JPS625674A - Semiconductor light emitting diode - Google Patents

Abstract

PURPOSE:To perform an LED having high light input to an optical fiber by using the entire disklike active layer having a diameter of specific value or lower as a light emitting region, and forming an acute angle between a boundary near a main light producing port of two hetero laminated layer boundary contacted with the active layer and the side of the active layer, thereby increasing the coupling efficiency without loss of light emitting efficiency. CONSTITUTION:An active layer 13 limited to a disk state of 30mum or less of diameter is formed, the entire layer 13 is used as a light emitting region, and an acute angle is formed at an angle theta between a boundary near a main light producing port 15 of two hetero laminated layer boundary contacted with the layer 13 and the side of the layer 13. For example, an N-type semiconductor clad layer 12, an N-type semiconductor active layer 13, a P-type semiconductor clad layer 14 are sequentially formed on an N-type semiconductor substrate 11, and the layer 13 is limited to a disklike active layer region 13 of approx. 30mum or less of diameter. A P-type electrode 15 is formed on the entire surface of the P-type clad layer directly above the region 13 so that the entire region 13 becomes a light emitting region to produce an output light from a light producing window 15 formed on the surface of the substrate 11. Further, an angle theta formed between the boundary of the layers 13 and 12, and the side of the layer 13 is made in an acute angle.

Description

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

(Prior art and its problems) LEDs will become increasingly important as light sources for optical communication systems in the future. For such LEDs, it is important that the luminance is high and the light input to the optical fiber is large. For that,
In addition to the luminous efficiency of the light emitting region, the coupling efficiency to the optical fiber becomes an issue. When coupling LED light to a graded index fiber, which is commonly used as an optical communication fiber, the coupling efficiency 11e is determined by the fiber core diameter Df.
, the numerical aperture NA of the fiber, the emission diameter Da of the LED, and the following equation.

ric;Nup2(i)2 (1), that is, L
The smaller the emission diameter Da of the ED, the higher the coupling efficiency. Therefore, it is desirable to make the emission diameter as small as possible.

Several current confinement methods have been used to reduce the emission diameter (optical communication device engineering).

Engineering books. (1983) P128-P134). A typical structure is one 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 is performed near the element surface, the current spreads laterally until it reaches the active layer and within the active layer, so the emission diameter becomes several pm larger than the current confinement diameter, and the radial distribution of emission intensity changes. A significant sore occurred. Therefore, in order to reduce the emission diameter, there is a problem in that the current confinement diameter must be further reduced by several pm or more. 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-emissive states, and the luminous efficiency of the light emitting part is significantly reduced. There was a problem with the decline.

(Object of the Invention) The present invention eliminates such conventional drawbacks, increases coupling efficiency without impairing luminous efficiency, and realizes 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 laminated structure having an active layer has an active layer limited to a disk shape with a diameter of 30 pm or less, and the disk-shaped active layer A semiconductor light-emitting diode characterized in that the entire area is a light-emitting region, and the angle between the side surface of the active layer and the interface closer to the main light extraction port among two hetero-laminated interfaces in contact with the active layer is an acute angle. be.

(Operation, principle of invention) FIG. 1 is a diagram showing the operation and principle of the present invention.

On the n-type semiconductor substrate 11, an n-type semiconductor cladding layer 12,
An n-type semiconductor active layer 13 and a p-type semiconductor cladding layer 14 are formed in this order, and the active layer is limited to a disk-shaped active layer region 13 having a diameter of about 30 pm or less. A p-type electrode 1 is provided on the surface of the p-type cladding layer directly above the disk-shaped active layer region 13.
5 is formed on the entire surface, so that the entire disk-shaped active layer region 13 becomes a light emitting region. n-type semiconductor substrate 11
Output light is extracted from a light extraction window 16 provided on the surface of the.

In the present invention, since the active layer is limited to a disk shape, current is injected only to this disk-shaped region 13, and light is emitted uniformly. As a result, the emission intensity distribution in the radial direction becomes a very sharp rectangular shape, and the droop in the distribution that was conventionally seen disappears. As a result, the coupling efficiency with optical fibers is significantly improved. According to the inventor's experimental results, conventionally, when the emission diameter is about 30 μm or less, the increase in coupling efficiency is not large even if the emission diameter is made small, and the coupling efficiency is saturated. This is because as the diameter of the emitted light becomes smaller, the influence of the current wave on the emitted light distribution becomes greater, and the emitted light is no longer effectively coupled. Experiments have revealed that the present invention significantly improves binding efficiency.

Especially when the emission diameter is about 30 pm or less, the improvement is about 1°5~
It was twice as remarkable, 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.

Furthermore, by setting the angle θ between the interface between the active layer 13 and the cladding layer 12 and the side surface of the active layer 13 to be an acute angle,
Even higher output was obtained. This is because if the angle between the interface and the side surface is a right angle or close to it, the proportion of light that travels in the horizontal direction within the active layer is reflected at the side surface and travels back to the horizontal direction of the active layer. The light amplification width becomes stronger. Therefore, a problem arises in that the originally required light intensity in the direction perpendicular to the active layer is reduced. On the other hand,
In the present invention, since this angle is an acute angle, even if light traveling in the horizontal direction within the active layer is reflected from the side surface of the active layer, the proportion of light traveling in the horizontal direction within the active layer again becomes extremely small. The light amplification in the direction becomes small, and the light intensity in the direction perpendicular to the active layer can be improved. Furthermore, since the light reflected on the side surface of the active layer travels toward the substrate 11, which is the main light extraction port, it can be used as output light, resulting in even higher output.

(Example) FIG. 2 is a diagram showing an embodiment of the present invention.

On the n-type InP substrate 11, an n-type InP layer 12. n-type In
GaAsP active layer 13. P-type InP layer 14. P-type InG
The aAsP contact layer 17 is sequentially formed by, for example, liquid phase epitaxial method. Subsequently, an n-type InGaAsP active layer 13. The P-type InP layer 14 and the P-type InGaAsP contact layer 17 are left in a circular mesa shape so that the diameter of the active layer 13 is 30 μm or less, and the rest are removed by chemical etching using Br-methanol or the like. Here, the depth of etching is determined from the interface between active layer 13 and n-type InP layer 12 to P
By making the value approximately 20 to 50% larger than the distance to the surface of the contact layer 17, the angle between the side surface of the active layer 13 and the interface can be made acute to about 45 degrees. A 5i02 film 18 is formed around the mesa, and a P-type InG film 18 is formed around the mesa.
aAsP:7 A TiPt film is formed on the surface of the contact layer 17 to form a P-type electrode 15.

After polishing the n-type InP substrate 11 to a thickness of about 1100p,
An AnGeNi film is formed concentrically with the circular mesa except for the light extraction window 16 with a diameter of approximately 10011 m, and an n-type electrode 1 is formed.
form 8.

Finally, a gold plating layer 19 is formed on the P electrode 15.

(Effects of the Invention) According to the present invention, the coupling efficiency of the output light of the LED to the optical fiber has been significantly improved, and the fiber power has been improved by more than 2 to 3 times compared to the conventional method.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention, and FIG. 2 is a diagram showing an embodiment. In the figure, 13 indicates an active layer, and 12 and 14 indicate a cladding layer, respectively.

Claims (1)

[Claims] In a semiconductor light-emitting diode with a double-hetero laminated structure having an active layer, the active layer is limited to a disk shape with a diameter of 30 μm or less, and the entire disk-shaped active layer is used as a light emitting region. A semiconductor light-emitting diode characterized in that, of two contacting hetero-laminated interfaces, the angle between the interface closer to the main light extraction port and the side surface of the active layer is an acute angle.