JPS61125092A - Semiconductor light emitting diode - Google Patents

Abstract

PURPOSE:To improve coupling efficiency without impairing light emitting efficiency, by providing a ring shaped groove, whose diameter is less than a specified length and which penetrates an active layer, and using the entire active layer at the inner side of the groove as a light emitting region. CONSTITUTION:On an N type semiconductor substrate 11, an N type semiconductor clad layer 12, an N type semiconductor active layer 13 and P type semiconductor clad layer 14 are sequentially formed, and a double heterogeneous laminated structure is obtained. A ring shaped groove 15 penetrates through the active layer 13 and has an inner diameter less than about 30mum. A P type electrode 16 is formed on the entire surface of the P type clad layer 14 at the inner side of the groove. The entire active layer 13 at the inner side of the groove 15 is made to be a light emitting region. Output light is taken out of a light output window 17, which is provided on the surface of the N type semiconductor substrate 11. A current is injected into the entire active layer 13 and the inner side of the groove 15. Therefore, the entire active layer 13 uniformly emits light, and the coupling efficiency is strikingly improved. Since the inner diameter of the groove 15 is made to be less than about 30mum, the effect is remarkable.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to semiconductor light emitting diodes (hereinafter referred to as LEDs) that are effective as light sources for optical communication systems, and particularly to surface emitting diodes (hereinafter referred to as LEDs) that emit light in a direction perpendicular to the surface of a semiconductor substrate. Regarding type LEDK.

(Prior art and its problems) LEDs will become increasingly important as light sources for optical communication systems in the future. It is important for LEDs such as those that the luminance is high and the light input to the optical fiber is large. In order to achieve this, the issue is not only the luminous efficiency of the light emitting region but also the coupling efficiency to the optical fiber. When coupling the light from an LED to a graded index fiber, which is a common fiber for optical communication, the coupling efficiency ηC is determined by the relationship between the core diameter Df of the fiber, the numerical aperture N of the fiber, and the emission diameter Da of the LED as shown in the following equation. expressed.

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

Conventionally, several current confinement methods have been used to reduce the luminous diameter (optical communication device engineering, engineering books, etc.).
(1983) p 128-9134). A typical structure is one in which the stain flow is constricted by an oxide film, and the current is constricted by a pn junction formed by a diffusion region provided near the surface. In these structures where current is constricted near the surface of the device, the current spreads laterally until it reaches the active layer and within the active skin, so the diameter of the emitted light becomes several micrometers larger than the diameter of the current confinement, and the distribution of the emitted light intensity in the radial direction changes. A significant sore occurred. Therefore, in order to reduce the emission diameter, the current confinement diameter should be set several μm beyond that.
There is a problem in that it has to be made smaller than that. Furthermore, as the emission diameter becomes smaller, the influence of the drop in the emission intensity distribution becomes larger, and the coupling efficiency deviates greatly from the relationship expressed by equation (1), so that there is a problem that the coupling efficiency does not improve even if the emission diameter is made smaller.

Further, there is a structure in which a high resistance region is provided in the active layer by proton irradiation to constrict the current. In this case, the drop in the emission intensity distribution becomes smaller, but since 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 to non-emission, and the light-emitting efficiency of the light-emitting part decreases significantly. There was a problem.

(Object of the Invention) The present invention aims to eliminate such conventional drawbacks, increase coupling efficiency without impairing luminous efficiency, and realize an LED with 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 stack structure having an active layer has an annular groove having an inner diameter of about 30 μm or less and penetrating through the active layer, A semiconductor light emitting diode characterized in that the entire active layer of the semiconductor light emitting diode is used as a light emitting region.

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

An n-type semiconductor layer 12 . is formed on the n-type semiconductor substrate 11 . n
An il semiconductor active layer 13 and a p-type semiconductor cladding layer 14 are formed in this order to form a cedar pull hetero-stack structure.

Further, a ring-shaped groove 15 having an inner diameter of about 30 μm or less is formed passing through the active layer 13 . A p-type electrode 16 is formed entirely on the surface of the P-type cladding layer 14 inside the groove 15, so that the entire active layer 13 inside the groove 15 becomes a light-emitting region. Output light is extracted from a light extraction window 17 provided on the surface of the n-type 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 has a very sharp rectangular shape, eliminating the droop in the distribution that was conventionally seen. As a result, the coupling efficiency with optical fibers is significantly improved.

Figure 2 shows the emission diameter Da and coupling efficiency η. This is a diagram showing the relationship between
When a is about 30 μm or less, the increase in binding efficiency is not large and becomes saturated. This is because as the emission diameter becomes smaller, the influence of the drooping of the emission distribution due to current waves is no longer effectively combined. According to the present invention, the coupling efficiency was significantly improved as shown by the solid line in FIG. The improvement is particularly remarkable when the emission diameter is about 30 μm or less, and 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, improvement in coupling efficiency directly leads to improvement in coupling power, resulting in high fiber power.

By the way, in the mesa-shaped LID that has been reported so far, a current confinement means is provided on the surface of the mesa, and the current is injected only near the center of the mesa (Hitachi Review Vol.
1.65yNolO (1983) p49-52). However, this structure is basically the same as the current confinement due to the insulating film and active 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 into the entire active layer inside the groove, the entire active layer emits light uniformly and the coupling efficiency is significantly improved, and this effect is remarkable when the inner diameter of the groove is about 30 μm or less. This has become clear through experiments.

Furthermore, since 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, it protects the semiconductor layer inside the trench from defects during the device manufacturing process, increasing yield. It is possible to raise the shi. Furthermore, since stress is not concentrated only on the semiconductor layer inside the groove, there is an advantage that reliability is high.

(Example) FIG. 3 is a cross-sectional structural diagram of an element showing an embodiment of the present invention.

An n-type InP layer 12 and an n-type InG layer are formed on an n-type InP substrate 11.
aAsP active layer 13 yp type InP layer 14, p type InGa
The AsP contact layer 18 is sequentially formed by, for example, a liquid phase epitaxial method. Subsequently, by chemical etching using, for example, Br methanol, a ring-shaped groove 15 having an inner diameter of 25 μm and penetrating the active layer is formed. Except for the surface of the p-type InGaAsP contact layer 18 inside the trench 15, S
The entire iO□ film 21 is coated with T on the surface of the p-type contact layer 18.
An ilt film is formed to serve as a p-type electrode 16. After polishing the n-type InP substrate 11 to a thickness of about 100 μm, a light extraction window 17 with a diameter of about 100 μm is formed in the annular groove concentrically, and an AuGeNi film is formed thereon to form the n-type electrode 19. Finally p
A gold plating layer 20 with a thickness of 10 to 20 μm is formed on the mold electrode 16.

FIG. 4 shows current vs. fiber human power characteristics for an LED of the present invention and a conventionally constructed LED of 8i02 current constriction made from the same Univar. The fiber is a graded index fiber with a core diameter of 50 μm and a numerical aperture NA=0.2. In this example, LE
The coupling efficiency of iD's output light to the fiber has been significantly improved, and the fiber power is more than 100 μW, more than twice as high as before. Furthermore, because of the groove structure, the manufacturing yield was significantly improved compared to a simple mesa structure without a semiconductor layer outside the groove.

(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 without impairing the luminous efficiency, and the light input to the optical fiber was significantly improved, with a high manufacturing yield.

The present invention can be applied not only to LEDs using InGaAsP as an active layer but also to LEDs using other semiconductors such as GaAs.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 2 illustrate the principle of the present invention, and FIG. 1, FIG. 2, and FIG. 2 illustrate embodiments of the present invention. 1,000 2 Figure 9 - Optical diameter, Do (μm) 20.4 The moon and green onion. Tei 4 mouths

Claims (1)

[Claims] In a semiconductor light-emitting diode with a double-hetero laminated structure having an active layer, a ring-shaped groove having an inner diameter of about 30 μm or less and penetrating the active layer is provided, and the entire active layer inside the groove is used as a light-emitting region. Features of semiconductor light emitting diodes.