JPS5891689A - Semiconductor light-emitting diode - Google Patents

Abstract

PURPOSE:To increase light-emitting volume without enlarging the diameter of light emission, to improve the saturation of optical output and to obtain high fiber combination power by unevenly forming the upper surface and lower surface of an active layer. CONSTITUTION:The plane light emission type semiconductor light-emitting diode, which has double-hetero structure and extracts beams in the vertical direction to the main surface of a semicondutor substrate, is formed. The diode is formed in such a manner that an N type InP layer 13, an N type InGaAsP layer 14 functioning as the active layer and a P type InP layer 15 are shaped onto the N type InP substrate 11, a high-concentration region 17 through the diffusion of Zn is molded and ohmic electrodes 18, 19 are shaped. The upper surface and the lower surface in at least light-emitting section of the active layer 14 are formed in uneven and corrugated shape, and the thickness of the active layer is made approximately constant. Accordingly, substantial light-emitting volume is increased, the rate of Auger recombination currents is reduced, and optical output is augmented.

Description

[Detailed description of the invention] Semiconductor light emitting diode (hereinafter referred to as LED) manufactured by the present inventor
In particular, it relates to a so-called 111 Ia K light emitting device which extracts light from a direction perpendicular to a semiconductor substrate.

It is important as a light source for IJD a and optical communication systems, and research and development are being actively conducted on it. In particular, the emission wavelength is 0.
．． The 8 μm band G6mua/AJG-muS OLE has already been put to practical use. The advantages of Ia as a light source for optical communications are that it is inexpensive, has excellent reliability, and has excellent linearity in current-light output characteristics, especially for analog It plays an important role as a light source in modulation type communication systems. Now, as the loss of optical fibers has decreased in recent years, the long wavelength band, such as wavelengths of 1 μm to 1.7 μm, has become the region with the lowest transmission loss. Along with this, I output light in this wavelength range as a light source.
Research and development of nGa5sP/InP-based Ia is progressing. However, in the conventional InG-P/InP double heterostructure LED, the optical output saturates as the current increases, and the linearity of the current-light output characteristic is extremely poor.

For this reason, the great advantage of LEDs, which is that they are suitable for analog modulation communication systems, has been lost. Furthermore, due to the saturation of the optical output, the luminous efficiency was poor under normal operating conditions, making it impossible to obtain high output.

By the way, recent research by the present inventors, including O Research 4, shows that the saturation of this current-light output characteristic is not only due to the emission current proportional to the square of the carrier concentration n injected into the InGaAlIP active layer, but also due to the saturation of the current-light output characteristic, which is approximately 3 of n. This is because there is a non-luminescent current proportional to the power of the current, and as the current increases, the ratio of this non-luminescent current component to the total current increases, and this non-luminescent current is extremely likely to be caused by Auger recombination. It has become clear.

Based on these research results, increasing the thickness of the active layer to reduce the saturation of the current-light output characteristics, or
A possible strategy is to increase the emission diameter to operate in a state where the injected carrier concentration is low. In fact, as the active layer becomes thicker and the emission diameter becomes larger, the saturation is improved to some extent. The distribution in the thickness direction within the active layer may become non-uniform, resulting in the problem of a significant loss of optical output, and it has been extremely difficult to effectively control the crystal growth as the thickness increases. Increasing the emission diameter causes fewer problems in terms of light absorption, distribution of injected carriers, and crystal growth, but in order to significantly improve saturation, it is necessary to make the emission diameter extremely large. When coupled to an optical fiber with a core diameter of several 10 μm and 11 degrees used in communications, there is a problem in that the coupling loss is large and the fiber coupling power is significantly impaired.

Furthermore, there are research results that show that Auger recombination can occur to the same degree or more than InGgAsP with other semiconductor materials that can be used as light sources with wavelengths of 1 to 1.7 μm, rather than just aInGgAaP. It is also difficult to solve this problem. To solve the problem of saturation of the current-light output characteristics, no practically effective means have been found to date.The present invention has been made to eliminate these drawbacks. Improved characteristic saturation, large fiber-coupled power, and excellent linearity
It provides ED.

That is, in a balanced light emitting type semiconductor light emitting diode made of an m-v group compound semiconductor, having a double heterostructure, and emitting light in a direction perpendicular to the main surface of a semiconductor substrate, at least the upper surface and the light emitting part of the active layer are This semiconductor light emitting diode is characterized in that the lower surface is uneven and wavy, and the thickness of the active layer is approximately constant.

According to the present invention, since the upper and lower surfaces of the active layer are made uneven, the light emitting volume can be increased without increasing the light emitting diameter and the active layer thickness.

This eliminates the traditional drawbacks and improves the saturation of light output.
Moreover, it is now possible to obtain high fiber coupling power9.

The present invention will be explained in detail below using the drawings. InGg sP/Imp LED with emission wavelength of 1.3 μm
will be explained along with an example.

FIG. 1 is a diagram showing the uO layer structure of an embodiment of the present invention. FIG. 1(,) shows the top surface of the LED, and FIG. 1(b) shows the A-R
FIG. 1(e) shows a BB' cross section. A mask is formed in stripes on the surface of the n-type InP substrate 110 using a 7-layer photoresist.

The surface of the substrate 11 is selectively etched by chemical etching, etching, or ion etching to form grooves with a depth of about 1 to 5 μm at intervals such that a plurality of grooves are formed within the light emitting region, for example, from several μm to several μm. 10μ
- formed at intervals. After removing the mask, an n-type InP layer or an n-type InGa layer 8P is formed on the substrate 11 in which the groove is formed.
Layer (band gear, wave length: 1.3 am) 13, n MliInGaAsP layer (/(band gear, wave length: 1.3 μm), active layer) 14, PtliInP layer 15
Liquid phase Evita +7/-4J method, side phase epitaxial method,
It is formed continuously by a molecular beam epitaxial method or the like. n
l! The InP layer 13 has a thickness of about 1 μm or less and is made of n-type InGaA.
When the sP active layer 14 is made to have a thickness of 1 to 2 μm or less, the upper and lower surfaces of the active layer 14 are uneven and have a thickness of 1 to 2 μm. '! F! ! 'An active layer 14 is formed. 2 p-type InPM*15
When the thickness is -3 .mu.m or more, the surface of this layer 15 becomes almost flat, resulting in an overall layered structure as shown in FIG. 1(b). Next, G is applied to the surface of the p-type I nP 15.
After forming the membrane 16, a pattern is formed using photoresist, and Ji+QJ is removed in a circular shape with a diameter of 20 to 40 μm. This E? +Q, Cd using film 16 as a mask
A high concentration region 17 is formed by diffusing X and n. , SiO
*A P-type ohmic electrode 18 is formed by depositing an AuZn film 18 on the surface of the film 16 and the high concentration region 17 by vapor deposition, and alloying AuZn by heat treatment in an atmosphere. Next, n fjl I nP substrate 11
After polishing to a thickness of approximately 100 μm, A is applied to this surface.
Form uGeNi vapor deposition IE19. Photoresist with 5iONt6 circular butter/1juGeNi
A pattern is formed on the film 19, and the AuGeNi is removed in a circular shape with a diameter of about 120 μm to form a light extraction window 20. Finally, the AuGeN
It is n-type ohmic by t-alloying.

Then, an electrode 19 is formed.

In the LED of this example, the upper and lower surfaces of the active layer are uneven, making it a so-called wavy active layer, and the thickness is almost constant, so it emits less light than the conventional IJD, which has a flat active layer. Even if the diameter and active layer thickness are the same, the σ emission volume becomes larger. For example, as shown in Figure 1, if the cross section of the active layer is a V-shaped waveform (4), the angle is approximately 60°.
In the case of a flat active layer 12), the light emitting volume is approximately twice that of an LED. As a result, when compared at the same current value, the injected carrier chain degree is lowered by 9, the proportion of Auger recombination current is reduced, the optical output is increased, and the linearity of the current-optical output characteristic is also improved. FIG. 2 shows the current vs. fiber coupling power characteristics for υ of this example, and for comparison, the characteristics of the conventional active layer thickness and emission diameter Ia are also shown. As described above, in this embodiment, the fiber coupling power was increased by several hundred points and the linearity of the current-light output characteristic was also improved compared to the conventional one.

FIG. 3 is a diagram showing another embodiment of the present invention, and FIG.
) is the top surface of the LED, FIG. 3(b) is the A-N cross section,
FIG. 3(c) shows a BB' cross section.

After forming an eye-shaped mask on the surface of the n-type 1nP substrate 11 using photoresist, the substrate 1 is
A groove 12 is formed on the surface of the substrate 1 in the shape of a base. After that, the first
n-type InpH3, n
A type InGgAsP layer 14 and a p-type InP layer 15 are formed, and electrodes 18 and 19 are formed.

The LED of this example is the same as the first example in that the upper and lower surfaces of the active layer are uneven to form a wavy active layer, but the dotted line and wave direction are different. The point is that there is a direction. That is, the active layer has a wavy shape in the cross section KA- shown in FIG. 3, which is perpendicular to the cross-section B'. Therefore, the light emitting volume becomes larger than that of the first embodiment.

The light emitting volume is 3 to 5 times larger than I@ of a flat active layer.

As a result, the current-light output characteristics were further improved, and as shown in FIG. 4, the fiber-coupled power was greatly improved to about twice that of the conventional one, and the current-light output characteristics were also significantly improved.

Also, when the active layer has a concentric waveform as shown in FIG. 5, the same effect as in the second embodiment can be obtained.

In addition to the effects described above, the advantages of the present invention include:
It also has the following effect of improving light output. In other words, since the active layer is uneven, for example, light that once exits from the recesses of the active layer to the cladding layer passes through the cladding and cladding layers.
This has the effect of increasing so-called photon recycling, in which carriers are re-excited by entering the recess next to the active layer.

Therefore, it has the advantage that the optical output is further improved.

As described above, according to the present invention, it is possible to obtain U with excellent linearity of current-optical output characteristics and high fiber-coupled power! ! friend. Note that the present invention relates to InGaAa
It is constructed not only from P/I nP system but also from other side-V group compound semiconductor materials and is effective for nine circles.

[Brief explanation of the drawing]

FIG. 1 shows the structure of U in the first embodiment of the present invention, FIG. 82 shows its characteristics, FIG. 3 shows the LID structure in the second embodiment, FIG. 5 each shows the structure of the third embodiment. In the figure, 11 is a substrate, 14 is an active layer, 16 is a SiO film, and 18 and 19 are electrodes. Electric Distress 4 Zuden Years Old

Claims (1)

[Claims] ■-■ group compound semiconductor), has a double heterostructure and extracts light in a direction perpendicular to the main surface of the semiconductor substrate.
A semiconductor light emitting diode of flat light emitting type, characterized in that at least the upper and lower surfaces of the active layer, which are located in the light emitting part, are uneven and wavy, and the thickness of the active layer is approximately constant. .