JPH0319293A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To confine a light in a direction parallel to an active layer and to guide the light by forming AlGaInP or AlInP layers having smaller refractive index than that of an AlGaInP clad layer at both sides of a stripe. CONSTITUTION:An n-type AlGaInP clad layer 102, a GaInP active layer 103, a P-type AlGaInP clad layer 104, and a P-type GaInP buffer layer 105 are grown on an n-type GaAs substrate 101. Then, with an SiO2 film 106 as a mask the layers 105, 104 are etched to form the layer 104 in an inverted mesa shape. Then, with the layer 106 as a mask a P-type AlInP layer 107 and a GaAs layer 108 having lower refractive index than that of the layer 104 are crystalline- grown. Thereafter, an SiO2 film 109 is formed in a stripe state on the layer 108, with the film 109 as a mask the layers 108, 107 are etched to form the layer 107 in an inverted mesa state. Then, with the film 109 as a mask an n-type GaAs current block layer 110 is formed. Thus, a light is confined in a direction parallel to the layer 103 to be guided, and its heat dissipation is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor laser which is made of a material such as AlGaInP and has a controlled transverse mode, and a method for manufacturing the same. Semiconductor lasers are attracting attention as light sources for use in optical discs, laser printers, barcode leagues, etc. Among them, semiconductor lasers that use GaAs as a substrate and are lattice-matched to it. sI n*. s
P (abbreviated as GaInP in the following explanation) or (
A I XG a I-X) s. s I n s. 6
A double heterojunction semiconductor laser having P (abbreviated as AIGaIrrP in the following explanation) active JiLAAlGaInP as a cladding layer is lattice matched to GaAs7-9
Since it can emit light with the shortest wavelength among the group compound semiconductors, it is a promising material for visible light semiconductor lasers. Figure 3 shows a cross section of a conventional transverse mode control type AlGaInP semiconductor laser during each manufacturing process. First, as shown in Fig. 3(a), the structure is shown as G, :, (100
) on the surface of an n-type GaAs substrate 301 whose main surface is n
type AlGaInP cladding layer 302, Ga I nP active layer 303, p type AIGa I nP cladding layer 304
, p-type Ga I nP buffer 7 layers 305 are MO-VPE
The crystallization process is carried out sequentially using the organic metal vapor phase control method.Next
Side film 3 formed in a stripe shape in the <011> direction
06 as a mask, the p-type GaInP buffer layer 305 is etched by, for example, RIE (reactive ion etching) using CC Ia gas, and then the p-type AlGa
For example, when the InP cladding layer 304 is etched with hot concentrated sulfuric acid at 40° C., as shown in FIG. After removing the S j OtM 30 6 used as a mask for selective crystal lengthening, a p-type GaAs contact layer 308 is formed on the entire surface by MO-V as shown in FIG. 3(c).
When the crystal is lengthened by the PE method, stripes are embedded as shown in Figure 3(d).Finally, Au/Zn/
A p-type ohmic contact layer 309 made of Au is formed, the back surface is polished and etched to make the substrate thin, and an n-type ohmic contact layer 310 made of Au-Ge/Ni/Au is formed.
As shown in figure (e), the conventional transverse mode control type AlGa
Although InP-based semiconductor lasers are perfect, in this conventional laser, the n-type GaAs current blocking layer 307 electrically plays the role of a current confinement layer, and for light, it acts as a p-type AlG
The refractive index is thicker than that of the aInP cladding layer 304 <GaI
Since the nP active layer 303 absorbs the emitted light, it plays the role of an absorption type anti-waveguide layer. 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). Because the gain waveguiding property remains strong, the wavefront of the guided light in the direction parallel to the active layer is bent.
As a result, there is a problem that a large astigmatism difference is created.Therefore, the conventional transverse mode control type Al
When trying to apply GaInP semiconductor lasers to optical equipment, the scope of application is limited because a normal convex lens cannot convert the laser beam into parallel light or focus it on a single point. −． n-type GaAs
Since the current blocking layer absorbs the light emitted by the active layer, there is a loss for the light that is guided through the active layer, and the oscillation threshold increases by this loss. The present invention provides a means for controlling such a conventional transverse mode control type AlGaI
Things that have been done to solve the problems in nP semiconductor lasers (1) One conductivity type AlGaInP cladding layer is formed on a GaAs substrate. and the other conductivity type A on both sides of the stripe.
The other conductivity type AlG is formed on the surface of the lGaInP cladding layer.
AlGaInP, which has a lower refractive index than the aInP cladding layer
Alternatively, a structure in which an AlInP layer is formed in a pair of stripes and a current blocking layer of one conductivity type is further formed on the outside thereof (2) GaA with (100) as the main surface
One conductivity type AlGaInP cladding on the s substrate.The other conductivity type Al is thick in the active layer and the stripe portion formed in the <01> direction and has an inverted mesa-shaped cross section.
the other conductivity type AlGa having a GaInP cladding layer;
The other conductivity type AlG is formed on the reverse mesa surface of the InP cladding layer.
AlGaInP, which has a lower refractive index than the aInP cladding layer
Alternatively, an IL structure in which an AlInP layer is formed and a current blocking layer of one conductivity type is further formed on the outside thereof.
(3) One conductivity type AlGaInP cladding layer is formed on the GaAs substrate, and the other conductivity type AlGaInP cladding layer is thicker in the active layer and stripe portions.
Al having a lower refractive index than the other conductivity type AlGaInP cladding layer is formed on both surfaces of the stripe of the P cladding layer.
A GaInP or AlInP layer is formed in a pair of stripes, and one side is formed on both sides of the stripes of the other conductivity type AlGaInP cladding layer on the outside thereof and in the region where the low refractive index AlGaInP or AlInP layer is not formed. A structure in which a conductivity type current blocking layer is formed JliL (4) One conductivity type AlGaInP is deposited on a GaAs substrate having a (100) main surface.
Step of forming an active layer and an AlGaInP cladding layer of the other conductivity type;
a step of etching the nP cladding layer so that it has a striped inverted mesa shape in the <011> direction and is thicker in the striped portion; etching the other conductivity type AlGaInP layer having the inverted mesa shape; selectively forming an AlGaInP or AlInP layer having a lower refractive index than the other conductive type AlGaInP cladding layer on the side surface;
selectively forming a current blocking layer of one conductivity type on the surface of the nP cladding layer, and the other conductivity type AlGa
AlG with low refractive index on stripe of InP cladding layer
According to the above-mentioned structure of the present invention, the present invention can be applied to a structure including a step of forming a contact layer of the other conductivity type on the surface of the aInP or AlInP layer and the surface of the current blocking layer of the one conductivity type. In structures (1) and (2), which have the following effects, AlG, which has a lower refractive index than the AlGaInP cladding layer, is formed on both sides of the stripe.
Since an aInP or AlInP layer is formed, it is possible to confine and guide light even in a direction parallel to the active layer, and since a one conductivity type GaAs current blocking layer is formed on the outside of the active layer, an AlGaInP or AlInP layer can be formed.
Although heat dissipation is better than when using an InP layer as a current blocking layer, AlGaIn on both sides of the stripe
If the AlGaInP or AlInP layer, which has a smaller refractive index than the P cladding layer, is of the other conductivity type, it can confine and guide light even in the direction parallel to the active layer; Current is also injected into the active layer from the conductive AlInP layer, so even if the refractive index of the active layer decreases due to current injection, it has little effect on the waveguide mode.1 Therefore, in the directions parallel and perpendicular to the active layer. Since both the refractive indexes are guided stably, the astigmatism difference is much smaller than that of the laser shown in the conventional example. Small AlGaIn
Because the P or AlInP layer is provided, the guided light is completely confined in the stripe, and the emitted light has a small astigmatism difference.Moreover, the area where the AlGaInP or AlInP layer with a small refractive index is embedded is In other regions, the same gain waveguide principle as in the conventional example remains, so the longitudinal mode of laser oscillation becomes a multimode. It is also possible to perform certain actions. In the manufacturing method (4), the other conductivity type Al having a lower refractive index than the cladding layer formed on the side surface of the reverse mesa is used.
The side surfaces of the GaInP or other conductive type AlInP layer also have an inverted mesa shape, and the width can be made narrower. Therefore, the stripe width for refractive index waveguide can be made narrower, and the stripe width for current injection can also be made narrower at the same time. Although single transverse mode oscillation can be obtained with a low threshold current, the present invention will be explained below with reference to the examples. A schematic cross-sectional structure diagram for each manufacturing process is shown. First, as shown in FIG. 1(a), for example, n-type AlG
aInP cladding layer l02 (e.g. x=0.6, carrier density 5X10'▼cm-" thickness l, um), Ga
InP active layer l03 (for example, thickness 0.2 μm), p
Type A] GaInP cladding layer l04 (for example x =
0.6, carrier density 1xlo"cm" thickness 0.7
μm), p-type GaInP buffer layer 105 (for example, carrier density 3xlO"Cm-" thickness 0.3 μm)
) is lattice-matched to the n-type GaAs substrate 101 using the MO-VPE method, and the crystals are sequentially lengthened.
Seven p-type GaInP buffer layers 10 using the film 106 as a mask
5 by RIE using, for example, CC 14 gas, and further etching the p-type AlGaInP cladding layer 104 with hot concentrated sulfuric acid at 40° C. for 4 minutes, so that the p-type AlGaInP cladding layer 104 has a thickness of 0 on the outside of the stripe. If .2μm remains, Figure 1(b)
This implementation is shown in the figure below. In the example the stripe is <0
Since it is formed in the 11> direction, the p on both sides of the stripe
Although the type AlGaInP cladding layer 104 is etched into an inverted mesa shape, the SiO2 film 106 is then selectively used as a mask for a certain length to form a p-type AlInP layer 107 with a refractive index lower than that of the p-type AlGaInP cladding layer 104 (for example, a carrier density of 5x10''c). m-” thickness 0.5 μm> and p-type GaAs layer 108 (e.g. carrier density 5×
lO"cm-" Thickness 0. 3μm) as shown in Figure 1(C).Next, p-type GaAs
For example, Sj is formed in a stripe shape with a width of 8 μm on the surface of the layer l08.
Forming an ot film 109 Using the L SiO2 film 109 as a mask, the p-type GaAs layer 108 is coated with, for example, H! SOa: Ha
re: H*O=1: l: 3 with a mixture of 1 and 0
After etching for 0 seconds, the p-type AlInP layer 107 is further etched with hot sulfuric acid at 30°C, as shown in Fig. 1(d).
As shown in , a p-type AlInP layer 107 is formed in a reverse mesa shape on the side surface of the p-type AlGaInP cladding layer 104 in a reverse mesa shape. When the crystal is lengthened, a p-type GaAs contact layer 1 is formed on the entire surface after removing the Sins film 109.
11 (for example, carrier density 5xlO'●C m-'', thickness 3 μm) is crystallized by MO-VPE method.
As shown in Figure <f>, even after the stripes are embedded, a p-type ohmic contact electrode 112 made of Cr/Au is finally formed on the front surface, and the back surface is polished and etched to thin the substrate, and then Au-Ge/Ni/ When the n-type ohmic contact electrode 113 made of Au is shaped, it becomes A of the first embodiment of the present invention, as shown in FIG. 1(g).
In the first embodiment of the present invention described above, the p-type AlInP semiconductor laser is perfect.
P-type AlGaInP cladding layer 1 instead of P layer 107
It is also possible to use p-type AlGaInP, which has a refractive index lower than that of 04.The feature of the first embodiment of the present invention described above is that, structurally, there is a p-type AlGaInP cladding layer 104 on both sides of the stripe, which has a refractive index lower than that of the p-type AlGaInP cladding layer 104. Since the p-type AlGaInP or p-type AlInP layer 107 with a small refractive index is formed, it is possible to confine and guide light even in the direction parallel to the active layer. Since current is injected into the active layer from 107 as well, even if the refractive index of the active layer decreases due to current injection, the refraction between the inside and outside of the stripes of the AlGaInP cladding layer 104 (the region where the p-type AlInP layer 107 is formed) is maintained. Since the difference in refractive index hardly changes, it has little effect on the waveguide mode.Therefore, since the refractive index wave is guided stably in both parallel and perpendicular directions to the active layer, the astigmatism difference is also lower than in the conventional laser. Even though it is much smaller, the thermal conductivity of the p-type AlInP layer buried on both sides of the stripe is 0. 09W/cm-deg and Ga
In the first embodiment of the present invention, the p-type AlInP layer is buried only in the trenches on both sides of the stripe, and the outside is The core of the n-type GaAs current blocking layer is
The p-type AlInP layer does not deteriorate the dissipation of heat generated in the vicinity of the active layer.Furthermore, in the first embodiment of the present invention described above, the p-type GaAs contact layer 11
When crystal No. 1 is made to have a certain length, the surface becomes flat and the contact area with the p-type ohmic contact electrode 112 is wide, making it easy to lower the contact resistance. The feature is that the side surface of the p-type AlGaInP or p-type AlInP layer 107, which has a lower refractive index than the p-type GaInP cladding layer 104 formed on the side surface of the reverse mesa, also has a reverse mesa shape.
Therefore, it is possible to narrow the stripe width of refractive index guiding and simultaneously narrow the stripe width of current injection. Obtaining single transverse mode oscillation with a low threshold current. A second embodiment of the present invention is shown in FIG. 2. In FIG. 2, 201 is an n-type GaAs group K, 202 is an n-type AlGaInP clad #203 is a GaInP active layer, and 204 is a p-type AlG
aInP cladding 205 is p-type GaInP buffer 207 is p-type AlInP 210 is n-type GaAs
Current block 凰 211 is py! :! GaAs contact #2l2 is p-side ohmic contact voltage IIL21
3 is the n-side ohmic contact electrode. In Fig. 2, the cross-sectional structure of the laser is different between region A and region B.
In area A, the cross-sectional structure is the same as that of the first embodiment of the present invention, and in area B, the cross-sectional structure is the same as the conventional example. Since the p-type AlInP layer 207 having a lower refractive index than the p-type AlGaInP cladding layer 204 is provided, the guided light is completely confined in the stripes, so that in region A, the waveguide light is completely confined in the stripes, and therefore in the direction parallel to and perpendicular to the active layer. Since the light is guided by the refractive index, the astigmatism difference of the light emitted from region A is reduced.Moreover, in region B, the same gain waveguide effect as in the conventional example remains, so the longitudinal mode of laser oscillation becomes multimode. As a result, the semiconductor laser according to the second embodiment of the present invention can operate stably without being affected much by disturbances such as returned light. The semiconductor laser of this example can be manufactured by combining the conventional example and the first embodiment of the present invention. p-type GaInP cladding layer 1
p-type Al with a lower refractive index than 04 (or 204)
Instead of the GaInP or p-type AlInP layer 107 (or 207), a semi-insulating AlGaInP layer, a semi-insulating AlInP layer, an n-type AlGaInP, or an n-type AlInP layer may be formed. The AlGaInP or AlInP layer plays the role of confining light in the stripe due to its refractive index and blocking current flowing to areas other than the stripe. The block layer part is also semi-insulating or n-type AlGaInP or AlInP.
The thermal conductivity of the 4tAlInP layer is 0.09W/cm-deg, which is 0.54W of GaAs.
If the value is lower than /am-deg, heat dissipation will worsen. In the present invention, since the n-type GaAs current blocking layer 1lO (or 2lO) is provided over almost the entire surface on both sides of the stripe, heat dissipation is good. p-type GaI on the surface of the type AlGaInP cladding layer
The force t explained for the structure forming the nP layer is p
In order to reduce the current barrier effect due to spikes in the valence band existing at the heterojunction interface between the AIGaI nP cladding layer and the p-type GaInP layer or the interface between the p-type GaInP layer and the p-type GaAs layer. However, if the carrier density of each of these layers is increased, the p-type GaInP layer may not be necessary.
It goes without saying that the conductivity type may be reversed in the second embodiment. Furthermore, in the first and second embodiments of the present invention, the stripe orientation is in the <01th block> direction. However, when the orientation of the stripes is set in the <011> direction, the stripes become trapezoidal normal mesas instead of inverted mesas.It goes without saying that the same effect can be obtained as described above. As described above, the present invention has the following effects.In the first embodiment of the present invention, A is provided on both sides of the stripe.
AlGa has a lower refractive index than the lGaInP cladding layer.
Since an InP or AlInP layer is formed, it is possible to confine and guide light even in the direction parallel to the active layer, and since an n-type GaAs current blocking layer is formed on the outside, it is possible to confine and guide light in the direction parallel to the active layer. Although heat dissipation is better than when used as a current blocking layer, AlGaInP or Al has a lower refractive index than the AlGaInP cladding layers on both sides of the stripe.
When the InP layer is p-type, light can be confined and guided in the direction parallel to the active layer, and current can also be injected into the active layer from the p-type AlGaInP or p-type AlInP layer, which has a small refractive index. Therefore, even if the refractive index of the active layer decreases due to current injection, the effect on the waveguide mode is small (
Therefore, since the refractive index wave is stably guided in both directions parallel and perpendicular to the active layer, the astigmatism difference is much smaller than that of the conventional laser. The side surfaces of the p-type AlGaInP or p-type AlInP layer, which has a lower refractive index than the cladding layer, also have an inverted mesa shape, and the width can be made narrower. In the second embodiment of the present invention, a cladding layer is formed on both sides of the stripe in the vicinity of the emission end facet of the laser. A with a small refractive index
Because the lGaInP or AlInP layer is provided, the guided light is completely confined in the stripe, and the emitted light has a small astigmatism difference. In other regions, the same gain waveguide effect as in the conventional example remains, so the longitudinal mode of laser oscillation becomes a multimode. Even if you can perform certain actions,

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are the first and second parts of the present invention, respectively.
The structural cross-sectional diagram of each manufacturing process of the semiconductor laser according to the embodiment is as shown in Fig. 3.
In the structural cross-sectional diagrams of each manufacturing process of a P-based semiconductor laser, lO1, 201.301... n-type GaAs base K 1
0 2, 2 0 2, 3 0 2...n
Type AlGaInP clad ML 103, 203
, 303--GaInP activity JiiiL 104
, 204, 304-"p-type AlGaInP clad ML107,207...p-type AlInPJtiL
110,210,307...n-type GaAs current block ! l1, 211, aos---p-type GaAs=:l contact 凰

Claims (6)

[Claims] (1) A GaAs substrate has an AlGaInP cladding layer of one conductivity type, an AlGaInP cladding layer of the other conductivity type that is thicker in the active layer and the stripe portion, and the surface of the AlGaInP cladding layer of the other conductivity type on both sides of the stripe. AlGaInP or AlInP having a lower refractive index than the other conductivity type AlGaInP cladding layer.
A semiconductor laser characterized in that the layers are formed in a pair of stripes, and a current blocking layer of one conductivity type is further formed on the outer side of the layers. (2) One conductivity type AlGaInP cladding layer, active layer and <01@
The other conductive type AlGaInP cladding layer has a thick stripe portion formed in the 1@> direction and has an inverted mesa shape in cross section, and the other conductive type AlGaInP is formed on the reverse mesa surface of the other conductive type AlGaInP cladding layer. AlGaInP or Al, which has a lower refractive index than the cladding layer
A semiconductor laser comprising an InP layer and a current blocking layer of one conductivity type formed outside the InP layer. (3) A GaAs substrate has an AlGaInP cladding layer of one conductivity type, an AlGaInP cladding layer of the other conductivity type whose thickness is thicker in the active layer and the stripe portion, and the AlGaInP cladding layer of the other conductivity type is formed in a region near the laser beam emission end face.
Al having a lower refractive index than the other conductivity type AlGaInP cladding layer is formed on both surfaces of the stripe of the P cladding layer.
A GaInP or AlInP layer is formed in a pair of stripes, and one side is formed on both sides of the stripes of the other conductivity type AlGaInP cladding layer on the outside thereof and in the region where the low refractive index AlGaInP or AlInP layer is not formed. A semiconductor laser characterized in that a conductive current blocking layer is formed. (4) AlGaInP or AlInP with low refractive index
4. A semiconductor laser according to claim 1, wherein the conductivity type of the layer is the other conductivity type. (5) Claim 4 characterized in that the other conductivity type contact layer is formed on the other conductivity type AlGaInP having a lower refractive index or on the other conductivity type AlInP layer.
Semiconductor laser described in section. (6) A step of forming one conductivity type AlGaInP cladding layer, an active layer, and the other conductivity type AlGaInP cladding layer on a GaAs substrate having (100) as a main surface, the step of forming the other conductivity type AlGaInP cladding layer <01@1@> A step of etching the material so that it has an inverted mesa shape with stripes in the direction and is thicker at the stripe portions;
AlGaInP or AlIn having a lower refractive index than the other conductivity type AlGaInP cladding layer is formed on the reverse mesa side surface of the other conductivity type AlGaInP layer having the reverse mesa shape.
selectively forming a P layer, selectively forming a current blocking layer of one conductivity type on the surface of the other conductivity type AlGaInP cladding layer exposed on the surface, and on the stripe of the other conductivity type AlGaInP cladding layer, A method for manufacturing a semiconductor laser, comprising the step of forming a contact layer of the other conductivity type on the surface of the AlGaInP or AlInP layer having a low refractive index and the surface of the current blocking layer of the one conductivity type.