JPS62179179A - Light emitting device and manufacture of same - Google Patents

Abstract

PURPOSE:To obtain a light emitting device which has an excellent efficiency of taking out a light by a method wherein a light guide layer is provided over the whole top surface of a island-shape laminated unit and a reflective layer whose refractive index is smaller than the refractive indices of 1st cladding layer, an active layer and 2nd cladding layer is provided. CONSTITUTION:On a foundation, for instance a P-type GaAs substrate 31, a P-type AlwGa1-wAs layer 33 as 1st cladding layer, a P-type AlxGa1-xAs layer 35 a an active layer, an N-type AlyGa1-yAs layer 37 as 2nd cladding layer and an N-type AlzGa1-zAs layer (light guide layer) 39 as 1st cap layer are successively formed to provide an island-shape laminated unit 41. If GaAs-AlAs formed to provide an island-shape laminated unit 41. If GaAs-AlAs mixed crystal ratios (v), (w), (x), (y) and (z) of the substrate 31, the 1st cladding layer 33, the active layer 35, the 2nd cladding layer 37 and the 1st cap layer 39 respectively are so selected as to conform to the relations x<v, z<w and z<v, 3rd-5th cladding layers 53, 55 and 57 function as a reflective layer 65 which can reflect a light emitted in the active layer 35 toward the laminated unit 41 side so that the light emitted in the active layer 35 can be confined in the laminated unit 41 with the direction parallel to the laminated surface.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a structure of a light emitting element suitable for use as a light source in an optical fiber communication system and a method for manufacturing the same.

(Prior Art) As optical fiber communication systems reach the stage of practical use, reliable and inexpensive light emitting elements are required as light sources for these systems. Light-emitting devices have been proposed.

Such a light-emitting element is disclosed, for example, in a document (IEICE technical report R84-70), and this element is manufactured to have a structure effective for carrier confinement and to enable high-speed modulation. .

Hereinafter, the structure of the light emitting element disclosed in this document and its manufacturing method will be briefly explained according to the manufacturing process diagrams shown in FIGS. 3(A) to 3(C).

First, an n-type GaAs layer 13 is formed on a P-type GaAs substrate 11 by first liquid phase epitaxial growth, and then a hole 15 with a diameter of 30 μm is formed in this n-type GaAs layer 13 by a normal photoetching technique. As a result, an evaporative structure as shown in FIG. 3(A) is obtained. Further, the board 11 is exposed through this hole 15, and this hole 15
The n-type GaAs layer 13 remaining around the current confinement layer 13
becomes.

Next, by second liquid phase epitaxial growth, P-type A
ILx Ga 1-xA s first cladding layer 17;
P-type AI1. , Ga, -, As active layer 19 and the N-type side. Ga + -
5 is sequentially formed on the exposed substrate to obtain a wafer structure as shown in FIG. 3(B).

Next, a partial region of the cap layer 23 corresponding to the hole 15 is removed in a circular shape, and then an upper electrode 25 is provided on the remaining cap layer 23, and a lower electrode 27 is provided on the F side of the substrate 11.
A light emitting device as shown in FIG. 3(C) was obtained by providing a light emitting device.

In such a light-emitting device, if the carrier concentration in the active layer is increased to a certain degree, the number of non-luminous centers increases, thereby improving the frequency characteristics, and therefore, it is possible to obtain an optical signal with a fast rise time.

(Problems to be Solved by the Invention) However, in the above-mentioned light-emitting element p, when the carrier concentration of the active layer is increased in order to shorten the rise time, the luminous efficiency decreases, and as a result, the luminous output decreases. The problem of doing this was solved.

The object of the first invention of this application is to provide a light emitting device with excellent light extraction efficiency, which does not cause a decrease in the light emission output of the device as a whole even when the carrier concentration is increased to shorten the rise time. There is a particular thing.

A second object of the invention of this application is to provide a manufacturing method that can easily manufacture a light emitting element with excellent light extraction efficiency.

(Means for Solving the Problems) In order to achieve this object, the present invention provides a light-emitting device that includes at least a laminate on a base, comprising a first cladding layer, an active layer, and a second cladding layer. , this laminate is an island-like laminate, and a light guide layer is provided on the entire upper surface of the island-like laminate opposite to the substrate, and at least the above-described layer is provided adjacent to the periphery of the island-like laminate. It is characterized by comprising a reflective layer having a refractive index smaller than the refractive index of the first cladding layer, the active layer, and the second cladding layer.

Further, according to the manufacturing method of the present invention, there is a step of forming an island-like laminate having a first cladding layer, an active layer, and a second cladding layer sequentially on a base, and a light guide is provided on the entire upper surface of the island-like laminate. forming a layer, the first cladding layer being adjacent to at least the periphery of the island-like laminate and on a substrate other than the island-like laminate;
forming a reflective layer having a refractive index smaller than the refractive index of the active layer and the second cladding layer.

Furthermore, in carrying out the present invention, the formation of the above-mentioned island-like laminate and light guide layer involves sequentially forming a first cladding layer, an active layer, a second cladding layer, and a semiconductor layer for forming the light guide layer on the base. It is preferable to grow the first cladding layer, the active layer, the second cladding layer, and the semiconductor layer for forming the light guide layer to remain in the same contour shape.

(Function) According to the structure of the light emitting device of the present invention, the light that reaches the reflective layer out of the light emitted by the active layer is reflected by the reflective layer toward the island-like laminate. Therefore, light is confined within the island-like laminate in a direction parallel to the lamination plane.

However, since the light guide layer on the upper surface of the island-like laminate efficiently guides the light inside the island-like laminate, the light emitted from the active layer and guided to the light guide layer side is transmitted directly and through the reflective layer. After being reflected, it can be efficiently taken out to the outside of the light emitting element.

According to the method for manufacturing a light emitting device of the present invention, an island-like laminate is first formed, for example, by a normal etching process, and then the refractive index is lower than that of the first cladding layer, the active layer, and the second cladding layer. Since the reflective layer having the reflective layer is laminated at least adjacent to the periphery of the island-like laminate, manufacturing is simple and easy.

In addition, when forming a light guide layer on the entire upper surface of the island-like laminate,
For example, the first cladding layer, the active layer, the second cladding layer, and the semiconductor layer for forming the light guide layer may be successively grown on the base, and then each layer may be left in the same contour shape. , it becomes easy to align the active layer, which is a light emitting part, and the light guide layer.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same components are designated by the same reference numerals. Further, these drawings are only schematic representations to the extent that the present invention can be understood, and the dimensions, shapes, and arrangement relationships of each component are not limited to the illustrated examples.

FIG. 1 is a sectional view of a main part for explaining one embodiment of a light emitting device of the present invention, and hatching representing an interrupted plane in the figure is omitted to avoid complicating the figure.

Although details will be described later, in this example, the light guide layer was composed of a first cap layer, and the reflective layer had a three-layer structure of a third clad layer, a fourth clad layer, and a fifth clad layer. An example will be explained.

In the structure shown in FIG. 1, for example, p-type GaA
P-type AR,X as a first cladding layer is placed on the s substrate 31.
Ga, -, As layer 33 and p-type AJZ as an active layer,
A Ga, -, As layer 35, an N-type An, Gat-, As layer 37 as a second cladding layer, and an N-type iL, 'Ga, -, As layer 39 as a first cap layer are sequentially formed. The island-shaped laminate 41 (hereinafter sometimes simply referred to as a laminate) is provided. In this embodiment, the island-like laminate 41 is a laminate whose cross section taken parallel to the laminated surface has a predetermined circular shape.

First, an n-type GaAs layer 51 as a current confinement layer is provided on the substrate around the laminated body 41, and a reflective layer 65 is further provided on the current confinement layer 51 adjacent to the circumferential side of the laminated body. equip This reflective layer 65 is a P-type AIL as a third cladding layer, which is laminated sequentially from the substrate side.
N as third and fourth cladding layer on vGa, -vAsAs layer
Type AI1. n-type GaAs layer 57 as a fifth cladding layer; It is equipped with Furthermore, one electrode 61 is provided on the lower surface of the substrate 31, and the other electrode 63 is provided on the second cap layer 59.

In such a device, the positions of the first, second, third, fourth and fifth claddings, the substrate 31, the first cladding layer 33, the active layer 35, the second cladding layer 37 and the first cap layer 39 If the relationship is as shown in Figure 1, the GaA of each layer
s-AfiAs mixed crystal ratio V.

w, x, and y are configured to satisfy the relationships x<v, z<w, and z<v. With this configuration, each layer 33, 35, 37, .
39, respectively. Therefore, the third
The fourth and fifth cladding layers act as a reflective layer 65 that can reflect the light emitted from the active layer 35 toward the laminate 41 side, and therefore reflect the light emitted within the active layer 35 in a direction parallel to the laminate surface. It can be confined within the laminate 41. moreover,
When the above-mentioned relationship of the mixed crystal ratio is satisfied, the first cap layer 39 acts as a light guide layer that efficiently guides the light from the active layer 35 upward. Therefore, the light guide layer 35 allows the light emitted from the active layer to be emitted upward (towards the second cladding layer) and the light reflected by the reflective layer 65 and directed upward to the outside of the light emitting element. radiated to. Therefore, the efficiency of light extraction is good.

Further, in this embodiment, each layer is provided so that the height of the surface of the first cap layer 39 is higher than the height of the surface of the fifth cladding layer 57 (dimension indicated by d in FIG. 1). With such a structure, the first cap layer 39 has a portion (protrusion) 39a that protrudes from the fifth cladding layer 57, and therefore light is effectively guided to the upper surface of the protrusion 39a. Light extraction efficiency is further improved.

The following is a second example of the method for manufacturing a light emitting device of the present invention.
This will be explained with reference to FIGS. (A) and (B) and FIG. 1.

First, P-type AJ2X Ga as a first cladding layer is grown by a suitable method such as liquid phase epitaxial growth.
, p-type An, Ga as the 3 active layers on the 3 -XAs layers
+-y As layer 35 and N as a second cladding layer
A type An, 1Gap-XAsAs layer 7 and 8fL z Ga + -z A 5 layers 39 as a first cap layer are sequentially formed on the substrate 31 (FIG. 2(A)).

Next, for example, a circular resist pattern (not shown) having a predetermined diameter is left on the first cap layer 39 by, for example, a common photoetching technique, and then the exposed surface of the first cap layer 39 is etched. to the substrate 31, unnecessary portions of each of the layers 9.37.35 and 33 are etched away to form an island-like stacked body 41,
A wafer structure as shown in Figure (B) is obtained.

Next, by second liquid phase epitaxial growth, an n-type GaAs layer 51 as a current confinement layer and a P-type layer as a third cladding layer are formed on the nv Ga 1-vAs layer 51 as a fourth cladding layer. Look at the mold.

An N-type A° C., Gap, As layer 57 as a fifth cladding layer and an n-type GaAs layer 59 as a second cap layer are stacked on the Ga, -vAsAs layer except for the upper surface of the island-like stack 41. They are sequentially formed on the exposed surface 31a exposed by etching around the body. In this embodiment, liquid phase growth is performed so that the upper surface of the fifth cladding layer 57 is lowered by a height indicated by d in FIG. 1 from the upper surface of the first cap layer 39. or,
In each liquid phase epitaxial growth, the mixed crystal ratio v, w of GaAs-AJZAs.

This is done so that the relationships between X and y satisfy the following relationships: x<v, z<w, and z<v.

Next, by a suitable method such as photo-etching technique,
By forming one electrode 61 on the lower surface of the substrate 31 and the other electrode 63 on the upper side of the second cap layer, a light emitting device of the present invention as shown in FIG. 1 can be obtained.

Note that this invention is not limited to the embodiments described above.

For example, in this embodiment, an example in which the reflective layer 65 is composed of three layers has been described, but the reflective layer may be composed of a single layer, two layers, or four or more layers. Further, the light guide layer 39 may be composed of a plurality of layers. Furthermore, the reflective layer 65 and the guide layer 39 may be made of other suitable materials than those used in the embodiments.

In addition, in the above-mentioned embodiments, the first cap layer (light guide layer)
Although the explanation has been given using an example in which the - part of 39 protrudes from the reflective layer 65 on the side opposite to the substrate 31, the protruding part 'r Q 2
fy We L+ii&l! 1; A plan - top 1+
-, knQQ, nT: /y The upper surface of the cladding layer 7 may be at the same height.

Furthermore, although the above-mentioned embodiments have been described with respect to a light-emitting element using a P-type GaAs substrate as the base, the same effect can be expected in the present invention even when the base is an n-type GaAs substrate and the conductivity types of each layer are opposite conductivity types.

Alternatively, the base may be an AlAs-GaAs mixed crystal substrate. Alternatively, the base may be composed of a substrate and a buffer layer suitable for this substrate.

Further, the present invention is not limited to only GaAs-based compound semiconductor materials, and can be formed in the same manner as in the embodiments using other suitable materials, such as InP-based materials, and the same effects can be obtained. I can expect it.

Further, in the above-mentioned embodiment, the island-like laminate was explained as an example in which the cross section taken parallel to the laminate surface was circular, but the shape of the light emitting part may be any other suitable shape depending on the design of the element. .

Furthermore, the method of forming the island-like laminate is not limited to the method of the embodiment, and other suitable methods may be used.

Further, instead of the liquid phase epitaxial growth method used to form each layer, other suitable methods such as molecular beam epitaxial growth (MBE) or other methods may be used.

(Effects of the Invention) As is clear from the above explanation, according to the structure of the light emitting device of the present invention, light emitted from the active layer is confined within the island-like laminate by the reflective layer in a direction parallel to the laminate surface. I can do it. Further, among the light reflected by the reflective layer, the light that goes upward (to the side opposite to the substrate) and the light that goes upward among the light emitted by the active layer are guided by the light guide layer, and then, It can be taken out outside the light emitting element.

In addition, since this light guide layer is provided on the entire upper surface of the above-mentioned island-like laminate, its area is necessary and minimum compared to the area of the active layer (light emitting part). Therefore, when compared with conventional light emitting elements, the light emitting element of the present invention can efficiently extract light emitted from the light emitting section to the outside of the light emitting element.

Therefore, even if the carrier concentration is increased to shorten the rise time, the light emitting output of the device as a whole increases, and therefore a light emitting device with excellent light extraction efficiency can be obtained.

Further, according to the manufacturing method of the present invention, the reflective layer and the light guide layer can be easily formed using ordinary techniques, so that a light emitting element with excellent light extraction efficiency can be easily manufactured.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the main parts of the light emitting device of the present invention, FIGS. 2(A) and (B) are manufacturing process diagrams for explaining the manufacturing method of the light emitting device of the present invention, and FIG. )～(C)
FIG. 2 is a diagram used to explain the prior art. 31-p-type GaAs substrate, 31a, exposed surface 33 of one substrate
- P type AnXGa, -, As first cladding layer 35 - P type AIL, Ga, -, As active layer 37 - N type AIL, lG
a, -XAs second cladding layer 39 - N type AIL, Ga,
-, As first cap layer (optical layer) 39a --- protrusion, 41... island-shaped laminate 5
l---n type current confinement layer 53-P type A4v Ga, -vAs third cladding layer 55
-N type AJ! vGa, -vAs fourth cladding layer 57-N
Type Aj2=Ga,,As fifth cladding layer 59-n type G
aAs second cap layer 61--one electrode, 63--other electrode 6
5-...Reflection layer. Patent applicant Oki Electric Industry Co., Ltd. Jf P type (
raAs@1 anti J3: P type Mx (ta
r-xΔs%-kuku, ton police 35: P'i AJ
, y(rat-yAs tract layer J7/N type Ajx(xa
t-xAs'J=Kuhupud layer JQ: N? Al
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Ast5UL953: PQ Alv(rat-vA
s'! 43 cladding layer 55 N-type Alv (rat-v
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Claims (3)

[Claims] (1) In a light-emitting element comprising at least a laminate consisting of a first cladding layer, an active layer, and a second cladding layer on a base, the laminate is an island-like laminate, and the entire upper surface of the island-like laminate is illuminated. It is characterized by comprising a guide layer, and a reflective layer having a refractive index smaller than the refractive index of the first cladding layer, the active layer, and the second cladding layer adjacent to the periphery of the island-like laminate at least. Light emitting element. (2) a step of forming an island-like laminate having a first cladding layer, an active layer, and a second cladding layer sequentially on a base; a step of forming a light guide layer on the entire upper surface of the island-like laminate; and at least Adjacent to the periphery of the island-like laminate, a reflective layer having a refractive index smaller than the refractive index of the first cladding layer, the active layer, and the second cladding layer is provided on a substrate other than the base including the island-like laminate. 1. A method of manufacturing a light emitting element, the method comprising: forming a light emitting element. (3) The formation of the island-like laminate and the light guide layer involves sequentially and continuously growing the first cladding layer, the active layer, the second cladding layer, and the semiconductor layer for forming the light guide layer on the base, and then, 3. The method of manufacturing a light emitting device according to claim 2, wherein each layer described above is left in the same contour shape.