JPH03225988A - Light-emitting element provided with active waveguide and its manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light emitting device having an active waveguide, particularly a semiconductor laser, a superluminescence diode, and a method for manufacturing the same.

[Prior art] Conventionally, a light emitting device with a gain waveguide structure, which is advantageous for obtaining a stable and practical light emitting device, has been developed, in which a trapezoidal mesa stripe is formed on a semiconductor substrate and epitaxial growth is performed on the mesa stripe, which is advantageous for obtaining a stable and practical light emitting device. The method is known, for example, in Japanese Patent Publication No. 136715.

Two methods have been proposed for this.

One is to form a trapezoidal mesa stripe on the surface of a semiconductor substrate, grow a first epitaxial layer on the substrate surface including the trapezoidal mesa, and then grow the first epitaxial layer so that the entire mesa stripe surface is exposed. The epitaxial layer is partially removed, and after this removal, a second epitaxial layer is grown on the remaining first epitaxial layer and the exposed mesa surface.

The other method is to form the same (trapezoidal mesa/stripe) on the semiconductor substrate surface, and then sequentially grow the first and second epitaxial layers on the substrate surface including the trapezoidal mesa/stripe. The first and second epitaxial layers are partially removed so that the surfaces are exposed.

The difference between the two methods is that the entire mesa/stripe surface is exposed after growing the first epitaxial layer, or the entire mesa/stripe surface is exposed after growing the first and second epitaxial layers.

However, both have trapezoidal mesa stripes and wide tops, so they have the following points in common: In other words, when growing an epitaxial layer over the entire surface of a substrate, it is necessary to make the epitaxial layer grown on the top surface thinner.
It is inevitable that an epitaxial layer will grow on top of the stripe. Therefore, when exposing the entire mesa/stripe surface, even if part of the epitaxial layer is removed by etching, etc., part of the epitaxial layer near the mesa/stripe will also be removed, and the area near the mesa/stripe after treatment will be removed. The surface cannot be made flat.

[Problems to be Solved by the Invention] In the above method in which trapezoidal mesa stripes are formed on a semiconductor substrate and epitaxial growth is performed thereon, a current is applied to the mesa stripes 10 as shown in FIG. 2(a), for example. When the barrier layer 2 is epitaxially grown, a trapezoidal mesa/
Unless the top surface of the stripe 1o is made extremely narrow, the current barrier layer 2 is also epitaxially grown on the top surface.

Typically, the current barrier layer 2 on the trapezoidal mesa stripe 10 is
It is removed by melt-back processing or chemical etching, but at this time, part of the current barrier layer 2 near the mesa stripe 10 is also removed as described above, so the surface near the mesa stripe 10 after processing is It cannot be made flat, and the mesa stripe 10 remains in a convex shape, as shown in FIG. 2(b). Therefore, a cladding layer, an active layer, etc. are epitaxially grown on the remaining convex surface (convex portion).

Conventionally, when these layers were formed on a surface that remained in a convex shape using a liquid phase epitaxial growth method (LPE method), there was not much problem.

In addition, when forming a GaA12As layer on a conventional GaAs substrate, GaAs and GaAL6. Since the lattice constants of s are almost the same, epitaxial growth on such convex portions did not impair crystallinity.

However, in recent years, metal-organic pyrolysis vapor phase epitaxy (MO
For the technology of vapor phase growth method and molecular beam growth method (hereinafter simply referred to as vapor phase growth method etc.) such as VPE method (MOCVD method) and molecular beam epitaxial growth method (MBE method), The formation of crat layers, active layers, etc. using these vapor phase growth methods has been carried out. Furthermore, recently, semiconductor lasers that oscillate at a wavelength around 67 Onm have been developed.
InGaP, InGaAQP-based mixed crystals have been manufactured by epitaxial growth on GaAs substrates using the MOVPE process, which generally suffers from the problems associated with In.

InGaP, InGaAQ using MOV P E method
When growing a P-based mixed crystal, etc., it is necessary to simultaneously and strictly control the composition ratio and lattice constant, unlike in the case of GaAijAs-based materials. It is known that when such a mixed crystal is grown on a surface having the above-mentioned convex portions, the lattice constant of that portion is shifted and the crystallinity is impaired. This has made it difficult to mass-produce stable and highly reproducible semiconductor lasers.

This can also be said about MBE, which is difficult for P systems.

Also, is it possible to use a superlattice structure in the active layer, etc.? Even when such a structure is formed, the structure is disordered at the convex parts and the crystallinity decreases, making it difficult to obtain a high-quality superlattice structure. It is difficult to obtain.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to use a mesa-strive structure which is advantageous for obtaining a stable and practical semiconductor laser, while also forming a flat rad layer and a layer by vapor phase growth. An object of the present invention is to provide a light emitting device having a novel active waveguide on which an active layer and the like can be formed.

Another object of the present invention is to provide a method for manufacturing a light emitting device having an active waveguide, which is easy to manufacture and has excellent reproducibility and stability, by eliminating the drawbacks of the prior art described above. be.

[Means for Solving the Problems] A light emitting device having an active waveguide of the present invention has a convex mesa.
In a semiconductor substrate having a first conductivity type formed on the surface of a stripe, a convex mesa stripe is formed in a pointed shape, and a height approximately the same as that of the mesa stripe is formed on the semiconductor substrate surface at least in the periphery of the mesa stripe. An epitaxial layer such as a current barrier layer having a second conductivity type, or an epitaxial layer such as a current barrier layer having a second conductivity type of At least a cladding layer and an active layer having a conductivity type are provided. The epitaxial layer having the second conductivity type and having approximately the same height as the mesa stripe may be provided to extend further outward than the periphery of the mesa stripe. Note that it is conceivable to flatten at least the peripheral area, including mesas and stripes, not at the time of forming the epitaxial layer, but after that, it is difficult to do so, and it also complicates the process. There's no real advantage.

In addition, in the method of manufacturing a light emitting device having an active waveguide of the present invention, a mesa stripe with a convex cross section is formed on the surface of a semiconductor substrate, and the mesa stripe is etched with a pointed cross section by chemical etching that is commonly used. After forming an epitaxial layer such as a current barrier layer to approximately the same height as the mesa stripe on the surface of the semiconductor substrate at least in the periphery of the mesa stripe, this surface is then formed into -
A chemical etching or melt-back process is used in the shell to expose a portion of the mesa stripe, on which a cladding layer and an active layer are grown at least epitaxially.

In the above manufacturing method, in order to form the mesa stripe into a pointed shape, the mesa stripe with a convex cross section formed on the surface of the semiconductor substrate is heated using phosphoric acid, hydrogen peroxide, etc.
It is preferable to form the top surface of the mesa stripe into a pointed shape by chemically etching with a water-based etchant or a sulfuric acid/hydrogen peroxide/water-based etchant.

Further, in order to grow the current barrier layer in the above manufacturing method, epitaxial growth is performed on the surface of the semiconductor substrate on which the mesa stripes are formed, and at least the peripheral portion of the mesa stripes is grown at approximately the same height as the mesa stripes.
It is also preferable to form the current barrier layer flatly.

Furthermore, in the above manufacturing method, in order to expose a part of the mesa stripe, the semiconductor substrate after epitaxially growing the current barrier layer is subjected to chemical etching or meltback treatment to expose at least the peripheral part of the mesa stripe. It is preferable to expose a portion of the mesa stripe without compromising flatness.

[Function] When a convex mesa stripe formed on a semiconductor substrate is formed into a pointed mesa stripe instead of one with a trapezoidal cross section, unlike the case where a mesa stripe with a trapezoidal cross section is used,
When an epitaxial layer such as a current barrier layer is formed at approximately the same height as the mesa stripe, the epitaxial layer formed at least in the peripheral portion including the mesa stripe becomes flat when the epitaxial layer is formed.

In this way, it is possible to flatten the epitaxial layer by making the mesa stripe into a pointed shape. Alternatively, it is formed by chemical etching using sulfuric acid, hydrogen peroxide, and water-based etchants.

In addition, if epitaxial growth is performed on a substrate on which pointed mesa stripes are formed under appropriate growth conditions, the surface of the semiconductor substrate at the periphery of the mesa stripes will be very flat and at the same height as the mesa stripes. An epitaxial layer grows.

By performing chemical etching or melt hacking on this flatly grown epitaxial layer, a part of the mesa stripe can be exposed without impairing the flatness of the surface after epitaxial growth. As a result, epitaxial layers having exactly the same height as the mesa stripes are arranged on both sides of the mesa stripes, and a structure in which the surface around the mesa stripes is flattened can be realized. Since the surface around the mesa stripe becomes flat, if a cladding layer or active layer is grown on it, the L
Flattening can be achieved not only by PE but also by vapor phase growth. Therefore, a high-quality crystal growth layer can be obtained, and a light-emitting element with excellent light-emitting characteristics and lifetime characteristics can be manufactured.

Furthermore, even when InGaP5 InGaAffP is grown on a substrate with mesa/stripe steps, deterioration in crystal quality due to lattice misalignment can be avoided.

Furthermore, by controlling the width of the flat portion of the epitaxial growth layer around the mesa stripe, it is also possible to create an index-guided semiconductor laser.

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

In this example, a p-type GaAs substrate is used as the semiconductor substrate, and InGaP, InGaA (2P system wavelength 670
Although this is an example of fabricating a nm semiconductor laser, it goes without saying that the present invention can also be achieved by using an n-type substrate, or by appropriately combining other substrates and other mixed crystal semiconductors.

First, a mesa stripe 10 whose cross section is a mold as shown in FIG. 1(a) is formed on a p-type GaAs substrate 1 using photolithography. When the substrate 1 on which the mesa stripes 10 have been formed is etched using a phosphoric acid/hydrogen peroxide/water-based etchant, the mesa stripes shown in FIG. 1(a) become pointed as shown in FIG. 1(b). The mesa stripe 10b can be formed into a mesa stripe 10b. As the etchant, a sulfuric acid/hydrogen peroxide/water based etchant may be used, but the phosphoric acid/hydrogen peroxide/water based etchant is superior in terms of controllability and stability.

Next, an n-type current barrier layer is epitaxially grown on this substrate 1 using the LPE method. At this time, if the cooling rate, supersaturation degree, and growth time during growth are appropriately set in consideration of the height of the pointed mesa stripe 10b in FIG. 1(b), the result is shown in FIG. 1(C). As a result of experiments, it was found that epitaxial growth occurs as shown in FIG. This is because the current barrier layer 2 epitaxially grown around the mesa stripe 10b has grown to exactly the same height (thickness) as the mesa stripe 10b, and with very good flatness. Stripe 1. A flat hill 2a is formed around Ob. This phenomenon is only possible by forming the mesa stripe IOb into a pointed shape, and does not occur when growing into a conventional mold mesa stripe.

Next, this wafer is etched using an etchant that does not impair the surface flatness, so that part of the mesa stripe 10b or a certain width is exposed as shown in FIG. 1(d). Several types of etchants are generally known that do not impair surface flatness, and one of them was used.

It has been found that if this treatment is performed immediately before the next vapor phase growth, it can also serve as a pretreatment for the next vapor phase growth as an incidental effect. This is because chemical etching can provide a clean surface.

In this example, the first wafer is processed using the MOVPE method.
A crat layer 3, an active layer 4, a second crat layer 5, and a contact layer 6 were successively grown. The first cladding layer 3 is p
l n x (G a yA12+-y) +-xP and x=0.5. y=0.3, and the active layer 4 is undoped I n , Ga 1-, Pte x=0.5. The second cladding layer 5 is n −1n x (G ayAL-y) l
-11P, x-0°5y=0.3, and the contact layer 6 is n''-GaAs.

Since all the layers were grown flat on the current barrier layer 2 shown in FIG. 1(d), the interface between each layer was also steep, and a good epitaxial layer was obtained.

Furthermore, when electrodes were attached to this structure and the semiconductor laser was divided into chips to create a semiconductor laser, both the light emission characteristics and the life characteristics were very good.

As described above, according to this embodiment, the following remarkable effects are achieved.

By making the mesa stripe formed on the surface of the semiconductor substrate 1 have a pointed cross-sectional shape, the mesa stripe 1. It is possible to epitaxially grow a very flat current barrier layer 2 having the same height as the mesa stripe 1O around the Ob.

Therefore, if chemical etching or melt-back treatment is performed without impairing the flatness of this surface, a part of the mesa stripe 10b can be exposed very flatly and with good linearity, and the current around the mesa stripe 10b can be Since the barrier layer 2 is also at the same height as the mesa stripe 10b and is very flat, it is not possible to epitaxially grow the cladding layers 3, 5, the active layer 4, etc. thereon evenly using the vapor phase growth method. can.

Therefore, the crystallinity of each growth layer and the growth interface thereof is good, and there is no possibility of lattice constant deviation as seen in InGaP and InGaAQP systems, and the light emission characteristics and lifetime characteristics can be greatly improved. .

The cross-sectional shape of the mesa stripe 10b can be easily made into a pointed one by chemically etching it after forming the mesa strife 10 with a metal mold cross section.This method is reproducible. Because it has excellent properties and stability,
It can easily be adapted to mass production.

By using the pointed mesa stripe 110b, it is possible to easily obtain an epitaxial layer having the same height and flatness around the mesa stripe 10b. In semiconductor lasers and the like, this layer is usually used as the current barrier layer 2, or the current barrier layer 2 can be stably manufactured to the same height and flatness as the mesa stripe 10b with good reproducibility.

Furthermore, by controlling the epitaxial growth conditions, mesa and
The width of the portion that grows flat at the same height as the mesa stripe 10b at the periphery of the stripe 10b, that is, the first
Since the width of the portion indicated by the arrow in Figure (C) can be changed, there is an advantage that it is possible to create not only a gain waveguide type but also a refractive index waveguide type semiconductor laser structure.

After growing the current barrier layer 2, chemical etching to expose a part of the mesa stripe 10b without impairing the surface flatness can be easily carried out using a commonly known etchant that does not impair the flatness. It can be carried out. Therefore, it can easily be adapted to mass production. It is also possible to use melt-back treatment.

Although the above embodiments have been described with reference to semiconductor lasers, the present invention is not limited thereto, and can also be applied to, for example, light emitting diodes and superluminescence.

[Effects of the Invention] Since the present invention is configured as described above, it produces the following effects.

In the light emitting device having an active waveguide according to claim 1, since the mesa stripe is particularly pointed, vapor phase growth can be performed while using the mesa stripe structure which is advantageous for obtaining a stable and practical semiconductor laser. A flat rad layer, an active layer, etc. can also be formed by the above method. Therefore,
The crystallinity of each growth layer and its growth interface is good, and in particular, there is no shift in lattice constant as seen in InGaP and InGaA (7P systems), and the light emission characteristics and life characteristics can be greatly improved. .

In the method of manufacturing a light emitting device having an active waveguide according to claim 2, the mesa stripe formed on the surface of the semiconductor substrate has a pointed cross-sectional shape, and mesa stripes are formed on the periphery of the mesa stripe. After growing an epitaxial layer of the same height and exposing a part of the mesa stripe,
By making the epitaxial layer around the mesa stripe the same height as the mesa stripe, the exposed mesa
Since the epitaxial layer in and around the stripe is made flat, it is possible to epitaxially grow a crat layer, an active layer, etc. on the epitaxial layer even if vapor phase growth is used.

In the method of manufacturing a light emitting device having an active waveguide according to claim 3, in order to make the cross-sectional shape of the mesa stripe point-like, the mesa stripe having a trapezoidal cross section is formed, and then chemical etching is performed. Since the formation method is easy and has excellent reproducibility and stability, it can easily be mass-produced.

In the method of manufacturing a light emitting device having an active waveguide according to claim 4, a pointed mesa stripe is formed.

Since the epitaxial layer is grown on the surface of the substrate, the epitaxial layer can be manufactured stably with good reproducibility and flatness at the same height as the mesa/stripe.

In the method of manufacturing a light emitting device having an active waveguide according to claim 5, by using generally known chemical etching and meltback, mesa stripes can be formed after epitaxial layer growth without impairing surface flatness. Since a portion can be exposed, it is easy to manufacture and can be easily adapted to mass production.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the main steps of the method for manufacturing a light emitting device having an active waveguide according to the present invention, and Fig. 2 shows a conventional method for epitaxial growth on a semiconductor substrate on which a mesa stripe with a trapezoidal cross section is formed. FIG. 2 is a sectional view showing a state in which the film is removed, and a sectional view showing a state after melt-back treatment or chemical etching is performed thereon. 1 is a semiconductor substrate, 2 is a current barrier layer which is an epitaxial layer, 3 is a first cladding layer, 4 is an active layer, 5 is a second cladding layer, 6 is a contact layer, 10 is a trapezoidal mesa stripe, and 10a is a pointed layer. It is a head-shaped mesa stripe. (a) (b) (C) 14 噸・Figure 2 (d) (e) 563-

Claims (5)

[Claims] (1) In a semiconductor substrate having a first conductivity type in which a convex mesa stripe is formed on the surface, the convex mesa stripe is formed in a pointed shape, and at least in a peripheral portion of the mesa stripe, An epitaxial layer having a second conductivity type and having approximately the same height as the mesa stripe is provided so that at least a peripheral portion including the mesa stripe is flat when this layer is formed; 1. A light emitting device having an active waveguide, characterized in that at least a cladding layer and an active layer having one conductivity type are provided. (2) Forming a mesa stripe with a convex cross section on the surface of the semiconductor substrate, forming the mesa stripe so that the cross section has a pointed shape by chemical etching, and then forming a mesa stripe on at least the peripheral portion of the mesa stripe. An epitaxial layer with approximately the same height as the mesa stripe is grown, and then this surface is chemically etched or melted back to expose a part of the mesa stripe, and at least a cladding layer and an active layer are epitaxially grown on this. 1. A method for manufacturing a light emitting device having an active waveguide, the method comprising: (3) Mesa stripes with a convex cross section formed on the surface of the semiconductor substrate are chemically etched using an etchant of phosphoric acid/hydrogen peroxide/water, or sulfuric acid/hydrogen peroxide/water. 3. The method of manufacturing a light emitting device having an active waveguide according to claim 2, wherein the top surface is formed into a pointed shape. (4) Performing epitaxial growth on the surface of the semiconductor substrate on which the mesa stripes are formed to form a current barrier layer at least at the periphery of the mesa stripes at approximately the same height as the mesa stripes and flat. 4. A method for manufacturing a light emitting device having an active waveguide according to claim 2 or 3. (5) The semiconductor substrate on which the epitaxial layer or the current barrier layer has been epitaxially grown is subjected to chemical etching or melt-back treatment to form the mesa stripes without impairing the flatness of at least the peripheral portion of the mesa stripes. 5. The method for manufacturing a light emitting device having an active waveguide according to claim 2, wherein a portion of the light emitting device is exposed.