated with the heat generation, resulting in poor lateral mode controllability. Further, when ions reach the active layer, lattice defects are generated, which causes defect growth and affects the reliability of the device. On the other hand, if the ion implantation layer is moved away from the active layer, current confinement does not function sufficiently. For this reason, this technique is not suitable for mass production.

  An object of the present invention is to provide a surface emitting laser and a method of manufacturing the same that can perform laser oscillation of a single-peak optical profile with low resistance operation and can be manufactured at low cost.

A surface emitting laser provided by one embodiment of the present invention includes:
A first multilayer reflective film composed of a plurality of pairs, each of which includes a pair of a low refractive region having a thickness of 1 / 4λ and a high refractive region having a thickness of 1 / 4λ.
An active layer provided on the first multilayer reflective film;
A current confinement structure provided on the active layer;
A spacer layer provided on the current confinement structure;
A second multilayer reflective film that is provided on the spacer layer and includes a plurality of pairs each including a pair of a low refractive region having a thickness of 1 / 4λ and a high refractive region having a thickness of 1 / 4λ. ,
The current confinement structure is:
A first conductivity type semiconductor layer;
A second conductivity type semiconductor layer provided on the first conductivity type semiconductor layer and having a conductivity type opposite to the first conductivity type;
A tunnel junction region formed by the first conductive semiconductor layer and the second conductive semiconductor layer;
A current blocking layer provided between the first conductive semiconductor layer and the second conductive semiconductor layer;

A method of manufacturing a surface emitting laser provided by another aspect of the present invention includes:
Forming a first multilayer reflective film on the substrate;
Forming a first spacer layer on the first multilayer reflective film;
Forming an active layer on the first spacer layer;
Forming a second spacer layer on the active layer;
Forming a first conductivity type semiconductor layer on the second spacer layer;
Forming a current blocking layer on the first conductive semiconductor layer;
A patterning step of removing a portion corresponding to a tunnel junction region in the current blocking layer to expose the first conductive type semiconductor layer;
Forming a second conductivity type semiconductor layer opposite to the first conductivity type on the current blocking layer so as to cover the exposed portion of the first conductivity type semiconductor layer;
Forming a third spacer layer on the second conductive semiconductor layer;
Forming a second multilayer reflective film on the third spacer layer;

  According to the present invention, it is possible to provide a surface emitting laser capable of low resistance operation with a single peak optical profile and capable of being manufactured at low cost.

Sectional drawing which shows the surface emitting laser of embodiment of this invention. Process sectional drawing for demonstrating an example of the manufacturing method of the surface emitting laser shown in FIG. Sectional drawing of the surface emitting laser of related technology. Process sectional drawing for demonstrating the manufacturing method of the surface emitting laser of related technology.

  Hereinafter, preferred embodiments of the present invention will be described.

  A surface-emitting laser according to an embodiment of the present invention includes a first multilayer reflective film including a plurality of pairs, each of which includes a pair of a low refractive region having a thickness of 1 / 4λ and a high refractive region having a thickness of 1 / 4λ. An active layer provided on the first multilayer reflective film, a current confinement structure provided on the active layer, a spacer layer provided on the current confinement structure, and provided on the spacer layer; A second multilayer reflective film composed of a plurality of pairs, each of which includes a pair of a low refractive region having a thickness of 1 / 4λ and a high refractive region having a thickness of 1 / 4λ. The current confinement structure includes a first conductivity type semiconductor layer, a second conductivity type semiconductor layer opposite to the first conductivity type provided on the first conductivity type semiconductor layer, and the first conductivity type. A tunnel junction region formed by a semiconductor layer and the second conductive semiconductor layer; and a current blocking layer provided between the first conductive semiconductor layer and the second conductive semiconductor layer.

  In the tunnel junction region, it is preferable that the first conductive semiconductor layer and the second conductive semiconductor layer are in direct contact with each other.

  The current blocking layer may be formed so as to surround the tunnel junction region.

  The structure sandwiched between the first multilayer reflective film and the second multilayer reflective film has a current injection region including the tunnel junction region and a current block region including the current block layer, and the current block region It is desirable that the optical film thickness of the structure part in is thicker than the optical film thickness of the structure part in the current injection region. The structure portion sandwiched between the first multilayer reflective film and the second multilayer reflective film can function as a resonator.

  The difference between the optical thickness of the structure portion in the current blocking region and the optical thickness of the structure portion in the current injection region is λm / 2 or more and λm / 2 + λ / 4 or less (m = 0, 1, 2,..., M represents 0 or a natural number, except that the difference in optical film thickness = 0 is desirable. From the viewpoint of film formation control and the like, m is preferably 2 or less.

  As the current blocking layer, a semi-insulating layer or an insulating layer in which the semi-insulating layer is insulated by doping can be provided. The current blocking layer may be formed of a material having a high etching selectivity (etching selection ratio) with respect to the material forming the first conductivity type semiconductor layer. The current blocking layer is formed of a semiconductor material not containing phosphorus when the semiconductor material forming the first conductive semiconductor layer contains phosphorus, and the semiconductor material forming the first conductive semiconductor layer When phosphorus is not contained, it can be formed from a semiconductor material containing phosphorus.

  In the method of manufacturing the surface emitting laser according to the embodiment of the present invention, the current blocking layer is formed of a material having high etching selectivity with respect to a material for forming the first conductive type semiconductor layer in the etching performed later. The patterning process of the current blocking layer can be performed by masking and etching a region other than the portion where the current blocking layer is removed.

In the surface emitting laser according to the present embodiment, by providing a current blocking layer such as a semi-insulating layer between layers forming a tunnel junction, the tunnel effect is partially inhibited, and an npin current blocking structure can be formed. Also, by providing the current blocking layer, the thickness of the structural band sandwiched between the first multilayer reflective film and the second multilayer reflective film (corresponding to the resonator length) is made thicker in the current block area than in the current injection area. By adjusting the thickness of the current blocking layer, the optical film thickness difference between the structural bands can be increased from λm / 2 to λm / 2 + λ / 4 (m = 0, 1, 2,..., M Represents 0 or a natural number, except that the optical film thickness difference is 0). As a result, Δn _eff <0 from equation (1), and an anti-waveguide structure can be obtained.

  According to this embodiment, a current confinement structure can be obtained by providing a current blocking layer between layers forming a tunnel junction (pn junction). Further, when a semi-insulating layer is used as the current blocking layer, there is an effect of reducing the element capacitance, and a high-speed response is possible.

  In addition, according to the present embodiment, laser oscillation with a single-peak optical profile can be obtained by using an anti-waveguide structure. As a result, the surface emitting laser can be coupled with the multimode fiber or the multimode waveguide with high efficiency. Thereby, the link loss budget at the time of transmission can be improved. Further, the device resistance can be reduced by the tunnel junction, so that the IC can be driven with low power consumption. As a result, an optical module with low power consumption can be realized.

  Furthermore, according to this embodiment, a structure that can operate with a single-peak optical profile can be formed by a simple process, and a surface-emitting laser can be manufactured at low cost. In addition, since the device can be manufactured without ion implantation, variation in threshold current is suppressed and the cause of defects can be reduced, so that device reliability can be improved.

In addition, the optical film thickness in this invention is the thickness defined with respect to the light whose wavelength is known. When the actual thickness (physical film thickness) of the film is d and the refractive index of the material of the film is n with respect to the wavelength λ, the optical film thickness of the film is nd. Therefore, for example, when there are two films made of materials having different refractive indexes and their optical film thickness is λ / 4, the refractive index and physical film thickness of the materials of the two films are respectively n ₁ , n ₂ , Assuming d ₁ and d ₂ , n ₁ d ₁ = n ₂ d ₂ = λ / 4. However, since n ₁ ≠ n ₂ , d ₁ ≠ d ₂ .

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of the surface emitting laser of this embodiment.

  On the n-type conductive semiconductor substrate 101, a first multilayer reflective film 102, a first n-type spacer layer 103, an active layer 104, a p-type spacer layer 105, a high-concentration p-type layer 106 forming a tunnel junction, and a half An insulating layer 116, a high-concentration n-type layer 107 that forms a tunnel junction, a second n-type spacer layer 108, and a second multilayer reflective film 109 are provided in this order. A positive electrode 110 is provided on the second multilayer reflective film 109, and a negative electrode 111 is provided on the back side of the substrate. The region corresponding to the tunnel junction is the current injection region 113, and the region where the semi-insulating layer 116 is formed between the high concentration p-type layer 106 and the high concentration n-type layer 107 is the current block region 114. Light emission occurs in the active layer in the current injection region.

The uneven step at the interface 112 between the second n-type spacer layer 108 and the second multilayer reflective film 109 has an optical film thickness difference of λ _m / 2 to λ _m / 2 + λ / 4 (m = 0, 1, 2, ..., m represents 0 or a natural number, except that the optical film thickness difference = 0 is desirable, and the thickness of the structural band (resonator length) between the reflective films is equal to this optical film thickness difference. It is desirable that the current block region is thicker than the current injection region 113. The uneven step at the interface 112 is controlled by the growth and etching of the semi-insulating layer and the subsequent growth of the high-concentration n-type layer 107 and the second n-type spacer layer 108.

  Next, with reference to FIGS. 2A to 2D, an embodiment of the method for manufacturing the surface emitting laser described with reference to FIG. 1 will be described.

  First, as shown in FIG. 2A, semiconductor layers from the first multilayer reflective film 102 to the semi-insulating layer 116 are formed on an n-type conductive semiconductor substrate 101 by metal organic vapor phase epitaxy (MOVPE). Growth by phase epitaxy).

  Thereafter, as shown in FIG. 2B, after forming a resist mask by photolithography, the semi-insulating layer 116 is processed by etching to form a circular opening. Although a circular opening is formed here, the processing shape is arbitrary depending on the design, and may be processed into a polygonal shape or a ring shape.

  Next, as shown in FIG. 2C, a high-concentration n-type layer 107 and a second n-type spacer layer 108 are grown so as to embed the semi-insulating layer 116. As a result, a tunnel junction is formed in the region (in the opening) where the semi-insulating layer 116 has been etched away. A current block structure is formed in the region where the semi-insulating layer 116 remains.

  Thereafter, as shown in FIG. 2D, a second multilayer reflective film 109 having a laminated structure of a low refractive index layer and a high refractive index layer is formed on the entire surface. At that time, the low refractive index layers are sequentially laminated. The second multilayer reflective film can be composed of a semiconductor or a dielectric.

  Next, the second n-type spacer layer 108 is exposed by dry etching the second multilayer reflective film 109. Next, the positive electrode 110 is formed on the exposed second n-type spacer layer 108, the negative electrode 111 is formed on the back surface side of the substrate, and electrode alloying is performed to complete the device.

  The second multilayer reflective film 109 can be formed by sputtering (RF sputtering or reactive sputtering), electron beam evaporation, chemical vapor deposition, ion beam assisted deposition, MOVPE, molecular beam epitaxy (MBE). Such a method may be used.

Examples of the material of the second multilayer reflective film include Si, Sb ₂ S ₃ , ZnSe, CdS, ZnS, and TiO ₂ as high refractive index materials, and SiO ₂ , SiN _x , MgO, CaF ₂ as low refractive index materials, and the like. such as MgF _2, Al ₂ O ₃ and the like, it can be used to select a transparent material to the oscillation wavelength.

  In the case where the first multilayer reflective film is made of a semiconductor, in order to facilitate the injection of current and to reduce the element resistance, the low refractive index layer having a large band gap and the high refractive index layer having a small band gap are used. A barrier relaxation layer having an intermediate band gap for relaxing the band discontinuity may be introduced.

  If it is difficult to etch the material constituting the second multilayer reflective film, a lift-off process may be used. For the film formation when the lift-off process is used, electron beam evaporation, ion beam assisted deposition, MBE, or the like can be used.

  By energizing the obtained element and confirming a far-field image, it is understood that laser oscillation with a single-peak optical profile can be obtained, and a stable single transverse mode can be obtained even at high injection. According to the present embodiment, even when long-distance optical communication is performed with high-speed modulation, transmission quality is hardly deteriorated, and transmission over a distance of over 300 m at 20 Gbps is possible even when a multimode fiber is used.

  In addition, by using the tunnel junction, the element resistance can be reduced to 50 Ω or less, and driving with an IC with low power consumption is possible.

  In addition, since it oscillates with a single-peak optical profile, high direct coupling efficiency can be obtained even when combined with an optical circuit composed of multimode waveguides having different near-field image sizes.

  The uneven step at the interface 112 between the second n-type spacer layer 108 and the second multilayer reflective film 109 (corresponding to the thickness difference between the current injection region and the current block region of the structural band between the reflective films) is the optical film thickness difference. When λm / 2 + λ / 4, there is a boundary condition between refractive index guiding and anti-guiding, but when current is injected, heat is generated in the light-constricted light-emitting region (current injection region), and the effective refractive index of the light-emitting region Shifts to a higher side than the peripheral part (current block region), so that a basic transverse mode operation, which is a stable unimodal optical profile, can be obtained.

  The active layer of this embodiment includes an InGaAs quantum well, an AlGaAs quantum well, an InGaAlP quantum well, a GaInNAs (Sb) quantum well, a GalnNAs quantum well, a GaAs (Sb) quantum well, and a (Ga) InAs quantum. Various semiconductor materials such as dots can be used. Furthermore, this embodiment can be applied to surface-emitting laser elements having wavelengths of 780 nm, 850 nm, 980 nm, 1100 nm, 1200 nm, 1300 nm, 1480 nm, 1550 nm, and 1650 nm.

  The semi-insulating layer is preferably made of a material containing P when the high-concentration p-type layer 106 forming the tunnel junction is made of a material not containing phosphorus (P) in order to ensure etching selectivity. . In this case, as the etching solution, a mixed solution of nitric acid-hydrogen peroxide solution-water can be used. The semi-insulating layer is preferably made of a material not containing P when the high-concentration p-type layer 106 is made of a material containing P. In this case, a mixed solution of hydrochloric acid and phosphoric acid can be used as the etching solution.

  For example, on a GaAs substrate, (In) GaAs (Sb) and (In) GaAs (N) are mentioned as materials not containing P, and InGa (Al) P is mentioned as a material containing P. On the InP substrate, InGaAs and In (Ga) AlAs are listed as materials not containing P, and InP and InGaAsP are listed as materials containing P.

  In the step shown in FIG. 2A, a thin semiconductor layer made of the same material as that forming the tunnel junction below the semi-insulating layer may be formed over the semi-insulating layer 116. If the material has high etching selectivity, it is possible to select an etching solution in which the other is easily etched with respect to the other. Therefore, the thin semiconductor layer formed on the outermost surface can be used as an etching mask.

  The semi-insulating layer may be completely insulated by doping with CrO, Fe, or Ru.

  In addition to the AlGaAs-based semiconductor multilayer mirror on the GaAs substrate, an AlGaAs (Sb) -based semiconductor multilayer mirror or an AlGaInAsP-based semiconductor multilayer mirror on the InP substrate is used as the first multilayer reflective film. I can do it.

  As the substrate, a GaAs substrate, an InP substrate, a GaInAs ternary substrate, or the like can be used.

  Also, without forming the first multilayer reflective film on the substrate, the structure above the n-type spacer layer is formed first, and then the substrate is etched away, and the first multilayer reflective film is formed in the removed region of the substrate. It is also possible to form a dielectric DBR.

  Although an n-type conductive substrate is used here, a semi-insulating substrate or a p-type conductive substrate may be used. When a semi-insulating substrate or a p-type conductive substrate is used, both the positive electrode and the negative electrode may be taken out from the surface of the substrate.

  The reflectivity of the first multilayer reflective film and the second multilayer reflective film can be set to 99% or more from the viewpoint of obtaining a desired threshold and suppressing deterioration of characteristics, and the reflection of the multilayer reflective film on the side from which light is not extracted. The rate is preferably higher than 99.6%, more preferably 99.9% or more, and the reflectance of the multilayer reflective film on the light extraction side is preferably in the range of 99 to 99.6%. In FIG. 1 referred to in this embodiment, since the electrode is formed on the substrate side, the multilayer reflective film on the side from which light is not extracted becomes the first multilayer reflective film. The multilayer reflective film on the light extraction side is the second multilayer reflective film. However, in the case of a configuration in which both the positive electrode and the negative electrode are taken out from the surface side of the substrate (upper side in the drawing) as shown in FIG. 3, the side corresponding to the side from which light is not taken out (lower side in the drawing) in FIG. The multilayer reflection film is the second multilayer reflection film, and the multilayer reflection film on the side corresponding to the light extraction side in FIG. 1 (upper side in the figure) is the first multilayer reflection film, and light is extracted from the back side of the substrate. It is good also as a structure. In that case, it is desirable that the back surface of the substrate is mirror-polished and a non-reflective coating corresponding to the oscillation wavelength is applied in the final manufacturing process.

  Next, the present embodiment will be further described using specific examples.

  The structure of the surface emitting laser of this example will be described with reference to FIG. 1, and an example of the manufacturing method will be described with reference to FIG.

As shown in FIG. 1, the surface emitting laser of this example has an oscillation wavelength λ of 1.07 μm on an n-type conductive GaAs semiconductor substrate 101 with an optical film thickness of 1 / 4λ and Si-doped AlAs low refractive index. 40.5 pairs of first multilayers composed of an index layer (n = 8 × 10 ¹⁷ cm ⁻³ ) and a Si-doped GaAs high refractive index layer (n = 8 × 10 ¹⁷ cm ⁻³ ) with an optical thickness of ¼λ Reflective film 102; first n-type spacer layer 103 made of Si-doped GaAs (n = 8 × 10 ¹⁷ cm ⁻³ ); active layer 104 made of In _0.3 Ga _0.7 As / GaAs quantum well; C-doped GaAs ( p = 8e + 17cm ^-3) made of p-type spacer layer 105; C-doped GaAs (p = 1e + 20 cm consisting ^-3) high-concentration p-type layer 106 to form a tunnel junction; undoped InGaP semi-insulating layer 116 (210 m); a second n-type composed of Si-doped ^{GaAs (n = 8 × 10 17} cm -3); Si -doped GaAs to form a tunnel junction ^{(n = 2 × 10 19 cm} -3) the high concentration n-type layer 107 A spacer layer 108; and three pairs of an SiO ₂ low refractive index layer (thickness 181.2 nm) having an optical thickness of 1 / 4λ and an Si high refractive index layer (thickness 71.5 nm) having an optical thickness of 1 / 4λ. A laminated structure including the second multilayer reflective film 109 is provided. A positive electrode 110 made of Au / Ge / Ni is provided on the second n-type spacer layer 108, and a negative electrode 111 made of Au / Ge / Ni is provided on the back side of the substrate 101.

  The length from the bottom surface of the first n-type spacer layer 103 to the top surface of the second n-type spacer layer 108 through the tunnel junction is an optical film thickness of 2λ, and the active layer 104 is at the antinode position of the standing wave. The tunnel junction was placed at the standing wave node.

  Both the high-concentration p-type layer 106 and the high-concentration n-type layer 107 constituting the tunnel junction have a thickness of 15 nm.

  The uneven step at the interface 112 between the second n-type spacer layer semiconductor 108 and the second multilayer reflective film 109 is 200 nm. When converted as the resonator length between the first and second multilayer reflective films, λ / 2 This corresponds to an optical film thickness difference that is larger and slightly shorter than 3 / 4λ. For this reason, it has an anti-waveguide structure.

  The reflectance of the first multilayer reflective film is 99.9%, and the reflectance of the second multilayer reflective film is 99.5%.

  Next, with reference to FIGS. 2A to 2D, a method for manufacturing the surface emitting laser will be described.

  First, as shown in FIG. 2A, the semiconductor layers from the first multilayer reflective film 102 to the semi-insulating layer 116 were grown on the n-type conductive semiconductor substrate 101 by MOVPE.

  Thereafter, as shown in FIG. 2B, after forming a resist mask by photolithography, the semi-insulating layer 116 was processed into a circle by etching. Since the etching selectivity between InGaP and GaAs is high, the etching can be stopped with GaAs, and the reproducibility of device fabrication is high.

  Next, as shown in FIG. 2C, a high-concentration n-type layer 107 and a second n-type spacer layer 108 were grown so as to embed the semi-insulating layer 116.

  When the step difference was measured in advance before forming the low refractive index layer of the second multilayer reflective film 109, it was 200 nm.

After that, as shown in FIG. 2D, the second multilayer reflective film 109 was sequentially formed on the entire surface from the low refractive index layer (SiO ₂ ).

  Next, the second n-type spacer layer 108 was exposed by dry etching the second multilayer reflective film 109. Thereafter, a positive electrode 110 made of Au / Ge / Ni is formed on the exposed second n-type spacer layer 108, a negative electrode 111 is formed on the back side of the substrate, and electrode alloying is performed at 375 ° C. for 10 seconds. A completed device was obtained.

  When the obtained device was energized and a far-field image was confirmed, laser oscillation with a single-peak optical profile was obtained. A stable single transverse mode was obtained even at high injection. As a result, even if long-distance optical communication is performed with high-speed modulation, there is little deterioration in transmission quality, and transmission over a distance of more than 300 m is possible at 20 Gbps even using a multimode fiber.

  In addition, by using a tunnel junction, the element resistance can be reduced to 50 Ω or less, and it is possible to drive with a low power consumption IC.

  Moreover, since it oscillates with a single-peak optical profile, high direct coupling efficiency was obtained even when combined with an optical circuit composed of multimode waveguides having different near-field image sizes.

  The surface-emitting laser according to the embodiment of the present invention described above can be applied to a surface-emitting laser that requires a low cost for an ultrahigh-speed computer.

Reference Signs List 101 substrate 102 first multilayer reflective film 103 n-type spacer layer 104 active layer 105 p-type spacer layer 106 high-concentration p-type layer 107 high-concentration n-type layer 108 second n-type spacer layer 109 second multilayer reflective film 110 positive electrode 111 Negative electrode 112 Interface between second n-type spacer layer semiconductor and second multilayer reflective film 113 Current injection region 114 Current block region 116 Semi-insulating layer 701 Substrate 702 First multilayer reflective film 703 First n-type spacer layer 704 Active Layer 705 p-type spacer layer 706 high-concentration p-type layer 707 high-concentration n-type layer 708 second n-type spacer layer 709 second multilayer reflective film 710 positive electrode 711 negative electrode 712 second n-type spacer layer semiconductor and second Multilayer reflective film interface

Claims (8)

A first multilayer reflective film composed of a plurality of pairs, each of which includes a pair of a low refractive region having a thickness of 1 / 4λ and a high refractive region having a thickness of 1 / 4λ.
An active layer provided on the first multilayer reflective film;
A current confinement structure provided on the active layer;
A spacer layer provided on the current confinement structure;
A second multilayer reflective film that is provided on the spacer layer and includes a plurality of pairs each including a pair of a low refractive region having a thickness of 1 / 4λ and a high refractive region having a thickness of 1 / 4λ. ,
The current confinement structure is:
A first conductivity type semiconductor layer;
A second conductivity type semiconductor layer provided on the first conductivity type semiconductor layer and having a conductivity type opposite to the first conductivity type;
A tunnel junction region formed by the first conductive semiconductor layer and the second conductive semiconductor layer;
A surface emitting laser comprising a current blocking layer provided between the first conductive semiconductor layer and the second conductive semiconductor layer. The structure sandwiched between the first multilayer reflective film and the second multilayer reflective film has a current injection region including the tunnel junction region, and a current block region including the current block layer,
2. The surface emitting laser according to claim 1, wherein an optical film thickness of the structure portion in the current block region is larger than an optical film thickness of the structure portion in the current injection region.   The difference between the optical film thickness of the structure part in the current block region and the optical film thickness of the structure part in the current injection region is λm / 2 or more and λm / 2 + λ / 4 or less (m is 0 or a natural number). However, the surface emitting laser according to claim 2, wherein the optical film thickness difference = 0 is excluded).   4. The surface emitting laser according to claim 1, wherein the current blocking layer is a semi-insulating layer or an insulating layer formed by insulating a semi-insulating layer by doping. 5.   The current blocking layer is formed of a semiconductor material not containing phosphorus when the semiconductor material forming the first conductivity type semiconductor layer contains phosphorus, and the semiconductor material forming the first conductivity type semiconductor layer is made of phosphorus. The surface emitting laser according to any one of claims 1 to 4, wherein the surface emitting laser is formed of a semiconductor material containing phosphorus when not included. A substrate,
A second conductivity type spacer layer provided between the first multilayer reflective film and the active layer;
A first conductivity type spacer layer provided between the active layer and the first conductivity type semiconductor layer;
The first multilayer reflective film is provided on the substrate;
6. The surface emitting laser according to claim 1, wherein the spacer layer provided between the current confinement structure and the second multilayer reflective film is a second conductivity type layer. 7. Forming a first multilayer reflective film on the substrate;
Forming a first spacer layer on the first multilayer reflective film;
Forming an active layer on the first spacer layer;
Forming a second spacer layer on the active layer;
Forming a first conductivity type semiconductor layer on the second spacer layer;
Forming a current blocking layer on the first conductive semiconductor layer;
A patterning step of removing a portion corresponding to a tunnel junction region in the current blocking layer to expose the first conductive type semiconductor layer;
Forming a second conductivity type semiconductor layer opposite to the first conductivity type on the current blocking layer so as to cover the exposed portion of the first conductivity type semiconductor layer;
Forming a third spacer layer on the second conductive semiconductor layer;
A method of manufacturing a surface emitting laser, comprising a step of forming a second multilayer reflective film on the third spacer layer. The current blocking layer is formed of a material having high etching selectivity with respect to a material for forming the first conductivity type semiconductor layer in etching performed later.
8. The surface emitting laser manufacturing method according to claim 7, wherein the patterning step of the current blocking layer is performed by etching while masking a region other than a portion where the current blocking layer is removed.

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