JP2000114639A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the swell appearing on a far-field pattern by adequately setting the length of a reference plane between a resonator end face and end part and the height from the reference plane to a light emitting point. SOLUTION: The degree of swell on a far-field pattern is expressed as (p2-v)/p1 wherein p1 and p2 are light intensities of the far-field pattern at a first peak and a second peak, and (v) is the light intensity at a min. between the first and second peaks. The height (a) of a light emitting point s0 and the length (c) of an etching bottom plane 5 are optimized so that (p2-v)/p1 is not greater than a desired value. The far-field pattern is variable according to set values of the height of the light emitting point s0 and the length (c) of the bottom plane 5. By setting the height (a) of the light emitting point s0 and the length (c) of the bottom plane 5, the swell can be suppressed with (p2-v)/p1 set not greater than the desired value about the far-field pattern vertical to a junction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly, to a semiconductor laser suitably applied to an etched mirror laser having a cut surface formed by etching as an end face of a resonator.

[0002]

2. Description of the Related Art Conventionally, as a kind of semiconductor laser,
A cut surface (etched mirror) formed by etching is used as a cavity end face, that is, a so-called etched mirror.
Lasers are known. In particular, in a GaN-based semiconductor laser using a sapphire substrate, it is difficult to cleave the substrate together with the semiconductor layer forming the laser structure. Therefore, the semiconductor layer forming the laser structure is etched by a dry etching method. In many cases, an etched mirror formed by the above method is used as a cavity end face.

[0003]

However, in a GaN-based semiconductor laser employing the structure of the conventional etched mirror laser, the far-field image of the laser light emitted from the end face of the cavity has a perpendicular to the junction. Since the pattern in the direction has a large fringe structure, there has been a problem in applying this semiconductor laser to a light source of an optical disk device and the like (for example, S. Nakamura et.al., Appl. Phys.
Lett. Vol. 72, p. 2014 (1998)).

Here, the fringe structure (undulation) that appears in the far-field image in the vertical direction with the junction of the etched mirror laser is caused by the interference effect due to the scattering of the emitted light at the etching bottom surface adjacent to the resonator. However, no detailed analysis has been reported so far, and no specific measures have been shown to suppress the fringe structure to a level that does not pose a problem in application. It is.

Accordingly, an object of the present invention is to provide a semiconductor laser capable of suppressing undulations occurring in a far-field image when a cut surface formed by etching is used as a cavity end surface.

[0006]

Means for Solving the Problems In order to solve the above problems of the prior art, the present inventors have conducted intensive studies.
The outline is shown below.

That is, as already described,
It is considered that the fringe structure appearing in the far-field image in the direction perpendicular to the junction between the mirror and the laser is caused by the interference effect due to the scattering of the emitted light at the etching bottom surface. Therefore, the present inventors obtained a far-field image of an etched mirror laser by calculation based on the following model, and analyzed it.

FIGS. 1 and 2 show an example of a semiconductor laser model used for the analysis of a far-field image. FIG. 1 is a perspective view of a semiconductor laser used for analysis of a far-field image, and shows the vicinity of a light emitting end face. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1 and shows a cross section of the semiconductor laser shown in FIG. 1 in a direction parallel to the cavity length direction.

In FIG. 1, reference numeral 1 denotes a substrate, and reference numeral 2 denotes a semiconductor layer forming a laser structure. The semiconductor layer 2 forming the laser structure includes at least a first cladding layer of a first conductivity type (for example, an n-type cladding layer) on the substrate 1;
It comprises an active layer thereon and a second cladding layer of the second conductivity type thereon (for example, a p-type cladding layer). In some cases, the active layer further includes an active layer between the n-type cladding layer and the active layer. A first optical waveguide layer (for example, an n-type optical waveguide layer) and a second optical waveguide layer (for example, a p-type optical waveguide layer) between the first and second p-type cladding layers. The semiconductor layer 2 has
It is assumed that a predetermined stripe structure 3 that defines an optical waveguide is formed. This semiconductor laser is SCH (Se
In the case of a GaN-based semiconductor laser having a parate confinement heterostructure (structure), for example, a sapphire substrate is used as the substrate 1, and among the semiconductor layers 2 forming the laser structure, the cladding layer is an AlGaN layer, and the optical waveguide layer is GaN.
The layer and the active layer are composed of a GaInN layer.

As shown in FIG. 1, in a general etched mirror laser, a semiconductor layer 2 forming a laser structure provided on a substrate 1 is patterned into a predetermined shape by dry etching. A resonator is constituted by the semiconductor layer 2 thus formed. Reference numeral 4 denotes a resonator end face made of an etched mirror formed at one end of the resonator, and reference numeral 5 denotes an etched bottom surface. In this case, on the etching bottom 5, the semiconductor layer 2 is etched by forming the cavity end face 4.
Is removed, and the substrate 1 is exposed. The resonator end face 4 is formed substantially perpendicular to the main surface of the substrate 1, and therefore, the resonator end face 4 and the etched bottom face 5 are orthogonal to each other. Although not shown in FIG. 1, the other end of the resonator is also configured in the same manner as described above. In FIG. 1, the electrodes (p-side electrode and n-side electrode) of the semiconductor laser are not shown.

In this semiconductor laser, the substrate 1 on which the laser structure is formed as described above is cut at a position separated from the resonator end face 4 by a predetermined distance, and chipped. In FIG. 1, reference numeral 6 denotes an end (an end of the etched bottom surface 5) formed at a cutting position of the substrate 1.

In this semiconductor laser, laser light L is extracted from a resonator end face 4 which is one end face of the resonator. Reference numeral 7 denotes a light emitting area on the resonator end face 4. The light-emitting region 7 represents a region where the light amplitude is 1 / e or more of the peak value in the near-field image of the laser light L on the resonator end face 4. In the light emitting area 7, a light emitting point indicated by reference symbol s0 corresponds to a point in the light emitting area 7 where the light amplitude is maximum. It is assumed that the near-field image of the laser beam L has a unimodal Gaussian distribution.

In this semiconductor laser, if the cutting position of the substrate 1, that is, the position of the end 6 of the etching bottom surface 5 is too far from the cavity end face 4, the laser light emitted from the cavity end face 4 After a part of L enters the etching bottom surface 5, it is reflected there, and as a result, a phenomenon occurs that the junction of the laser beam L and the far-field image in the vertical direction are disturbed. This phenomenon will be described with reference to FIG. 2 which is a cross-sectional view of FIG. FIG. 2 is a cross-sectional view of the semiconductor laser shown in FIG. 1 cut along a direction perpendicular to the junction and in a direction parallel to the cavity length direction at a position passing through the light emitting point s0 on the cavity facet 4. In the following, the etched bottom surface 5 on which light emitted from the resonator end face 4 is incident (reflected) will be referred to as a reference plane.

[0014] In FIG. 2, define x ₀ axis normals etching bottom 5 through the emission point s0 (reference plane), the normals of the cavity end face 4 through the light emission point s0 the z-axis. x ₀ point on the axis s2
Is the intersection of the x ₀ axis and the etched bottom surface 5, which in this case corresponds to the lower end of the resonator end face 4 on the x ₀ axis. On the other hand, a point s1 on x ₀ axis corresponds to the upper end of the cavity end face 4 on the x ₀ axis. Further, in FIG. 2, the point corresponding to the end portion 6 of the substrate 1 to a point s3, define a normal line of the etching bottom surface 5 through the point s3 to x ₁ axis. Then, (the same applies in the x ₁ axis) positive set in the direction of the resonator x ₀ in a direction toward the upper side from the lower end side of the end face 4 axis, the direction toward the end portion 6 side from the cavity end face 4 side Determined in the positive direction of the z-axis.

Here, the height (| s0−s2 |, hereinafter also referred to as the height of the light emitting point s0) from the etching bottom surface 5 which is the reference plane to the light emitting point s0 is a, and the cavity end face 4 is The length of the etched bottom 5 between the end 6 (| s
2-s3 |, hereinafter also referred to as the length of the etched bottom surface 5), and the coordinates of the light emitting point s0 are (0,
0), the coordinates of the point s2 are represented by (−a, 0), and the coordinates of the point s3 are represented by (−a, c).

As shown in FIG. 2, in this semiconductor laser, a laser beam is emitted from the light emitting point s0 on the cavity facet 4 with a certain spread, and a part of the emitted light is reflected by the etching bottom surface 5. . Here, the reflected light obtained by reflecting the light emitted from the light emitting point s0 at the etching bottom surface 5 is a mirror image point s0 'of the light emitting point s0 with respect to the etching bottom surface 5 (the coordinates are represented by (-2a, 0)). Outgoing light. And the length c of the etched bottom surface 5
Determines the position of the opening that satisfies x ₁ ≧ −a for each of the light emitted from the light emitting point s0 and the light emitted from the mirror image point s0 ′. In this semiconductor laser, the light emitting point s0
Of the etched bottom surface 5 where the light emitted from the substrate is the reference surface.
The diffracted light diffracted by the above and the diffracted light diffracted at the end 6 of the etching bottom surface 5 by the light emitted from the mirror image point s0 'interfere with each other, thereby causing undulations in the junction and the far-field image in the vertical direction. Will be. In this case, the theoretical formula representing the far-field image in the direction perpendicular to the junction is derived as follows, considering a one-dimensional model.

That is, it is assumed that the near-field images of the light emitted from the light emitting point s0 and the light emitted from the mirror image point s0 'each have a unimodal Gaussian distribution. In this case, assuming that the size of the near-field image in the direction perpendicular to the junction at the resonator end face 4 is ω and the complex reflectance at the etching bottom face 5 as the reference plane is r (assumed to be a constant value), the light near the light emitting point s0 is The amplitude distribution f ₀ (x ₀ ) and the light amplitude distribution f ₁ (x ₀ ) near the mirror image point s0 ′ are respectively

[0018]

(Equation 1)

[0019]

(Equation 2)

## EQU1 ## Note that the size ω of the near-field image in the direction perpendicular to the junction on the resonator end face 4 is equal to the peak amplitude of 1
/ E in this case, and corresponds to the radius in the direction perpendicular to the junction of the light emitting region 7 on the cavity facet 4. The angle of the far-field image viewed from the light emitting point s0 is α (unit: rad, x ₁
> Α corresponding to the direction of> 0), the oscillation wavelength is λ, and the transfer function H (α) and the aperture function f _ap are respectively

[0021]

(Equation 3)

[0022]

(Equation 4)

In other words, far-field images FFP (α) in the x ₀ direction (the same applies to the x ₁ direction) are represented by f ₀ (x ₀ ), f ₁ ( x ₀ ), H (α), and f _ap, and can be expressed as the following equation (Equation (5)). That is,

[0024]

(Equation 5)

Here, as an example, the semiconductor laser shown in FIG. 1 is a GaN-based semiconductor laser having an oscillation wavelength λ of 42.
0 nm, and the size ω of the near-field image in the direction perpendicular to the junction at the resonator end face 4 is 250 nm. It is also assumed that the complex reflectance r when the light emitted from the resonator end face 4 is reflected by the etching bottom face 5 is constant at -1. In this semiconductor laser, a far-field image in a direction perpendicular to the junction when the height a of the light emitting point s0 is 2 μm and the length c of the etching bottom surface 5 is 6 μm is calculated by using the theoretical expression shown in Expression (5). The result obtained by the calculation is shown in FIG. FIG.
, The horizontal axis represents the angle, and the vertical axis represents the light intensity of the far-field image. Here, the discrete Fourier transform is used when calculating on the computer, and the numerical value of the angle shown in FIG. 3 is the value used for the calculation at that time. In this case, the numerical value 257 on the horizontal axis corresponds to the center of the far-field image, that is, α = 0. The value on the horizontal axis is 0.4 per digit.
7 °, in which case the value 258 is α = +
0.47 ° and the numerical value 256 correspond to α = −0.47 °.

FIG. 3 shows that the oscillation wavelength λ = 420 nm and the size ω of the near-field image perpendicular to the junction at the resonator end face 4.
= 250 nm, complex reflectance r at the etched bottom surface 5
= −1, the height a = of the light emitting point s0
When the length c of the etched bottom 5 is 2 μm and the length c is 6 μm, the far-field image in the vertical direction of the junction has several large fringe structures on the side of α> 0, that is, on the side of x ₁ > 0 in FIG. However, it can be seen that the deviation from the unimodal distribution increases.

Here, in the far-field image obtained from the theoretical formula, the peak with the highest light intensity (first peak) is P ₁ , and the peak with the second highest light intensity (second peak) is P ₂ . . Further, among the minimums existing between the first peak P ₁ and the second peak P ₂ , V is the minimum having the minimum light intensity.
In the example shown in FIG. 3, the first peak P ₁ and the second peak P _1
2 are adjacent to each other, and the minimum between the two corresponds to the minimum V described above. Here, the light intensity at the first peak P ₁ p1, the light intensity at the second peak P ₂ p2, minimum V
Is defined as v, and the degree of undulation of the far-field image is expressed as (p2-v) / p1 using p1, p2, and v. In applying a semiconductor laser, various inconveniences occur if the swell of the far-field image is large.
v) It is necessary to suppress the value of / p1 to a level that does not cause a problem.

For example, assume that the semiconductor laser shown in FIG. 1 is used as a light source of an optical disk device. A general optical disc device has a semiconductor laser as a light source,
A predetermined optical system for guiding the emitted light of the semiconductor laser to the optical disk, for example, a collimator lens, a beam splitter, an objective lens, a detection lens, a light receiving element for signal light detection, a signal light reproducing circuit, and the like are provided. In such an optical disk device, restrictions on the undulation of the far-field image of the semiconductor laser are imposed by the optical system, particularly the objective lens.

Specifically, for example, a digital video
In a disk (DVD) device, the light intensity (rim intensity) at the edge of the objective lens is 90% or more of the peak value in the radial direction (radiation direction) of the optical disk, and the peak value is 60% in the tangential direction (concentric direction). ７０70% or more. Normally, the full-width at half maximum θ⊥ of the far-field image in the vertical direction with the bonding of the semiconductor laser is selected in the radial direction of the optical disk. It is required that the degree of undulation of the far-field image in the vertical direction is 10% or less. Here, actually, the emitted light from the semiconductor laser is first converted into parallel light through a collimating lens and then enters the objective lens. Therefore, the restriction on the swell of the far-field image in the direction perpendicular to the junction is less than 10%. Although it is alleviated, it is preferable that the degree of the undulation is suppressed to 20% or less even in consideration of this point.

Incidentally, the far-field image represented by the above-mentioned theoretical formula can be changed by the set values of the height a of the light emitting point s0 and the length c of the etched bottom surface 5, as is clear from the derivation process. It is. Therefore, it can be said that it is effective to optimize the height a of the light emitting point s0 and the length c of the etching bottom surface 5 in order to suppress the undulation of the far-field image in the direction perpendicular to the junction.

Then, based on the theoretical formula of the far-field image (formula (5)), (p2-
v) The height a of the light emitting point s0 at which the value of / p1 is 0.2 or less.
The range of the length c of the etched bottom surface 5 was calculated. Here, the oscillation wavelength λ of the semiconductor laser is set to 420 n
m, the size ω of the near-field image in the direction perpendicular to the junction at the resonator end face 4 was set to 250 nm, and the complex reflectance r at the etching bottom face 5 was assumed to be constant at −1. FIG. 4 shows the results. In FIG. 4, the horizontal axis represents the height a of the light emitting point s0.
(Μm), and the vertical axis represents the length c (μm) of the etching bottom surface 5.
m).

In FIG. 4, the curve indicated by A is λ =
In a semiconductor laser with 420 nm and ω = 250 nm,
This represents the locus of (a, c) where (p2−v) /p1=0.2 when r = −1. In this case, the area under the curve A (including the point on the curve A) on the ac plane is λ = 42
When 0 nm, ω = 250 nm, and r = −1, the height a of the light emitting point s0 and the etched bottom surface 5 where the value of (p2-v) / p1 in the far-field image perpendicular to the junction is 0.2 or less are 0.2 Represents the range of the length c. In other words, in the far-field image perpendicular to the junction, (p2−v) / p1 ≦
In order to realize 0.2, the height a of the light emitting point s0 and the length c of the etching bottom surface 5 are set such that (a, c) exists in the area below the curve A on the ac plane. That's all I need to do.

Here, in the above-mentioned model, it is assumed that the light emitted from the resonator end face 4 is reflected by the surface of the substrate 1 corresponding to the etched bottom face 5, and the complex reflectance r at this time is assumed to be -1. However, the complex reflectance of r = -1 can also be realized by coating a metal film on a portion of the substrate 1 corresponding to the etched bottom surface 5. Further, a film (light absorbing film) for absorbing light emitted from the resonator end face 4 is provided on the portion of the substrate 1 corresponding to the etching bottom surface 5.
, A complex reflectance of r = 0 can be realized. Here, the oscillation wavelength λ = 420 nm, the size ω of the near-field image in the direction perpendicular to the junction at the resonator end face 4
= 250 nm, the range of the height a of the light emitting point s0 and the length c of the etched bottom surface 5 where the value of (p2-v) / p1 in the far-field image perpendicular to the junction is 0.2 or less is set. , And the complex reflectance r = 0 is shown in FIG. That is, in FIG.
The curve shown by (p2-p) in a semiconductor laser with λ = 420 nm and ω = 250 nm when r = 0.
v) represents the locus of (a, c) where p1 = 0.2. In this case, the area under the curve B (including the points on the curve B) on the ac plane is λ = 420 nm, ω = 250 nm, and r =
In the case of 0, (p2
−v) The range of the height a of the light emitting point s0 and the length c of the etched bottom surface 5 where the value of / p1 is 0.2 or less is shown. From FIG. 4, when the complex reflectance r is r = 0, r
= (− 1−0.2) /p1≦0.2
It can be seen that the range of (a, c) is expanded.

When a reflectance control film such as a metal film or a light absorption film is coated on the etched bottom surface 5, the surface of the reflectance control film is used as a reference surface. Therefore, in this case, the dimension a representing the height of the light emitting point s0 may be replaced with the height from the surface of the reflectance film control film to the light emitting point s0.

The present invention has been devised based on the results of the above studies by the present inventors. That is, in order to achieve the above object, the present invention provides a resonator comprising a semiconductor layer forming a laser structure on a substrate, and having a cut surface formed by etching the semiconductor layer as a resonator end face. And a reference surface on which a part of light emitted from a light emitting point on the end face of the resonator is incident on a portion corresponding to an etching bottom surface formed on the substrate or the semiconductor layer in an etching region when the resonator is formed. Then, the diffracted light where the light emitted from the light emitting point is diffracted at the end of the reference surface, and the diffracted light where the part of the light emitted from the light emitting point is reflected at the end of the reference surface is diffracted. In the semiconductor laser in which undulation occurs in the far-field image, the light intensity at the first peak having the largest light intensity in the far-field image is p1, and the light intensity at the second peak having the second largest light intensity is p2
When the light intensity at the minimum value where the light intensity is the minimum among the minimum values existing between the first peak and the second peak is represented by v,
The length of the reference plane between the cavity end face and the end and the height from the reference plane to the light emitting point are set so that the value of (p2-v) / p1 is equal to or less than the desired value. It is a feature.

Here, the light emitting point on the cavity facet corresponds to the point where the light amplitude becomes maximum in the light emitting region on the cavity facet. The desired value is a value determined according to the optical system of the device or system in which the semiconductor laser is used, and differs depending on the device or system.

In the present invention, a film for controlling the reflectance may be coated on the bottom surface (etched bottom surface) formed on the substrate or the semiconductor layer. In the case where the bottom surface formed on the substrate or the semiconductor layer is not coated, the bottom surface serves as a reference surface. In this case, the height from the reference surface to the light emitting point is defined on the substrate or the semiconductor layer. Refers to the height from the bottom to the light emitting point. Further, when a film for controlling the reflectance is coated on the bottom surface formed on the substrate or the semiconductor layer, the surface of the film for controlling the reflectance is a reference surface, in this case,
The height from the reference plane to the light emitting point refers to the height from the surface of the film for controlling the reflectance to the light emitting point. Examples of the film for controlling the reflectance include a light absorbing film that absorbs light emitted from the end face of the resonator, and a metal film that reflects light emitted from the end face of the resonator. When the film for controlling the reflectance is a light absorbing film that absorbs the light emitted from the end face of the resonator, a complex reflectance of approximately r = 0 is realized on the reference surface, and the complex reflectance is compared with the case where no coating is applied. , (P2-v) / p1 has an advantage that the allowable range of the length of the reference plane and the height from the reference plane to the light emitting point can be expanded to be equal to or less than the desired value.

According to the present invention having the above-described structure, in the semiconductor laser having the cut surface formed by etching as the cavity end surface, the length and the reference surface of the reference plane between the cavity end surface and the end portion are provided. By optimizing the height from to the emission point, (p2-v) /
The value of p1 (where p1 is the light intensity at the first peak with the largest light intensity, p2 is the light intensity at the second peak with the second largest light intensity, and v is the first peak and the second peak. (The light intensity at the minimum with the smallest light intensity among the minimums existing between them) can be suppressed to a desired value or less. This makes it possible to realize a semiconductor laser in which the swell of the far-field image is well suppressed.

[0039]

Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described. 5 and 6 show a semiconductor laser according to the first embodiment of the present invention. Here, FIG. 5 is a perspective view of the semiconductor laser according to the first embodiment, showing the vicinity of the light emitting end face. FIG. 6 shows VI-VI of FIG.
FIG. 2 is a cross-sectional view taken along a line, showing a cross section of the semiconductor laser according to the first embodiment in a direction parallel to a cavity length direction.
This semiconductor laser is a GaN-based semiconductor laser and has an electrode stripe structure and an SCH structure.

As shown in FIG. 5, in the semiconductor laser according to the first embodiment, for example, an n-type GaN contact layer 13 is formed on a c-plane sapphire substrate 11 via an undoped GaN buffer layer 12 formed by low-temperature growth. n-type A
1GaN cladding layer 14, n-type GaN optical waveguide layer 15, G
aInN active layer 16, p-type GaN optical waveguide layer 17, p-type A
An lGaN cladding layer 18 and a p-type GaN contact layer 19 are sequentially stacked. Hereinafter, these layers may be collectively referred to as an AlGaInN-based semiconductor layer 20. n-type GaN contact layer 13, n-type AlGaN
The cladding layer 14 and the n-type GaN optical waveguide layer 15 are doped with, for example, Si as a donor, and the p-type GaN optical waveguide layer 17, the p-type AlGaN cladding layer 18, and the p-type GaN
The contact layer 19 is doped with, for example, Mg as an acceptor.

The AlGaInN-based semiconductor layer 20 forming the laser structure is patterned into a predetermined shape by etching, and the patterned AlGaInN-based semiconductor layer 20 forms a resonator. Sign 2
Reference numeral 1 denotes a resonator end face made of an etched mirror formed at one end of the resonator, and reference numeral 22 denotes an etching bottom face. In this case, on the etching bottom surface 22,
The AlGaInN-based semiconductor layer 20 is removed, and the surface of the c-plane sapphire substrate 11 is exposed. The resonator end face 21 is formed substantially perpendicular to the main surface of the c-plane sapphire substrate 11, so that the resonator end face 21 and the etched bottom face 22 are orthogonal to each other. Although not shown in FIG. 5, the other end of the resonator has the same configuration as described above.

In the AlGaInN-based semiconductor layer 20, n
Upper portion of n-type GaN contact layer 13, n-type AlGaN cladding layer 14, n-type GaN optical waveguide layer 15, GaInN active layer 16, p-type GaN optical waveguide layer 17, p-type AlGaN cladding layer 18, and p-type GaN contact layer 19 Has a mesa shape having a predetermined width extending in a direction parallel to the resonator length direction.

On the p-type GaN contact layer 19 in the mesa portion, for example, a p-side electrode 23 having a Ni / Pt / Au structure is provided in ohmic contact. On the n-type GaN contact layer 13 adjacent to the mesa portion, for example, T
An n-side electrode 24 having an i / Al / Pt / Au structure is provided in ohmic contact.

In this semiconductor laser, the c-plane sapphire substrate 11 on which the laser structure has been formed as described above is cut at a position away from the cavity end face 21 by a predetermined distance and chipped. In FIG. 5, reference numeral 25 denotes c
The end (the end of the etched bottom) formed at the cutting position of the planar sapphire substrate 11 is shown.

In this semiconductor laser, laser light L is extracted from the cavity facet 21. Reference numeral 26 indicates a light emitting area on the resonator end face 21. Here, the light-emitting region 26 corresponds to a region in the near-field image of the laser light L on the resonator end face 21 where the light amplitude is 1 / e or more of the peak value. Also, in FIG.
The light-emitting point indicated by the symbol s0 corresponds to a point in the light-emitting region 26 where the light amplitude is maximum. This emission point s0 is Ga
It is located at substantially the center in the thickness direction of the InN active layer 16. It is assumed that the near-field image of the laser beam L has a unimodal Gaussian distribution.

Here, the oscillation wavelength of this semiconductor laser is λ
And the size of the near-field image in the direction perpendicular to the junction at the resonator end face 21 is ω. The oscillation wavelength λ is determined according to the effective band gap of the active layer. In this semiconductor laser, for example, λ = 420 nm. Further, the near-field image is determined according to the waveguide mode. The size ω of the near-field image in the direction perpendicular to the junction at the resonator end face 21 is 1/1 / peak amplitude.
In this case, it corresponds to the radius in the direction perpendicular to the junction of the light emitting region 26 on the cavity end face 21. In this semiconductor laser, for example, ω = 250 nm. Also, in this semiconductor laser, no coating is applied on the etched bottom surface 22, and therefore, the etched bottom surface 22 is a reference surface.

Next, a method of manufacturing the semiconductor laser according to the first embodiment will be described.

First, at 560 ° C. on the c-plane sapphire substrate 11 by metal organic chemical vapor deposition (MOCVD).
The undoped GaN buffer layer 12 is grown at the growth temperature. Next, the n-type GaN contact layer 1 is formed on the undoped GaN buffer layer 12 by MOCVD.
3, n-type AlGaN cladding layer 14, n-type GaN optical waveguide layer 15, GaInN active layer 16, p-type GaN optical waveguide layer 1
7. A p-type AlGaN cladding layer 18 and a p-type GaN contact layer 19 are sequentially grown. Here, the n-type GaN contact layer 13 which is a layer containing no In, the n-type AlG
aN cladding layer 14, n-type GaN optical waveguide layer 15, p-type G
The growth temperature of the aN optical waveguide layer 17, the p-type AlGaN optical waveguide layer 18, and the p-type GaN contact layer 19 is, for example, 100
The temperature is set to 0 ° C., and the growth temperature of the GaInN active layer 16 which is a layer containing In is set to, for example, 700 to 800 ° C. n-type GaN
The contact layer 13, the n-type AlGaN cladding layer 14, and the n-type GaN optical waveguide layer 15 have, for example, Si as a donor.
, The p-type GaN optical waveguide layer 17 and the p-type AlGaN
The cladding layer 18 and the p-type GaN contact layer 19 are doped with, for example, Mg as an acceptor. Thereafter, the electrical activation of the donors and acceptors doped in these layers, in particular, the p-type GaN optical waveguide layer 17, p-type AlG
aN cladding layer 18 and p-type GaN contact layer 19
Heat treatment for electrical activation of the doped acceptor is performed. The temperature of this heat treatment is, eg, 700 ° C.

Next, a stripe-shaped resist pattern (not shown) having a predetermined width extending in the direction perpendicular to the cavity length direction of the semiconductor laser is formed on the AlGaInN-based semiconductor layer 20, and this resist pattern is used as a mask. For example, the c-plane sapphire substrate 11 is etched by a reactive ion etching (RIE) method to a depth at which the c-plane sapphire substrate 11 is slightly etched. Thereby, the AlGaInN-based semiconductor layer 2
Resonator end face 2 consisting of an etched mirror at a predetermined portion of 0
1 is formed, and an etching bottom surface 22 is formed on the c-plane sapphire substrate 11 corresponding to the etching region.

Next, a stripe-shaped resist pattern (not shown) having a predetermined width extending in the resonator length direction is formed on the AlGaInN-based semiconductor layer 20 patterned in the resonator shape. As a mask, for example, the AlGaInN-based semiconductor layer 2 is formed by the RIE method.
0 is etched to an intermediate depth in the thickness direction of the n-type GaN contact layer 13. Thereby, n-type Ga
Upper layer of N contact layer 13, n-type AlGaN cladding layer 14, n-type GaN optical waveguide layer 15, GaInN active layer 1
6. The p-type GaN optical waveguide layer 17, the p-type AlGaN cladding layer 18, and the p-type GaN contact layer 19 are patterned into a predetermined mesa shape.

Next, the p-type GaN contact layer 1 in the mesa portion
9, a p-side electrode 23 made of, for example, a Ni / Au film or a Ni / Pt / Au film is formed, and the n-type GaN contact layer 13 in an etched portion adjacent to the mesa portion is formed.
For example, an n-side electrode 24 is formed thereon.

Next, after the c-plane sapphire substrate 11 on which the laser structure is formed is processed into a bar shape, the c-plane sapphire substrate 11 is cut at a portion corresponding to the etching bottom surface 22 to obtain a bar. Into chips. Thus, the intended semiconductor laser is manufactured.

FIG. 6 shows the semiconductor laser according to the first embodiment shown in FIG. 5 cut at a position passing through the light emitting point s0 on the cavity facet 21 in a direction perpendicular to the junction and in a direction parallel to the cavity length direction. The cross section at the time is shown.

In FIG. 6, the normal of the etched bottom surface 22 (reference surface) passing through the light emitting point s0 on the resonator end surface 21 is defined as x _0.
An axis and a normal line of the resonator end face 21 passing through the light emitting point s0 are defined as the z axis. x ₀ point s2 of the on-axis, x ₀ axis and etching the bottom face 2
It is the intersection of the 2, corresponding to the lower end of the cavity end face 21 in this case x ₀ axis. On the other hand, a point s1 on x ₀ axis,
x ₀ corresponds to the upper end of the cavity end face 21 along the axis. In FIG. 6, the end 25 of the c-plane sapphire substrate 11 is shown.
And the point s3 points corresponding to define a normal line of the etching bottom surface 22 through the point s3 to x ₁ axis. Then, the direction toward the upper side from the lower end side of the cavity end face 21 and the positive direction of the x ₀ axis (the same applies in the x ₁ axis), in a direction toward the end portion 25 side from the cavity end face 21 side z The positive direction of the axis.

Here, the etching bottom surface 22 as the reference surface
Is the height (| s0−s2 |, hereinafter also referred to as the height of the light emitting point s0) from a to the light emitting point s0, and the length of the etching bottom surface 22 between the cavity end face 21 and the end part 25. (| S2-s3 |, hereinafter, the etching bottom surface 2
2), and the coordinates of the light emitting point s0 are (0, 0), the coordinates of the point s2 are (−a,
0), the coordinates of the point s3 are represented as (-a, c). Also,
x ₀ point on the axis s0' is etched bottom surface 2 of the light emitting points s0
2 represents the mirror image point, and the coordinates of the mirror image point s0 'are expressed as (-2a, 0).

As shown in FIG. 6, in the semiconductor laser according to the first embodiment, similarly to the models shown in FIGS. 1 and 2, light emitted from the light emitting point s0 is reflected by the etched bottom surface 22. The light can be considered as the light emitted from the mirror image point s0 '. Therefore, in the semiconductor laser according to the first embodiment, the distance in the direction perpendicular to the junction is measured by the same mechanism as the model shown in FIGS. Swelling occurs in the field image. Here, r (constant value) is a complex reflectance when light emitted from the resonator end face 21 is reflected by the etching bottom face 22 which is a reference face. In this case, the far-field image in the direction perpendicular to the junction is expressed by the theoretical expression shown in Expression (5), similarly to the models shown in FIGS. in this case,
Since the oscillation wavelength λ = 420 nm and the size of the near-field image ω = 250 nm in the direction perpendicular to the junction at the resonator end face 21, assuming that the complex reflectance r = −1 at the etching bottom face 22, the height a of the light emitting point s 0 is By giving the length c of the etched bottom surface 22, the far-field image in the direction perpendicular to the junction at that time can be obtained by calculation.

By the way, the above-mentioned semiconductor laser is expected to be applied to various devices or systems including an optical disk device. At this time, it is necessary to suppress the swell of the far-field image in the direction perpendicular to the junction to a level that does not cause a problem so as not to cause a problem in applying the semiconductor laser. Therefore, in this first embodiment, the light intensity p1 at the first peak P ₁ light intensity is maximum in the far field pattern of bonding the vertical direction obtained from the theoretical formula, the light intensity is the second largest light intensity at the peak P ₂ of 2 p2, first peak P ₁ and the second peak P ₂
The height a of the light emitting point s0 and the etching are set so that the value of (p2-v) / p1 when the light intensity at the minimum V where the light intensity is the minimum among the minimums between v and v is equal to or less than a desired value. The length c of the bottom surface 22 is set.

That is, for example, the value of (p2−v) / p1 is 0.2 or less with respect to the far-field image in the direction perpendicular to the junction of the semiconductor laser from the side of the device or system in which the semiconductor laser is used. It is assumed that restrictions are imposed as follows. In this case, λ = 420 nm, ω = 250 nm, r
= -1 in the far-field image perpendicular to the junction in the semiconductor laser according to the first embodiment.
In order to make the value of v) / p1 0.2 or less, (a,
The height a of the light emitting point s0 and the length c of the etched bottom surface 22 are set so that c) exists in the area below the curve A (including the point on the curve A) on the ac plane in FIG. do it.

Taking the above points into consideration, in the first embodiment, the height a of the light emitting point s0 and the length c of the etching bottom surface 22 are, for example, a = 2.5 μm
And a semiconductor laser is designed and manufactured so that c = 4 μm. FIG. 4 shows (a, c) = (2.5 μm, 4 μm)
m) was plotted with open circles. Here, for comparison, FIG.
Numerical values used in the calculation of the far-field image shown in FIG.
c) = (2 μm, 6 μm) is plotted with a black circle in FIG. From FIG. 4, (2.5 μm, 4 μm) certainly shows curve A
It can be seen that (2 μm, 6 μm) exists in the area above the curve A.

FIG. 7 shows that λ = 420 nm and ω = 250 n.
In the semiconductor laser according to the first embodiment in which m and r = −1, the junction and the far-field image in the vertical direction when a = 2.5 μm and c = 4 μm are expressed by a theoretical expression shown in Expression (5). The result obtained by calculation based on the above is shown. In FIG. 7, the horizontal axis represents the angle, and the vertical axis represents the light intensity of the far-field image. The numerical value of the angle shown in FIG. 7 is a value used for the calculation. In this case, the numerical value 257 on the horizontal axis corresponds to the center of the far-field image, that is, α = 0. The value on the horizontal axis is 1
This corresponds to 0.47 ° per digit, where the value 258 is α = + 0.47 ° and the value 256 is α =
-0.47 °. Also, in FIG. 7, for comparison, only the length of the etching bottom surface 22 is set to c = 0,
The other parameters also show the results obtained by calculating the far-field image in the vertical direction and the joining under the same conditions by calculation based on the theoretical formula shown in Expression (5). When c = 0, the emitted light is not affected by the etching bottom surface.
The far-field image perpendicular to the junction has a unimodal Gaussian distribution.

When comparing FIG. 7 with FIG. 3, the semiconductor laser according to the first embodiment in which (a, c) exists in the area below the curve A on the ac plane in FIG. 4 (see FIG. 7). 4), the swell is better suppressed and the distribution is almost unimodal, as compared with the semiconductor laser (see FIG. 3) in which (a, c) exists in the region above the curve A on the ac plane in FIG. It can be seen that a far-field image close to is obtained. That is, in the first embodiment, the semiconductor laser is designed and manufactured so that (a, c) exists below the curve A in FIG. The swell of the image is suppressed.

In the semiconductor laser according to the first embodiment, the height a of the light emitting point s0 is controlled by AlGa.
It can be realized by controlling the thickness of each layer in the InN-based semiconductor layer 20 and the etching depth when forming the resonator end face 21, and the length c of the etching bottom face 22 can be controlled by the c-plane sapphire substrate. 11 can be realized by controlling the cutting positions.

As described above, according to the first embodiment, in the etched mirror laser, the height a of the light emitting point s0 and the length c of the etching bottom surface 22 are optimized. Since the value of (p2-v) / p1 in the far-field image in the direction perpendicular to the junction can be suppressed to a desired value or less, it is possible to realize a semiconductor laser in which the swell of the far-field image is well suppressed. Thereby, an advantage that application of the semiconductor laser to an optical disk device or the like can be easily obtained can be obtained.

Next, a second embodiment of the present invention will be described. In the semiconductor laser according to the second embodiment, a light absorbing film that absorbs light emitted from the resonator end face 21 is provided on the etching bottom surface 22 in the same semiconductor laser as that of the first embodiment. in this case,
The surface of the light absorbing film provided on the etching bottom surface 22 serves as a reference surface, and a complex reflectance of r = 0 is realized on the reference surface. Therefore, in the second embodiment, the value of (p2-v) / p1 in the far-field image perpendicular to the junction can be made equal to or less than the desired value according to the theoretical expression of Expression (5) (a, c). When the range of ()) is obtained, the calculation may be performed assuming that the complex reflectance r on the reference plane is r = 0. In the second embodiment, since the surface of the light absorbing film provided on the etching bottom surface 22 is the reference plane, the dimension a representing the height of the light emitting point s0 is equal to the height of the light absorbing film. It corresponds to the height from the surface to the light emitting point s0.

Specifically, in the case of the semiconductor laser according to the second embodiment, as in the first embodiment, the value of (p2-v) / p1 is set to 0.1 in the far-field image perpendicular to the junction. In order to set the height to 2 or less, the height of the light emitting point s0 is set so that (a, c) exists in the area below the curve B (including the point on the curve B) on the ac plane in FIG. a and the length c of the etching bottom surface 22 are set. Here, from FIG. 4, in the case of the semiconductor laser with λ = 420 nm and ω = 250 nm, the case where the complex reflectance r on the reference plane is r = 0 is larger than the case where r = −1 (p2−2). v) /
It can be seen that the allowable range of (a, c) where p1 ≦ 0.2 is expanded. In this case, in particular, the value of c can be set large on the side of a ≦ 2.5 μm.
This can be said to be desirable in actually manufacturing a semiconductor laser.

The configuration of the semiconductor laser according to the second embodiment other than the above is the same as that of the semiconductor laser according to the first embodiment, and a description thereof will be omitted.

According to the second embodiment, the same advantages as those of the first embodiment can be obtained. In addition, since the complex reflectance r on the reference plane is set to 0, the complex reflection on the reference plane can be obtained. Compared with the semiconductor laser according to the first embodiment in which the rate r is -1, for example, (p2-v) / p1
Since the allowable range of (a, c) for realizing ≦ 0.2 is expanded, the process conditions for manufacturing a semiconductor laser in which the undulation of the far-field image is suppressed can be relaxed, and The advantage of increased design freedom can be obtained.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above embodiments, and various modifications based on the technical idea of the present invention are possible. For example, the numerical values, materials, laser structures, and the like described in the embodiments are merely examples, and the present invention is not limited thereto.

In the first and second embodiments described above, (p2-
v) The height a of the light-emitting point and the length c of the etched bottom surface are set so that the value of / p1 is 0.2 or less. However, restrictions on the undulation of the far-field image of the semiconductor laser are as follows.
The semiconductor laser can vary in various ways depending on the device or system in which it is used. In this case, too, the emission point is calculated using the theoretical formula of the far-field image so as to satisfy the request from the device or system. What is necessary is just to determine the allowable range of the height a and the length c of the etching bottom surface.

In the first and second embodiments described above, the case where the present invention is applied to a GaN-based semiconductor laser has been described. , AlG
The present invention can be applied to any semiconductor laser such as an aInP-based semiconductor laser and a semiconductor laser using a II-VI compound semiconductor.

[0072]

As described above, according to the present invention, in a semiconductor laser having a cut surface formed by etching as a cavity end surface, the length of the reference plane between the cavity end surface and the end portion is determined. By optimizing the height from the reference plane to the light emitting point, (p2-v) /
The value of p1 (where p1 is the light intensity at the first peak with the largest light intensity, p2 is the light intensity at the second peak with the second largest light intensity, and v is the first peak and the second peak. (The light intensity at the minimum with the smallest light intensity among the minimums existing between them) can be suppressed to a desired value or less. This makes it possible to realize a semiconductor laser in which the swell of the far-field image is well suppressed, and has the effect of facilitating the application of the semiconductor laser as a light source of an optical disk device.

[Brief description of the drawings]

1A and 1B are a perspective view and a cross-sectional view illustrating an example of a semiconductor laser model used for analyzing a far-field image.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 shows a far-field image perpendicular to the junction of the semiconductor laser shown in FIG. 1 at an oscillation wavelength λ = 420 nm, a near-field image ω = 250 nm perpendicular to the junction at the resonator end face, and a complex reflectance r = -1, height of light emitting point a = 2
6 is a graph showing the results obtained by calculation with μm and the length c of the etched bottom being 6 μm.

FIG. 4 is a graph for explaining the principle of the present invention.

FIG. 5 is a perspective view of the semiconductor laser according to the first embodiment of the present invention.

FIG. 6 is a sectional view taken along the line VI-VI in FIG. 5;

FIG. 7 shows a far-field image in the vertical direction of the junction of the semiconductor laser according to the first embodiment of the present invention and an oscillation wavelength λ = 420 n;
m, near-field image ω = perpendicular to the junction at the cavity facet
250 nm, complex reflectance r = −
1. A graph showing the result obtained by calculation when the height a of the light emitting point a = 2.5 μm and the length c of the etched bottom is c = 4 μm, and the far field image in the direction perpendicular to the junction is obtained only for the length c of the etched bottom. = 0 μm, and other parameters are graphs showing results obtained by calculation under the same conditions.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Semiconductor layer, 4, 21 ... Resonator end face, 5, 22 ... Etching bottom face, 6, 25 ...
· Edges, 7, 26 ··· light emitting region, 11 ··· c-plane sapphire substrate, 12 ··· undoped GaN buffer layer,
13 ... n-type GaN contact layer, 14 ... n-type A
1GaN cladding layer, 15... n-type GaN optical waveguide layer,
16 ... GaInN active layer, 17 ... p-type GaN optical waveguide layer, 18 ... p-type AlGaN cladding layer, 19
..P-type GaN contact layer, 20 ... AlGaIn
N-based semiconductor layer, 23 ... p-side electrode, 24 ... n-side electrode, s0 ... light emitting point, s0 '... mirror image point

Claims (5)

[Claims] 1. A resonator comprising a semiconductor layer forming a laser structure on a substrate and having a cut surface formed by etching the semiconductor layer as an end face of the resonator. A portion corresponding to a bottom surface formed on the substrate or the semiconductor layer in an etching region in forming the semiconductor substrate, a reference surface on which a part of light emitted from a light emitting point on the resonator end face is incident; The diffracted light in which the light emitted from is diffracted at the end of the reference plane, and the reflected light in which a part of the light emitted from the light emitting point is reflected on the reference plane is diffracted at the end of the reference plane. In the semiconductor laser in which undulation occurs in the far-field image, the light intensity at the first peak having the largest light intensity in the far-field image is p1, and the light intensity at the second peak is the second largest. To p2 , The first peak and the second peak
When the light intensity at the minimum value where the light intensity is the minimum among the minimum values existing between the peaks is represented by v, (p2−v) / p1
The length of the reference plane between the resonator end face and the end and the height from the reference plane to the light-emitting point are set so that the value is equal to or less than a desired value. Semiconductor laser. 2. The semiconductor laser according to claim 1, wherein said reference plane is said bottom surface formed on said substrate or said semiconductor layer. 3. A reflectivity controlling film is provided on the substrate or the bottom surface formed on the semiconductor layer, and the reference surface is a surface of the reflectivity controlling film. Item 2. The semiconductor laser according to item 1. 4. The semiconductor laser according to claim 3, wherein the film for controlling the reflectance is a light absorbing film for absorbing the emitted light. 5. The semiconductor laser according to claim 3, wherein the film for controlling the reflectance is a metal film.