JPH067603B2 - Light emitting diode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light emitting diode which is useful as a light source for an optical fiber gyro, an optical disk, and the like, and which can emit incoherent light with a large intensity and a small emission angle.

(Problems to be Solved by Prior Art and Invention) In a light emitting diode that intends to extract high-power incoherent light from an end surface of an active layer, it is important to suppress laser oscillation in a Fabry-Perot (hereinafter referred to as FP) mode. Conventional methods for suppressing laser oscillation include non-reflective (hereinafter referred to as AR) coating on the end face, forming a non-excitation region, or obliquely etching the end face, or by applying light to the end face of the active layer such as embedding the end face. Methods have been used to reduce reflectance.

However, it was difficult to sufficiently suppress the FP mode oscillation only with the AR coating on the end face. Further, in the conventional method of forming the non-excited region, since the current injection region and the active layer have the same width, carriers are excited in the non-excited region by the optical guide effect, and the absorption coefficient becomes small. However, there is a drawback that the non-excitation region must be lengthened. In addition, this structure has a problem that it is necessary to selectively form electrodes for the current injection portion and the non-excitation region, which complicates the process steps. Further, in the case of oblique etching of the end surface, embedding of the end surface, or suppression of FP mode oscillation due to the combined use of these, the difference in the refractive index on the end surface is unexpectedly large, and the reflectance is 1% compared to the case of the remote field.
Reach a degree. In particular, if the active layer is thickened, this effect becomes large and the reflectance also increases.
There is a drawback that it is difficult to suppress P-mode oscillation.

For example, as an example of suppressing FP mode oscillation, FIG.
(a), (b) and (c) are schematic views of an embedded type light emitting diode having a conventional structure, where (a) is a plan view, (b) and (b) are
(c) is a longitudinal sectional view and a transverse sectional view, respectively. In the figure, 1 is an n-type InP substrate, 2 is an n-type GaInAsP optical guide layer, 3
Is an undoped GaInAsP active layer, 4 is a p-type InP clad layer,
5 is a P-type GaInP electrode layer, 6 is a p-type InP current confinement layer, and 7 is n
-Type InP current confinement layer, 8 is a p-type ohmic electrode layer, and is composed of a current injection part 9, a non-excitation region 10 and an end face buried part 11.
It is formed from two areas. Further, 12 is an n-type ohmic electrode.

The width of the active layer 3 in the non-excitation region 10 is equal to the width of the active layer 3 in the current injection part 9.
Is the same as the width of the
Even in the case of 10, a large amount of carriers are generated, the absorption coefficient becomes small, and the length equal to or more than that of the current injection portion 9 is required to suppress the FP mode oscillation. Further, since the window layer of the end surface burying layer 11 has a large amount of light reflected on the end surface, it is necessary to form the window layer to a length of about 100 μm or longer. Furthermore, since the current confinement layer is not inserted in the cross section of the non-excitation region 10, the ohmic electrode 8
Need to be selectively formed only on the surface of the current injection portion 9. Thus, the conventional structure has complicated process steps.

(Object of the invention) The present invention has been made in order to solve the drawbacks of these conventional structures, and the effect of setting the non-excitation region is increased, and the active state in the non-excitation region is effectively suppressed to effectively suppress the FP mode oscillation. The layer width is tapered in the non-excitation region, and the light generated in the current injection part is diverged without being guided in this part to efficiently absorb the light. The purpose is to shorten the device length. However, it is to obtain an incoherent light emitting diode that can sufficiently suppress FP mode oscillation.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a buried light emitting diode in which a current injection portion is formed by narrowly embedding an active layer so as to form a refractive index guide. In the injection portion, the light generated in the current injection portion is formed by expanding the active layer in a taper shape so as to spread in the in-plane direction without being guided in a specific direction, and compared with the active layer formed in the current injection portion. The gist of the invention is a light emitting diode characterized by being widely embedded.

Embodiments of the present invention will be described below with reference to the drawings.
Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

1 (a) and (b), 2 (a) and (b) InP / GaI of the present invention
FIG. 1 is a diagram for explaining the first embodiment using an nAsP-based material, and FIG.
(a) is a vertical sectional view, (b) is a horizontal sectional view, (b) is a perspective view of the first growth, and (b) is a plan view.

In order to obtain the light emitting diode of the present invention, liquid phase epitaxy (LPE) and vapor phase epitaxy (VPE, Mo-) are used as the first growth.
CVD) or molecular beam epitaxy (MBE) method, etc., and n-type GaInAsP optical guide layer (λ:
1.1 μm composition) 2, non-doped GaInAsP active layer (λ:
1.3 μm composition) 3, and p-type InP clad layer 4 is grown. Next, by using the photoresist as a mask by the photo-etching technique, the current injection portion 9 is left in a stripe shape of about 400 μm with a width of about 3 μm along the <110> direction, and then in the non-excitation region 10 a width of 3 μm (the current injection portion stripe). Width) and finally to a width of 40 to 50 μm in a taper shape over a length of about 200 μm. Subsequently, the end face embedding portion 11 is about 50 μm, and no mask is formed. Further, the current injection part 9 and the non-excitation region 10 on which the resist mask is formed.
The resist mask is not formed at intervals of 10 to 20 .mu.m around the circumference of, but the resist mask is formed on all other remaining portions. Then, each layer of the n-type GaInAsP optical guide layer 2, the non-doped GaInAsP active layer 3 and the p-type InP clad layer 4 is etched by the bromine methanol etching solution using the resist mask as a mask until the substrate 1 is reached. Two grooves (17) sandwiching the groove (17) and the window layer portion (18) of the end face embedded portion (11) are formed. At this time, the end face embedded portion 11 and the non-excitation region
The boundary of 10 is obliquely etched. The state before the second growth is shown in FIGS. 2 (a) and 2 (b).

Next, as a second growth, growth for current confinement of the p-type InP current confinement layer 13 and the n-type InP current confinement layer 14 is performed by LPE. At this time, in the current injection part 9, the p-type InP current confinement layers 13 and n are formed on the striped active part sandwiched between the two grooves 17.
Each layer of the InP-shaped current confinement layer 14 does not grow and other portions (groove 1
7 and the upper part of the cladding layer 4) are selectively grown. In the non-excitation region 10, selective growth is performed up to about 20 μm from the left end of the tapered stripe in the same manner as the current injection portion 9 (selective growth is performed up to a stripe width of about 5 μm), and all others. The crystal is grown in the part of. In the end face buried portion 11, crystal growth is performed on all layers including the n-type GaInAsP optical guide layer 2, the non-doped GaInAsP active layer 3, and the end face oblique etching part of the p-type InP clad layer 4, and there is no selective growth. . In the region where each of the p-type InP current constriction layer 13 and the n-type InP current confinement layer 14 has grown, it becomes a non-excitation portion in which no current flows. Next, p-type InP
The buried layer 15 and the p-type GaInAsP electrode layer 16 were grown in all the regions of the current injection part 9, the non-excitation region 10 and the end face buried part 11.
Au-Zn is vapor-deposited on the upper surface of the thus obtained wafer to form a p-type ohmic electrode 8, and Au-Ge-Ni is vapor-deposited on the substrate 1 side after polishing to a total thickness of about 80 μm. Then, the n-type ohmic electrode 12 was formed on the entire surface. The structure of each layer of the light emitting diode thus obtained is as follows in the state of FIG. 3, and each crystal layer matches the lattice constant of InP.

1; Sn doped n-type InP substrate, thickness 80 μm, carrier density 3 × 10 ¹⁸ cm ^-3 , EPD 5 × 10 ⁴ cm ^-2 , 2; n-type GaInAsP optical guide layer, thickness 0.2 μm, Sn dop
ed, carrier density 5 × 10 ¹⁷ cm ⁻³ , 3; n-type GaInAsP active layer, thickness 0.2 to 0.3 μm, undoped, 4; p-type InP crystal layer (clad layer), thickness 0.5 μm, Zn
doped, carrier density 5 × 10 ¹⁷ cm ^-3 , 13; p-type InP current confinement layer, thickness 0.7 μm, Zn doped,
Carrier density 1 × 10 ¹⁷ cm ^-3 , 14; n-type InP current confinement layer, thickness 0.7 μm, Sn doped,
Carrier density 1 × 10 ¹⁷ cm ⁻³ , 15; p-type InP buried layer, thickness 1.5 μm, Zn doped, carrier density 5 × 10 ¹⁷ cm ⁻³ , 16; p-type GaInAsP electrode layer, thickness 0.5 μm, Zn dope
d, carrier density 2 × 10 ¹⁸ cm ^-3 , this light emitting diode was divided into pellets with a length of 650 μm and a width of 400 μm, mounted on a heat sink with Au-Sn solder, and the current and light output characteristics were measured. In continuous operation at 25 ° C, the optical output increased without oscillating according to the current injection, and an incoherent optical output of 3 mW could be obtained at 200 mA.

Compared with the conventional light emitting diode, there is no guide for the injected light in the non-excitation region 10 and the light is diverged, so that the light can be absorbed efficiently, so that the optical path length can be shortened to about half. Further, the amount of light leaked into the end face embedded portion 11 was small, and this distance was about half of that of the conventional light emitting diode, and the FP mode oscillation could be sufficiently suppressed. Combined current confinement layer
Since 13 and 14 are automatically formed during the second crystal growth, it is not necessary to selectively form the p-type ohmic electrode 8 in the current injecting portion 9, so that it is possible to easily form the p-type ohmic electrode 8 using the entire surface electrode.
Since the leakage current through the InP embedding amount 15 also disappeared, the FP mode oscillation suppressing effect of the non-excitation region 10 could be sufficiently exerted. Further, in the light emitting diode having the non-excitation region 10 of 300 μm, even the light emitting diode having the structure in which the end face embedded portion 11 is cut off could sufficiently suppress the FP mode oscillation.

Although the present invention has been described with reference to the example using the n-type InP substrate, the same effect can be obtained by using the p-type InP substrate. In that case, n is p and p is an n-type impurity. It goes without saying that it is good.

Next, FIGS. 3 (a) and (b), FIGS. 4 (a) and (b) are diagrams for explaining the second embodiment of the present invention, and FIG. 3 (a) is a longitudinal sectional view,
FIG. 4B is a cross-sectional view, FIG. 4A is a plan view after forming mesas,
The same figure (b) is a side view.

In the present embodiment, a p-type InP substrate can be used to perform a series of crystal growth including the current confinement layer 14 in one growth.

To obtain this light emitting diode, S is formed on the entire surface of the p-type InP substrate 1 '.
After forming a thin film of iO ₂ or SiN by sputtering or CVD, the current injection part 9 opens a stripe-shaped window of ~ 3 μm in the <10> direction by the photoetching technique. Following the injection part 9, a window is opened in a tapered shape. No window is opened in the portion corresponding to the end face embedded portion 11 '. By etching the portion where the window is opened with hydrochloric acid, the current injection portion 9 can be formed into a V-shaped groove, and the non-excitation region 10 can be formed into a tapered groove with a flat bottom. The dimensions of the current injection portion 9, the non-excitation region 10 and the end face buried portion 11 'shown in FIGS. 4 (a) and 4 (b) are the same as those in the first embodiment.

When crystals grow on the p-type InP substrate 1'obtained in this way, the first n-InP current confinement layer 14 does not grow inside the groove of the current injection portion 9, but only on other flat portions. grow up. Further, in the non-excitation region 10, when the groove width becomes 5 μm or more, the non-excitation region 10 also grows inside the groove, and the current confinement layer 14 can be automatically formed. In addition, in the end face buried 11 ', the current confinement layer 1
4 grows. Next, the p-type GaInAsP guide layer (composition λ:
1.2 μm), the current confinement layer 14 was not selectively grown inside the groove (current injection portion 9 and non-excitation region 10).
Part of) will also be grown. The subsequent series of growth and fabrication steps are the same as in the first embodiment. Also in this light emitting diode, the same characteristics as in the first embodiment could be obtained.

In the example, the InP-GaInAsP-based semiconductor having a wavelength of 1.3 μm has been described, but an incoherent light-emitting diode using another wavelength band and a semiconductor different from this example (GaAs-GaAlAs-based etc.) is also used in the present invention. It is clear that this method can be applied.

Further, although the embodiment has described the case where the current blocking structure is automatically formed in the non-excited portion, it is needless to say that a normal BH structure can be applied when the electrode is partially formed.

(Effects of the Invention) As described above, according to the present invention, the width of the active layer in the non-excitation region is expanded in a taper shape so that the difference in the refractive index between the excitation region and the excitation region is made as small as possible, and It was possible to sufficiently suppress the FP mode oscillation by diverging the light without guiding in this portion and efficiently absorbing the light, thereby shortening the non-excitation region and thus the entire device length. As a result, the wafer utilization efficiency is increased and the device productivity is improved. Further, since the current confinement layer can be automatically formed in the non-excitation region, it is not necessary to selectively form electrodes, the process steps are simplified, and the leakage current to the non-excitation region can be reduced.

[Brief description of drawings]

1 (a) and (b) and FIGS. 2 (a) and (b) show the InP / G of the present invention.
It is a figure explaining the 1st example by aInAsP system material.
Figure (a) is a vertical sectional view, Figure (b) is a horizontal sectional view, and Figure 2 (a) is 1
Perspective view of the second growth, the same figure (b) is a plan view, FIG. 3 (a)
And (b), Fig. 4 (a) and (b) are diagrams for explaining the second embodiment of the present invention, Fig. 3 (a) is a longitudinal sectional view, and Fig. 3 (b) is a lateral sectional view. FIG. 4 (a) is a plan view after forming the mesa, FIG. 4 (b) is a side view of the same, and FIGS. 5 (a), (b) and (c) are schematic views of a conventional embedded light emitting diode. In the figure, (a) is a plan view, and (b) and (c) are a vertical sectional view and a horizontal sectional view, respectively. 1 ... n-type InP substrate 2 ... n-type GaInAsP optical guide layer 3 ... non-doped GaInAsP active layer 4 ... p-type InP clad layer 5 ... p-type GaInAsP electrode layer 6 .... p-type InP current confinement layer 7 ... n-type InP current confinement layer 8 ... p-type ohmic electrode 9 ... current injection part 10 ... non-excitation region 11 ...・ End face buried part 12 ・ ・ ・ ・ ・ ・ n-type ohmic electrode 13 ・ ・ ・ ・ p-type InP current blocking layer 14 ・ ・ ・ ・ ・ ・ n-type InP current blocking layer 15 ・ ・ ・ ・ ・ ・ p-type InP buried layer 16 ・ ・・ ・ P-type GaInAsP electrode layer 17 ・ ・ ・ ・ ・ ・ Groove 18 ・ ・ ・ ・ End face embedded part 19 ・ ・ ・ ・ End face oblique etching part 1 '・ ・ ・ ・ P type InP substrate 11' ・ ・ ・ ・ End face embedded Corresponding part 2 '... P-type GaInAsP optical guide layer 3' ... P-type GaInAsP active layer 4 '... N-type InP clad layer 16' ... N-type GaInAsP electrode layer

Claims (1)

[Claims] 1. In an embedded light emitting diode, an active layer is narrowly embedded so as to form a refractive index guide in a current injection portion, and light generated in the current injection portion is guided in a specific direction in a non-injection portion. A light emitting diode, characterized in that the active layer is formed so as to be expanded in a taper shape so as to be spread in the in-plane direction without being formed, and is wider than the active layer formed in the current injection portion.