JPS5990972A - Semiconductor light-emitting diode - Google Patents

Abstract

PURPOSE:To obtain the LED, in which the linearity of currents-optical output characteristics is improved remarkably without damaging fiber coupling power, by forming a first conduction type semiconductor layer between an active layer and a first conduction type ohmic electrode and forming a region, in which first conducton type impurity carrier concentration is increased with a separation from the central axis of a light- emitting region, in the semiconductor layer of the first conduction type semiconductor layer. CONSTITUTION:An N type InP layer 31 and a P type InGaAsP layer 34 are formed on an N type InP substrate 30, an SiO2 film is formed to the surface of the P type InGaAsP layer 34, a pattern is formed, the SiO2 film is left circularly, and others are removed. A P type impurity such as Zn is diffused while using the SiO2 film as a mask, and high-concentration diffusion regions 35 are formed in a P type InP layer 33. A TiPt film 37 is formed on the surfaces of the P type InGaAsP layer 34 and the SiO2 film 36, and the P type ohmic electrode 38 is formed through heat treatment in H2 or N2. Lastly, N type ohmic electrodes 39 are formed through heat treatment in a H2 or N2 atmosphere. When forward currents are flowed through the LED, a light-emitting diameter expands in a low current region, current concentration becomes more conspicuous with the increase of currents, and the extension of the light-emitting diameter reduces to several mum or less in a high current region.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light emitting diode (hereinafter referred to as LgD).

LEDs are important as light sources for optical communication systems and are being actively researched and developed.

In particular, GaAs/AJGaAs with an emission wavelength of 0.8 μm band
LEDs of this type are already in practical use. by the way,
The advantages of LEDs as light sources for optical communication are that they are inexpensive, have excellent reliability, and have excellent linearity in optical output characteristics, especially when using analog modulation methods. It plays an important role as a light source for communication systems. Now, as optical fibers have become lower in loss in recent years, the longer wavelength band (4.7 μm in total, 1 μm in wavelength) has become the region with the lowest transmission loss. Along with this, L of InGaAsP/InP yarn that outputs light in this wavelength range can also be used as a light source.
Research and development of ED is progressing. However, conventional fnoa, AsP/In, and P thread LEDs exhibit a saturation phenomenon in which the light output saturates as the current increases, and the linearity of the current-light output characteristics is extremely poor. For this reason, the great advantage of LEDs, which is limited to analog modulation type communication systems, has been lost.

By the way, recent research, including research by the inventors, has revealed that the saturation of this current-light output characteristic is caused by n in addition to a light emitting current component proportional to the square of the carrier concentration n injected into the InGa-AsP active layer. This is because there is a non-luminescent current component proportional to the third power of It has become clear that there is an extremely high level of sexuality. Based on these research results, it is possible to increase the thickness of the active layer in order to reduce the saturation of the current-light output characteristics, or to operate with a low injected carrier concentration by increasing the light emitting area. It will be done. In fact, saturation can be improved to some extent by making the active layer thicker or by increasing the light emitting area. However, if the active layer is thickened to 2 to 3 μm or more, the light absorption within the active layer decreases by 1f.
As l increases, the distribution of injected carries in the thickness direction within the active layer becomes uneven, causing problems such as a significant loss of optical output. However, it is extremely difficult to significantly improve saturation by increasing the thickness of the active layer. In addition, increasing the light emitting area poses few 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 light emitting area extremely large. Core diameter number 10 used in optical communication
When coupled to an optical 7-eyeper of about μm, there is a problem in that the coupling loss becomes large and the fiber coupling power is significantly impaired.

Furthermore, such Auger recombination is possible in InGaAs
There are also research results showing that the problem is not only caused by P, but also by other semiconductor materials that can be used as a light source with a wavelength of 1 to 1.7 μm, to the same extent or more than InGaAsP, and it is difficult to solve the problem by changing the semiconductor material.

In this way, to deal with the problem of saturation of electrolyte precipitation and optical output characteristics,
No practically effective means have been available so far.

The present invention was made in order to eliminate these power defects.
The present invention proposes an LED in which the linearity of the current-light output characteristic is significantly improved without significantly impairing the fiber-coupled power. That is, the light emitting diode of the present invention has a double heterostructure, and is a planar light emitting type semiconductor light emitting diode that emits light in a direction perpendicular to the main surface of a semiconductor substrate. at least 1 between
A first conductivity type semiconductor layer having a layer force of 1 is provided, and in at least one semiconductor layer of the first conductivity type semiconductor layer, the central axial force of the light emitting region is increased by 1, and the first conductivity type impurity carrier concentration increases. It is out of configuration with a region.

The present invention will be explained in detail below using the drawings. Figure 1 is from Book 4: A diagram for explaining the principle of light emitting diode. Figure 1 (,) shows the cross-sectional front sound of the LED. Figure 1 (b) and (C) show the conventional and uninvented L 1!3 D
◎ In the conventional LED, the carrier concentration distribution in the P-type cladding layer 11 in the horizontal direction is uniform, but in the T of the present invention,
ET), the gear concentration on the outside is higher than in the center of the current flow path.

When a forward current is passed from the P-type insulator 12 with a diameter Dc provided on the surface of the P-type cladding layer 11, the current shield 1 spreads in the P-type cladding layer 11 and the active a layer 13. Current flows in a region wider than the diameter Dc, and the emission diameter Da becomes larger than the electrode diameter Dc. Here, the diameter where the emission intensity is 10 at the center is defined as the emission diameter.

The current wave in the P-type cladding layer 11 increases as the electrical conductivity of the P-type cladding layer 11 increases, that is, as the carrier concentration increases. Furthermore, as the current increases, the ratio of the current flowing through the central part to the peripheral part of the current flow path increases, and the degree of current concentration increases. The LED of the present invention actively utilizes this current wave. Figure 1 (
As shown in C), in the LED of the present invention, a region having a higher carrier concentration than the center is provided at a position away from the center of the current in the P cladding layer. Therefore, in the low current region, the current wave becomes even larger than in the high concentration region. On the other hand, in a high current region, the current mainly flows through the center, and the influence of the high concentration regions provided at the periphery is reduced, resulting in smaller current waves. Therefore, looking at the change in the emission diameter ratio with respect to the electric current,
As shown in FIG. 2, this shows an extremely large change compared to the conventional method.

A pattern is formed using resist and has a diameter of approximately 120 μm.
The AuGeNi is removed in a circular shape to form a light extraction window 40. Finally, an n-type ohmic electrode 39 is formed by heat treatment in an H or N atmosphere. This LED
When a forward current is applied to , the current increases to 3 N as shown in Figure 4.
In the low current range below O+nA, the emission diameter expands by about 10-30 μm, and as the current increases, current concentration becomes more pronounced.
In the high current range of 10100-2O0, the emission diameter expands to several μm or less.

When the diameter of the P sub-electrode 38 is 20/jln, the emission diameter is 4
It changes from about 5 μm to 25 μm 4M*t. Therefore, when this LED is coupled to, for example, a graded indetatus 7 eyeper with a core diameter of 50 μm, the coupling efficiency increases as the current increases.
Unprecedented excellent L Iy D characteristics with significantly improved linearity of current-light output characteristics were obtained.

FIG. 6 is a diagram showing another implementation of the present invention, and FIG. 7(a)
FIG. 6 shows the cross-sectional structure of L18D (bl shows the carrier concentration distribution of the P-type cladding layer 33, respectively.

In this embodiment, a high concentration region 35 is provided at the periphery of the P-type cladding layer 33 and the current flow path, and a high concentration region 41 is also provided at the center of the flow path.

This high concentration region 41 can be formed by diffusion of PM impurities as in the embodiment shown in FIG. M3. High concentration area 41 in the center
Since the concentration of current in the center in the high current range is more pronounced than in the example shown in Figure 3, the fiber-coupled power at high currents becomes larger, further improving the linearity of the current-optical output characteristics. I was able to do something.

In the embodiments shown in FIGS. 3 and 6, the high concentration region is P-In.
Although it is formed in both the P cladding layer and the P-InOaAsP contact layer, it is similar even if it is not formed in both layers or only in either the cladding layer or the contact layer. effect can be obtained.

Furthermore, the high concentration region can be formed by a method other than impurity-based methods, for example, by scraping off a portion that should become a high concentration region and then forming a high sensitivity region in that portion by crystal growth, the same effect can be obtained.

The effects of the present invention can also be obtained with a structure in which the electrically conductive molding of each layer is reversed with respect to the embodiments shown in FIGS. 3 and 6, that is, a structure in which Pg is reversed to n-type.Carrier concentration When the values are the same, the electrical conductivity of n-type InP is several tens of times higher than that of p-type InP.

Therefore, to obtain the same current spreading effect, compared to the P type, the
There is a great manufacturing advantage in that an amount of impurity is required to be an order of magnitude lower.Also, if the carrier concentration is the same as in the P-type case, the thickness of the n-type InP layer can be made thinner, reducing series resistance and heat. It also has the advantage of being able to reduce resistance. In the embodiments so far, an InGaAsP/InP-based LED DVC has been shown, but the present invention can also be applied to LEDs using other Ⅰ-v group compound semiconductor materials.

As described in detail above, according to the present invention, it was possible to obtain an LED in which the linearity of the current-light output characteristic was significantly improved without impairing the fiber-coupled power.

[Brief explanation of drawings]

Figures 3(a) and 6(b) to 6(a) are for clarification. (b) is a detailed illustration of the present invention. In the figure, 13.32 is an active layer, 11.33 is a P-type rad layer, 34 is a P-type contact layer, 30.31 is an n-type semiconductor, 35.41 is a high impurity carrier concentration region, and 36 is an 8i
(J film 12, 37, 38, 39 indicates the electrode metal, and 40 indicates the light extraction window. (b) 35 38 35 37 (b) 0 50 to. mA) Figure 5 (b) Figure 6

Claims (1)

[Claims] It has a double hetep structure, and on the main surface of the semiconductor substrate,
In a planar light emitting type semiconductor light emitting diode that extracts light in the vertical direction, at least one first conductivity type semiconductor layer is provided between the active layer and the first conductivity type ohmic electrode, and the first conductivity type semiconductor layer is provided with at least one first conductivity type semiconductor layer. A semiconductor light emitting diode, comprising a region in at least one semiconductor layer, the region having a first conductivity type impurity carrier concentration increasing as the distance from the central axis of the light emitting region increases.