JPS60242692A - Light-emitting element and manufacture thereof - Google Patents

Abstract

PURPOSE:To oscillate a light-emitting element at a low threshold, a stable transverse fundamental mode and a high output by constituting a grooved current constriction layer and double hetero-structure to laminated structure on a substrate. CONSTITUTION:A first p type InP layer 3, a GaInAsP active layer 4 and a second p type InP layer 5 forming a current constriction layer 2 are grown on a p type InP substrate 1. A groove is formed through etching up to depth reaching to the first p type InP layer 3 on the side lower than the n type InP layer 4 to the substrate 1 side from the surface 5a. A first clad layer 7, an active layer 8 and a second clad layer 9 shaping double hetero-structure are grown on the current constriction layer 2 through a liquid phase epitaxial growth method. Since the active layer takes such structure, the light-emitting element can be oscillated at a low threshold, a stable transverse fundamental mode and a high output.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a Ga1nAsP/
The present invention relates to an InP-based semiconductor light emitting device and a method for manufacturing the same.

(Description of background technology) A document in which Ga1nAsP/InP-based light emitting elements have been proposed for optical communication: ELECTRO
NIGSl,ETT'ERS 15th 0ctobe
r 1981 Vol, 17 No, 21. As disclosed in P782, a buried semiconductor laser device using a p-type InP substrate has an n-type current blocking layer, so it is different from the conventional n-type substrate (in this case, the current blocking layer is a p-type layer). Higher output operation was possible than when using FIG. 3 shows such a known GaInAsP/In
FIG. 4 is a cross-sectional view schematically showing a semiconductor laser device having a P-buried heterostructure, and FIG. 4 is a cross-sectional view for explaining the features of the laser device having this structure.

In the structure shown in FIGS. 3 and 4, 20 is P type 1n
21 is a p-type Ga InAsP active layer, 22 is an n-type InP second rad layer, 23 and 24 are both n-type InP and p-type InP for current and light confinement.
It is a buried layer. In the element with the structure shown in Fig. 3,
The n-type 1nP buried layer 23 was grown to exist at a position below the active layer 21. As shown in FIG. 4, if the boundary between the NfilnP buried layer 23 and the P-type Inp buried layer 24 is grown in a position above the active layer 21, then in that case, Leakage current path ■ is n-type second cladding layer 22 → n-type InP
The buried layer 23 becomes the P-type first cladding layer 20, and the resistance of this current path I becomes the leakage current path I with the structure shown in FIG.
, that is, the n-type second cladding layer 22→Py! ! ! I
This is because the resistance of the nP buried layer 24 becomes two orders of magnitude lower than the resistance exhibited by the p-type first cladding layer 20, which increases leakage current and makes it impossible to obtain high output.

(Problems to be Solved) For these reasons, a buried heterostructure laser element was formed as shown in Figure 3.
In order to stop the growth of the n-type 1nP buried layer 23 below the active layer 21, etching to obtain an inverted mesa structure must be performed sufficiently deep to the bottom of the active layer 21, or the n-type 1nP buried layer 23 must be It is necessary to grow 23 extremely thin.

By the way, when a laser element is viewed as a light emitting element for optical communication, it is essential that the element oscillates in a transverse fundamental mode. To do this, the width of the active layer must be set to 1. B p,tm
It is necessary to keep it below. To achieve this, in the structure shown in FIG. 3, if reverse mesa etching is performed sufficiently deep to the bottom of the active layer 21, the width of the constriction of the reverse mesa structure will be approximately 0.5 g, l. This makes it difficult to control this etching and increases the series resistance, making it impossible to perform such deep etching in practice.

Further, the thickness of the n-type 1nP buried layer 23 is set to 0, for example.
．． When the thickness is reduced to about 5 gts, there are many pinhole-like growth defects, which also has the disadvantage that these parts become leakage current paths.

For the reasons explained above, in the buried laser device on the p-type substrate that has been proposed so far, the active layer 21
below this active layer 21.

The main focus was on obtaining a high-output laser element by deep etching, and the goal was to give up on achieving stable transverse fundamental mode oscillation and low threshold oscillation.

(Objective of the Invention) In view of the above-mentioned drawbacks of the conventional light emitting device, the object of the present invention is to provide a light emitting device having a structure that can oscillate in a stable transverse fundamental mode with a low threshold and high output. The purpose is to provide a manufacturing method.

(Means to Solve the Problem) In order to achieve this objective, according to the present invention, p-type 1
In a light emitting device having a double heterostructure on an nP substrate, the substrate includes a -th P-type InP layer, an n-type InP layer and a second PffiInP layer, and the -th P-type InP layer is reached from this second pyJInP layer. A P-type InP first rad layer comprising a current confinement layer having a groove, forming at least a double heterostructure in the groove and growing sequentially;
It comprises an InAsP active layer and an n-type InP second cladding layer, and the surface portion of the first cladding layer that is in contact with the sidewall of the trench is located above the n-type InP layer. do.

Furthermore, according to the method of the present invention, when manufacturing a light emitting device by providing a double heterostructure on a P-type rnP substrate, a p-th 1nP layer, an n-type InP layer and a second p-type InP layer are formed on this substrate. a step of sequentially growing InP-type InP layers; a step of etching a groove from the surface of the second p-type 1nP layer to the -th p-type 1nP layer to form a grooved current confinement layer; A P-type 1nP first cladding layer constituting a double heterostructure is formed on the layer by liquid phase epitaxial growth, and the surface portion of this first cladding layer in contact with the sidewall of the groove mentioned above is larger than the n-type InP layer. Then, Ga1 is grown on the above-mentioned first cladding layer.
The method is characterized in that it includes a step of sequentially growing an nAsP active layer and an n g InP second cladding layer.

(Function) According to the light emitting device having such a configuration, the width of the active layer is narrow, so transverse fundamental mode oscillation is possible. Furthermore, in addition to the narrow width of the active layer, the active layer is the current confinement layer ny11.
Since it is not in contact with the 1nP layer and the contact portion of this active layer with the sidewall of the trench is located above this n-type 1nP layer, the leakage current path that is formed is also a path with high resistance. Therefore, the leakage current can be kept extremely low, and low threshold oscillation can be performed.

As a result, the effective current flowing through the active layer increases, making it possible to oscillate at high output.

Further, according to the method of the present invention, each layer to be a current confinement layer is grown in advance, and then a groove is dug, and at least a first cladding layer forming a double heterostructure in the groove,
Since the active layer and the second cladding layer are grown, it is easy to control the film thickness of each layer that will become the current confinement layer, and etching the groove is easy, and it is easy to control the width of the groove and therefore the width of the active layer. Furthermore, since this active layer can be grown easily and thinly in a position where it does not form a leakage current path with low resistance, it can be grown in a transverse fundamental mode, with a low threshold value, and A light emitting element that oscillates at high output can be manufactured.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing a laser device which is an embodiment of the light emitting device of the present invention. In this figure, l is p
This is a type 1nP substrate, and 2 is a grooved current confinement layer formed on this substrate 1 by any conventionally known method. 3. Consists of an n-type InP layer 4 and a second p-type 1nP layer 5. The thickness of each of these layers 3.4.5 can be set to any desired thickness according to the design, and also,
The carrier concentration can be set to a desired value of 1 degree. For example, the thickness of layer 3 is about 31 Lm, and the thickness of layer 4 is 0.0 degrees.
74ts, layer 5 is about 21L11, and the carrier concentration of layer 4 is about 5X10'c layer-3, even when a voltage of 20V is applied to this wafer, 10. Since only a current of about A flows through this structure, it becomes a good current blocking structure.

6 is the n-type 1nP layer 4 from the surface 5a of the second p-type 1nP layer 5
This is a striped groove that reaches to a portion of the -P-type InP layer 3 slightly below. The depth direction of this V-groove 6 is the (100) direction perpendicular to the substrate surface 1a of the substrate 1, and the direction of the stripes is the (011) direction. In this embodiment, the substrate surface 1a of the inclined side wall 6a of this V-groove 6 is
The angle of inclination is approximately 58 degrees. Therefore, if the thickness of each layer 3.4, 5 is set as described above, and the depth of the lower part of the n-type InP layer 4 of this V groove 6 is set to 0.5, this layer 4 ■Groove 6 in the upper end surface 4a
The width of is approximately 1.4 pLIl. Therefore, if an active layer is formed at a position near this point as will be described later, the width of the active layer is sufficiently narrow, so that transverse fundamental mode oscillation can be sufficiently guaranteed.

7. 8 and 9 respectively indicate at least a P-type InP first rad layer, a Ga1nAsP active layer, and an n-type InP second rad layer that constitute the double heterostructure in the structure and are grown sequentially. . In this case, these layers 7, 8 and 9 have also grown outside the range of the V-groove 6 of the current confinement layer 2. The position where the surface of this p-type 1nP first rad layer 7 is in contact with the side wall 8a of the V-groove 6 is the upper end surface 4 of the n-type 1nP layer 4.
Since the active layer 8 is located above this n-type I
It has a structure above the nP layer 4 and not in contact with this layer 4.

In this embodiment, the active layer 8 has a crescent shape in the illustrated cross section within the groove 6, and the thickness at the center thereof is 0.
It can be set to 15 p, m or less. In this way, the primary mode cutoff condition is satisfied in relation to the width of the active layer 8, and transverse fundamental mode and low threshold oscillation are possible.

IO and 11 are an n-side electrode provided on the upper surface 9a of the second cladding layer 9 and a p-side electrode provided on the lower surface 1b of the substrate 1, respectively.

According to such a structure, since the width of the active layer 8 is narrower than that of a conventional element, it is possible to oscillate in a stable transverse fundamental mode. Additionally, since the leakage current path that is likely to occur is a path with little leakage current, it is possible to oscillate at a low threshold. In addition, the injection current is
Since the flow is effectively concentrated in the active layer 8 inside, it is possible to oscillate with high output.

Next, with reference to FIGS. 2A to 2C, a method for manufacturing a light emitting device according to the present invention will be described using a laser device as an example.

First, as shown in FIG. 2(A), a radio wave confinement layer 2 is formed on the (100) substrate surface la of a p-type InP substrate l.
A pffilnP layer 3, a GarnAsρ active layer 4, and a second p-type InP layer 5 are grown in sequence. Any epitaxial growth method can be used for this growth, and the growth conditions at that time can be appropriately set according to the design.

Next, as shown in FIG. 2(B), the second P-type 1nP layer 5
Etching is performed on the substrate 1 side from the surface 5a to a depth extending to a portion of the -p-th InP layer 3 slightly below the n-type InP layer 4, thereby forming a groove of a desired shape according to the design.

In this example, prior to etching, a second p-type 1nP
On the surface 5a of the layer 5, an etching mask 12 having a width of, for example, about 2 pLm and having a striped window !2a in a direction perpendicular to the paper plane of the figure, that is, in the (011> direction) is formed. Preferably, it is formed from a film.

Next, dry etching or wet etching may be used, but in this embodiment, wet etching is performed using a hydrochloric acid-based etching solution, for example, a mixed solution of hydrochloric acid and phosphoric acid at a volume ratio of 3:1.

Due to this etching, etching progresses in the depth direction ((100> direction) as well as side etching, and a V-groove 6 as shown in FIG. 2(B) is dug.

The inclined side wall 6a of this groove 6 is a (111)B plane, and the angle of inclination of this side wall 6a with respect to the substrate surface 1a is approximately 58 degrees, as described above.

Next, after removing this etching mask 12 by an appropriate method, as shown in FIG. The cladding layer 7, the active layer 8, and the second cladding layer 9 are sequentially grown using a liquid phase epitaxial growth method. In this case, for the first cladding layer 7, for example, 600
By setting the degree of supercooling to about 5°C at a temperature around 5°C, and growing L'f for about 10 seconds, the layer 7 is grown only on the bottom of the V-groove 6, and the surface of this layer 7 forms a layer on the sidewall of the groove 6. This first cladding M7 can be grown and lengthened well so that the position in contact with the current confinement layer 6a is above the n-type InP layer 4 of the current confinement layer 2. Constriction layer 2
Of course, it also grows above the surface 5a of the second p-type InP layer 5.

Subsequently, when the active layer 8 is grown, it grows in a crescent shape within the V-groove 6 and also grows outside the groove 6. Subsequently, a second cladding layer 9 is grown in the same manner, and finally, an n-side electrode 10 and a p-side electrode 11 are deposited to complete the laser device.

It is clear that the invention is not limited to the embodiments described above. For example, the shape and dimensions of each layer can be appropriately set according to the design.

Further, the etching may be dry etching or wet etching, and the cross-sectional shape of the groove can be any suitable shape other than the square shape.

Appropriate conditions such as growth conditions and etching conditions for each layer can be set according to the design.

Further, the etching mask may also be a film made of a material other than the above-mentioned 5iOz IFJ.

Furthermore, although the laser element was explained in the above-mentioned embodiment, by setting the reflectance of the rear end face small, it is possible to operate the laser element as a light emitting diode at high output.

(Effects of the Invention) As is clear from the above description, the light emitting device of the present invention has a lower threshold value than conventional light emitting devices.
It can oscillate in a stable transverse fundamental mode and at high output.

Furthermore, according to the method for manufacturing a light emitting device of the present invention, the width and thickness of the active layer can be formed narrower and thinner than in conventional light emitting devices, and the leakage current path can be suppressed to a path with extremely low leakage current. In addition, compared to conventional methods, it is extremely simple and easy to control kneeling and ching, and furthermore, it has the advantage that pinhole-like growth defects do not occur during the growth of each layer. Compared to conventional light emitting elements, it is possible to simply and easily produce a light emitting element that oscillates at a low threshold, in a stable transverse fundamental mode, and at high output.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing a laser device which is an embodiment of the light emitting device of the present invention, and Figs. 2 (A) to (C) illustrate a method of manufacturing the laser device which is an embodiment of the invention. FIGS. 3 and 4 are cross-sectional views for explaining the structure and manufacturing method of a conventional laser element. DESCRIPTION OF SYMBOLS 1...p-type InP substrate, la...substrate surface 2...current confinement layer, 3...-th p-type InP layer 4...n-type I
nP corridor, 4a... (n-type InP layer) upper end surface 5...
・Second P-type InP layer 5a...Surface 6 (of the second p-type nP layer)...V groove,
6a...(■ groove) side wall 7...p-type InP first rad layer 8--Ga1nAsP active layer 9...n-type 1nP second cladding layer 9a...(second cladding layer) ) Surface 10... n-side electrode, 11... p-side electrode 12... etching mask 12a... window (of the etching mask). Patent applicant Oki Electric Industry Co., Ltd. Figure 1 Figure 3 Figure 4 Figure 2 to e

Claims (1)

[Claims] 1. In a light emitting element having a double heterostructure on a p-type 1nP substrate, a -p-type 1nP layer and an n-type 1nP layer are provided on the substrate.
The second p-type InP layer is composed of a P layer and a second p-type InP layer.
a p-type InP first cladding layer comprising a current confinement layer having a groove reaching from M to the -th P-type 1nP layer, at least forming the double heterostructure in the structure and growing sequentially;
The first cladding layer comprises a Ga1nAsP active layer and an n-type InP second cladding layer, and a surface portion of the first cladding layer that is in contact with the sidewall of the trench is located above the n-type rnP layer. A light-emitting element that 2. When manufacturing a light emitting device by forming a double heterostructure on a p-type 1nP substrate, a -th p-type InP layer, an n-type 1nP layer and a second P-type InP layer are formed on the substrate.
a step of sequentially growing InP type layers, and a step of growing the second p-type InP layer;
forming a grooved current confinement layer by etching a groove from the surface of the P layer to the -th P-type InP layer; and forming the double heterostructure on the grooved current confinement layer by liquid phase epitaxial growth. The constituting P-type InP first cladding layer is grown such that the surface portion of the second cladding layer that contacts the sidewall of the trench is above the n-type InP layer, and then the first GaI on the cladding layer
A method for manufacturing a light emitting device, comprising a step of sequentially growing an nAsP active layer and an n-type 1nP second cladding layer.