JPH07106703A - Semiconductor laser and its producing method - Google Patents

Abstract

PURPOSE:To provide a longitudinal multimode in a wide-stripe range and reduce the noise by a method wherein the stripe width is large enough to cause a single transverse mode oscillation near, at least, one end face of a resonator but wider at other area than this end face. CONSTITUTION:A multilayer structure has a semiconductor substrate 1, an active layer 4 formed thereon, a pair of clad layers 3 and 5 sandwiching the layer 4, and current constricting layer 7 for injecting a current into a stripe-like region of the layer 4. At least one of the clad layers 3 and 5 has a stripe-like ridge extending in the direction of a resonator of a semiconductor layer, and its stripe width is large enough to cause a single transverse mode oscillation near, at least, one end face of the oscillator and wider at other area than the resonator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having good noise characteristics and a method of manufacturing the same.

[0002]

2. Description of the Related Art Semiconductor lasers that emit laser light in the visible light range to emit light have applications such as light sources for optical information processing such as laser beam printers and optical disks, and their importance has recently been increasing. Above all, (Al _x Ga _1-x ) _0.5
The In _0.5 P-based material has a wavelength of 0.69 μm by lattice matching with GaAs, which is a good substrate, and changing the composition x.
To 0.56 μm, it is possible to obtain laser oscillation, and therefore, it is drawing attention.

A conventional semiconductor laser having a double hetero structure and a lateral mode control type having an oscillation wavelength in the red region will be described below with reference to FIG. This semiconductor laser is
n-GaAs buffer layer 2, n on n-GaAs substrate 1
-(Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 3, Ga
_0.5 an In _0.5 P active layer _{4, p- (Al 0.6 Ga 0.4} ) 0. 5 I
n _0.5 P clad layer 5, p-Ga _0.5 In _0.5 P layer 6, n
A -GaAs current confinement layer 7 and a p-GaAs cap layer 8 are provided. A p-side electrode 9 is formed on the cap layer 8 and an n-side electrode 10 is formed on the back surface of the substrate 1.

In this semiconductor laser, metalorganic vapor phase epitaxy
A crystal growth technique such as the MOVPE method is used.
Using these crystal growth techniques, on the n-GaAs substrate 1
N-GaAs buffer layer 2, n- (Al_0.6Ga_0.4)
_0.5In_0.5P clad layer 3, Ga0.5In0.5P active layer
4, p- (Al_0.6Ga_0.4)_0.5In_0.5P clad layer 5
And p-Ga_0.5In_0.5The P layer 6 is sequentially deposited. next
P- by photolithography technology and etching technology
Ga_0.5In_0.5P layer 6 and p- (Al_0.6Ga_0.4) _0.5I
n_0.5A part of the P clad layer 5 is etched into a trapezoidal shape.
Forming a striped ridge on the cladding layer 5. That
The n-GaAs current confinement layer 7 is formed by using the post MOVPE method or the like.
Selectively deposited on the outside of the stripe, and p-Ga
The As cap layer 8 is deposited.

In the structure of such a semiconductor laser, n-
The GaAs current confinement layer 7 can confine the current, and when the p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 5 is trapezoidally etched, the cladding layer 5 outside the striped ridge is formed. By optimizing the thickness and the width of the stripe-shaped ridge, an effective refractive index difference satisfying the condition of the single transverse mode can be provided inside and outside the trapezoidal stripe, and the clad layer 5 of the active layer 4 can be formed. Light can be effectively trapped under the striped ridge. The stripe width is typically about 5 μm.

However, in the above structure, the longitudinal mode tends to be a single mode. Therefore, when used in an optical disc or the like, it causes noise. The noise includes return light induced noise, mode hopping noise, and the like.

Return light induced noise is noise generated when laser light emitted from a semiconductor laser is reflected by a lens, an optical disk or the like and returns to the inside of the resonator of the semiconductor laser. A single longitudinal mode semiconductor laser has strong coherence, and changes in optical output and spectrum (mode hopping) occur depending on the position of a reflecting surface such as a lens or an optical disk surface or the intensity of reflected light, resulting in noise.

Mode-hopping noise occurs especially when the ambient temperature of the semiconductor laser changes. As the temperature changes, when the vertical mode jumps to the next mode, that is, when mode hopping, random oscillation is repeated alternately between the vertical modes, and the optical output level varies between the vertical modes and the optical output fluctuates. Both things result in noise.

When these semiconductor lasers are applied to optical discs, these noises impair sound quality and image quality, so
It becomes a problem.

Therefore, a structure for improving the noise characteristic has been proposed (Japanese Patent Laid-Open No. 62-39084). As shown in FIG. 19, this semiconductor laser has an n-GaAs substrate 201, an internal current confinement layer 203, and a buffer layer 20.
4, n-clad layer 205, active layer 206, p-clad layer 207, p-GaAs layer 208, p electrode 209, n
It consists of electrodes 210. The material forming this semiconductor laser is AlGaAs. In the region B near the end face of the resonator, the waveguide structure is bent as shown in FIG.
On the other hand, the region A near the center has a wide stripe width. The current is injected into a desired region of the active layer 206 by the internal current confinement layer 203. Resonator length is about 300 μm, B region length is about 30
μm, width is about 2.5 μm, length of area A is about 240 μm
m, the width is about 8 μm.

This is an attempt to improve the noise characteristics by making the longitudinal mode multimode in the central area A.

[0012]

However, in the case where the internal current confinement layer is provided on the n-GaAs substrate 201 side as in the structure of the conventional example shown in FIG. Overlying in the horizontal direction, it becomes difficult to inject a current into a desired active layer region. Therefore, there arise problems that the transverse mode becomes unstable and the driving current of the semiconductor laser increases.

On the other hand, if the current confinement layer 203 is p-
It is assumed that it is provided on the clad layer 207 side. In this case, since the hetero barrier against holes between the p-clad layer 207 and the p-GaAs layer 208 provided on the p-clad layer 207 for providing the electrode thereon is large, in the A region. The holes injected from the p-electrode 209 spread too much,
There are problems that the driving current of the semiconductor laser rises and that the spread of the injected holes changes with the change of the environmental temperature. In particular, when the structure as shown in FIG. 19 is used for the AlGaInP-based material, the influence thereof becomes large because the hetero barrier in the valence band is larger than that of the AlGaAs-based material. For example, in a red semiconductor laser having an oscillation wavelength in the 670 nm band, injected holes spread horizontally in each layer by as much as 50 μm, which increases the drive current and is not practical.

Furthermore, when the area A having a wide stripe width is too long, the noise characteristics tend to deteriorate. In particular, if the ratio of the length l of this region to the resonator length L exceeds 0.3,
The relative noise intensity (RIN) is -130 dB / Hz or more, which is not practical.

Further, in a semiconductor laser using AlGaInP as a material, providing an active layer on a bent substrate makes it difficult to grow crystals, and it is difficult to obtain high quality crystals.

An object of the present invention is to solve such problems and to provide a semiconductor laser with low noise and a method for manufacturing the same.

[0017]

A semiconductor laser of the present invention has a semiconductor substrate and a laminated structure formed on the semiconductor substrate, wherein an active layer, a pair of clad layers sandwiching the active layer, and A laminated structure having a current confinement layer for injecting a current into a stripe-shaped predetermined region of an active layer, wherein at least one of the pair of cladding layers has a cavity direction of the semiconductor laser. Has a stripe-shaped ridge extending along the width of the stripe, and the width of the stripe is such that a single transverse mode oscillation can be obtained in the vicinity of at least one resonator end face. The width is wider than the width of the stripe near the resonator, which achieves the above object.

In one embodiment, the width of the stripe in the vicinity of the resonator is 1 μm to 7 μm, the width of the stripe other than in the vicinity of the resonator is 7 μm or more, and resonance occurs with the length l of the region of 7 μm or more. The ratio 1 / L of the vessel length L is 0.3 or less, and the carrier injection width is almost the same as the stripe width.

In one embodiment, the stripe width between the stripe-shaped ridge near the resonator and the stripe-shaped ridge other than the resonator is changed linearly or curvedly.

The semiconductor laser of the present invention comprises a semiconductor substrate and a laminated structure formed on the semiconductor substrate, wherein an active layer, a pair of clad layers sandwiching the active layer, and a stripe-shaped predetermined layer of the active layer. A laminated structure having a current confinement layer for injecting a current into a region, wherein at least one of the pair of clad layers has a stripe shape extending along a cavity direction of the semiconductor laser. The striped ridge having a ridge, and the difference between the effective refractive index of the striped ridge portion near at least one resonator end face and the effective refractive index outside the striped ridge is other than near the resonator end face. It is larger than the difference between the effective refractive index of the portion and the effective refractive index outside the striped ridge, thereby achieving the above object.

In one embodiment, the effective refractive index outside the striped ridge in the vicinity of at least one resonator end face is smaller than the effective refractive index outside the striped ridge other than in the vicinity of the resonator end face. There is.

In one embodiment, at least one of the pair of cladding layers has a convex striped ridge extending along the cavity direction of the semiconductor laser.
A current confinement layer is provided on the clad layer outside the stripe, and the thickness of the clad layer below the current confinement layer is thin near at least one resonator end face.

In one embodiment, other than near the cavity facets,
When the length of the region having a small difference between the effective refractive index of the striped ridge portion and the effective refractive index outside the striped ridge is 1, and the resonator length is L, l / L is 0.3 or less.

In one embodiment, at least one of the pair of clad layers has a stripe ridge extending along the cavity direction of the semiconductor laser device, and the width of the stripe is the same throughout the cavity. Has become.

The method of manufacturing a semiconductor laser of the present invention is a method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, and the step further comprises the first step.
A step of forming a clad layer, a step of forming an active layer on the first clad layer, a step of forming a film to be a second clad layer on the active layer, and selectively forming the film on the film. A step of depositing a first insulating film for etching, and a part of the second cladding layer is etched using the insulating film as a mask to form a striped ridge extending in the cavity direction of the semiconductor laser device. A step of forming, a step of depositing a second insulating film, a step of etching a part of the second clad layer using the first insulating film and the second insulating film as a mask, and a second step Remove the insulating film,
Forming a current confinement layer for injecting a current in a stripe-shaped predetermined region in the active layer on a portion of the second cladding layer other than the stripe-shaped ridge portion; and removing the first insulating film. The above-mentioned object is achieved thereby.

[0026]

In the semiconductor laser of the present invention, at least one of the pair of clad layers sandwiching the active layer has a stripe-shaped ridge extending along the cavity direction of the semiconductor laser, and the width of the stripe is The width is such that single transverse mode oscillation can be obtained in the vicinity of at least one of the resonator end faces, and the width of the stripe is wider than in the vicinity of the resonator except in the vicinity of the resonator end face. For this reason, in the region where the stripe width is wide, the longitudinal mode is multimode, and as a result, noise can be reduced.

In the current confinement layer of the semiconductor laser of the present invention, carriers are injected only into a predetermined region of the active layer corresponding to the region where the current confinement layer does not exist. The carrier injection width is substantially the same as the stripe width. That is, it is narrow in the vicinity of the end face of the resonator and thick in areas other than the end face of the resonator. Since carriers are injected according to the width of the stripe, stable characteristics can be obtained without causing non-uniformity in carrier injection due to changes in environmental temperature and the like.

The stripe width in the vicinity of the cavity end face is 1 μm to 7 μm, the width of the stripe other than in the vicinity of the cavity end face is 7 μm or more, and the carrier injection width is almost the same as the stripe width. It is the same. Since the stripe width is 1 μm to 7 μm near the end face of the resonator, laser oscillation in the fundamental transverse mode is possible. 7μ
Since the ratio 1 / L of the length 1 of the region of m or more to the length L of the region of 1 μm to 7 μm is 0.3 or less, the relative noise intensity is not increased.

A striped ridge near the end face of the resonator;
A structure in which the stripe width changes linearly or curvedly between the striped ridges other than in the vicinity of the end face of the resonator. Therefore, when manufacturing the semiconductor laser, it is possible to obtain a highly reliable semiconductor laser without generating crystal defects between the vicinity of the resonator end face having a narrow stripe width and the vicinity other than the vicinity of the wide resonator end face. it can.

The semiconductor laser of the present invention has a semiconductor substrate, and a laminated structure formed on the semiconductor substrate. The active layer, a pair of clad layers sandwiching the active layer, and the stripe-shaped predetermined active layer. A laminated structure having a current blocking layer for injecting a current into a region, wherein at least one of the pair of clad layers has a stripe shape extending along a cavity direction of the semiconductor laser. The striped ridge having a ridge, and the difference between the effective refractive index of the striped ridge portion near at least one resonator end face and the effective refractive index outside the striped ridge is other than near the resonator end face. It is larger than the difference between the effective refractive index of the portion and the effective refractive index outside the striped ridge, thereby achieving the above object. That is,
Light confinement is small in the region where the effective refractive index difference is small,
Higher-order transverse modes are also likely to oscillate, and the longitudinal modes are multimode, resulting in low noise of the semiconductor laser.

The method of manufacturing a semiconductor laser according to the present invention is a method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, the step further comprising the first step.
A step of forming a clad layer, a step of forming an active layer on the first clad layer, a step of forming a film to be a second clad layer on the active layer, and selectively forming the film on the film. A step of depositing a first insulating film for etching, and a part of the second cladding layer is etched using the insulating film as a mask to form a striped ridge extending in the cavity direction of the semiconductor laser device. A step of forming, a step of depositing a second insulating film, a step of etching a part of the second clad layer using the first insulating film and the second insulating film as a mask, and a second step Remove the insulating film,
Forming a current confinement layer for injecting a current in a stripe-shaped predetermined region in the active layer on a portion of the second cladding layer other than the stripe-shaped ridge portion; and removing the first insulating film. The process including the steps described above is included, which makes it possible to manufacture a semiconductor laser having excellent noise characteristics with a high yield.

[0032]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a lateral mode control type red semiconductor laser according to an embodiment of the present invention.

This semiconductor laser, as shown in FIG.
For example, on an n-GaAs substrate 1, an n-GaAs buffer layer
Ga through 2_0.5In_0.5P active layer 4 (thickness 600Å)
N- (Al_0.6Ga_0.4)_0.5In_0.5P clad layer 3
And p- (Al_0.6Ga_0.4) _0.5In_0.5P clad layer 5
It has a double hetero structure sandwiched between. p- (Al_{0. 6}
Ga_0.4)_0.5In_0.5On top of the P clad layer 5, p-
Ga_0.5In_0.5P layer 6 (thickness 0.1 μm), p−
Ga_0.5In_0.5P layer 6 and p- (Al_0.6Ga_{0 .Four})
_0.5In_0.5Part of the P-clad layer 5 has a trapezoidal strike.
It is processed into a ridged ridge. In the clad layer 5,
The thickness of the tripe ridge is 1 μm, the stripe ridge
The thickness of the portion other than the portion is 0.25 μm.

P- (Al on both sides of the striped ridge
_0.6 Ga _0.4 ) _0.5 In _0.5 P On the clad layer 5, n-
A GaAs current confinement layer 7 is deposited. n-GaAs
The current confinement layer 7 has a function of injecting carriers into a desired region of the active layer 4 and a function of controlling a lateral mode of the semiconductor laser. The forbidden band width of the current confinement layer 7 of the present invention is smaller than that of the active layer 4, and part of the light generated by the recombination of carriers is absorbed by the current confinement layer 7. When the width of the striped ridge is about 5 μm, the amount of light absorbed in the higher-order transverse modes higher than the first-order mode is large and the waveguide loss becomes large, so that oscillation in a single transverse mode is possible.

In the present invention, the current confinement layer 7 is provided on the p-clad layer 5 side. If it is provided on the n-clad layer side. In this case, since the electrons, which are the majority carriers of the n-cladding layer, have a high mobility, the electrons that have passed through the current confinement layer easily spread in the horizontal direction with each layer, so that the effect as the current confinement is weakened and the driving current is reduced. Rises and destabilizes the transverse mode.

In the present invention, the current confinement layer is provided in the thin portion of the p-clad layer 5 processed into the convex ridge shape in all regions in the resonator. If the current confinement layer 7 is provided above the p-Ga _0.5 In _0.5 P layer 6 via a hetero interface, for example. In this case, since the hetero barrier between the p-clad layer 5 and the p-Ga _0.5 In _0.5 P layer 6 is large, the holes injected from the p-side electrode 9 spread too much in each layer in the horizontal direction, so that the semiconductor laser There arise problems that the driving current increases and that the spread of the injected holes changes with the change of the environmental temperature. The injected holes spread in the direction perpendicular to the striped ridge, that is, in each layer in the horizontal direction by as much as 50 μm, increasing the drive current, which is not practical. Further, the spread of this current also changes depending on the temperature.

FIG. 2 is a sectional view of the semiconductor laser shown in FIG. 1 taken along the section a. The width of the striped ridge is about 5 μm in the region near the cavity facet and about 16 μm in the region other than the cavity facet. The width in the vicinity of the end face of the cavity is such that a sufficient difference in gain between the fundamental transverse mode and a higher-order transverse mode can be obtained, which enables single transverse mode oscillation of the semiconductor laser. Outside the stripe ridge, that is, under the current confinement layer 7, p- (Al _0.6 G
The thickness of the a _0.4 ) _0.5 In _0.5 P cladding layer 5 is uniform in the cavity direction. In the present embodiment, the striped ridge has a trapezoidal sectional shape, but the sectional shape may be rectangular.

In the semiconductor laser of the present invention, the width of the striped ridge and the width of the injected current, that is, the width of the opening of the current confinement layer 7 are substantially the same. If the width of the striped ridge and the width of the current injection region are extremely different,
Since the mobility of carriers varies with the change of the environmental temperature, the way of injecting the carriers changes, which makes the characteristics of the semiconductor laser, especially the driving current depending on the temperature unstable.

FIG. 3 is a top view of the semiconductor laser shown in FIG. 1. The width of the striped ridge is shown by a wavy line for easy understanding. The cavity length of this semiconductor laser is 35
The width of the stripe-shaped ridge is 60 μm, and there is a region where the width gradually changes between the wide region and the narrow region of about 4 μm. In this way, by forming a region where the stripe width gradually changes between the striped ridge near the cavity facet and the striped ridge other than near the cavity facet, the It is possible to obtain a highly reliable semiconductor laser without generating crystal defects between the vicinity of the narrow cavity end face and the vicinity of the wide cavity end face.

FIG. 4 shows the relationship between the optical output and the drive current for the semiconductor laser of the present invention. Threshold current is 3
At 7 mA, single transverse mode oscillation is limited by a 16 mW kink. It can be said that the semiconductor laser of the present invention has obtained a sufficient optical output because it is used at about 5 mW in a read-only optical disk.

In the wide area of the striped ridge, the longitudinal mode is multimode, and this effect causes this semiconductor laser to oscillate in multimode. Due to the multi-mode oscillation, this semiconductor laser has good noise characteristics, and at a temperature of 25 ° C., a light output of 3 mW, and a return light amount of 0.1%, R
IN showed a value of -133 dB / Hz.

FIG. 5 shows RI when the stripe width is changed near the center of the semiconductor laser, that is, in a region other than the vicinity of the resonator.
It is the stripe width dependency of N. 5 μm is when there is no region with a wide stripe width, that is, when the stripe width is uniform in the entire cavity direction. If the stripe width is increased, RIN tends to decrease. -120d at 5μm
It is B / Hz, but it is -130d at about 7 μm or more.
Values below B / Hz were obtained. This is because when the thickness exceeds 7 μm, the difference in threshold gain between the basic transverse mode and the higher-order transverse mode becomes small, and the longitudinal mode becomes multimode. When the stripe width was 7 μm or more, all semiconductor lasers showed a value of −130 dB / Hz or less.

FIG. 6 shows the relationship between RIN and the length 1 of the wide stripe region. The width of the wide stripe region is 16 μm. When 1 is 0, there is no region having a wide stripe width, that is, when the stripe width is uniform in the entire resonator direction. When 1 exceeds about 20 μm, RIN drops to −130 dB / Hz or less.
It rises from about 90 μm, and −120 d above 100 μm.
The value was about B / Hz. From this, in order to obtain good noise characteristics, the length of l should be 20 μm or more and 100 μm or more.
I found that it had to be: l depends on the resonator length L, and the value of l / L needs to be 0.3 or less in order to reduce noise.

As described above, a semiconductor laser having a low relative noise intensity can be obtained by making the longitudinal mode multimode.

Example 2 Another semiconductor laser according to the present invention will be described with reference to FIG.

This semiconductor laser has an n-GaAs substrate 1
Ga _0.5 In _0.5 on the n-GaAs buffer layer 2
P-active layer 4 (thickness 600 Å) is n- (Al _0.6 Ga _0.4 ).
_0.5 In _0.5 P cladding layer 3 and p- (Al _0.6 G
a _0.4 ) _0.5 In _0.5 P It has a double hetero structure sandwiched by the clad layers 5. p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5
A p-Ga _0.5 In _0.5 P layer 6 is formed on the P clad layer 5.
(Thickness 0.1 μm) and has a p-Ga _0.5 In _0.5 P layer 6
A part of the p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P cladding layer 5 is processed into a trapezoidal striped ridge. The thickness of the striped ridge in the clad layer 5 is 1 μm. The thickness of the portion other than the striped ridge portion is 0.25 μm near the cavity facet (indicated by H ₁ in FIG. 7) and 0.45 μm near the cavity facet (H in FIG. 8).
And has a display in _2). The width of the striped ridge is 5
μm.

In the present embodiment, the stripe-shaped ridge has a trapezoidal sectional shape, but the sectional shape may be rectangular.

P- (Al on both sides of the striped ridge
_0.6 Ga _0.4 ) _0.5 In _0.5 P On the clad layer 5, n-
A GaAs current confinement layer 7 is deposited. n-GaAs
The current confinement layer 7 has a function of injecting carriers into a desired region of the active layer 4 and a function of controlling a lateral mode of the semiconductor laser.

In the present invention, the current confinement layer 7 is provided on the p-clad layer 5 side. If it is provided on the n-clad layer side. In this case, since the electrons, which are the majority carriers of the n-cladding layer, have a high mobility, the electrons that have passed through the current confinement layer easily spread in the horizontal direction with each layer, so that the effect as the current confinement is weakened and the driving current is reduced. Rises and destabilizes the transverse mode.

Further, in the present invention, the current confinement layer 7 is provided on the p-cladding layer 5 outside the stripe processed into the convex ridge shape in all regions in the resonator. If the current confinement layer is provided on the p-Ga _0.5 In _0.5 P layer 6 via a hetero interface such as the upper portion, the p-Ga _0.5 In _0.5 P layer 6 may be provided between the p-clad layer 5 and the p-Ga _0.5 In _0.5 P layer 6. Since the hetero barrier is large, the holes injected from the p-side electrode 9 spread to each layer in the horizontal direction too much, the driving current of the semiconductor laser rises, and the holes injected spread as the environmental temperature changes. However, there is a problem that the value fluctuates. The injected holes spread in each layer in the horizontal direction by as much as 50 μm, which increases the drive current, which is not practical. The spread of the holes also changes depending on the temperature.

FIG. 8 is a sectional view of the semiconductor laser shown in FIG. 7 taken along the section a. Between H ₁ and H ₂ , H ₁ <
The relationship of H ₂ holds. The effective refractive index on the outside of the striped ridge is 3.303 near the resonator end face, and is 3.309 outside the resonator end face, that is, at a section a, which is low near the resonator end face. The effective refractive index inside the striped ridge is 3.313. In the a-section, the difference in effective refractive index inside and outside the ridge on the stripe is small, and the difference in threshold gain between the fundamental transverse mode and the higher-order transverse mode is small, and as a result, the longitudinal mode becomes multimode.

In the semiconductor laser of the present invention, the width of the stripe ridge and the width of the current injected, that is, the width of the opening of the current confinement layer are substantially the same. That is, it is 5 μm over the entire resonator. A desired noise characteristic can be obtained by providing the thickness of the p-cladding layer outside the striped ridge with the distribution as in this embodiment in the resonator direction. Example 1 at the same time as the width of the striped ridge
It goes without saying that RIN can be reduced even if the distribution as shown in FIG. However, widening the stripe width increases the driving current. Therefore, it is preferable to use a semiconductor laser in which the width of the stripe ridge is uniform in the cavity direction.

FIG. 9 shows the relationship between the optical output and the drive current for the semiconductor laser of the present invention. Threshold current is 2
At 2 mA, single transverse mode oscillation is limited by a 22 mW kink. It can be said that the semiconductor laser of the present invention has obtained a sufficient optical output because it is used at about 5 mW in a read-only optical disc.

In the region where the thickness of the p-cladding layer 5 outside the stripe ridge is large, the difference in effective refractive index between the inside and outside of the stripe ridge is small, and the transverse mode becomes multimode, and this effect makes the longitudinal mode multimode. There is. Due to the multi-mode oscillation, this semiconductor laser can obtain good noise characteristics, the temperature is 25 ° C., the optical output is 4 mW, and the return light amount is 0.1%.
In, RIN showed the value of -132 dB / Hz.

FIG. 10 is a diagram showing the relationship between the RIN of the semiconductor laser and the length l of the region other than the vicinity of the resonator, that is, the region where the p-cladding layer 5 is thick. When 1 is 0, there is no region where the p-cladding layer is thick outside the stripe ridge, that is, when the thickness of the p-cladding layer is uniform in the entire cavity direction. When 1 exceeds about 20 μm, RIN drops to −130 dB / Hz or less. About 10
It rises from 0 μm, and −125 dB / above 125 μm.
The value was about Hz. From this, it is understood that the length of l must be 20 μm or more and 100 μm or less in order to obtain good noise characteristics. l depends on the resonator length L, and the value of l / L needs to be 0.3 or less in order to reduce noise.

As described above, a semiconductor laser having a low relative noise intensity can be obtained by making the longitudinal mode multimode.

Next, a method of manufacturing this semiconductor laser will be described with reference to FIGS. First, a crystal growth method such as MOVPE is used to form an n-GaAs buffer layer 2 and n- (Al _0.6 Ga _0.4 ) on an n-GaAs substrate 1.
_{A 0.5} In _0.5 P clad layer 3, a Ga _0.5 In _0.5 P active layer 4, a p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 5, and a p-Ga _0.5 In _0.5 P layer 6 are epitaxially grown (FIG. 11). SiO ₂ 101 was p-typed by thermal CVD
After being deposited on the Ga _0.5 In _0.5 P layer 6, the SiO ₂ 101 is deposited using photolithography and etching techniques.
Are processed into stripes (FIG. 12). SiO ₂ 101
Has a width of about 5 μm. After that, Si ₃ N ₄ 102 is deposited by plasma CVD, and stripe-shaped SiO ₂ 1
01 and Si ₃ N ₄ 1 in a vertical stripe
02 is processed (FIG. 13). The width of Si ₃ N ₄ 102 is 75
μm. After that, SiO ₂ 101 and Si ₃ N ₄ 102
Was an etching mask, p-Ga _0.5 In _0.5 P layer 6 and _{p- (Al 0.6 Ga 0.4) 0.5} In 0 .5 partially etching the P-cladding layer 5 (Figure 14). At this time, p- (Al
_0.6 Ga _0.4 ) _0.5 In _0.5 P Clad layer 5 has a step of 0.2
μm. After that, the Si ₃ N ₄ 102 is selectively removed, and the p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 5 is formed.
Are further etched (FIG. 15). And MOVP
Using the selective growth technique of the E method, n is used as the current blocking layer.
Without depositing the GaAs current confinement layer 7 on the SiO ₂ 101, p- (Al _0.6 G on both sides of the stripe)
Crystals are grown on the a _0.4 ) _0.5 In _0.5 P cladding layer 5 (FIG. 16). After that, SiO ₂ 101 is removed, and p-G
Crystal growth of the aAs cap layer 8 is performed (FIG. 17). Finally, Cr / Pt / Au is deposited on the p-GaAs contact layer 8 to form the p-side electrode 10, and A is formed on the n-GaAs substrate 1.
u / Ge / Ni is deposited to form the n-side electrode 11.

With this manufacturing method, a lateral mode control type red semiconductor laser as shown in FIG. 7 can be manufactured.

[0060] In the above embodiment has been designated a material constituting the semiconductor laser, the cladding layer is _{(Al y Ga 1-y)} 0.5 I
Even when n _0.5 P and the active layer are (Al _z Ga _1-z ) _0.5 In _0.5 P (where 0 ≦ z ≦ y ≦ 1), a semiconductor laser with low relative noise intensity can be easily manufactured. . When a multi-quantum well or a strained multi-quantum well is used for the active layer, the single longitudinal mode property is strong and the noise characteristic tends to be deteriorated, but according to the semiconductor laser of the present invention, a semiconductor laser with low relative noise intensity is obtained. be able to.

In the above embodiment, the material is AlGaIn.
Although the semiconductor laser using P has been described, it goes without saying that the effect of the present invention is great even if other materials are used. III-
The effect of the present invention is great not only for the V group semiconductor laser but also for the semiconductor laser made of the II-VI group material.

[0062]

According to the semiconductor laser of the present invention, (1) In the semiconductor laser of the present invention, at least one of the pair of clad layers sandwiching the active layer is a stripe extending along the cavity direction of the semiconductor laser. A ridge, the width of the stripe is such that a single transverse mode oscillation can be obtained in the vicinity of at least one of the resonator end faces, and the width of the stripe is in a resonator other than in the vicinity of the resonator end face. Since the width is larger than that in the vicinity, the longitudinal mode becomes multi-mode in the region where the stripe width is wide, and as a result, noise can be reduced.

According to the semiconductor laser of the present invention, (2) in the current confinement layer, carriers are injected only into a predetermined region of the active layer corresponding to the region where the current confinement layer does not exist, and the carrier injection width is the stripe width. Since the width is almost the same as that of the stripes, the carriers are injected in accordance with the width of the stripe, so that the characteristics of the carriers are not unevenly caused by the change of the environmental temperature and the like, and stable characteristics can be obtained.

According to the semiconductor laser of the present invention, (3) the stripe width in the vicinity of the cavity facet is from 1 μm to 7 μm.
Since it is μm, laser oscillation in the fundamental transverse mode is possible, and the ratio l of the length l of the region of 7 μm or more and the cavity length L is l.
Since / L is 0.3 or less, the relative noise intensity is not increased.

According to the semiconductor laser of the present invention, (4) a structure in which the stripe width changes linearly or curvedly between the striped ridge near the cavity end face and the striped ridge other than near the cavity end face. Has become. Therefore, when manufacturing the semiconductor laser, it is possible to obtain a highly reliable semiconductor laser without generating crystal defects between the vicinity of the resonator end face having a narrow stripe width and the vicinity other than the vicinity of the wide resonator end face. it can.

According to another semiconductor laser of the present invention, (5) a semiconductor substrate, and a laminated structure formed on the semiconductor substrate, the active layer and a pair of clad layers sandwiching the active layer, A semiconductor laser having a laminated structure having a current blocking layer for injecting a current into a stripe-shaped predetermined region of the active layer, wherein at least one of the pair of clad layers is a resonator of the semiconductor laser. Having a stripe-shaped ridge extending along the direction, and the difference between the effective refractive index of the stripe-shaped ridge portion and the effective refractive index outside the stripe-shaped ridge in the vicinity of at least one resonator end face is
It is larger than the difference between the effective refractive index of the stripe-shaped ridge portion and the effective refractive index outside the stripe-shaped ridge except in the vicinity of the end face of the resonator, so that light confinement is small in a region where the effective refractive index difference is small. The longitudinal mode is multimode, and as a result, the noise of the semiconductor laser can be reduced.

According to the semiconductor laser of the present invention, (6) the length of a region having a small difference between the effective refractive index of the striped ridge portion and the effective refractive index outside the striped ridge portion other than near the cavity end face is l, When the resonator length is L, l /
Since L is 0.3 or less, the relative noise intensity is not increased.

According to the method of manufacturing a semiconductor laser of the present invention, (7) a method of manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, the step further comprising the first cladding. A step of forming a layer, a step of forming an active layer on the first clad layer, a step of forming a film to be a second clad layer on the active layer, and selectively forming the film on the film. A step of depositing a first insulating film for etching, and a part of the second cladding layer are etched by using the insulating film as a mask to form a striped ridge extending in the cavity direction of the semiconductor laser device. A step of depositing a second insulating film, a step of etching a part of the second cladding layer using the first insulating film and the second insulating film as a mask, and the second insulating Remove the membrane and above 2 a step of forming a current confinement layer for injecting a current into a stripe-shaped predetermined region in the active layer on a portion of the clad layer other than the stripe-shaped ridge portion, and a step of removing the first insulating film Therefore, a semiconductor laser having good noise characteristics can be manufactured with high yield.

[Brief description of drawings]

FIG. 1 is a sectional view of a lateral mode control type red semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a semiconductor laser according to an embodiment of the present invention except for the vicinity of a cavity end face.

FIG. 3 is a top view of a semiconductor laser according to an embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the optical output and the drive current of the semiconductor laser of the embodiment of the present invention.

FIG. 5 is a diagram for explaining the effect of the semiconductor laser of the present invention, showing the relationship between the relative noise intensity and the width of the striped ridge other than in the vicinity of the cavity facet.

FIG. 6 is a diagram for explaining the effect of the semiconductor laser of the present invention, showing the relationship between relative noise intensity and the length of a striped ridge other than in the vicinity of the cavity facet.

FIG. 7 is a cross-sectional view of a lateral mode control type red semiconductor laser according to another embodiment of the present invention.

FIG. 8 is a cross-sectional view of the semiconductor laser according to the embodiment of the present invention except the vicinity of the cavity end face.

FIG. 9 is a diagram showing the relationship between the optical output and the drive current of the semiconductor laser of the example of the present invention.

FIG. 10 is a diagram for explaining the effect of the semiconductor laser of the present invention, showing the relationship between the relative noise intensity and the length of the striped ridge other than in the vicinity of the cavity facet.

FIG. 11 is a first diagram showing a manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 12 is a second diagram showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 13 is a third process showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 14 is a fourth process showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 15 is a fifth view showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 16 is a sixth view showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 17 is a seventh step showing the manufacturing process of the semiconductor laser of the present invention.
Process cross-sectional view

FIG. 18 is a sectional view of a conventional red semiconductor laser.

FIG. 19 is a top view and a sectional view of another conventional semiconductor laser.

[Description of Reference Signs] 1 n-GaAs substrate 2 n-GaAs buffer layer 3 n- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 4 Ga _0.5 In _0.5 P active layer 5 p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 6 p-Ga _0.5 In _0.5 P layer 7 n-GaAs current confinement layer 8 p-GaAs contact layer 9 p-side electrode 10 n-side electrode 101 SiO ₂ 102 Si ₃ N ₄ 201 n-GaAs substrate 203 internal current Constriction layer 204 n-GaAs buffer layer 205 n-Ga _0.5 Al _0.5 As clad layer 206 Ga _0.86 Al _0.14 As active layer 207 p-Ga _0.5 Al _0.5 As clad layer 208 p-GaAs layer 209 p-electrode 210 n-electrode

Front page continuation (72) Inventor Kiyoji Ohnaka 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (9)

[Claims] 1. A semiconductor substrate, an active layer formed on the semiconductor substrate, a pair of clad layers sandwiching the active layer, and a current confinement layer for injecting a current into a stripe-shaped predetermined region of the active layer. And a laminated structure having the following: at least one of the pair of clad layers has a stripe ridge extending along the cavity direction of the semiconductor laser, and the width of the stripe. Is a width at which a single transverse mode oscillation can be obtained in the vicinity of at least one end face of the resonator, and the width of the stripe other than the vicinity of the resonator is wider than the width of the stripe in the vicinity of the resonator. . 2. The semiconductor laser according to claim 1, wherein
The width of the stripe near the resonator is 1 μm to 7 μm
And the width of the stripe other than the vicinity of the resonator is 7 μm.
m or more and a length l and a resonator length L of a region of 7 μm or more
The ratio 1 / L is 0.3 or less, and the carrier injection width is substantially the same as the stripe width. 3. The semiconductor laser according to claim 1, wherein:
A semiconductor laser characterized in that the stripe width changes linearly or curvedly between a stripe-shaped ridge near the resonator and a stripe-shaped ridge other than near the resonator. 4. A semiconductor substrate, an active layer formed on the semiconductor substrate, a pair of clad layers sandwiching the active layer, and a current confinement layer for injecting a current into a stripe-shaped predetermined region of the active layer. And a laminated structure having the following: at least one of the pair of cladding layers has a stripe-shaped ridge extending along the cavity direction of the semiconductor laser, and at least one of the resonances The difference between the effective refractive index of the striped ridge portion near the cavity end face and the effective refractive index of the striped ridge outside the striped ridge is A semiconductor laser characterized by being larger than the difference in effective refractive index. 5. The semiconductor laser according to claim 4, wherein
The effective refractive index outside the striped ridge in the vicinity of at least one resonator end surface is other than in the vicinity of the resonator end surface,
A semiconductor laser characterized by being smaller than the effective refractive index outside the striped ridge. 6. The semiconductor laser according to claim 4, wherein:
At least one of the pair of clad layers has a convex striped ridge extending along the cavity direction of the semiconductor laser, and a current constriction layer is provided on the clad layer outside the stripes. The semiconductor laser is characterized in that the thickness of the cladding layer below the current confinement layer is thin near at least one of the cavity end faces. 7. The semiconductor laser according to claim 4, wherein:
When the length of a region having a small difference between the effective refractive index of the stripe-shaped ridge portion and the effective refractive index outside the stripe-shaped ridge other than the vicinity of the end face of the resonator is 1, and the resonator length is L, 1 / L
Is 0.3 or less. 8. The semiconductor laser according to claim 4, wherein:
At least one of the pair of clad layers has a stripe ridge extending along the cavity direction of the semiconductor laser device, and the width of the stripe is the same throughout the cavity. laser. 9. A method for manufacturing a semiconductor laser including a step of forming a laminated structure on a semiconductor substrate, the step further comprising the step of forming a first clad layer, and the step of forming a first clad layer on the first clad layer. A step of forming an active layer on the substrate, a step of forming a film to be a second cladding layer on the active layer, and a step of depositing a first insulating film on the film for selectively etching the film. And a step of forming a striped ridge extending in the cavity direction of the semiconductor laser device by etching a part of the second cladding layer using the insulating film as a mask, and a step of depositing the second insulating film. A step of etching a part of the second clad layer using the first insulating film and the second insulating film as a mask, removing the second insulating film, and removing the second clad layer from the second clad layer. Other than the striped ridge A semiconductor laser including a step of forming a current confinement layer for injecting a current into a stripe-shaped predetermined region in the active layer, and a step of removing the first insulating film. Manufacturing method.