JPH03196688A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE:To reduce an oscillation threshold value by forming a confinement layer of n-type AlInP, AlGaInP or AlGaAs whose refractive index is lower than that of a p-type AlGaInP clad layer on a surface of the p-type AlGaInP clad layer at both sides of a stripe. CONSTITUTION:An n-type AlInP confinement layer 105 whose refractive index is lower than that of a p-type AlGaInP clad layer 104 is formed on a surface of the p-type AlGaInP clad layer 104 at both sides of a stripe 10. Since the refractive index of an n-type AlInP clad layer 102 is lower than that of the p-type AlGaInP clad layer 104, light oozes largely to the side of the p-type AlGaInP clad layer 104; therefore, it is possible to confine and wave-guide light effectively also in a direction parallel to an active layer 103 by the n-type AlInP confinement layer 105 whose refractive index is smaller than that of the AlGaInP clad layer 104 provided to both sides of the stripe. Thereby, an oscillation threshold value can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser made of a material such as AlGaInP and having a controlled transverse mode, and a method for manufacturing the same.

2. Description of the Related Art Semiconductor lasers that emit light at visible wavelengths of 700 nm or less are attracting attention as light sources for use in optical discs, laser printers, bar code readers, and the like. Among them, GaAs is used as a substrate and lattice-matched to it.
a, sP (abbreviated as GaInP in the following explanation) or (A l x Ga I-X) Q, 6 Ins
, a double heterojunction semiconductor laser with 6P (abbreviated as AlGaInP in the following explanation) as an active layer and AlGaInP as a cladding layer is lattice matched to GaAs ■-■
Since it can emit light with the shortest wavelength among group compound semiconductors, it is a promising material for visible light semiconductor lasers.

FIG. 3 shows the cross-sectional structure of a conventional transverse mode control type AlGaInP semiconductor laser during each manufacturing process. First, as shown in FIG. 3(a), an n-type A
lGa1nP cladding layer 302, GaInP active layer 30
3. p-type AlGa I nP cladding layer 304, p-type G
The aInP buffer layer 305 is successively crystal-grown using the Mo-vpE method (organic metal vapor phase epitaxy). Next, using the 5i02 film 306 formed in stripes in the <011> direction as a mask, the p-type Ga1nP buffer layer 305 is
When the p-type AlGaInP cladding layer 304 is etched by RIE (reactive ion etching) using 4 gases, and the p-type AlGaInP cladding layer 304 is etched, for example, with hot concentrated sulfuric acid at 40.degree. C., it becomes as shown in FIG. 3(b). Next, using the SiO2 film 306 as a mask, an n-type GaAs current blocking layer 307 is selectively crystal-grown by MO-VPE, as shown in FIG. 3(C).
It becomes as shown in . Si used as a mask for selective growth
After removing the O2 film 306, a p-type GaAs contact layer 308 is crystal-grown over the entire surface by MO-VPE, and stripes are embedded as shown in FIG. 3(d). Finally, a p-type ohmic contact layer 309 made of Au/Zn/Au is formed on the front surface, and the back surface is polished and etched to make the substrate thinner, and then an n-type ohmic contact layer 309 made of Au-Ge/Ni/Au is formed. 10, the conventional transverse mode control type Al
A GaInP semiconductor laser is completed.

In this conventional laser, the n-type GaAs current blocking layer 307 electrically plays the role of a current confinement layer, and the Ga1nP active layer 303 has a larger refractive index than the p-type AlGa1nP cladding layer 304 for light. Since it absorbs the emitted light, it plays the role of an absorption type anti-waveguide layer. Therefore, this conventional transverse mode control type AlGaI
An nP semiconductor laser oscillates at a low threshold.

Problems to be Solved by the Invention In such conventional transverse mode control type AlGaInP semiconductor lasers, although the transverse mode is controlled, light is not confined by the refractive index in the direction parallel to the active layer. The problem is that the wavefront of the guided light in the direction parallel to the active layer is bent, resulting in a large astigmatism difference. Therefore, the conventional transverse mode control type AlGaI
When applying nP semiconductor lasers to optical equipment, the scope of application is limited because a normal convex lens cannot convert laser light into parallel light or focus it on one point.

Furthermore, as mentioned above, since the light is not confined by the refractive index in the direction parallel to the active layer, the light emitting spot spreads in the direction parallel to the active layer, and the radiation angle θ11 of the emitted light in the direction parallel to the active layer increases. It had gotten smaller. Therefore, there is a problem that the light radiation angle becomes flat as θ11×θ=9×3B′.

In addition, since the n-type GaAs current blocking layer absorbs light emitted from the active layer, there is a loss for the light that is guided through the active layer, so there is a problem that the oscillation threshold increases by this loss. there were.

Another problem is that if the thickness of the p-type AlGa1nP cladding layer on both sides of the stripe is made thinner in order to control the transverse mode, punch-through is likely to occur in that area, increasing leakage current. Ta.

Means for Solving the Problems The present invention is directed to the conventional transverse mode control type AlGaI
This was done to solve the problems in nP-based semiconductor lasers. (1) N-type A on a GaAs substrate.
lInP cladding layer, active layer and p-type AlGaInP
p-type AlGaI on both sides of the stripe with cladding layer
n-type AlGaInP or AlI, which has a lower refractive index than the p-type AlGaInP cladding layer, is formed on the surface of the nP cladding layer.
An nP confinement layer is formed and the p-type AlG on the stripe
A method in which a p-type AlGaInP buried layer is formed on the surface of an aInP cladding layer; (2) a p-type AlGaInP cladding layer having an n-type AlInP cladding layer, an active layer, and a p-type AlGaInP cladding layer thicker in the active layer and stripe portions on the GaAs substrate; However, it has means for forming an n-type AlGaInP or AlInP confinement layer having a lower refractive index than the p-type AlGaInP cladding layer on the surface of the p-type AlGaInP cladding layer on both sides of the stripe.

In addition, in the manufacturing method (3) n
type AlInP cladding layer, active layer, p type AlGaInP
A step of forming a cladding layer and an n-type AlInP confinement layer, a step of selectively etching the n-type AlInP confinement layer to form striped grooves, a step of etching the surface of the striped grooves and the p-type AlGaInP cladding layer The present invention provides a means comprising a step of forming an AlGaInP type buried layer.

Effects The present invention has the following effects by means of the present invention described above.

In means (1) and (2), since the refractive index of the n-type AlInP cladding layer is lower than the refractive index of the p-type AlGaInP cladding layer, the light largely seeps into the p-type AlGaInP cladding layer, and the light is transmitted to both sides of the stripe. n, which has a lower refractive index than the AlGaInP cladding layer.
The AlGaInP or AlInP type confinement layer allows light to be efficiently confined and guided even in a direction parallel to the active layer. In addition, as mentioned above, the light is transmitted to p-type Al
Since the p-type AlGaInP cladding layer largely seeps into the GaInP cladding layer, the thickness of the p-type AlGaInP cladding layer can be increased to obtain the effect of confinement by the refractive index, so that punch-through is less likely to occur and leakage current is reduced. moreover,
Since the light largely seeps into the p-type AlGaInP cladding layer, the light emission spot becomes large in the direction perpendicular to the active layer, and the light is confined by the n-type AlInP confinement layer, so the light emission spot in the direction parallel to the active layer becomes small. Become. Therefore, the radiation angle of light from the end face becomes close to a circle.

Further, in the manufacturing method of means (3), crystal growth is performed twice and selective growth is not required. Furthermore, since the width of the stripes can be made narrower than in the conventional example, the radiation angle of light from the end face can be made closer to a circle.

Example Hereinafter, the present invention will be explained based on examples.

FIG. 1 shows schematic cross-sectional structural diagrams in each manufacturing process of an AlGaInP semiconductor laser according to an embodiment of the present invention. First, as shown in FIG. 1(a), for example, (100)
An n-type AlInP cladding layer 102 (for example, a carrier density of 5×
10"cm-3 thickness 1μm), Ga I nP active layer 1
03 (for example, thickness 0.07 μm), p-type AlGaInP
Cladding layer 104 (for example, X=0.6, carrier density 1
×10”crrr3 thickness 0.2μm), n-type AI I
nP confinement layer 105 (e.g. carrier density 3×10”
cm-” thickness 0.5 μm), p-type Ga I nP protective layer 106 (e.g. carrier density 5×10” cm-”
0.2 μm thick) is lattice-matched to the n-type GaAs substrate 101 by MO-VPE, and crystals are grown sequentially.

Next, 5iO2H10 was deposited and patterned on the surface.
7 as a mask, for example, a width of 3 in the <011> direction.
A p-type Ga1nP protective layer 106 is etched on the μm stripe by, for example, RIE using CCIJ gas,
Furthermore, the n-type AlInP confinement layer 105 is coated with, for example, HCl.
When etching is performed with a mixed solution of HaP Oa=1:10, grooves 10 are formed as shown in FIG. 1(b). In this embodiment, since the stripe grooves 10 are formed in the <011> direction, the n-type AlIn on both sides of the stripe
The P confinement layer 105 is etched into a forward mesa shape.

Next, after removing the 5i02 film 107, the entire surface is covered with p-type AlGa.
InP buried layer 108 (for example, x = 0.6, carrier density l x 101" cm -" thickness 0.5 μm), p
type GaInP buffer layer 109 (for example, carrier density 3
x10"cm-" thickness 0.2μm) and p-type Ga
As cap layer 110 (e.g. carrier density 5×10”
cm-'' thickness 2 μm) is sequentially grown using the MOVPE method.Finally, a p-side ohmic contact electrode 111 made of Cr/Au is formed on the front surface, and the back surface is polished and etched to make the substrate thinner. G e
When the n-side ohmic contact electrode 112 made of /N i /A u is formed, an AlGaInP semiconductor laser according to an embodiment of the present invention is completed as shown in FIG. 1(C).

Note that in the embodiment of the present invention described above, n-type AlGaInP having a lower refractive index than the p-type AlGaInP cladding layer 104 may be used instead of the n-type AlInP confinement layer 105.

The feature of the embodiment of the present invention described above is that structurally, the refractive index of the n-type AlInP cladding layer 102 is lower than the refractive index of the p-type AlGa1nP cladding layer 104, as shown in FIG. 2(a). As shown, the light largely seeps toward the p-type AlGaInP cladding layer 104. FIG. 2(b) compares the light intensity distribution of the guided mode in the direction parallel to the stripes between the conventional example and the above-described embodiment of the present invention.

As shown in FIG. 2(b), the AlInP layer 105 has a lower refractive index than the AlGaInP cladding layer 104 provided on both sides of the stripe.
It can be seen that light can be efficiently confined and guided even in directions parallel to the . Moreover, as mentioned above, the light is transmitted to p-type AlGaIn.
Since the p-type AlGaInP cladding layer 104 can be made thicker to obtain the confinement effect due to the refractive index, bunch-through is less likely to occur. The current will decrease. Furthermore, the light is applied to the p-type AlGaInP cladding layer 1.
04, the light emitting spot becomes large in the direction perpendicular to the active layer, and the light is confined by the n-type AlInP confinement layer 105, so the light emitting spot in the direction parallel to the active layer becomes small. FIG. 2(C) compares the far-field images of a conventional example and an embodiment of the present invention. In the present invention, the emission angle becomes small in the direction perpendicular to the active layer because the emission spot becomes large, and the emission angle becomes large in the direction parallel to the active layer because the emission spot becomes small. Therefore, the far-field image becomes close to a circle as shown in FIG. 2(C).

Furthermore, since the refractive index waveguide is stably guided both in the direction parallel to and perpendicular to the Ga I nP active layer 103, the astigmatism difference is also much smaller than that of the laser shown in the conventional example.

Therefore, since the n-type AlInP confinement layer 105 is for optical confinement using the refractive index, the p-type AlInP confinement layer 105
Of course, it may be an n-type AlGaInP layer or an n-type AlGaAs layer having a higher Al composition and lower refractive index than the P cladding layer 104.

Further, in the manufacturing method of one embodiment of the present invention, crystal growth is performed twice and selective growth is not required. Furthermore, since the width of the stripes can be made narrower than in the conventional example, the radiation angle of light from the end face can be made closer to a circle.

In addition, in the description of one embodiment of the present invention described above, p-type Al
A p-type GaInP layer is formed on the surface of the GaInP buried layer 108.
Although the P buffer layer 109 has been described with respect to the layered structure 09, this is composed of the p-type AlGaInP buried layer 108 and the p-type G
a I Interface with nP buffer layer 1゜9 or p-type G
It is inserted in order to reduce the current barrier effect due to the spike in the valence band that exists at the heterojunction interface between the a I nP buffer layer 109 and the layered 09As cap layer 110, and the If the carrier density is increased, the p-type GaInP buffer layer 109 is unnecessary.

Furthermore, it goes without saying that the conductivity types may be reversed in the embodiment of the present invention described above. However, in the case of the conductivity type described in the embodiment of the present invention, the n-type AlInP cladding layer 102 is an indirect transition type, and ΔEc is AlG with x=0.6.
Although it is smaller than aInP, ΔEv is larger, so the height of the barrier becomes higher for holes injected from the p-type AlGa1nP cladding layer 104 to the GaInP active layer 103, and the leakage current becomes smaller.

In addition, in the conventional example, the n-type AlGaInP cladding layer 3
02, an n-type AlInP cladding layer is used, and an n-type AlInP cladding layer is used instead of the n-type GaAs current blocking layer 307.
It goes without saying that the case where a P confinement layer is used is also similar to that described in the embodiment of the present invention.

Furthermore, in one embodiment of the present invention described above, p-type AlGaI
The AI composition X of the nP buried layer 108 is set to p-type AlGa1n.
When it is made smaller than the P cladding layer 104, the p-type AlG
The refractive index of the aInP buried layer 108 is p-type AlGaIn.
Since it is larger than the p-type AlGaInP cladding layer 104, it becomes more difficult for light to seep into the p-type AlGaInP cladding layer 104, so that the light radiation angle θ becomes smaller, and the radiation angle from the end face becomes closer to a circle.

Further, in an embodiment of the present invention, the same effect can be achieved even if a p-type AlGaAs buried layer is used instead of the p-type AlGaInP buried layer 108, and if the refractive index of the p-type AIGaAS buried layer is made larger than that of the p-type AlGaInP cladding layer 104. The light emission angle from the end face can be made close to a circle.

As described in detail, the present invention has the following effects.

The refractive index of the n-type AlInP cladding layer 102 is higher than that of the p-type A.
Since the refractive index is lower than that of the lGaInP cladding layer 104, the light largely seeps into the p-type AlGaInP cladding layer 104, and the AlGaInP cladding layer 104 provided on both sides of the stripe
n-type AlIn with a lower refractive index than the P cladding layer 104
The P confinement layer 105 can efficiently confine and guide light even in a direction parallel to the active layer, and has the effect of lowering the oscillation threshold.

In addition, as mentioned above, since light largely seeps into the p-type AlGaInP cladding layer 104, it is necessary to obtain the confinement effect by the refractive index.
Since the thickness can be increased, bunch-through is less likely to occur and leakage current is reduced. Furthermore, since the light largely seeps into the p-type AlGaInP cladding layer 104, the light is confined by the active n-type AlInP confinement layer 105, so that the light emitting spot in the direction parallel to the active layer becomes smaller. Therefore, the radiation angle of light from the end face becomes close to a circle. It also has this effect.

Furthermore, when the conductivity type of the AlInP cladding layer 102 is n type, there is an effect that leakage of holes injected into the GaInP active layer 103 can be prevented.

Further, the manufacturing method requires two crystal growths and does not require selective growth. Furthermore, since the width of the stripes can be made narrower than in the conventional example, there is an effect that the radiation angle of light from the end face can be made closer to a circle.

[Brief explanation of drawings]

1(a) to 1(C) are structural cross-sectional schematic diagrams in each manufacturing process of a semiconductor laser according to an embodiment of the present invention, and FIG. 2(a)
), (b) is a diagram showing the light intensity distribution of the waveguide mode in one embodiment of the present invention and a comparative distribution with the conventional one,
) is a comparison diagram of far-field patterns, and FIGS. 3(a) to 3(e) are schematic cross-sectional views of the structure in each manufacturing process of a conventional transverse mode control type AlGaInP semiconductor laser. 101**en type GaAs substrate, 102---n type Al
InP cladding layer, 103**eGaInP active layer, 1
04-...p-type AlGaInP cladding layer, 105...
・N-type AlInP confinement layer, 107...p-type AIG
, aInP buried layer, 109-.phi.p type GaAs cap layer.

Claims (6)

[Claims] (1) Having an AlInP cladding layer of one conductivity type, an active layer, and an AlGaInP cladding layer of the other conductivity type on a GaAs substrate, and the AlGaInP cladding layer of the other conductivity type on both sides of the stripe.
The other conductivity type AlGaInP is formed on the surface of the nP cladding layer.
One conductivity type AlInP with a lower refractive index than the cladding layer,
A semiconductor laser characterized in that an AlGaInP or AlGaAs confinement layer is formed. (2) The semiconductor laser according to claim 1, wherein an AlGaInP buried layer of the other conductivity type is formed on the surface of the AlGaInP cladding layer of the other conductivity type on the stripe. (3) The semiconductor laser according to claim 2, wherein the Al composition of the AlGaInP buried layer of the other conductivity type is smaller than the Al composition of the AlGaInP cladding layer of the other conductivity type. (4) The semiconductor laser according to claim 1, wherein an AlGaAs layer of the other conductivity type is formed on the surface of the AlGaInP cladding layer of the other conductivity type on the stripe. (5) One conductivity type AlInP cladding layer is formed on the GaAs substrate, and the other conductivity type AlGaInP cladding layer is thickened at the active layer and the stripe portion, and the surface of the other conductivity type AlGaInP cladding layer is formed on both sides of the stripe. A semiconductor laser comprising an AlInP, AlGaInP, or AlGaAs confinement layer of one conductivity type having a lower refractive index than the AlGaInP cladding layer of the other conductivity type. (6) The semiconductor laser according to any one of claims 1 to 5, characterized in that one conductivity type is n type and the other conductivity type is p type (7) On a GaAs substrate One conductivity type AlInP cladding layer and active layer, the other conductivity type AlGaInP cladding layer and one conductivity type AlInP.
Step of forming a confinement layer, the one conductivity type AlInP
The method further comprises a step of selectively etching the confinement layer to form striped grooves, and a step of forming an AlGaInP buried layer of the other conductivity type on the stripe grooves and the surface of the other conductivity type AlGaInP cladding layer. A method for manufacturing a semiconductor laser characterized by: