JP2004253788A - Face emitting semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more effectively suppress the interference pattern (mutilation of FFP) of light, which leaks from an n-type contact layer than a conventional one in a stably oscillating semiconductor laser. <P>SOLUTION: The distance Λ of the interference pattern appearing in a conventional n-type contact layer is expressed by the formula: (f (λ) = λ(n<SP>2</SP>-n<SB>eq</SB><SP>2</SP>)<SP>-1/2</SP>/2) (wherein, λ is the emitting wavelength of the light emitting from an emission outputting section 104, n is the refractive index of the n-type contact layer, and n<SB>eq</SB>is an equivalent refractive index of guided mode in the n-type contact layer). Further, the thickness of a residual film δ of the n-type contact layer 102 in a recess D on the back of a crystal growth substrate may be about Λ/2. If at least a part of the n-type contact layer located underneath an resonator is left with film thickness δ, since a contact with a negative electrode can be well secured even beneath the resonator, the mutilation of FFP caused by the light leaking from the n-type contact layer can be sufficiently suppressed based on an effective light containment action, and simultaneously, a semiconductor laser is stably oscillated. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

The present invention relates to an edge-emitting semiconductor laser in which a resonator or the like is formed by stacking a plurality of semiconductor layers on a crystal growth substrate. An object of the present invention is to provide a semiconductor laser having a highly convergent output characteristic in which a far field pattern (FFP) of output light (beam) is arranged.
Therefore, the semiconductor laser manufactured based on the present invention is extremely useful in the fields of, for example, an information input / output processing device, an information processing device, an information transmission device, and a processing device using laser beam irradiation.
About.

As described in Non-Patent Document 1 below, as a problem of the semiconductor laser, there is a phenomenon that a sub-peak appears in a direction perpendicular to the optical axis of the guided light, and a far field pattern (FFP) is disturbed.
FIG. 10 is a cross-sectional view of a semiconductor laser illustrating the phenomenon that the FFP is disturbed. Such a phenomenon that the FFP is disturbed is caused by light leaking from the n-type contact layer as a sub-waveguide. As described in Non-patent Document 1 below, light causing such disturbance forms interference fringes in the n-type contact layer and is output from the main waveguide (active layer + guide layer). Is emitted to the outside together with the emitted light.
The prior art described in Non-Patent Document 1 below attempts to suppress the disturbance of the FFP by making the thickness of the n-type cladding layer at least 0.8 μm or more.

Further, Patent Document 1 below mentions a concave structure on the back surface side of a crystal growth substrate of a semiconductor light emitting device, external quantum efficiency, device durability, device productivity, and the like. Some effectiveness is recognized. However, Patent Document 1 does not specifically disclose an appropriate range or the like regarding the thickness of a specific semiconductor layer as in Non-patent Document 1 described below. Does not suggest any specific or effective technique with respect to means and methods for eliminating disturbances in FFP centered on the n-type contact layer of the semiconductor laser. That is, from Patent Document 1, we cannot know any effective and specific means or method for eliminating the disturbance of the FFP of the semiconductor laser.
SHARP Technical Journal No. 9, No. 77, “Oscillation Mode of Blue-violet Ridge Waveguide Semiconductor Laser” JP-A-10-308560

Therefore, when a prototype of the semiconductor laser disclosed in the above-mentioned Patent Document 1 is produced as it is, there is no guarantee that a semiconductor laser without FFP disturbance can be obtained, and from such a prototype, FFP is not disturbed and stable. It is extremely difficult to obtain a semiconductor laser that oscillates.
For example, if the contact layer below the resonator is not deleted, light leaks from that part (contact layer), and it is impossible to expect efficient and stable laser oscillation. In addition, when the contact layer below the resonator is removed, the electrical connection between the resonator and the negative electrode is not good, and it is difficult to form a good current density distribution. Therefore, also in this case, it is not possible to expect efficient and stable laser oscillation.

On the other hand, as described in Non-Patent Document 1, by setting the film thickness of the n-type cladding layer to at least 0.8 μm or more, FFP disturbance can be suppressed to some extent.
However, according to this method, although it depends on the composition of each semiconductor layer such as the active layer, the light guide layer, and the n-type cladding layer, unless the n-type cladding layer is laminated with a thickness of at least 0.8 to 1 μm or more. In addition, a sufficient effect of suppressing interference fringes (FFP disturbance) of the n-type contact layer cannot be obtained. For this reason, the conventional technology of Non-Patent Document 1 cannot but be said to have low productivity in the crystal growth step of the n-type cladding layer.

Further, the conventional technique of Non-Patent Document 1 employs an extremely natural method in which the peak intensity of the interference fringes decreases as the film thickness of the n-type clad layer increases, so that the method is based on this method. Although the peak intensity of the interference fringes created by the light leaking from the n-type contact layer can be reduced, the interference fringes cannot be completely eliminated based on this method.
Also, from the viewpoint of the heat radiation effect centering on the resonator or the internal quantum efficiency (threshold voltage), increasing the film thickness of the n-type cladding layer as described above is not always necessary in terms of the configuration of the semiconductor laser. It is hard to say.

As another light confinement method, for example, a method in which the above-described n-type clad layer made of n-type GaN is changed to an n-type AlGaN layer and laminated is considered. According to such a method, since AlGaN has a relatively small refractive index, it is considered that an effect of confining light inside the resonator can be obtained.
However, in such a method, since a problem of internal stress between semiconductor layers based on a difference in lattice constant is caused, it is very difficult to form a thick film, and it is practically impossible to manufacture a semiconductor laser.

  Further, a method of adding another impurity to the n-type cladding layer to suppress the refractive index of the n-type cladding layer to be low can be considered. However, an impurity is added in such an amount that the refractive index changes significantly. In this case, the crystallinity of the n-type cladding layer and the semiconductor layers stacked thereafter becomes significantly deteriorated. Therefore, even by such a method, it is practically impossible to manufacture a semiconductor laser.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a semiconductor laser that oscillates stably, in which interference fringes of light leaking from an n-type contact layer more effectively than before. (Disruption of FFP).

In order to solve the above-mentioned problems, the following means are effective.
In other words, the first means of the present invention is to provide an edge-emitting type semiconductor laser in which a resonator or the like is formed by stacking a plurality of semiconductor layers on a crystal growth substrate, wherein the thickness of the n-type contact layer is At least immediately below the device, the emission wavelength λ of the active layer, the refractive index n of the n-type contact layer depending on the emission wavelength λ, and the equivalent refractive index n _eq of the waveguide mode of the n-type contact layer depending on the emission wavelength λ function of the emission wavelength lambda expressed using Application: "Λ≡f (λ) = λ (n 2 -n eq 2) -1/2 / 2 " is to thinner than a function value λ of.

However, when a plurality of semiconductor layers are stacked on a crystal growth substrate constituting a part of the semiconductor laser of the present invention, a group III nitride compound semiconductor can be used as these semiconductor layers. However, here referred to the "Group III nitride compound semiconductor" generally, binary, ternary, or quaternary _{"Al 1-xy Ga y In x} N; 0 ≦ x ≦ 1,0 ≦ y ≦ 1, Semiconductors having an arbitrary mixed crystal ratio represented by the general formula of 0 ≦ 1−xy ≦ 1 ”and further doped with p-type or n-type impurities are also referred to as“ III-groups ”. Nitride-based compound semiconductor ".
Further, at least a part of the group III elements (Al, Ga, In) is replaced with boron (B), thallium (Tl), or the like, or at least a part of nitrogen (N) is phosphorus (P). ), Semiconductors substituted with arsenic (As), antimony (Sb), bismuth (Bi), and the like are also included in the category of these “III-nitride compound semiconductors”.

As the p-type impurity, for example, magnesium (Mg) or calcium (Ca) can be added.
Further, as the n-type impurity, for example, silicon (Si), sulfur (S), selenium (Se), tellurium (Te), germanium (Ge), or the like can be added.
Further, two or more elements may be simultaneously added to these impurities, or both types (p-type and n-type) may be added simultaneously.

  According to a second aspect of the present invention, in the first aspect, the refractive index of at least a region immediately below the resonator and immediately below the n-type contact layer is set to be smaller than the above-described refractive index n. .

  A third means of the present invention is that, in the first or second means, a recess or a cavity is formed at least immediately below the resonator.

  Further, according to a fourth aspect of the present invention, in the above third aspect, the concave portion or the cavity portion is formed by volatilizing at least a part of the semiconductor layer located at least immediately below the resonator by laser irradiation. It is to be.

According to a fifth aspect of the present invention, in an edge-emitting semiconductor laser in which a resonator or the like is formed by laminating a plurality of semiconductor layers on a crystal growth substrate, the thickness of the n-type contact layer is set to be active. It is expressed using the emission wavelength λ of the layer, the refractive index n of the n-type contact layer depending on the emission wavelength λ, and the equivalent refractive index n _eq of the waveguide mode of the n-type contact layer depending on the emission wavelength λ. function of the emission wavelength lambda: "Λ≡f (λ) = λ (n 2 -n eq 2) -1/2 / 2 " until the thinner position than the function value Λ of the crystal which is located at least below the resonator A concave portion is formed below the resonator by removing the growth substrate and the semiconductor layer from the back surface side of the crystal growth substrate.

  In a sixth aspect of the present invention, in any one of the first to fifth aspects described above, at least a bottom portion of the n-type contact layer located immediately below the resonator is provided in the resonance direction of the resonator. A distributed feedback structure (DFB structure) that resonates light is provided.

  According to a seventh aspect of the present invention, in any one of the third to sixth aspects, the dielectric layer having a lower refractive index than the n-type cladding layer is formed on the bottom surface of the n-type contact layer exposed in the recess. Laminating a body film or a semiconductor film.

  According to an eighth aspect of the present invention, in any one of the third to seventh aspects, a metal layer or a metal portion is provided on at least a part or all of the inside of the concave portion.

  According to a ninth aspect of the present invention, in the above-mentioned eighth aspect, a negative electrode is formed of the metal layer or the metal part.

  In a tenth aspect of the present invention, in any one of the first to ninth aspects, the exposed surface of the n-type contact layer which is exposed upward by etching from the upper side of the plurality of semiconductor layers. A negative electrode is provided thereon, and a semiconductor layer made of a p-type or undoped group III nitride compound is provided between the n-type contact layer and the crystal growth substrate.

Further, an eleventh means of the present invention is the liquid crystal display device according to any one of the first to tenth means, wherein the film thickness δ of the n-type contact layer located immediately below the resonator is Λ / 5 or more and less than Λ. It is to set.
By the means of the present invention described above, the above problems can be effectively or rationally solved.

The effects obtained by the above means of the present invention are as follows.
That is, according to the first means of the present invention, it is possible to obtain an effect of suppressing interference fringes (FFP disturbance) of the n-type contact layer.
When a plurality of interference fringes appear in the n-type contact layer, the interval (spatial period) between the fringes coincides with the above function value Λ, as can be seen from Non-Patent Document 1. Therefore, if the film thickness of the n-type contact layer is set to be less than this function value Λ, the interference fringe (peak) does not appear in the n-type contact layer.

  If the n-type contact layer located immediately below the resonator is entirely removed, the current density distribution will be deviated, and it will not be possible to efficiently supply current to the resonator. Is set to the above-mentioned thickness at the very least, so that a good contact with the negative electrode can be ensured immediately below the resonator. For this reason, according to this configuration, the current density distribution in the resonator and around the resonator can be maintained in an ideal state.

That is, according to the present invention, a semiconductor laser that oscillates stably based on an ideal current density distribution and an effective light confinement function can be manufactured, and interference fringes of the n-type contact layer can be more effectively formed than before. It is possible to obtain a sufficient effect of suppressing (FFP disturbance). Such a structure of the semiconductor laser is advantageous in accurately controlling the irradiation position (irradiation area) of the laser beam because the FFP in the vertical direction is not disturbed. It is very useful in realizing.
Therefore, a semiconductor laser manufactured according to the present invention is, for example, an information input / output processing device, an information processing device, an information transmission device, or a thermal processing device (laser beam irradiation device) that executes laser beam irradiation. It will be extremely useful in the field.

  Further, according to the second aspect of the present invention, the refractive index of at least the region immediately below the resonator and immediately below the n-type contact layer is set to be smaller than the above-mentioned refractive index n. It is effectively confined to the vessel side. Therefore, according to the second aspect of the present invention, the semiconductor laser oscillates efficiently and the laser output is stabilized.

Further, according to the third means of the present invention, the concave portion or the hollow portion is filled with a suitable or arbitrary gas such as air or an inert gas, or by making this space a substantially vacuum state, The above second means can be embodied inevitably.
However, this space (the above-mentioned concave portion or hollow portion) may be filled with an appropriate solid material as described later.

  Further, according to the fourth means of the present invention, such a space (the above-described concave portion or hollow portion) can be formed without necessarily removing the crystal growth substrate by etching or the like. In this laser irradiation, a laser is focused on a portion to be volatilized (removed) of the semiconductor, and a target portion is locally volatilized. As the type of laser to be used, YAG or Excimer is useful, but the latter is more advantageous in consideration of the flatness of the processed portion.

  Further, according to the fifth aspect of the present invention, the operation and effect of the present invention can be obtained in substantially the same manner as described above in a relatively simple form in which the crystal growth substrate is etched from the back surface. That is, even with such means, it is possible to obtain an effect of suppressing interference fringes (FFP disturbance) of the n-type contact layer.

  Therefore, according to the fifth means of the present invention, a semiconductor laser which oscillates stably on the basis of an ideal current density distribution and an effective light confinement function can be manufactured, and the n-type contact can be more effectively formed than before. A sufficient effect of suppressing interference fringes (disorder in the FFP) of the layer can be obtained. Such a structure of the semiconductor laser is advantageous in accurately controlling the irradiation position (irradiation area) of the laser beam because the FFP in the vertical direction is not disturbed. It is very useful in realizing.

  However, when the film thickness of the n-type contact layer is less than the above-mentioned thickness from the beginning, the thickness of the n-type contact layer from the back side of the crystal growth substrate until the bottom surface (crystal growth start surface) is exposed. It is sufficient to remove the crystal growth substrate and the like. Further, in order to ensure good or sufficient crystallinity of the n-type contact layer and each semiconductor layer to be laminated later (hence, above), the thickness of the n-type contact layer is usually It is desirable that the layers are once laminated to a thickness of at least Λ.

  Further, in the fifth means of the present invention, at least a region immediately below the resonator is not entirely removed, but a part thereof is always left. That is, if the thickness of the remaining portion of the n-type contact layer is described as δ, it should be 0 <δ <Λ. In addition, in the above-mentioned concave portion formed below the resonator, air may be arranged as it is, vacuum may be kept, or a refractive index may be higher than each semiconductor layer used. It may be filled with a transparent insulating material or an inert gas having a low density.

  According to the sixth aspect of the present invention, since the distributed feedback structure (DFB structure) for resonating light in the resonance direction of the resonator is formed at the bottom of the n-type contact layer, the laser emission can be performed in a substantially single mode. Be converted to This makes it possible to obtain sharp or pure emission characteristics with a sharp emission peak.

Further, according to the seventh aspect of the present invention, the effect of confining light in the above-described resonator is reinforced, so that the light emission efficiency of the laser can be increased.
For example, a plurality of dielectric layers or semiconductor layers may be sequentially stacked such that the refractive index monotonously decreases along the direction from the active layer side to the crystal growth substrate side. Alternatively, a single-layer dielectric film or semiconductor film whose refractive index decreases monotonously continuously in that direction may be formed. In these cases, a waveguide that returns light to the active layer side can be formed by a dielectric film or a semiconductor film. Further, the above-mentioned dielectric film or semiconductor film may of course be constituted by a single layer having a substantially uniform refractive index.

Examples of a dielectric that can be used as a material of such a reflection film include SiO ₂ and TiO _2, but of course, are not limited to these dielectric materials in general. Alternatively, the reflection film may be formed from a semiconductor layer such as Al _x Ga ₁ -xN (0 ≦ x ≦ 1). Since the refractive index of Al _x Ga ₁ -xN is a monotonically decreasing function of the aluminum composition ratio x, the composition ratio x is used as an adjustment parameter for changing the refractive index of the semiconductor layer stepwise or continuously. You can also.

For example, on the bottom surface of the n-type contact layer exposed in the concave portion, the refractive index monotonically decreases along the direction from the active layer side to the crystal growth substrate side, that is, the aluminum composition along the direction. A single semiconductor layer made of Al _x Ga ₁ -xN may be continuously formed so that the ratio x monotonically increases. Of course, a multilayer film may be formed by gradually increasing the aluminum composition ratio x. When these dielectric materials are used, the absorption and transmission of light can be suppressed more effectively than other materials such as air and metal, so that an optical waveguide with high energy efficiency can be formed.

  According to the eighth aspect of the present invention, such a metal layer or a metal portion efficiently conducts heat generated in the resonator to the outside and the periphery of a heat sink or the like, so that the oscillation operation of the semiconductor laser can be further improved. Can be stabilized. From these viewpoints, it is desirable that the above-mentioned metal layer or metal part has high thermal conductivity such as copper (Cu) or gold (Au). Of course, an alloy composed of a plurality of metals may be used. Alternatively, these metal layers and metal parts may have a multilayer structure made of different metals.

In addition, the above-mentioned metal layer or metal part forms a light reflecting surface, and thus also contributes to a light confinement effect inside the resonator. In this sense, it is desirable that the above-mentioned metal layer or metal part has a high reflectance for a desired emission wavelength λ, such as aluminum (Al), rhodium (Rh), silver (Ag), gold (Au), or the like. Alternatively, for example, an alloy obtained by mixing an appropriate amount of a metal having high corrosion resistance such as platinum (Pt) may be used.
The above-mentioned metal layer and metal part may be appropriately selected in consideration of these various conditions. Of course, an alloy composed of a plurality of metals may be used. Alternatively, these metal layers and metal parts may have a multilayer structure made of different metals.

According to the ninth aspect of the present invention, a negative electrode can be realized only by connecting a wiring or the like to the above-mentioned metal layer or metal portion connected on the exposed surface of the n-type contact layer exposed in the concave portion. it can. Therefore, according to such a configuration, the n-type contact layer is exposed upward by an etching process from the upper layer side of the plurality of semiconductor layers to the n-type contact layer, or the negative surface is exposed on the exposed surface of the n-type contact layer. It is not necessary to separately provide an electrode (another metal layer or a metal part). It is desirable that such a metal layer and a metal portion constituting the negative electrode have an excellent ohmic characteristic with respect to a semiconductor.
Therefore, an appropriate metal may be selected for the above-mentioned metal layer and metal part by sufficiently considering the above various conditions. Of course, an alloy composed of a plurality of metals may be used. Alternatively, these metal layers and metal parts may have a multilayer structure made of different metals.

Further, if a negative electrode is formed of a metal layer or a metal portion as described above, a negative electrode can be formed on the surface opposite to the positive electrode when a semiconductor wafer is manufactured. The number of semiconductor laser chips that can be taken out of the wafer can be increased as compared with the case where both electrodes are formed on the semiconductor layer stacking side (crystal growth side).
Therefore, according to the above-described means, it is possible to greatly improve the productivity of a semiconductor laser having a sufficient effect of suppressing interference fringes (FFP disturbance).

Further, according to the tenth aspect of the present invention, if a semiconductor layer (for example, a GaN layer) made of a group III nitride compound without impurities is provided between the n-type contact layer and the crystal growth substrate, Current component is suppressed, so that current injection efficiency is improved.
Further, if a semiconductor layer (for example, a GaN layer) made of a p-type group III nitride compound is provided between the n-type contact layer and the crystal growth substrate, pnp having no light-emitting action or light-receiving action is provided at this portion. Since a structure like a junction diode is formed, current leakage is prevented and the withstand voltage of the element is improved.
Such a configuration is particularly effective when an n-type conductive substrate such as silicon (Si) is used. For example, a general crystal growth substrate such as undoped silicon (Si) or a sapphire substrate may be used. A sufficient effect is exhibited even when used.

Further, according to the eleventh means of the present invention, the above-mentioned function and effect can be reliably obtained without impairing the function of the original n-type contact layer and keeping the contact with the negative electrode sufficiently good. . The thickness δ of the n-type contact layer located immediately below the resonator depends on the setting accuracy (processing accuracy) and the like, but the above-mentioned effects can be reliably obtained while keeping the contact with the negative electrode sufficiently good. For this reason, for example, in the case of a blue-violet light emitting laser, more ideally, it is more desirable that the thickness δ of the n-type contact layer is approximately in the range of Λ / 3 ≦ δ ≦ 2Λ / 3.
An appropriate lower limit of the film thickness δ at which the contact with the negative electrode can be kept sufficiently good depends on the dimensions of each part such as the stripe width of the resonator, the structure of the laser, and the like. It seems to be about 2 μm.

  If the value of the film thickness δ of the n-type contact layer located directly below the resonator is too large, the vicinity of the peak of the interference fringes appears in the output FFP, which is not desirable. The appearance of the interference fringes is suppressed as the value of the film thickness δ decreases. However, if the value of the film thickness δ is too small, it is difficult to secure a good contact on the negative electrode side, and thus it is difficult to make the current density distribution ideal, and as a result, the internal quantum efficiency is reduced. It is not desirable.

Hereinafter, the present invention will be described based on specific examples.
However, embodiments of the present invention are not limited to the individual examples described below.

FIG. 1 is a sectional view of a semiconductor laser 100α according to a first embodiment of the present invention.
A buffer layer 109α made of aluminum nitride (AlN) is stacked on a crystal growth substrate 101 made of sapphire. Furthermore, a high carrier concentration n-type contact layer 102 made of GaN doped with silicon (Si) and an n-type clad layer 103 made of GaN are sequentially stacked thereon.

Further thereon, a light emitting output section 104 composed of an active layer and light guide layers of each type located on the upper and lower sides thereof is formed. More specifically, the light emitting output unit 104 is composed of an n-type light guide layer made of Al _0.01 Ga _0.99 N and an active material of a general multiple quantum well (MQW) structure found in a known edge emitting laser diode. It is formed by sequentially laminating a layer and a p-type optical guide layer made of magnesium (Mg) -doped Al _0.01 Ga _0.99 N.

A total of two layers, a p-type clad layer made of p-type Al _0.12 Ga _0.88 N and a p-type contact layer made of p-type GaN doped with Mg, are sequentially formed on the light emitting output section 104. The p-type semiconductor layer 105 is formed.

Most of the n-type contact layer 102 is exposed by etching from above (the p-type semiconductor layer 105 side), and by this etching, a flat-top resonator portion standing substantially perpendicular to the substrate is formed. . On both sides of the resonator, an insulating protective film 110 made of SiO ₂ having a refractive index of about 1.4 is formed by sputtering.

The concave portion D on the back surface of the crystal growth substrate 101 is formed by etching, and the symbol δ indicates the remaining film thickness of the n-type contact layer 102 in the concave portion D.
Each value of the refractive index n of the n-type contact layer 102 and the equivalent refractive index n _eq of the waveguide mode of the n-type contact layer 102 depends on the emission wavelength λ of the light emitted from the emission output unit 104. The values of the emission wavelength λ, the refractive index n, and the equivalent refractive index n _eq are as shown in the following equations (1) to (3).
(Example of design parameters)
λ = 405 [nm] (blue purple) ... (1)
n = 2.525 (2)
n _eq = 2.502 (3)

Further, the function value Λ of the function f (λ) of the emission wavelength λ and the value of the remaining film thickness δ of the n-type contact layer in the concave portion D on the back surface of the crystal growth substrate are given by the following equations (4) and (5), respectively. expressed.
(Example of design parameters)
Λ≡f (λ) = λ (n 2 -n eq 2) -1/2 / 2
= 596 [nm] (4)
δ = 0.30 [μm] ≒ Λ / 2 (5)

  If the n-type contact layer located immediately below the resonator is entirely removed, the current density distribution will be deviated, making it impossible to efficiently supply current to the resonator. For example, as in the present embodiment, at least As for the n-type contact layer located immediately below the resonator, it is preferable to leave a part thereof. According to this configuration, good contact with the negative electrode can be ensured immediately below the resonator, so that the current density distribution in and around the resonator can be maintained in an ideal state.

Therefore, according to the above configuration, a semiconductor laser that oscillates stably based on an ideal current density distribution and an effective light confinement function can be manufactured, and the n-type contact layer can be formed more effectively than before. A sufficient effect of suppressing interference fringes (disorder of FFP) can be obtained.
Such a structure of the semiconductor laser is advantageous in accurately controlling the irradiation position (irradiation area) of the laser beam because the FFP in the vertical direction is not disturbed. It is very useful in realizing.

  In consideration of the light confinement effect, the securing of crystallinity, the productivity of semiconductor crystal, and the like, the appropriate range of the thickness of the n-type cladding layer 103 laminated on the n-type contact layer 102 is 0.1 to It is considered to be about 2.0 μm. In particular, in the range of about 0.4 to 0.8 μm, the productivity of the semiconductor crystal in the step of forming the n-type cladding layer 103 is improved more than before, and furthermore, the FFP has a finer and more convergent semiconductor than before. Lasers can be manufactured.

  In addition to the above-mentioned sapphire, known crystal growth substrate materials such as silicon, silicon carbide, and gallium nitride can be used for the crystal growth substrate 101. For example, if a bulk substrate made of non-doped gallium nitride (GaN) is used as a crystal growth substrate, a high-quality semiconductor crystal can be easily obtained, and advantages such as not having to form the buffer layer 109α and the like are also obtained. .

Hereinafter, with respect to other portions of the semiconductor laser 100α (FIG. 1) of the first embodiment, the structure, characteristic operation, and the like of each portion that contributes to stable laser oscillation will be disclosed.
(1) For example, as a configuration of an electrode formed on a semiconductor crystal, for example, nickel (Ni) and gold (based on nickel (Ni) as main components) are formed on the flat top portion (p-type semiconductor layer 105) of the resonator. A positive electrode 106A made of an alloy with Au) is formed by vapor deposition. In the exposed portion of the n-type contact layer 102, a negative electrode 106B made of, for example, an alloy of aluminum (Al) and vanadium (V) containing aluminum (Al) as a main component is subjected to a vapor deposition process from the front side of the chip. Is formed.

(2) Further, by employing a structure in which the resonator is sandwiched between the left and right sides by the insulating protective film 110, the width (thickness) of the resonator in the horizontal direction, particularly, the width of the light emitting output unit 104 and the p-type semiconductor layer 105 Can be made very thin, on the order of 1 to 3 μm, and a high current confinement effect can be obtained with these configurations. In addition, by narrowing the width of the resonator and embedding both sides of the active layer with an insulating material having a low refractive index (insulating protective film 110), the light output from the active layer is confined in the horizontal direction. Can be implemented effectively.

(3) The positive electrode 106A formed on the flat top of the resonator is also formed on the insulating protective film 110, and the film formation area of the positive electrode 106A is increased. No more local exfoliation. That is, the positive electrode 106A can stably maintain a state in which the positive electrode 106A is uniformly adhered to the flat top.

(4) Further, the heat generated in the light-emission output unit 104 and the periphery thereof is not limited to the heat dissipation path (heat conduction path) only on the flat top of the resonator, but also on the insulating protective film 110 and the insulating protective film 110. Heat can be dissipated to the heat sink (not shown) via the positive electrode 106A on which the film is formed. However, the heat sink can be externally attached to an arbitrary portion as long as it takes a configuration in which an undesired short circuit (short circuit) does not occur.
For example, a configuration is conceivable in which a large area of the positive electrode 106A is used and a heat sink is arranged so as to be in contact with most of the exposed surface.

(5) In the semiconductor laser 100α, the bottom (lower portion) of the resonator is thick. That is, the structure is such that the n-type cladding layer 103 and the n-type contact layer 102 left by the etching process support the resonator from both lower sides. Thereby, the physical strength of the resonator is reinforced, so that it is easy to form a narrow stripe width at the flat top of the resonator. Further, since the insulating protective film 110 supports the resonator, the formation of the concave portion D is easy or reliable. Further, the insulating protective film 110 is formed to extend to a part of the flat top of the resonator.
With these configurations, a structure having a high light confinement effect and a high current confinement effect can be easily obtained.

(6) In addition, a part of the insulating protective film 110 is extended and laminated on the negative electrode 106B, and the extended portion of the positive electrode 106A and the negative electrode 106A are extended through the extended part of the insulating protective film 110. The electrode 106B is stacked on top of the other. With this structure, there is no inconvenience that the heat radiation path is concentrated on one of the positive electrode 106A and the negative electrode 106B. In other words, the heat conduction efficiency between each part such as between the positive and negative electrodes is increased, and the temperature difference between each part is reduced, so that a high heat radiation effect is obtained.

The oscillation threshold value of the semiconductor laser 100α can be more effectively suppressed by the operations (1) to (6) described above.
For example, by configuring a semiconductor laser according to the present invention as described above, it is possible to realize a semiconductor laser with effectively suppressed driving voltage and oscillating continuously and stably with good convergence.

FIG. 2 is a cross-sectional view of the semiconductor laser 201 according to the second embodiment. The material (composition and physical properties) of each part of the n-type contact layer 102, the n-type cladding layer 103, the light-emission output unit 104, the p-type semiconductor layer 105, the insulating protective film 110, the positive electrode 106A of the semiconductor laser 201, and the resonator The lamination structure (lamination order and film thickness) of each layer at substantially the center is substantially the same as that of the semiconductor laser 100α of the first embodiment.
In addition, the remaining film thickness δ of the n-type contact layer 102 in the concave portion D after the etching process is set in accordance with the above formulas (4) and (5).

Although the configuration of the semiconductor laser 201 has many points in common with the configuration of the semiconductor laser 100α of the first embodiment, other main features of the semiconductor laser 201 (FIG. 2) are as follows.
(1) The ridge is formed by etching the cross-sectional shape of the p-type semiconductor layer 105 into a substantially trapezoidal shape.
(2) As a material of the crystal growth substrate 101a, a bulk crystal made of p-type or non-doped GaN is employed.
(3) The concave portion D is filled with a metal mainly composed of aluminum (Al) by vapor deposition, and the metal portion forms the light reflecting portion and the negative electrode 106C at the same time.

  For example, by forming the semiconductor laser 201 as described above, light is reflected toward the light emitting output unit 104 by the light reflecting surface formed by the boundary between the n-type contact layer 102 and the metal part (the negative electrode 106C). Therefore, a good light confinement effect can be obtained. Further, by using p-type or non-doped GaN for the crystal growth substrate 101a, an electric current does not pass through the crystal growth substrate 101a, so that ideal current confinement can be realized.

In addition, since a bulk substrate made of p-type or non-doped gallium nitride (GaN) is used as a crystal growth substrate, the above-described buffer layer 109α and the like need not be formed.
For example, even with the above configuration, it is possible to manufacture a semiconductor laser with a high convergence of the FFP that oscillates stably and efficiently continuously.

  FIG. 3 is a cross-sectional view of the semiconductor laser 202 according to the third embodiment. The present semiconductor laser 202 has substantially the same structure as the semiconductor laser 201 of the above-described second embodiment, but has an n-type cladding layer 103 made of Si-doped GaN on the bottom surface of the n-type contact layer 102 exposed in the concave portion D. A major feature is that the semiconductor multilayer film 107 having a smaller refractive index is stacked.

  The semiconductor multi-layer film 107 has a multi-layer structure, and after completion of etching of the n-type contact layer 102 from the back side of the substrate, eight semiconductor crystals are sequentially grown and laminated on the exposed surface of the n-type contact layer 102. is there. Therefore, a total of eight semiconductor layers constituting the semiconductor multilayer film 107 have a stacking order and a crystal growth direction opposite (downward) to the other semiconductor layers 102, 103, 104, 105 and the like.

The above eight semiconductor layers are formed by stacking Al _x Ga ₁ -xN (0 ≦ x ≦ 1) by crystal growth, and sequentially from the bottom (exposed surface) side of the n-type contact layer 102 in the following order. Of aluminum having a composition ratio x _m (m = 1, 2, 3,..., 8).
(Configuration Example of aluminum composition ratio x _m)
x ₁ = 0.13
x ₂ = 0.25
x ₃ = 0.38,
x ₄ = 0.50,
x ₅ = 0.63
x ₆ = 0.75
x ₇ = 0.88,
x ₈ = 1.00 (6)
These semiconductor crystals Al _x Ga ₁ -xN (0 ≦ x ≦ 1) are preferably made into n-type semiconductors by adding, for example, Si or the like in order to ensure an ideal current density distribution. .

According to the above configuration, the risk of light being absorbed by the metal light reflecting surface is reduced, and a light trapping effect with high energy efficiency can be obtained. Of course, the light reflecting action at the metal part can be obtained at the same time.
For example, even with such a configuration, it is possible to manufacture a semiconductor laser with a high convergence of the FFP that stably and efficiently continuously oscillates.

FIG. 4 is a sectional view of the semiconductor laser 203 of the fourth embodiment. The semiconductor laser 203 has substantially the same structure as the semiconductor laser 202 of the above-described second embodiment. However, a total of 16 semiconductor layers constituting the semiconductor multilayer film 107 ′ are formed of Al _x Ga ₁ -xN (0 < x ≦ 1) formed by crystal growth, in which layers having the following aluminum composition ratio x _m are formed in order from the bottom (exposed surface) side of the n-type contact layer 102.
(Configuration Example of aluminum composition ratio x _m)
x _m = m / 16 (m = 1, 2, 3,..., 16) (7)

  Each semiconductor layer constituting the semiconductor multilayer film 107 ′ is made into an n-type semiconductor crystal by adding an n-type forming additive such as Si at a high concentration, and the crystal growth substrate 101 a is made of undoped GaN. Alternatively, it is desirable to form the current density distribution ideally from p-type GaN or the like. Of course, also in this case, the negative electrode 106C is used as an electrode.

Note that current may not flow through the crystal growth substrate 101a and the semiconductor multilayer film 107 '. In such a case, as in the case of the semiconductor laser 100α in FIG. 1, if a negative electrode is formed on the front side (upper side) of the semiconductor wafer, laser oscillation can be performed. In this case, the negative electrode 106C does not act as an electrode, but as in the case described above, an effective heat conducting action for heat dissipation, a reflecting action for light leaking slightly from the semiconductor multilayer film 107 ', and the like. To play.
When realizing such a configuration, the crystal growth substrate 101a can be formed of, for example, sapphire, GaN with no added impurities, p-type GaN, or the like. In this case, needless to say, the semiconductor multilayer film 107 ′ may be similarly doped with no impurity or a p-type semiconductor layer.

  FIG. 5 is a sectional view of a semiconductor laser 100β according to a fifth embodiment of the present invention. The semiconductor laser 100β is obtained by partially modifying the semiconductor laser 100α of the first embodiment. The differences between the semiconductor laser 100β and the semiconductor laser 100α are as follows.

(1) The semiconductor layer 109β is stacked on the sapphire substrate 101 by crystal growth. The semiconductor layer 109β has a two-layer structure, and is formed by sequentially growing a buffer layer made of AlN and a p-type GaN layer from the bottom in order.
(2) A single dielectric layer 107β made of SiO ₂ is formed in the recess D below the resonator by sputtering. The single dielectric layer 107β may be formed of another dielectric material such as TiO ₂ .
(3) Further, the recess D is filled with aluminum (Al) by vapor deposition. As a result, a metal layer 108 for heat radiation is formed.

  Since the semiconductor layer 109β having the two-layer structure includes the p-type GaN layer, the heat dissipation metal layer 108 and the n-type contact layer 102 are sufficiently insulated. Further, in the above configuration, since the refractive index of the dielectric layer 107β is ensured to be low, the light confinement effect is effectively achieved. That is, the dielectric layer 107β effectively constitutes the optical waveguide. Further, the metal layer 108 for heat radiation has a good heat conduction effect (heat radiation effect).

  FIG. 6 is a cross-sectional view illustrating a mounted state of the semiconductor laser 100β. The lead frame 50 includes a metal stem 53 also serving as a heat sink, and a metal post 51. The post-side gold wire 57 and the metal stem-side gold wire 58 are both made of gold (Au), and electrically connect the positive and negative electrodes of the semiconductor laser 100β to the respective portions (57, 58) of the lead frame 50.

Usually, when manufacturing a semiconductor laser, there are many cases where diamond or the like having both high insulating properties and high thermal conductivity is used as a material of a submount or a heat sink. However, in the semiconductor laminated structure of FIG. 5 described above, the heat radiation metal layer 108 and the n-type contact layer 102 are sufficiently insulated, and a high withstand voltage is secured here. The submount 52 and the heat sink (metal stem 53) can be made of, for example, copper (Cu), which has both high electrical conductivity and high thermal conductivity and is inexpensive.
That is, according to the semiconductor lamination structure as shown in FIG. 5, for example, as illustrated in FIG. 6, it is possible to simultaneously effectively reduce the manufacturing cost of the semiconductor laser and improve the withstand voltage and the like. Or it may be easier.

  FIG. 7 is a sectional view of a semiconductor laser 100γ according to the sixth embodiment of the present invention. The semiconductor laser 100γ is an improvement of the semiconductor laser 100α of the first embodiment. However, in the drawing of FIG. 7, the structure of the semiconductor laser 100γ of the sixth embodiment is different from that of the semiconductor laser 100α described above. No difference is seen. However, the structural difference between the semiconductor laser 100γ of the sixth embodiment and the above-described semiconductor laser 100α can be seen on the cross section σ perpendicular to the x-axis shown. This cross section σ is parallel to the resonance direction of the resonator, and bisects the resonator along the vertical direction (z-axis direction).

FIG. 8 shows a schematic sectional view of a section σ of the semiconductor laser 100γ. The thicknesses D ₁ , D ₂ of each part of the unevenness in the y-axis direction of the distributed feedback structure (DFB structure) formed by repeating the periodic structure, that is, in the resonance direction of the resonator, substantially satisfy the following conditional expressions. I do.
(Conditional expressions for D ₁ and D ₂ )
D ₁ = kλ / (2n ₁ ),
D ₂ = kλ / (2n ₂ ) (8)
Here, n ₁ is the refractive index of the portion forming the concave portion, and n ₂ is the refractive index of the portion forming the convex portion protruding downward. K is an appropriate natural number. It is desirable that the value of k be appropriately determined according to conditions such as processing accuracy in the electron beam processing apparatus when forming the distributed feedback structure.

In the present embodiment (semiconductor laser 100γ), as can be seen from FIG. 7, since the above concave portion is naturally filled with air, n ₁ = 1.00, and the above convex portion (n-type contact layer) Since (the bottom of 102) is formed of GaN, n ₂ = 2.40. In this case, assuming that λ = 400 nm and k = 1, in the configuration of FIG. 8, from equation (8), D ₁ = 200 nm and D ₂ = 83 nm are appropriate lengths that define the above periodic structure. Further, the thickness (δ) of the n-type contact layer 102 may be about 300 nm, and the height h of the above-mentioned protrusion may be about 150 nm.

  According to the configuration incorporating such a distributed feedback structure (DFB structure), laser emission is made substantially in a single mode by the resonance action in the y-axis direction in the distributed feedback structure that resonates light in the resonance direction of the resonator. . Accordingly, the same operation and effect as those of the semiconductor laser 100α of the first embodiment can be obtained, and further, a sharp or pure light emission characteristic with a sharp emission peak can be obtained.

  Note that the effective range of the height of the convex portion to be formed by projecting the semiconductor layer downward, which forms the distributed feedback structure (DFB structure) in the semiconductor laser of the present invention, is generally about 10 nm to 1000 nm. More desirably, the height of the projection is more effective between 100 and 500 nm. By setting these conditions, an effective resonance action based on the distributed feedback structure can be obtained, and at the same time, the design parameter Λ The effect of suppressing the above-described interference fringes can be obtained by setting the film thickness δ of the n-type contact layer to an appropriate value.

FIG. 9 is a sectional view of a semiconductor laser 100δ according to the seventh embodiment of the present invention. This semiconductor laser 100γ is a modification of the semiconductor laser 100α of the first embodiment. Instead of the concave portion D in the semiconductor laser 100α, the air is filled directly below the n-type contact layer 102 directly below the resonator with the air. A cavity G is formed. That is, by adjusting the size (depth) of the cavity G, the film thickness δ of the n-type contact layer 102 directly below the resonator can be adjusted to a suitable or optimum film thickness, for example, as exemplified in the above-mentioned equation (5). Thickness is set.
However, the material of the crystal growth substrate 101δ used here is sapphire, and a GaN layer having a thickness of about 50 nm is laminated on the buffer layer 109δ at a crystal growth temperature of about 500 ° C.

Further, as a means for forming the cavity G, a method of volatilizing a semiconductor layer (a part of the buffer layer 109δ and a part of the n-type contact layer 102) laminated on a corresponding portion by laser irradiation is adopted. When GaN is heated by a laser, it is decomposed into nitrogen and gallium (N ₂ gas + 2Ga). Therefore, at least one end face of the semiconductor laser 100δ is set to an open system. Nitrogen and gallium (N ₂ gas + 2Ga) can be discharged from holes formed in the contact layer 102 (end face). The decomposed Ga can be exhausted as GaCl ₃ gas by continuously flowing HCl gas during laser irradiation, but may be removed with diluted hydrochloric acid or the like after laser irradiation.
Note that a YAG laser or an excimer laser can be used for laser irradiation when forming the cavity G, but it is preferable to use an excimer laser in consideration of processing flatness and the like.

  Even with the above configuration, an n-type contact layer (n-type contact layer 102) having an appropriate thickness for leading the above-described interference fringe suppressing action can be formed with high quality without scraping the crystal growth substrate from the back side. Can be.

For example, in the embodiment 6, by satisfying the air below the resonator has a refractive index n ₁ of the formula (8) 1.00, semiconductor laser 100Ganma (7 Example 6, FIG. 8 For example, a conductive material may be disposed directly below the n-type contact layer 102).
For example, indium tin oxide (ITO) may be arranged directly below the n-type contact layer 102 of the semiconductor laser 100γ (FIGS. 7 and 8) of the sixth embodiment instead of air. As an arrangement means, a sputtering device or the like is effective.
However, in the present embodiment 8, the refractive index n ₁ of the ITO is 2.02 because, from the foregoing equation (8), the proper value of the width D ₁ of the above-described defining a periodic structure of a distributed feedback structure, about 99nm It becomes.

Further, a metal material suitable for forming an electrode, such as copper, may be disposed immediately below ITO (conductive material). For example, in the cross-sectional view of FIG. 5, ITO is disposed at the position indicated by reference numeral 107β as described above, copper (Cu) is disposed at the position indicated by reference numeral 108, and the structure of the other parts is shown in FIGS. With the configuration similar to that described above, the operation and effect of the semiconductor laser 100β of the fifth embodiment (FIG. 5) and the operation and effect of the semiconductor laser 100γ of the sixth embodiment (FIGS. 7 and 8) are obtained. Can be obtained at the same time.
Therefore, according to such a configuration, it is possible to stably obtain a substantially single-mode laser emission output with suppressed interference fringes.

[Other modifications]
The embodiment of the present invention is not limited to the above-described embodiment, and may be modified as described below. Even with such modifications and applications, the effects of the present invention can be obtained based on the functions of the present invention.

(Modification 1)
Hereinafter, a modified example of the semiconductor laser 203 of the fourth embodiment will be described. As described in the fourth embodiment, the configuration of the negative electrode of the semiconductor laser 203 (FIG. 4) is arbitrary. That is, current may not flow through the crystal growth substrate 101a and the semiconductor multilayer film 107 'in FIG. Therefore, in the first modification, as mentioned in the second half of the description of the fourth embodiment, the negative electrode is formed on the front side (upper side) of the semiconductor wafer. In addition, the number of stacked semiconductor layers (the upper limit of m) constituting the semiconductor multilayer film 107 ′ of the semiconductor laser 203 is also arbitrary. Therefore, in the first modification, the number of layers is set to about 20 to 30. In this case, it is not necessary to expect the reflection effect of the metal layer 106C in the cross-sectional view of FIG.

As a semiconductor laser that satisfies these conditions, for example, a modification including the following configurations 1 to 5 based on the semiconductor laser 203 (FIG. 4) of the fourth embodiment can be considered.
(Configuration 1) No recess is provided in the crystal growth substrate. An insulating material such as sapphire or an undoped GaN bulk substrate is used for the crystal growth substrate. The insulating material may be any as long as it can be used as a well-known crystal growth substrate.
(Configuration 2) First, the semiconductor multilayer film 107 'is crystal-grown. That is, first, the semiconductor multilayer film 107 'is sequentially laminated for each layer in the same area as the crystal growth surface directly (or via an appropriate buffer layer) on the crystal growth surface of the crystal growth substrate 101a. The number of stacked semiconductor layers of the thin film constituting the semiconductor multilayer film 107 '(upper limit of m) is 25.

At this time, Al _x Ga ₁ -xN (0 ≦ x <1) is laminated as a thin semiconductor layer constituting the semiconductor multilayer film 107 ′. The aluminum composition ratio x _m of each layer is set in accordance with the following equation (9) in order from the bottom layer. Here, m is the number of each layer counted in order from the bottom layer located near the crystal growth substrate.
(Configuration Example of aluminum composition ratio x _m)
x _m = 1−m / 25 (m = 1, 2, 3,..., 25) (9)

(Configuration 3) Thereafter, the n-type contact layer 102 having a film thickness δ satisfying the relationship of the formulas (4) and (5) is formed on the semiconductor multilayer film 107 ′ already stacked on the crystal growth substrate. It is grown in the same area as the crystal growth surface.
(Structure 4) The laminated structure after the n-type cladding layer 103 and the structure of each electrode are based on the above-described Embodiment 4. As described above, the negative electrode is formed on the front side (upper side) of the semiconductor wafer.
(Configuration 5) A metal layer is formed on the substantially flat back surface of the crystal growth substrate in consideration of heat dissipation.

  According to such a configuration, the quality of the crystal quality is improved by stacking (crystal growth) of the semiconductor multilayer film 107 '. Therefore, even if the n-type contact layer 102 is formed thin from the beginning, the n-type contact layer The quality of the substrate 102 can be ensured, and there is no need to form a concave portion by etching the crystal growth substrate from the back surface or to reverse the crystal growth direction by turning the crystal growth substrate upside down. In addition, even with such a configuration in which the concave portion or the hollow portion is not provided, the operation and effect of the present invention can be obtained in the same manner as in the fourth embodiment.

In the first modification, the aluminum composition ratio x _m of the semiconductor multilayer film 107 ′ is monotonously reduced according to the lamination order as illustrated in the equation (9). A well-known DBR structure (: distributed Bragg reflection structure) may be constituted by these multilayer films by periodically changing the refractive index of each layer constituting the multilayer film exhibiting the confinement effect.
In the third and fourth embodiments, a multilayer film is formed using an appropriate semiconductor. However, these multilayer structures are made of a suitable dielectric material having a different refractive index such as SiO ₂ or TiO _2. It may be formed by using. Further, a well-known DBR structure may be constituted by these multilayer films.
Even with these modified configurations, a desired light confinement effect can be obtained based on the present invention.

Sectional view of semiconductor laser 100α according to Embodiment 1 of the present invention Sectional view of a semiconductor laser 201 according to a second embodiment of the present invention. Sectional view of a semiconductor laser 202 according to a third embodiment of the present invention. Sectional view of a semiconductor laser 203 according to a fourth embodiment of the present invention. Sectional view of a semiconductor laser 100β according to a fifth embodiment of the present invention. Sectional view for explaining the mounted state of semiconductor laser 100β of Example 5. Sectional view of a semiconductor laser 100γ according to a sixth embodiment of the present invention. Sectional view at section σ of the semiconductor laser 100γ of Example 6 Sectional view of a semiconductor laser 100δ according to a seventh embodiment of the present invention. Sectional view of a semiconductor laser illustrating a phenomenon in which FFP is disturbed.

Explanation of reference numerals

100α: semiconductor laser (Example 1)
201: Semiconductor laser (Example 2)
202: Semiconductor laser (Example 3)
203: Semiconductor laser (Example 4)
100β: semiconductor laser (Example 5)
100γ: semiconductor laser (Example 6)
100δ: semiconductor laser (Example 7)
101,
101a: crystal growth substrate 102: n-type contact layer 103: n-type cladding layer 104: light emitting output section (active layer and light guide layer)
105: p-type semiconductor layer (p-type cladding layer and p-type contact layer)
106A: Positive electrode 106B: Negative electrode (formed on the front side of the chip)
106C: negative electrode (formed on the back side of the chip)
107, 107 ',
107β: semiconductor multilayer film 108: heat dissipation metal layer 109α: buffer layer 109β: semiconductor layer (buffer layer and p-type GaN layer)
110: Insulating protective film 50: Lead frame 51: Metal post 52: Submount (conductive)
53: Metal stem (heat sink)
57: Post-side gold wire 58: Metal stem-side gold wire λ: Emission wavelength n: Refractive index of n-type contact layer n _eq : Equivalent refractive index of waveguide mode of n-type contact layer D: Depression δ on back surface of crystal growth substrate : Remaining film thickness of n-type contact layer in concave portion D f (λ): Function of emission wavelength λ ：: Function value of function f (λ)

Claims (11)

In an edge-emitting semiconductor laser in which a resonator or the like is formed by stacking a plurality of semiconductor layers on a crystal growth substrate,
The thickness of the n-type contact layer is at least immediately below the resonator,
The emission wavelength λ of the active layer;
A refractive index n of the n-type contact layer depending on the emission wavelength λ,
A function of the emission wavelength λ expressed using the equivalent refractive index n _eq of the waveguide mode of the n-type contact layer depending on the emission wavelength λ:
"Λ≡f (λ) = λ (n 2 -n eq 2) -1/2 / 2 " function value of Λ
A semiconductor laser characterized by being formed thinner than a semiconductor laser. At least immediately below the resonator, the refractive index of the region immediately below the n-type contact layer,
2. The semiconductor laser according to claim 1, wherein the refractive index is set to be smaller than the refractive index n. At least directly below the resonator,
3. The semiconductor laser according to claim 1, wherein a concave portion or a hollow portion is formed. The recess or the cavity,
4. The semiconductor laser according to claim 3, wherein at least a part of the semiconductor layer located immediately below the resonator is volatilized by laser irradiation. In an edge-emitting semiconductor laser in which a resonator or the like is formed by stacking a plurality of semiconductor layers on a crystal growth substrate,
When the thickness of the n-type contact layer is
The emission wavelength λ of the active layer;
A refractive index n of the n-type contact layer depending on the emission wavelength λ,
A function of the emission wavelength λ expressed using the equivalent refractive index n _eq of the waveguide mode of the n-type contact layer depending on the emission wavelength λ:
"Λ≡f (λ) = λ (n 2 -n eq 2) -1/2 / 2 " function value of Λ
Until it is thinner than
A semiconductor wherein a recess is formed below the resonator by removing the crystal growth substrate and the semiconductor layer located at least immediately below the resonator from the back side of the crystal growth substrate. laser. At least a bottom portion of the n-type contact layer located immediately below the resonator,
The semiconductor laser according to claim 1, further comprising a distributed feedback structure (DFB structure) that resonates light in a resonance direction of the resonator. 7. The dielectric film or the semiconductor film having a lower refractive index than the n-type cladding layer is laminated on the bottom surface of the n-type contact layer exposed in the recess. The semiconductor laser according to claim 1. The semiconductor laser according to any one of claims 3 to 7, wherein a metal layer or a metal portion is provided at least partially or entirely in the concave portion. 9. The semiconductor laser according to claim 8, wherein a negative electrode is formed by said metal layer or said metal part. A negative electrode on an exposed surface of the n-type contact layer which is exposed upward by an etching process from an upper layer side of the plurality of semiconductor layers;
10. The semiconductor device according to claim 1, further comprising a semiconductor layer made of a p-type or undoped group III nitride compound between the n-type contact layer and the crystal growth substrate. 3. The semiconductor laser according to claim 1. 11. The semiconductor laser according to claim 1, wherein a thickness δ of the n-type contact layer located immediately below the resonator is set to be equal to or more than Λ and less than Λ. 12. .

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