JP2005150442A - Surface-emitting laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize a current distribution inside a laminated structure composed of an active layer and a current narrow layer, to ensure an increase of an amount of charged current and also a practical use of a single lateral mode, and also to prevent an occurrence of a failure in forming an insulating film or a wiring. <P>SOLUTION: A laminated structure 10 containing an active layer 3 and a current narrow layer 5 is formed on a substrate 20. The laminated structure 10 has an inclined structure, and an electrode 8 is provided on its uppermost layer. An insulating layer 11 is provided along an inclined face (first inclined face) 10B on the obtuse angle side of the laminated structure 10, and a wiring 12 for the electrode 8 is formed on the surface of the insulating film 11. The electrode 8 is provided offset to a current narrow part 5A of the current narrow layer 5. Namely, an optical output window 13 of the electrode 8 is provided near to the first inclined face 10B, and an area near to an inclined face (second inclined face) 10A on the acute angle side of the electrode 8 is greater than an area near to the inclined face 10B on the obtuse angle side thereof. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface emitting laser element having a laminated structure including an active layer and a current confinement layer and emitting laser light from an optical output window of an electrode provided on the upper surface of the laminated structure.

  In the surface emitting laser element, a structure is known in which a so-called current confinement layer is formed so that a current is concentrated in a current confinement portion provided almost at the center of the current confinement layer.

  This current confinement portion oxidizes an AlAs (aluminum arsenic) layer in a DBR (Distributed Bragg Reflector; semiconductor multilayer mirror) to insulate the material of that portion, and only a portion of a predetermined small area in the center portion is dared. It is formed by leaving it unoxidized. In this oxidation process, the substrate is exposed to water vapor so that only the AlAs layer is selectively oxidized so that insulation is promoted from its surroundings, and selective oxidation is performed at an appropriate timing before the oxidation proceeds to the center of the current confinement layer. By stopping the step, the portion left unoxidized becomes a circular or rectangular current injectable region.

  Due to the intensive current injection to a small area by such a current confinement structure, the threshold current of the surface emitting laser becomes a value of several mA level, which is extremely lower than that of the edge emitting laser. Furthermore, the surface emitting laser element has good bonding properties with an optical fiber for optical communication and the like, and its external dimensions can be extremely small. From these features, the surface emitting laser element having a current confinement structure is expected to be applied as an element for outputting a laser for optical communication.

In order to realize application as a laser element for optical communication, in addition to the above-mentioned features, high output is possible in a single transverse mode as an output characteristic of the element, and specific polarization is obtained. It is requested. Of these requirements, in order to meet the latter requirement of obtaining linearly polarized light, a laminated structure formed by laminating an active layer, a current confinement layer, a DBR layer, etc. is inclined with respect to the surface of the substrate. There has been proposed a technique of making the structure (Patent Document 1). The present invention is an invention for solving the former of the above-mentioned ones, and is different from Patent Document 1 in its purpose and effect.
Japanese Patent Laid-Open No. 08-116125

  However, the conventional techniques as described above have the following problems. That is, the surface emitting laser element can control the transverse mode by controlling the size of the current injection area by the above-described current confinement structure by oxidation, and in order to realize the light output of the single transverse mode, The current injection area may be reduced by limiting the size of the current confinement portion, but this is inevitably accompanied by demerits such as an increase in device resistance and a decrease in light output. In other words, there is a restriction (limit) due to such a demerit in reducing the area of the current confinement portion.

  Further, if the injection current value is increased in order to realize higher output, the transverse mode is not single, and a so-called higher order transverse mode (multimode) is obtained.

  The present inventors considered that this is caused by the fact that the current density distribution at the current injection portion is small at the center and large at the outside when large current is injected. The non-uniformity of the current density is caused by the fact that the outer side of the current injection portion is the boundary between the oxidized portion and the non-oxidized portion, so that the state is different from the central portion of AlAs. They considered.

  In order to solve the non-uniformity of current density that occurs when realizing such high output, and hence the occurrence of higher-order transverse modes, structural improvements are necessary. A simple solution has never been proposed. Alternatively, the conventionally proposed methods have such inconveniences that the process is complicated and that it is difficult to put it into practical use and must be solved separately.

  In addition, an electrode made of a metal film is provided on the uppermost surface of the so-called post-type mesa structure of the surface emitting laser element, and this electrode is a current provided on the surface of the substrate on which the post-type mesa structure is standing. It must be electrically connected to the wiring for supply and the pad portion for wire bonding. Therefore, such wiring for electrical connection must be provided on the side surface (side wall) of the post-type mesa structure, for example, by attaching a metal film by vapor deposition.

  However, the side surface of the post-type mesa structure is a surface that stands up substantially at right angles to the substrate surface. Therefore, when forming a wiring by attaching a metal film to the steep side surface like this step, etc. In addition, there has been a problem in that metal film formation defects such as so-called step breakage and wiring shape formation defects frequently occur.

  The present invention has been made in view of such problems, and a first object thereof is to provide a surface-emitting laser element capable of ensuring the realization of a single transverse mode with a further increase in the amount of current injection. It is in.

  A second object of the present invention is to provide a surface emitting laser element capable of forming a wiring without generating a metal film formation failure or a wiring shape formation failure on the side surface of the post-type mesa structure. Is to provide.

  The first surface-emitting laser element of the present invention has a laminated structure in which at least an active layer and a current confinement layer are laminated in parallel to the surface of the substrate on the substrate, and the upper surface of the laminated structure. A surface-emitting laser element in which an electrode having a light output window is formed, wherein the stacked structure has a pair of opposing side surfaces inclined with respect to the surface of the substrate, and the electrode has the light output window Of the laminated structure near the first inclined surface where the angle formed by the inclined surface and the surface of the substrate is an obtuse angle, and the angle formed by the surface of the substrate is an acute angle. The area closer to the inclined surface 2 is set larger than the area closer to the first inclined surface.

  The second surface-emitting laser element of the present invention has a laminated structure in which at least an active layer and a current confinement layer are laminated in parallel to the surface of the substrate on the substrate, and the laminated structure A surface-emitting laser element in which an electrode having a light output window is formed on an upper surface of the stacked structure, wherein the stacked structure has a pair of opposing side surfaces inclined with respect to the surface of the substrate, and the stacked structure is inclined From the other wiring provided on the surface of the substrate with respect to the electrode on the first inclined surface having an obtuse angle between the inclined surface and the surface of the substrate among the surfaces Wiring for performing electrical connection is provided.

  The third surface emitting laser device of the present invention has a laminated structure in which at least an active layer and a current confinement layer are laminated in parallel to the surface of the substrate on the substrate, and the upper surface of the laminated structure. A surface emitting laser element having an electrode having a light output window formed thereon, wherein the stacked structure has a pair of opposing side surfaces inclined with respect to the surface of the substrate, and the electrode has the light output window formed thereon. The angle formed between the inclined surface of the laminated structure and the surface of the substrate is closer to the first inclined surface, which is an obtuse angle, and the angle formed with the surface of the substrate is an acute angle. The area closer to the inclined surface is set to be larger than the area closer to the first inclined surface, and the substrate is disposed on the first inclined surface with respect to the electrode with an insulating film interposed therebetween. To make electrical connection from other wiring provided on the surface of It is those having the wiring.

  In the first surface-emitting laser element of the present invention, the multilayer structure is formed in a shape inclined with respect to the surface of the substrate, and the light output window is inclined with respect to the inclined surface of the multilayer structure. An area formed near the first inclined surface having an obtuse angle between the surface and the surface of the substrate and having an acute angle formed with the surface of the substrate is closer to the first inclined surface. Therefore, the current distribution configured to inject current into the active layer through the current confinement portion of the current confinement layer is high in the stacked structure. A single transverse mode at the output can be realized.

  In the second surface emitting laser element of the present invention, the laminated structure is formed in a shape inclined with respect to the surface of the substrate, and the inclined surface of the laminated structure and the surface of the substrate On the first inclined surface having an obtuse angle, that is, on the surface of a gentle slope that is not in a so-called overhanging state with respect to the substrate surface, with respect to the electrode with an insulating film therebetween Since there is a wiring for making an electrical connection from other wirings provided on the surface of the substrate, when forming the wiring, metal film formation defects such as so-called step breakage and wiring shape The occurrence of frequent formation defects and the like is avoided.

  Further, the third surface emitting laser element of the present invention has the characteristics of the first and second surface emitting laser elements, and therefore, it is activated through the current confinement layer inside the laminated structure. The current distribution configured to inject current into the layer can achieve a single transverse mode at high power, and as a result, the realization of the single transverse mode is ensured with further increase in the amount of current injection When the wiring is formed, it is possible to avoid frequent occurrence of a metal film formation failure, a wiring shape formation failure, and the like such as so-called step breakage.

  According to the first or third surface emitting laser element of the present invention, the stacked structure has a pair of opposing side surfaces inclined with respect to the surface of the substrate, and the electrode has a light output window, the stacked structure of the stacked structure. Among the inclined surfaces, an area closer to the first inclined surface, which has an obtuse angle between the inclined surface and the surface of the substrate, and closer to the second inclined surface, the angle formed with the substrate surface being an acute angle. Is set to be larger than the area near the first inclined surface, so that the current distribution injected into the active layer through the current confinement layer in the stacked structure has a high output. The shape is such that a single transverse mode can be realized. As a result, the single transverse mode can be realized with a further increase in the amount of current injection.

  According to the second or third surface emitting laser element of the present invention, the first inclined surface having an obtuse angle between the inclined surface and the surface of the substrate among the inclined surfaces of the multilayer structure, that is, Electrical connection from other wiring provided on the surface of the substrate to the electrode with an insulating film on the surface of a gentle slope that is not in a so-called overhang state with respect to the substrate surface Therefore, when forming the wiring, it is possible to avoid the occurrence of metal film formation failure such as so-called step breakage, wiring shape formation failure, etc. It can be reliably formed by a simple method.

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

  FIG. 1 shows a configuration of a surface emitting laser element according to an embodiment of the present invention. This surface emitting laser element includes a laminated structure 10 on a substrate 20. In this laminated structure 10, an n-type DBR layer 1, an n-type cladding layer 2, an active layer 3, a p-type cladding layer 4, a current confinement layer 5, a p-type DBR layer 6 and a contact layer 7 are laminated in this order. The electrode 8 is provided on the upper surface. Further, the laminated structure 10 is provided with an insulating film 11 along one side surface, and a wiring 12 connected to the electrode 8 is formed on the surface of the insulating film 11.

  The n-type DBR layer 1 and the p-type DBR layer 6 are composed of a multilayer film in which a semiconductor having a small refractive index and a semiconductor having a large refractive index, such as a combination of AlGaAs and GaAs, are alternately stacked. The light emitted from the active layer 3 is reflected at a reflectivity of about 99% by stacking about 20 sets having the oscillation wavelength λ / 4n. That is, in this surface emitting laser element, the n-type DBR layer 1 and the p-type DBR layer 6 provided above and below the active layer 3 resonate the emitted light to generate laser oscillation.

  The current confinement layer 5 is disposed in the second layer, for example, counted from the active layer 3 side. The current confinement layer 5 is made of AlAs (aluminum arsenic) as a main material, and plays a role of causing a current to flow only in the current confinement portion 5A by an oxidation confinement process using water vapor.

  The active layer 3 constitutes MQW (Multi Quntum Well) of GaAs (gallium arsenide) and AlGaAs (aluminum gallium arsenide). In the active layer 3, stimulated emission light is generated by receiving electrons injected from the electrode 8 and concentrated in the current confinement portion 5 A by the current confinement layer 5.

  The p-type cladding layer 4 and the n-type cladding layer 2 positioned above and below the active layer 3 are semiconductors having a refractive index smaller than that of the active layer 3 and a large band gap, and confine electrons injected into the active layer 3. Is for. The contact layer 7 is for connection with a metal for current injection (so-called ohmic connection), and is made of, for example, GaAs or the like subjected to high doping.

  In the present embodiment, the laminated structure 10 has a shape that is inclined to one side, that is, an inclined structure. In the example shown in FIG. 1, the right inclined surface (second inclined surface) 10A of the laminated structure 10 has an acute angle (for example, 60) formed by the surface of the inclined surface 10A and the surface 20A of the substrate 20. On the other hand, the left inclined surface (first inclined surface) 10B has an obtuse angle (120 degrees) between the surface of the inclined surface 10B and the surface 20A of the substrate 20.

  Then, the insulating film 11 and the wiring 12 are both provided on the surface of the inclined surface 10B having the obtuse angle (left side in FIG. 1) without any disconnection or shape defect.

  It goes without saying that the insulating film 11 is provided in order to prevent an electrical short circuit or current leakage between the wiring 12 made of a metal material or the like provided on the insulating film 11 and the inclined surface of the laminated structure 10. If the insulating film 11 has step breakage or poor film deposition, it becomes impossible to prevent an electrical short circuit, current leakage, or the like between the wiring 12 and the inclined surface of the laminated structure 10. Must be formed with. In addition, if the wiring 12 is disconnected or has a defective shape, a sufficient current cannot be supplied or no current can be supplied at all. 12 must also be reliably formed in a precise shape with high reliability.

  In the surface emitting laser element according to the present embodiment, in response to such a request, the inclined surface of the insulating film 11 and the wiring 12 that forms an obtuse angle with the surface of the substrate 20, in other words, By providing on the surface of a gentle inclined surface with respect to the substrate 20 (the inclined surface that is not in an overhanging state with respect to the substrate 20), it is possible to reliably and easily cope with it. Yes. In the case of a surface emitting laser element having the conventional general post structure and the electrode 108 (symmetrical electrode) as shown in FIG. 5, a steep edge whose side surface stands up at about 90 degrees. Therefore, there is a high possibility that the insulating film 110 is disconnected at the edge portion, the film is poorly formed, the shape of the wiring 120 is poor, and the like. This can be solved with a laser element. In FIG. 5, the same parts as those in FIG. 1 are denoted by the same reference numerals.

  Further, as shown in FIG. 3, the electrode 8 provided on the uppermost surface of the laminated structure 10 has a light output window (also referred to as a so-called aperture) 13 near the inclined surface 10B having an obtuse angle. It is provided with an offset. As a result, the area of the electrode 8 near the inclined surface 10B on the obtuse angle side is smaller than the area near the inclined surface 10A on the acute angle side (in other words, the area closer to the inclined surface 10A on the acute angle side is closer to the obtuse angle side). It is larger than the area near the inclined surface 10B).

  As described above, in the present embodiment, the light output window 13 of the electrode 8 is provided offset from the current confinement portion 5A of the current confinement layer 5, so that the laminated structure 10 passes through the current confinement portion 5A. Thus, the current distribution injected into the active layer 3 becomes a current distribution 30 as schematically shown in FIG. With such a current distribution 30, a single transverse mode with high output can be realized.

  Incidentally, FIG. 6 shows a configuration of a surface emitting laser element having a conventional post-type laminated structure 100, but the electrode 108 has a symmetrical shape that is not offset as shown in FIG. The current distribution 130 in this case has a shape as shown in FIG. On the other hand, in the present embodiment, the current distribution 30 shown in FIG. 2 is obtained, and a charge flow component in the lateral direction is generated, so that the uniformity of the current density is high, and in the vicinity of the outer portion of the current confinement portion 5A. Concentration of current density can be prevented. As a result, the current density at the time of large current injection is maximized at the center, and a single transverse mode at a high output as shown in FIGS. 4A and 4B can be realized. In contrast, in the case of the conventional post-type laminated structure 100, as shown in FIG. 8A and FIG. 8B, the oscillation at the central portion is reduced and the current confinement portion 5A is reduced. There was a tendency that the current density was concentrated in the vicinity of the outer portion of the layer, and higher-order modes were generated in that portion.

  In the present embodiment, the current distribution 30 formed by the shape of the electrode 8 reduces the current in the region where the light emitted from the active layer 3 resonates, so that the interaction between light and electrons is more enhanced. As a result, it is expected to further stabilize the optical output and transverse mode.

  Next, an example of a manufacturing process of the surface light emitting element according to this embodiment will be described.

  First, an n-type contact layer (not shown) doped with Si (silicon) is grown by 300 [nm] on the substrate 20 made of n-type GaAs by MOCVD (Metal Organic Chemical Vapor Deposition).

  Subsequently, an n-type DBR layer 1 composed of an Al0.92 GaAs layer and an Al0.3 GaAs layer is formed by MOCVD so that the optical thickness becomes 1/4 of the oscillation wavelength.

  Subsequently, Al0.47GaAs is grown as the n-type cladding layer 2, and then GaAs, which is the MQW serving as the active layer 3, is grown, and Al0.47GaAs is grown as the p-type cladding layer 4. Further, a p-type DBR layer 6 doped with Zn (zinc) is grown in the same manner as the n-type DBR layer 1, and a p-type contact layer 7 is formed on the p-type DBR layer 6 with a thickness of 300 nm and a doping concentration. Laminate at about 1E19.

  Then, photolithography using ultraviolet rays and wet etching using hydrogen peroxide solution and ammonia solution are performed on the uppermost contact layer 7 to form a window structure having a diameter of about 10 [μm]. Subsequently, photolithography and RIE (reactive ion etching) are performed to produce a post-type mesa structure. At this time, by performing RIE by inclining the substrate 20, the post structure mesa structure 10 having the inclination shown in FIG. 1 can be manufactured.

  Thereafter, the current confinement layer 5 is oxidized and constricted by exposing the substrate 20 to a water vapor atmosphere. At this time, oxidation proceeds selectively only to the AlAs of the current confinement layer 5, but the oxidation proceeds from the periphery to the inside of the post-type mesa structure. The current constriction 5A can be formed by stopping the progress of the oxidation before reaching the central portion and leaving an energized region that is not oxidized only in the central portion. Such a current confinement structure may be provided above and below the active layer 3.

Thereafter, SiO ₂ is formed on the entire surface by the CVD method, and the insulating film 11 is formed on the inclined surface 10B side of the laminated structure 10 by photolithography and etching.

  Subsequently, after patterning by photolithography, a material such as a p-type electrode metal is vacuum-deposited, and the wiring 12 is provided on the insulating film 11 and the electrode 8 is provided on the uppermost surface of the laminated structure 10. Each is formed into a desired shape. As the p-type electrode metal, for example, Ti (titanium) / Pt (platinum) / Au (gold) is deposited by a thickness of 500/1000/4000 angstroms, respectively, so as to be an ohmic electrode with p-type GaAs. . Thereafter, the substrate 20 side is polished to a thickness of about 130 [μm] to form an n-type electrode (not shown) on the substrate 20 side. The metal material of the n-type electrode is, for example, AuGe (gold germanium) / Ni (nickel) / Au (gold), and each thickness may be 1600/450/5000 angstroms. Thereafter, heat treatment is performed at 420 ° C. for 1 minute for alloying, and the main part of the surface light emitting device according to the present embodiment is manufactured.

  As described above, the surface emitting laser element according to the present embodiment can have a current distribution that can avoid the concentration of the current density outside the current confinement portion 5A even when a large current is injected. Therefore, it is possible to achieve both high output and single mode.

  In addition, it is expected that the interaction between light and electrons can be further reduced by reducing the current in the resonance region (DBR portion) of the light emitted from the active layer 3. Therefore, further stabilization of the light output / transverse mode is expected.

  Further, since the insulating film 11 and the wiring 12 are provided on the gentle slope of the side surface of the laminated structure 10 as compared with the conventional post-type mesa structure, the insulating film 11 and the wiring 12 in this portion are provided. Occurrence of disconnection or film deposition failure is eliminated, and the highly reliable insulating film 11 and wiring 12 can be manufactured.

  Further, compared to the conventional general post structure, the area closer to the overhanging surface 10A of the overhanging side of the electrode 8 located at the uppermost portion (the inclined surface formed with an acute angle with the substrate 20). Therefore, the device resistance is expected to be reduced. As a result, the element resistance value required in the case of application to optical communication can be afforded, and the current confinement portion can be further narrowed, which has been difficult due to concern about high resistance. The threshold value can be lowered.

  The surface emitting laser element of the present invention can be suitably used for, for example, a laser light output element for an optical communication network.

It is a figure showing the structure of the principal part of the surface emitting laser element which concerns on one embodiment of this invention. It is the figure which represented typically the electric current distribution in the inside of a laminated structure. It is a figure showing an example of the shape of a light output window. It is a figure showing an example of the single transverse mode achieved with high output. It is a figure showing the structure of the principal part of the surface emitting laser element of the conventional general post structure. It is a figure showing the current distribution of the conventional post structure. It is a figure showing the shape of the electrode of the conventional post structure. It is a figure showing the example of the high-order transverse mode produced at the time of the high output of the conventional post structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... n-type DBR layer, 2 ... n-type clad layer, 3 ... Active layer, 4 ... p-type clad layer, 5 ... Current confinement layer, 5A ... Current confinement part, 6 ... p-type DBR layer, 7 ... p-type contact Layer, 8 ... electrode, 10 ... laminated structure, 11 ... insulating film, 12 ... wiring, 13 ... light output window

Claims (3)

A surface having a laminated structure in which at least an active layer and a current confinement layer are laminated in parallel to the surface of the substrate, and an electrode having a light output window on the upper surface of the laminated structure. A light emitting laser element,
The laminated structure has a pair of opposing side surfaces inclined with respect to the surface of the substrate, and the electrode includes the light output window, the inclined surface of the laminated structure, and the surface of the substrate. And an area closer to the second inclined surface having an acute angle formed with the surface of the substrate is closer to the first inclined surface. A surface-emitting laser element characterized by being set larger than the above. A surface having a laminated structure in which at least an active layer and a current confinement layer are laminated in parallel to the surface of the substrate, and an electrode having a light output window on the upper surface of the laminated structure. A light emitting laser element,
The laminated structure has a pair of opposing side surfaces inclined with respect to the surface of the substrate, and an angle formed by the inclined surface of the laminated structure and the surface of the substrate is an obtuse angle. A surface emitting laser element comprising: a wiring for electrically connecting to the electrode from another wiring provided on the surface of the substrate with an insulating film interposed therebetween on the inclined surface. A surface having a laminated structure in which at least an active layer and a current confinement layer are laminated in parallel to the surface of the substrate, and an electrode having a light output window on the upper surface of the laminated structure. A light emitting laser element,
The laminated structure has a pair of opposing side surfaces inclined with respect to the surface of the substrate, and the electrode includes the light output window with the inclined surface of the laminated structure and the surface of the substrate. The area formed near the first inclined surface having an obtuse angle is closer to the second inclined surface than the area inclined toward the first inclined surface. And a wiring for making an electrical connection from the other wiring provided on the surface of the substrate to the electrode with an insulating film in between on the first inclined surface A surface-emitting laser element comprising:

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