JPS6260278A - Semiconductor light emitting diode - Google Patents

Abstract

PURPOSE:To improve coupling efficiency by a method wherein a whole disk type active layer is used as a light emitting region and two semiconductor layers are contacted with the active layer to form a double-hetero laminated structure and one of the two semiconductor layers, which is contacted with a semiconductor substrate, is given an electric conductivity type of P and the other semiconductor layer is given a type of N. CONSTITUTION:A P-type semiconductor cladding layer 12, an N-type semiconductor active layer 13 and an N-type semiconductor cladding layer 14 are successively formed on an N-type semiconductor substrate 11 to form a double-hetero laminated structure. The active layer is limited to a disk type active layer region 13 with a diameter less than about 30mum. On the most part of the surface of the N-type cladding layer 14 formed immediately above the disk type active layer region 13, an N-type electrode 17 is formed to use the whole disk type active layer region 13 as a light emitting region. A P-type electrode 18 is formed on a part of the surface of the P-type semiconductor cladding layer 12 and an output light is taken out from the surface of the N-type semiconductor substrate 11.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a semiconductor light emitting diode (hereinafter referred to as LFiD) which is effective as a light source for an optical communication system, and particularly a surface emitting diode (hereinafter referred to as LFiD) that emits light in a direction perpendicular to the surface of a semiconductor substrate. Regarding board LED.

(Prior art and its problems) LEDs will become increasingly important as light sources for optical communication systems in the future. In such an LFSD, it is important that the luminance is high and the light input to the optical fiber is large. For this purpose, the coupling efficiency to the optical fiber becomes a problem as well as the luminous efficiency of the light emitting region. When coupling LED light to a graded index fiber, which is commonly used as an optical communication fiber, the coupling efficiency ηC is determined by the fiber core diameter Df.
.

It is expressed by the relationship between the numerical aperture NA of the fiber and the emission diameter Da of the LED as shown in the following equation.

That is, the smaller the emission diameter Da of the LED, the higher the coupling efficiency, so it is desirable to make the emission diameter as small as possible.

Conventionally, several current narrowing methods have been used to reduce the emission diameter (optical communication device engineering, engineering books,
(1983) P128-P134). The general structure is
This is a structure in which the current is constricted by an oxide film or by a pn junction formed by a diffusion region provided near the surface. In these structures where current confinement occurs near the element surface, the current is
Since it spreads laterally until it reaches the active layer and within the active layer, the emission diameter becomes several μm larger than the current narrowing diameter, and a significant droop occurs in the radial distribution of emission intensity. Therefore, in order to reduce the emission diameter, there is a problem in that the current narrowing diameter must be reduced by several μm or more.

Furthermore, as the emission diameter becomes smaller, the influence of the drop in the emission intensity distribution increases, and there is a problem that the coupling efficiency deviates greatly from the relationship expressed by equation (1), and the coupling efficiency does not improve even if the emission diameter is made small.

Further, there is a structure in which a high resistance region is provided in the active layer by proton irradiation to narrow the current. In this structure, the drop in the emission intensity distribution becomes smaller, but because the light-emitting region of the active layer is surrounded by a damaged layer due to proton irradiation, carriers are lost in the damaged layer through non-light-emitting processes, which increases the luminous efficiency of the light-emitting part. There was a problem in that the value decreased significantly.

(Objective of the Invention) An object of the present invention is to eliminate such conventional drawbacks, and to provide an LFiD that increases coupling efficiency without impairing luminous efficiency and allows high light input to an optical fiber.

(Structure of the Invention) According to the present invention, a semiconductor light emitting diode having a double-hetero laminated structure having an active layer on a semi-insulating or mouth-type electrically conductive semiconductor substrate is used to produce a semiconductor light emitting diode with a diameter of about 30a7F.
! It has an active layer limited to the following disk shape, the entire disk-shaped active layer serves as a light emitting region, and one of the two semiconductor layers that is in contact with this active layer and forms a double-hetero stacked structure with the active layer. A semiconductor light emitting diode is obtained in which the electrical conductivity type of the semiconductor layer on the side closer to the semiconductor substrate is P type, and the other semiconductor layer is of mouth type.

(Operation, principle of invention) FIG. 1 is a diagram showing an example of the cross-sectional structure of an element according to the present invention.

On the n-type semiconductor substrate 11, a p-type semiconductor cladding layer 12, n
A type semiconductor active layer 13 and an n-type semiconductor cladding layer 14 are formed in this order, exhibiting a double-hetero stacked structure. Further, the active layer has a disk-shaped active layer region fi with a diameter of about 30 μm or less.
Limited to 13. A mouth electrode 17 is formed on most of the surface of the n-type cladding layer 14 directly above the disc-shaped active layer region 13, so that the entire disc-shaped active layer region 13 becomes a light-emitting region. Moreover, the P-type semiconductor cladding layer 12
A Pfi electrode is formed on a part of the surface. and n
Output light is extracted from the surface of the semiconductor substrate 11.

In the present invention, a disk-shaped active layer is formed, and a current is injected into the entire disk-shaped active layer, so that light is emitted uniformly. As a result, the emission intensity distribution in the radial direction becomes a very sharp rectangular shape, eliminating the droop in the distribution that was previously observed. Therefore, the coupling efficiency with optical fibers is significantly improved.

Fig. 2 is a diagram showing the relationship between the emission diameter Da and the coupling efficiency WC. Conventionally, as shown by the broken line in Fig. 2, the coupling efficiency increases when the emission diameter Da is about 30 μm or less. is not large and saturated. This is because as the diameter of the emitted light becomes smaller, the effect of drooping of the emitted light distribution due to current waves increases, and the light is not coupled effectively. According to the present invention, the coupling efficiency was significantly improved as shown by the solid line in FIG. The improvement is particularly noticeable when the emission diameter is approximately 30 μm or less.
The smaller the diameter, the greater the improvement.

Furthermore, unlike conventional, for example, proton irradiation type LEDs, the active layer light emitting region is not surrounded by defective regions, so that there is no reduction in light emitting efficiency. As a result, the improvement in coupling efficiency directly leads to the improvement in coupling power, and high fiber power can be obtained.By the way, conventionally reported mesa-shaped LEDs
In this case, a current narrowing means is provided on the surface of the mesa, and the current is injected only near the center of the mesa ("Hitachi Review Vol. 1, 65. No. 0 (1983) P49-5
2). However, this structure is basically the same as the current confinement caused by the insulating film or diffusion layer described above, and does not solve the problem of deterioration in coupling efficiency due to the fluctuation of the emission intensity distribution that occurs when the emission diameter is made small. 'However, in the present invention, since the current is injected throughout the disk-shaped active layer, the entire active layer emits light uniformly and the coupling efficiency is significantly improved, and this effect is noticeable when the disk diameter is about 30 μm or less. It has been revealed through experiments that this is the case.

Further, of the two semiconductor cladding layers in contact with the active layer 13, the semiconductor cladding layer 12 on the side closer to the semiconductor substrate 11 is of the P type, and the other semiconductor cladding layer 14 is of the N type. Since the specific resistance of n[semiconductors is extremely small, several tenths or less of that of P-type, it is possible to significantly reduce the electrical resistance here by making the cladding layer 14, which has a narrow current flow path, of N-type. can. Furthermore, since the ohmic electrode resistance to an n-type semiconductor is smaller than that to a p-type semiconductor, by making the cladding layer 14 n-type, the resistance of the ohmic electrode to the cladding layer 14 having a small electrode area can be reduced. In this way, by making the cladding layer 14 on the opposite side of the semiconductor substrate from the active layer to NFI, it is possible to significantly reduce element resistance, reduce heat generation during DC operation, and improve optical output and reliability. can improve sexual performance.

Further, the electrical conductivity type of the semiconductor substrate 11 may be semi-insulating or NFI.
Therefore, compared to the P type, light attenuation due to free carrier absorption can be significantly reduced, and the light output extracted from the surface of the substrate 11 can be increased.

(Example) FIG. 3 is a cross-sectional structural diagram of an element showing a first example of the present invention. On the riiInP substrate 11, a P-type InP crat layer 12, an n-type InGaAsP active layer 13, an n-type InP
A P cladding layer 14 and an n-type InGaAsP:1 intact layer 15 are formed in this order by, for example, a liquid phase epitaxial method. Subsequently, a circular mesa is formed by chemical etching using, for example, Br methanol, so that the active layer 13 has a disk shape with a diameter of about 25 μm. 5i on the side of the mesa
(H film 16 is formed.

On the surface of the n-type InGaAsP contact layer 15,
A uGeNi film is formed as an n-type electrode 17, and a p-type electrode 1 is formed.
8. Finally, the substrate 11 is polished to a thickness of about 1100 Å.

This embodiment significantly improves the coupling efficiency of the output light from the LED to the fiber, and the fiber λ power is approximately 2
It has improved more than twice. Furthermore, since the cladding layer 14 was made of n-type, the element resistance was reduced to 175 or less compared to P-type, and heat generation during DC operation was significantly reduced, which also contributed greatly to the improvement of optical output. Furthermore, this reduction in heat generation greatly improved the reliability of the device.

FIG. 4 shows a second embodiment of the invention. Unlike the first embodiment, the active layer light emitting region 13 is limited to a disk shape with a diameter of about 25 μm by a groove 19 penetrating the active layer. Further, the conductivity type of the semiconductor substrate 11 is semi-insulating. P-type InP cryF layer 12 on semi-insulating substrate 11
, n-type InGaAsP active layer 13, n-type InP crystal layer 4. A nuInGaAs contact layer 15 is sequentially formed by, for example, a liquid phase epitaxial method. Subsequently, by chemical etching with Br methanol, an internal groove 19 having a ring shape of -9:25 .mu.m and penetrating the active layer is formed. Zn diffusion is performed from the surface of the n-type InGaAsP contact layer 15 outside the trench 19 to reach the P-type InP cladding layer 12 to selectively form a P-type diffusion region 20. An AuGeNi film is formed on the surface of the n-type I nGaAsP contact layer 150 inside the groove 19 to serve as the n-type electrode 17, and a film is formed on the surface of the P-type diffusion region 20 outside the groove 19.
A Zn film is formed, and a 5if2 film 21 is formed on the side surface of the groove 19 which will become the Pfi electrode 18. Gold plating layers 22 and 23 are formed on the surfaces of the P-type electrode 1g and the N-type electrode 17, respectively. Finally, the InP substrate 11 is polished to a thickness of about 100 μm to form a light extraction port.

In this example, in addition to the effects described in the first example, since the groove structure was used, the manufacturing yield was greatly improved compared to the first example in which there was no semiconductor layer outside the groove. This is because the surface of the semiconductor layer outside the trench is almost at the same height as the surface of the semiconductor layer inside the trench, so the semiconductor layer inside the trench is protected from defects during the device manufacturing process. This is because the yield can be increased. Furthermore, In
Since the P substrate 11 is semi-insulating, free carrier absorption is further reduced, and the optical output is improved compared to the first embodiment.

(Effects of the Invention) According to the present invention, it was possible to obtain a high-performance LED in which the coupling efficiency with the fiber was increased and the light input to the optical fiber was significantly improved without impairing the luminous efficiency at a high manufacturing yield.

Note 1: The present invention provides an LE having an active layer of InGaAsP.
It can be applied not only to LEDs made of D but also other semiconductors such as GaAs.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the principle of the present invention, FIG. 2 is a graph showing the relationship between emission diameter and coupling efficiency, and FIG. 3 is a graph showing the relationship between emission diameter and coupling efficiency. FIG. 4 is a sectional view showing each embodiment of the present invention. 11...Substrate, 12...Pg cladding layer, 13...Active layer, 14...n[cladding layer, 15...nfi contact layer, 16
．． 21...8i0-film, 17...n-type electrode, 18...--p type electrode, 19...groove, 20...P Type diffusion region, 22.23...
・Gold plating layer. Figure 1 rate 3 concave condolence 2 ward light emitting demonstration D order (μ penalty

Claims (1)

[Claims] A semiconductor light emitting diode having a double heterostack structure having an active layer on a semi-insulating or n-type electrically conductive semiconductor substrate, the active layer having a disk shape with a diameter of about 30 μm or less, The entire disk-shaped active layer is used as a light-emitting region, and of the two semiconductor layers that are in contact with this active layer and form a double-hetero stacked structure with the active layer, the electrical conductivity type of the semiconductor layer that is closer to the semiconductor substrate is determined. A semiconductor light emitting diode characterized in that the semiconductor layer is of P type and the other semiconductor layer is of N type.