JPS5853872A - Surface illuminating type light emitting diode - Google Patents

Abstract

PURPOSE:To obtain a high coupling efficiency while the positioning accuracy is eased during coupling to an optical fiber by providing a semiconductor layer having a larger refraction index than that of substrate between the active layer and semiconductor substrate and making the thickness maximum on the same center axis as that of the light emitting region. CONSTITUTION:The plane (001) of an InP substrate 21 is etched in circular with the HCl+H3PO4 solution, difference in shape at the cross sections (0-1-1), (01-1) is eased by the melt-back of proper composition and a smooth concave 23 is formed with good reproducibility. Then, the N-InGaAsP 22, N-InP 12, InGaAsP active layer 13, P-InP clad 14, P<+> InGaAsP cap 15 are stacked. The composition of active layer 22 should be selected so that the wavelength of light emitted is longer than the band gap of active layer and it becomes transparent for such wavelength. The electrodes 17, 18 are provided and the light emitted from the restricted region of the active layer 13 is converted to the parallel light beam when curvature of plane 23 of the lens layer 22 is selected adequately and it can be obtainedd from the plane 24 with good efficiency. Thereby, the pertinent diode can be connected to optical fiber with an efficiency near to the theoretical value while easing the aligning accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a surface emitting type light emitting diode.

By changing the composition of InGaAsP/InP light emitting elements, it is possible to easily obtain light emission wavelengths around 1.3 μm and 1.5 μm with extremely low optical fiber transmission loss, and they are highly reliable and can be made at low cost. It has been put into practical use as a light source for various medium- and long-distance optical communications and optical information systems.

To use a surface-emitting light emitting diode as an optical 7-eyeper reliable light source, its light-emitting area must be the same as the core of the fiber.
It is necessary to reduce the size to ＊ or less, increase the brightness, and increase the power donated to the optical fiber.0 When the emission diameter is smaller than the core diameter, use a rounded tip of a rod lens in a spherical lens or an optical fiber. Optical coupling circuits such as spherical fibers can be used to increase coupling efficiency to optical fibers.

These lens systems need to be placed close to the light emitting diode, and in the case of a spherical lens, there is a problem in maintaining O2, so a method of adhesively fixing the lens system to the surface of the light emitting diode with resin is adopted. In the first bulb lens and the first bulb fiber coupling method, a method is used in which a jig is created that is mechanically brought close to the stem of the light emitting diode, and the jig is fixed.

When these coupling circuits are applied to ordinary surface-emitting type light-emitting diodes, their positioning must be performed with extremely high precision in order to obtain a coupling efficiency as high as the theoretical value.

For example, a light emitting diode with a light emitting diameter of 35 μmφ and a core diameter of 5
When combining 0μmφ tip ball and eyeper, ±10μ
A positional shift of m causes a decrease in coupling efficiency of 0.5 to 1 dB. In order to eliminate these drawbacks, a method has been proposed to reduce the positioning accuracy by machining the emission surface of the light emitting diode into a dome shape to obtain high coupling efficiency. 1 piece 1
There are methods such as individual mechanical polishing, chemical etching, and ion beam etching. However, all of these methods have problems in terms of mass production and controllability, and it is extremely difficult to obtain high-quality spherical surfaces.

An object of the present invention was to solve the above-mentioned drawbacks.4 When coupling a surface-emitting type light emitting diode to an optical fiber, it is an object of the present invention to provide a structure in which a coupling circuit with high coupling efficiency can be installed while alleviating positioning accuracy when coupling to an optical fiber. Our goal is to provide light emitting diodes.

According to the present invention, in a surface emitting wave light emitting diode that extracts light from a substrate made of a first semiconductor transparent to the emission wavelength, there is a space between the active layer and the substrate.
a second semiconductor layer having a large refractive index;
A surface-emitting light-emitting diode is obtained in which the semiconductor layer has a shape that is thick on the same central axis as the light-emitting region and has a portion where the layer thickness decreases in the probing direction.

Although this invention can be applied regardless of the semiconductor material, it has the greatest effect on the emission wavelength when using a transparent substrate, so the following description will mainly focus on IIIG.
! The case of a double heterostructure light emitting diode made of IAIP IIIP system will be explained in detail with reference to the drawings.

FIG. 1 is a conceptual diagram showing the structure of a conventionally proposed light emitting diode with a dome.
nP by 7 y Plg, InGaAsP activity 7w1
3 and P-InP cladding layer 14 to form a double heterostructure, and furthermore, a P-InGaAsP cap layer 15 is successively grown thereon to obtain a good ohmic electrode. To form a dome on the opposite side of the n1nP substrate 11 from the growth layer, the photoresist surface is sphericalized by post-baking a photoresist of a predetermined diameter as large as luminescence, usually at a higher temperature. Using this photoresist film as a mask, etching is performed using an Ar ion beam. At this time, by appropriately selecting the incident angle of the ion beam and simultaneously rotating the sample, the surface shape of the photoresist can be transferred to the InP substrate 11. In this way, a dome 1 of a predetermined shape is formed on the nInP substrate 11.
6 and then following the normal process to form P-
A small-area electrode 17 is formed at the center of the surface of the InGaAsP cap layer 15 to limit the emission diameter.

This P electrode 17 is mainly made of AuZn alloy.

For example, an insulating film 19 as shown in Part 02 is formed around the 9P electrode 17, and then a metal layer 20 that is easily compatible with Jl;iLQ is deposited on the entire surface, and fixed to a predetermined heat sink or step It can be so.

On the other hand, the ISK outside the dome 16 on the surface of the n-substrate 110 is kuO.
An n-electrode 18 made of eNi or the like is formed.

In this way, when a voltage in the Klj direction is applied between the n-electrode 4118 and the p-electrode 17, a part of the active layer 13 emits light in an area slightly larger than the p-electrode 17. When this light is extracted to the upper surface, it acts as a dome lens and the coupling efficiency to the optical fiber becomes high. However, the shape of the conodome-shaped lens 16 is not so arbitrary, and the coupling efficiency cannot usually be obtained in accordance with the theoretical value.

Therefore, the coupling efficiency is further increased by using a tipped fiber or a second lens on the edge of the tipped rod lens. Optically, if a lens system is assembled using multiple lenses, various aberrations can be improved, and at the same time, the design of each lens becomes arbitrary.

Therefore, in order to maximize the coupling efficiency in a light emitting diode and optical fiber coupling circuit, it is easier to design it using two lenses than using one lens.
In this case, it is possible to reduce alignment accuracy.

However, in this conventionally known example, it is difficult to form the dome-shaped lens 16, and there are problems with uniformity and reproducibility within the well where many elements are lined up. It is extremely difficult and mourning. Nine, the formation of unevenness on the wafer surface means that
There was also the problem of the tendency to break during the process, and there was also the drawback of lowering the manufacturing yield.

FIG. 2 is a sectional view showing the concept i of an embodiment of the present invention. The same members as in FIG. 1 are given the same numbers.

In advance, a recess 23 with a predetermined diameter larger than the emission diameter and a predetermined depth is formed on one surface of n-InP by chemical etching, etc., and this is used as a substrate 21, and an n-InP film is formed on the surface with the recess.
nGaAsP layer 22, nInP cladding layer 12, In
GaAsP active layer 13 and PInP cladding layer 14,
Furthermore, a K FiP'' InGmAsP cap layer 15 is sequentially grown thereon. Here, the composition of the u-(i-P layer 22 is InGaA) so as to be transparent to the emission wavelength.
It must be covered so that it appears larger than the band gap of the sP active layer 13! There is. Both the P and n electrodes are formed in the same manner as in the case O in FIG.

The refractive index of InP and InGaAsP changes with respect to wavelength. As already known values, the refractive index for light with a wavelength of 1- is about 3.2 for InP and about 3 for IaGaAsP! It becomes s and enters.

The refractive index of the tn,n IEIGaAsP layer 22 is larger than that of the nInP 21 and 12 on both sides thereof.

Therefore, it can be seen that if a smooth curved surface 23 is formed on the layer 22 having a higher refractive index than ffcliH as in the embodiment shown in FIG. 2, this becomes a basic embedded lens. Therefore, by appropriately selecting the curvature of the lens layer 220-plane 23, the nine lights emitted in a limited area of the active layer 13 are converted into parallel rays, and the light can be efficiently extracted and extracted to the outside. I can do it with Jin.

In addition, by using another lens system such as a photosphere fiber or photosphere rod lens, the nine-ray bundle, which is once made into parallel light, can be coupled to an optical fiber with coupling efficiency close to the theoretical value while reducing alignment accuracy. become. Moreover, the element 111iK
The structure has no irregularities9, and the manufacturing yield is significantly improved.

FIG. 3 is a diagram showing a specific example of a method for forming an embedded lens. HQI on the (100) plane of the InP substrate 21
-((3PO4-based etching solution creates a circular selection error, and a (011) cross section perpendicular to this produces a shape as shown in Figure 3B.Then, set it in a liquid phase growth apparatus that can perform normal multilayer continuous growth. By melting the melt with an appropriate composition,
By performing backing, the anisotropy is relaxed and a smooth recess 23 is formed as shown in FIG. 3C with good reproducibility. As shown in the third diagram on top of the n-InGaAm
A P layer 22 is formed to have a nine-layer structure as shown in FIG. Etching liquids other than these may also be used, but the anisotropy will be different, and therefore an asymmetrical lens will be obtained. These steps can be carried out extremely stably and with good reproducibility by a conventional liquid phase growth method.

FIG. 4 is a sectional view showing another embodiment of the invention.

The luminous efficiency of the 2nd WjA n IaP cladding layer, which is close to the single Peter structure when omitted, is slightly inferior to that of the double Peter structure, but it has a further calendar number of 19, It has the characteristic of low manufacturing cost.

Although the InGaAsP/InP-based surface-emitting light emitting diode has been described in detail above, this invention can be applied to surface-emitting light-emitting diodes using any other semiconductor material.
Needless to say, the present invention can be applied to light emitting diodes as well as structures in which the conductivity types are switched.

[Brief explanation of drawings]

Fig. 1 is a sectional view of an example of a conventional dome-equipped light emitting diode, Fig. 2 is a sectional view of a first embodiment of the present invention, and Figs. The ninth sectional view for explaining an example of the forming method, and FIG. 4 is a sectional view of a second embodiment of the present invention. 11.21 ・-n-InP substrate, 12 ・=・n-I
nP layer, 22- n-InGaAsP layer, 13- Ia
GaAs)' active layer, 14--P InP cladding layer, l5=-P''-InGaAsP cap layer, 17
...P t &, 18-- n electrode, 20...
...Metal layer, 16...Dome-shaped lens, 2
3... Concavity for embedded lens, 24...
・Light extraction part. Forestry agent Susumu Uchihara Figure 7 t Figure 2 7F? A B 3

Claims (1)

[Claims] In a surface-emitting light emitting diode that extracts light from a substrate made of a first semiconductor transparent to the emission wavelength, a second semiconductor layer having a higher refractive index than the substrate is disposed between the active layer and the substrate. and the second semiconductor layer has a shape in which the second semiconductor layer is on the same central axis as the light emitting region and has a portion where the layer thickness is thicker and decreases in the rearward direction. type light emitting diode.