JPH08116088A - Manufacture of light emitting diode - Google Patents

Abstract

PURPOSE: To effectively eliminate only a sacrificial layer without exerting an influence upon other layers, in an interface reflection type LED. CONSTITUTION: A recessed part formed on the surface of a P-type GaAs substrate 5 is filled with an AlGaAs sacrificial layer 4. The conductivity type of the AlGaAs sacrificial layer for filling the recessed part is made N-type which is opposite to the substrate 5. A light emitting layer constituted of a P-type AlGaAs clad layer 3, a P-type AlGaAs active layer 2 and an N-type AlGaAs clad layer 1 are formed on the GaAs substrate 5 containing the sacrificial layer 4. After that, the sacrificial layer 4 which fills the recessed part is eliminated by etching, and a cavity part 9 is formed. Since, at this time, the sacrificial layer 4 is turned into N-type whose etching speed is high, only the sacrificial layer 4 is effectively eliminated by etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a light emitting diode (LED) having high light output and high reliability.

[0002]

2. Description of the Related Art Among LED characteristics, light emission output is the most important characteristic. Therefore, the improvement of the light emission output of the LED is
LED manufacturers are making efforts to develop the products.

For example, taking an AlGaAs LED as an example, a higher output has been promoted by improving the internal quantum efficiency from the single hetero structure to the dove hetero structure. Also G
By changing the conventional double hetero structure in which the light emitting layer is formed on the aAs substrate to the back surface reflection type structure in which the GaAs substrate on the back surface side is removed, the light extraction efficiency is improved and higher output is achieved. Up to now, this backside reflection type LED has been the LED which can obtain the highest light emission output, but it has been difficult to grow a thick epitaxial layer necessary for removing the substrate.

On the other hand, by providing a cavity between the GaAs substrate and the light emitting layer and reflecting the light at the interface between the light emitting layer and the cavity, an interface reflection type LED having a high output has been developed. (For example, Japanese Patent Application No. 5-160610). This is because many mesas are formed on the surface and Ga
Asperities are formed on an As substrate, the recesses of the GaAs substrate are filled with an AlGaAs layer serving as a sacrificial layer, and an epitaxial light emitting layer is formed on the GaAs substrate including the AlGaAs layer. The layer is removed by etching to form a cavity, and light is reflected at the interface between the cavity and the epitaxial layer. The interface reflection type LED has many advantages as compared with the back surface reflection type LED, such as high emission output, good in-plane uniformity, easy manufacture, and high speed and high output.

[0005]

However, in manufacturing the above-mentioned interface reflection type LED, there were the following problems.

(1) It is very difficult to effectively etch only the portion of the sacrificial layer. For example, when an undoped sacrificial layer is grown, the sacrificial layer actually becomes p-type due to dopant diffusion. Highly mixed crystal AlG sacrificial layer
In the case of aAs, a dilute solution of hydrofluoric acid is used to remove it by etching. However, since the p-type sacrificial layer is difficult to be etched, not only the sacrificial layer but also the periphery thereof is slightly etched. Therefore, it is difficult to form the cavity shape after etching with high accuracy.

In particular, a red LED in which the AlAs mixed crystal ratio of the epitaxial layer forming the light emitting layer is required to be high
In such cases, the etching amount of the clad layer and window layer that make up the light emitting layer becomes a problem, but the etching other than the sacrificial layer is also etched, so etching cannot be performed as designed and a sufficiently high light emission output is obtained. I couldn't.

(2) On the other hand, the interface reflection type LED constructed by removing all the sacrificial layers has a high emission output as described above, but has a problem in reliability. In particular, in a low temperature reliability test conducted when used for outdoor use, a large reduction in light emission output occurred.

(3) Further, in the interface reflection type LED, since the substrate and the epitaxial layer of the light emitting layer are connected only by the mesa portion, the heat generated in the light emitting layer does not escape easily. Therefore, as the current is increased, the forward voltage is increased and the response speed is decreased.

The object of the present invention has been described above by allowing the etching amount of the sacrificial layer to be etched at a rate larger than the etching amounts of the other layers in removing the sacrificial layer in the interface reflection type LED. A high output L capable of effectively removing only the sacrificial layer by eliminating the drawbacks of the conventional technique and without affecting other layers.
It is to provide a method for manufacturing an ED.

Another object of the present invention is to provide an LED capable of satisfying both high light emission output and high reliability at the same time.

It is another object of the present invention to provide a method for manufacturing an LED which, by improving heat dissipation, does not cause an increase in forward voltage or a decrease in response speed even if the current is increased. is there.

[0013]

First, in order to achieve the purpose of effectively removing only the sacrificial layer by etching, the present invention provides an interface reflection type LED that is grown between a substrate and an epitaxial layer to be a light emitting layer. The type of the sacrificial layer is n-type.

That is, the LED manufacturing method of the present invention is
A plurality of recesses formed on the surface of the semiconductor substrate are filled with a semiconductor layer that serves as a sacrificial layer, a light emitting layer is formed on the substrate including the semiconductor layer, and the semiconductor layer that serves as a sacrificial layer that fills the recesses is removed by etching. In a method of manufacturing a light emitting diode in which a cavity is formed and light is reflected at an interface between the cavity and the light emitting layer, a semiconductor layer that fills the recess has a conductivity type of n-type.

Further, according to the LED manufacturing method of the present invention, a plurality of recesses formed on the surface of the p-type GaAs substrate are filled with an AlGaAs layer having a high AlAs mixed crystal ratio as a sacrificial layer, and the AlG is formed.
GaAs or Al on the GaAs substrate including the aAs layer
A homojunction, single-heterojunction, or double-heterojunction light emitting layer made of GaAs is formed, and a cavity is formed by removing the AlGaAs layer with a high AlAs mixed crystal ratio, which serves as a sacrifice layer filling the recess. A method of manufacturing a light emitting diode, wherein light is reflected at an interface between the light emitting layer and the light emitting layer, the AlGa having a high AlAs mixed crystal ratio filling the recess.
The conductivity type of the As layer is n-type.

Next, in order to achieve the objectives of satisfying both high light emission output and high reliability at the same time and further improving heat dissipation, the present invention provides a substrate and a light emitting layer in an interface reflection type LED. The sacrificial layer grown between the epitaxial layers has a conductivity type opposite to that of the substrate, and the sacrificial layer is not completely removed but partially left.

That is, the manufacturing method of the LED of the present invention is as follows.
A plurality of recesses formed on the surface of the semiconductor substrate are filled with a semiconductor layer that serves as a sacrificial layer, a light emitting layer is formed on the substrate including the semiconductor layer, and the semiconductor layer that serves as a sacrificial layer that fills the recesses is removed by etching. In a method of manufacturing a light emitting diode, wherein a cavity is formed and light is reflected at an interface between the cavity and the light emitting layer, a semiconductor layer that fills the recess has a conductivity type opposite to that of the semiconductor substrate. The semiconductor layer serving as a sacrificial layer that fills the recess is partially left.

Further, the LED manufacturing method of the present invention is an epitaxial wafer in which a plurality of recesses formed on the surface of a semiconductor substrate are filled with a semiconductor layer serving as a sacrificial layer, and a light emitting layer is formed on the substrate including the semiconductor layer. Then, a partial electrode is formed on the front surface of the wafer and a full surface electrode is formed on the back surface, and the semiconductor layer serving as a sacrificial layer filling the recess is removed to form a cavity, and the cavity and the light emitting layer are formed. In the method for manufacturing a light emitting diode in which light is reflected at the interface of, the conductivity type of the semiconductor layer serving as a sacrificial layer filling the recess is n type,
When the semiconductor layer to be the sacrificial layer that fills the recess is removed, the semiconductor layer is partially left, and the diameter of the remaining region is set to 50% to 150% of the partial electrode.

Further, according to the method of manufacturing an LED of the present invention, a plurality of recesses formed on the surface of a p-type GaAs substrate are filled with an AlGaAs layer having a high AlAs mixed crystal ratio as a sacrificial layer, and the AlG is formed.
GaAs or Al on the GaAs substrate including the aAs layer
A homojunction, single heterojunction or double heterojunction light emitting layer made of GaAs is formed to form an epitaxial wafer, a partial electrode is formed on the front surface of the wafer, and a full surface electrode is formed on the back surface of the epitaxial wafer. A method of manufacturing a light-emitting diode, wherein an AlGaAs layer having a high AlAs mixed crystal ratio to be a layer is removed to form a cavity, and light is reflected at an interface between the cavity and the light emitting layer,
Al with a high AlAs mixed crystal ratio, which serves as a sacrificial layer filling the recesses
The conductivity type of the GaAs layer is n-type, and the AlGaAs layer having a high AlAs mixed crystal ratio, which serves as a sacrifice layer for filling the recess, is partially left, and the diameter of the remaining region is 50% of that of the partial electrode.
To 150%. The LE of the present invention
In the manufacturing method of D, the p-type and the n-type may be reversed.

AlGaAs with a high AlAs mixed crystal ratio as described above
The n-type dopant whose conductivity type of the sacrificial layer is n-type is Te,
It is preferably Sn, S, or Se. The epitaxial layer growth method may be a liquid phase epitaxial growth method, a vapor phase growth method, or a metal organic chemical vapor deposition method.

[0021]

In the present invention, when the sacrificial layer is of the n-type, only the sacrificial layer can be effectively removed while etching the other layers to a minimum. Therefore, it is possible to perform highly precise shape processing, and it is possible to manufacture the LED as designed, and it is possible to bring out higher output. Further, in order to form the n-type sacrificial layer, it suffices to add the n-type dopant to the growth solution of the sacrificial layer, and the manufacturing process is easy because it does not increase the number of steps.

By the way, if all the sacrificial layers are removed, there is a problem in reliability. Therefore, in another invention, the sacrificial layer is not completely removed but partially left. In this way, reliability can be improved.

In order to partially leave the sacrificial layer, etching may be stopped halfway. When the sacrificial layer is etched, the sacrificial layer is etched away from the periphery toward the center. Therefore, if etching is stopped halfway, the sacrificial layer is left in the vicinity of the central portion.

However, if a current flows through the remaining sacrificial layer, the light emitting portion is located directly below the partial electrode and light is blocked, so that the light extraction efficiency cannot be increased.
Therefore, the conductivity type of the sacrificial layer is set to the conductivity type opposite to the conductivity type of the substrate so that no current flows in the sacrificial layer. By doing so, it is possible to prevent the current from concentrating directly under the partial electrodes through the sacrificial layer, and to disperse the current. This makes it possible to obtain a highly reliable LED while keeping the light emission output high.

When the sacrificial layer is partially left, the epitaxial layer of the light emitting layer is also connected to the sacrificial layer, so that the heat generated in the light emitting layer escapes better.

[0026]

Embodiments of the LED of the present invention will be described below with reference to the drawings.

(Embodiment 1) Embodiment 1 in which the conductivity type of the sacrificial layer is n-type will be described with reference to FIGS. FIG. 1 is a cross-sectional structural view of a high-brightness red LED epitaxial wafer having an emission wavelength of 660 nm according to the present embodiment before removal of a sacrificial layer.

The structure of this epitaxial wafer is as follows. A large number of mesa portions 6 are formed in a matrix on the p-type GaAs substrate 5, and a large number of uneven portions are formed on the substrate surface. In the concave portion on the p-type GaAs substrate 5 in which this uneven portion is formed, n-type AlGaAs having a high AlAs mixed crystal ratio is formed.
The sacrificial layer 4 is embedded. Substrate 5 including this sacrificial layer 4
A light emitting layer having a pn junction is formed thereon. The light emitting layer is a p-type AlGaAs clad layer 3, p-type AlGaAs
It is composed of an active layer 2 and an n-type AlGaAs cladding layer 1, and has a double hetero structure.

Next, a method of manufacturing this epitaxial wafer will be described. As a manufacturing method, a liquid phase epitaxial method widely used for manufacturing AlGaAs LEDs was used, and a slide boat method, which is a kind of slow cooling method, was used in the liquid phase epitaxial method.

First, as the p-type GaAs substrate 5, one having a thickness of 350 μm and a carrier concentration of 2 × 10 ¹⁹ cm ⁻³ was used. The GaAs substrate 5 was subjected to photolithography and etching to form a mesa portion 6. The size of the mesa portion 6 was 15 μm in diameter, 10 μm in height, and 40 μm in the distance between the centers of adjacent mesa portions.

A p-type GaA having the mesa portion 6 formed on its surface
The substrate 5 was set on the substrate holder of the slide boat. The slide boat has four reservoirs. First of all
The solution reservoir contains metal Ga and metal A for n-type sacrificial layer growth.
1, GaAs polycrystal, and metal Te as a dopant were set. In the second solution reservoir, metal Ga, metal Al, GaAs polycrystal for growing the p-type cladding layer, and metal Mg as a dopant were set. In the third solution reservoir, metal Ga, metal Al, GaAs polycrystal, for growing the p-type active layer,
Metal Mg was set as a dopant. And the fourth
Metal Ga, metal Al, GaAs polycrystal for growing the n-type cladding layer, and metal Te as a dopant were set in the solution reservoir.

The compositions of the second to fourth solutions are the same as those used for growing the conventional DH structure red LED. The composition of the first solution reservoir was such that extra Al was added to grow the AlGaAs layer of high mixed crystal. Polycrystalline Ga
As may be large. Moreover, Te was 0.05 mg with respect to Ga: 1 g.

The slide boat containing the raw materials was set in the reaction tube, the inside of the reaction tube was replaced with hydrogen gas, and the temperature was raised to the growth temperature. After maintaining the growth start temperature for about 3 hours, slow cooling was started. After the slow cooling was started, the substrate holder on which the GaAs substrate was set was slid to bring the GaAs substrate into contact with the growth solution in the first solution reservoir. Due to this contact, a high mixed crystal (AlAs mixed crystal ratio of 0.
The n-type AlGaAs sacrificial layer of 9) was grown. About 2 μm
After the growth, the substrate holder was slid, the substrate was brought into contact with the growth solution in the second solution reservoir, and the p-type AlGaAs cladding layer was grown.

Although the thickness of the sacrificial layer of 2 μm seems to be theoretically unreasonable with respect to the depth of the concave portion of 10 μm, in reality, the growth of the concave portion of the mesa portion and the dissolution of the convex portion during the sacrifice layer growth. Simultaneously proceeded, the recesses grew to 2 μm and the protrusions to 7 μm.
There is no problem because melting occurs and it becomes fairly flat after the growth.

The p-type AlGaAs cladding layer is made of AlAs.
The mixed crystal ratio is 0.6, the carrier concentration is 5 × 10 ¹⁷ cm ^-3 ,
The thickness is 30 μm. Once the clad layer grows,
The substrate holder is moved to grow an active layer of p-type AlGaAs. The p-type AlGaAs layer has an AlAs mixed crystal ratio of 0.
35, carrier concentration 9 × 10 ¹⁷ cm ^-3 , thickness 1 μm
Is. After the active layer was grown, the substrate holder was further moved to grow an n-type AlGaAs cladding layer. The n-type AlGaAs layer has an AlAs mixed crystal ratio of 0.6, a surface carrier concentration of 1 × 10 ¹⁸ cm ⁻³ , and a film thickness of 40 μm.
After the growth of the n-type clad layer is completed, the substrate holder is further moved to separate the growth solution and the epitaxial wafer. When the separation was completed, the heater of the epitaxial furnace was turned off and the rapid cooling was started.

The cooled epitaxial wafer was taken out of the furnace, and a circular AuGe film having a diameter of 150 μm was formed on the wafer surface.
/ Ni / Au electrodes were formed in a matrix shape at intervals of 350 μm in length and width. Further, a full surface electrode of AuZn was formed on the back surface of the wafer. Next, in order to make a chip, the circular electrode 7 is placed so that the surface circular electrode 7 is located at the center.
Separation grooves were formed in the vertical and horizontal directions around by using a dicer. The formation depth of the groove is 100 μm. This grooved epitaxial wafer was subjected to an H ₂ SO ₄ system etching treatment, and the groove fracture surface by a dicer was removed by etching. When viewed from the surface, the chip size is 300 μm × 300 μ
m.

This epitaxial wafer is immersed in a dilute solution of hydrofluoric acid (volume ratio 1%) for 1 hour. The immersion condition is a time sufficient to completely remove the n-type sacrificial layer 4 by etching. By this immersion treatment, the highly mixed crystal n-type AlGaAs sacrificial layer 4 grown in the recess of the GaAs substrate 5 was removed by etching. An epitaxial wafer from which the sacrificial layer 4 has been removed is shown in FIG.

After that, the center of the groove was fully cut to separate the epitaxial wafer into chips. This chip was fixed to the stem by die bonding, wired by wire bonding, and resin-molded to manufacture an interface reflection type LED.

When the characteristics of this manufactured LED were measured using an integrating sphere, a high output of 8 mW was obtained at a forward current of 20 mA. This brightness corresponds to a commercially available 3000 mcd class LED as a red LED. Such a high-brightness LED could be manufactured because of high mixed crystal n-type AlGaA while etching other epitaxial layers was minimized.
This is because the sacrificial layer could be removed by etching.

By the way, regarding this interface reflection type LED, it is very important that only the sacrifice layer can be effectively etched. Therefore, the carrier concentration of the highly mixed crystal AlGaAs sacrificial layer was changed from p-type to n-type, and the etching rate thereof was examined. The result is shown in FIG. Zn was used as the p-type dopant and Te was used as the n-type dopant. The horizontal axis represents the carrier concentration (cm ⁻³ ), and the vertical axis represents the etching depth a (μm). The etching depth a is the diameter of the cavity 9 shown in FIG.

The composition of the etching solution was 100 parts by volume of water and 1 part of hydrofluoric acid. This composition may be thinner, but is not preferable because it requires etching time. It is not preferable to increase the concentration of hydrofluoric acid in order to shorten the etching time because the etching of the epitaxial layer, especially the n-type AlGaAs cladding layer on the surface becomes severe.

With this etching solution, n-type high mixed crystal AlGaA
s By etching the sacrificial layer, cutting the wafer and observing the cross section, the depth a of the sacrificial layer 4 that could be removed by etching (depth from the edge inward in the radial direction) was investigated. Since the area of the sacrificial layer is 300 μm square, it means that the entire area can be removed when the radial depth becomes 150 μm.

From FIG. 3, in the case of the p-type sacrificial layer, the etching is several tens of μm, which is very small. Although the etching depth increases due to the lower carrier concentration,
The etching amount is small. On the other hand, when the sacrificial layer becomes n-type, the etching amount sharply increases. It can be seen that when the n-type carrier concentration is further increased, the etching rate is also increased, and when the carrier concentration is 1 × 10 ¹⁷ cm ⁻³ , the sacrificial layer is completely melted.

Although Mg or the like was used as the p-type dopant in addition to Zn, the etching amount was small as in the case of Zn. In addition, as an n-type dopant, Sn, S,
Se or the like was used, but in this case, the etching rate was as high as that of Te. Therefore, it was confirmed that the reason for the high etching rate of the sacrificial layer was not the use of Te as a dopant but the n-type.

As described above, according to the first embodiment, the sacrificial layer is n.
The mold facilitates the sacrifice layer etching.
Further, since the sacrifice layer etching is facilitated, the yield of chip manufacturing can be significantly improved.

In the above-mentioned embodiment, the case of the AlGaAs red LED has been described. However, even in the AlGaAs infrared LED, when the sacrificial layer is etched, the other epitaxial layers are hardly etched and the sacrificial layer is not etched. Could be etched cleanly, selectively and quickly.

In the above embodiment, the case where the n-type AlGaAs sacrificial layer and the epitaxial layer to be the light emitting layer are formed on the p-type GaAs substrate has been described.
The same effect was obtained when the n-type AlGaAs sacrificial layer and the epitaxial layer serving as the light emitting layer were formed on the aAs substrate.

The LED manufactured based on this embodiment
In the case of red, it is a high-brightness LED for outdoor display, and because it is highly efficient, it is a low power consumption LED for mobile phones.
It can be applied to Further, with respect to the infrared LED, since the sacrifice layer can be etched with high accuracy, the output can be further increased and the mass productivity can be improved. Since the infrared LED has high speed and high output, it can be used for space transmission for audio and video transmission. Further, it is possible to meet the demand for low power consumption and long-distance transmission in the conventional remote control area, and it can be used more widely. Furthermore, it has high output characteristics required for information transmission on roads and the like.

(Embodiment 2) Next, with reference to FIGS.
A second embodiment in which a part of the sacrificial layer is left will be described. FIG. 4 is a cross-sectional structure diagram of an epitaxial wafer for a high-power infrared LED having an emission wavelength of 850 nm. The basic structure of the epitaxial wafer is basically the same as that of the first embodiment.

The method of manufacturing the epitaxial wafer is the same as that of Example 1 except for the following points. That is, the difference is that the p-type Al is used for the infrared LED.
The GaAs cladding layer 3 has an AlAs mixed crystal ratio of 0.3, a carrier concentration of 5 × 10 ¹⁷ cm ^-3 and a thickness of 50 μm. The p-type AlGaAs active layer 2 has an AlAs mixed crystal ratio of 0.05, a carrier concentration of 2 × 10 ¹⁸ cm ⁻³ and a thickness of 1.
μm. The n-type AlGaAs cladding layer 1 is made of AlA.
s mixed crystal ratio is 0.3, carrier concentration on the surface is 1 × 10 ¹⁸ cm
^-3 , and the film thickness is 30 μm.

In the second embodiment, the etching conditions are changed so that the sacrificial layer 4 is not completely removed but is left partially. The epitaxial wafer is immersed in a dilute solution of hydrofluoric acid (volume ratio 10%) for 15 minutes. By this treatment, high mixed crystal AlG grown in the recess of the GaAs substrate 5
The peripheral portion of the aAs sacrificial layer 4 is removed by etching,
The sacrificial layer in the center remains. This is shown in FIG.

The light emission output of the LED manufactured from this wafer in the same manner as in Example 1 was measured by an integrating sphere. The light emission output is 18 mW at a forward current of 50 mA. Also this LE
When a reliability test was performed on D, a deterioration rate after 1000 hours was 5% or less in a room temperature current test in which a current of 100 mA, which was twice the conventional current, was applied. Also 85 ℃, 50mA
In the high-temperature current application test, the deterioration rate after 1000 hours was 5% or less. Further, it was 5% or less in the high temperature and high humidity current test of 85 ° C., 85%, 50 mA. Also, -40 ℃, 50mA
In the low temperature energization test of No. 1, the deterioration rate after 1000 hours was 10% at the maximum, and it was confirmed that it could withstand a very severe environmental test.

It has been found that high light output and high reliability can be obtained at the same time by stopping the etching of the sacrificial layer in the middle without completely removing the sacrificial layer.

Next, in order to investigate the relationship between the remaining amount of the sacrificial layer and the reliability, LED chips were manufactured by changing the etching time of the sacrificial layer and variously removing the sacrificial layer. Emission output and relative intensity of this LED (reliability test)
I checked and. The result is shown in FIG. In FIG. 5, the horizontal axis represents the diameter b (μm) of the remaining sacrificial layer. The diameter b of this sacrificial layer was measured by cutting the chip and observing its cross section. The vertical axis on the left side indicates the light emission output, which is a value obtained by evaluating the light emission output when the forward current is 50 mA using an integrating sphere. The emission output is 120 when the diameter of the sacrificial layer is 120.
Up to about μm, the diameter gradually decreases as the diameter increases. Then, when the diameter exceeds 120 μm, the light emission output rapidly decreases. Normal DH structure LED (Ga
On the As substrate, a p-type clad layer serving as a light emitting layer, an active layer, n
The emission output is 1.5 times higher than that of an LED manufactured from an epitaxial wafer on which a mold window layer is grown, when the diameter of the sacrificial layer is up to 220 μm.

The vertical axis on the right side of FIG. 5 shows the relative light emission output with respect to the initial light emission output in the low temperature reliability test (-40 ° C., 50 mA, 1000 h). When the sacrificial layer is completely removed, the relative strength is reduced to 50%, which shows a significant deterioration rate. On the other hand, it can be seen that the reliability is significantly improved as the diameter of the remaining sacrificial layer increases. When the residual diameter of the sacrificial layer exceeds 60 μm, the relative strength becomes 75% or more, and the effect of leaving the sacrificial layer becomes clear.

Therefore, the diameter of the remaining region of the sacrificial layer is
60 μm to 220 μm is preferable. This is about 5 times the diameter of the circular electrode because the diameter of the circular electrode is 150 μm.
This corresponds to 0% to 150%. Further, the position of the remaining region of the sacrificial layer is preferably right below the circular electrode and the center thereof is the same as that of the circular electrode.

The shape of the sacrificial layer left here is not a perfect circle but a circle close to a square. Although the surface electrode is circular, it need not be circular as long as it is a partial electrode located substantially at the center of the chip. Further, a shape obtained by adding a cross to a circle may be used, and this is preferable because the current dispersion effect is enhanced.

In Example 2, since the etching amount of the sacrificial layer was small, the fabrication was easier than that of removing the sacrificial layer entirely. In addition, when the sacrificial layer is completely removed, a luminous intensity of 3000 mcd is obtained at a forward current of 20 mA, but even with an LED in which the sacrificial layer under the electrode is left,
A luminous intensity of 2600 mcd was obtained. The reason why such high luminous intensity is obtained is that the conductivity type of the sacrificial layer 4 is changed to p-type G
This is because the conductivity type opposite to that of the aAs substrate 5 and the p-type AlGaAs cladding layer 3 is n-type so that the current does not flow in the remaining sacrificial layer 4.

Regarding the low temperature reliability in Example 2, the relative intensity of the interface reflection type LED in which the sacrificial layer is completely removed is reduced to 50%, but the ordinary DH structure LED is used.
Although the relative strength was slightly lower than (relative strength of 98%), the relative strength of 80% or more could be obtained.

As described above, the infrared LED having the structure of the second embodiment has been developed, whereby it becomes possible to manufacture a highly reliable interface reflection type LED with a high light emission output. For this reason, LEDs that were previously only available for indoor information transmission,
It can be widely used for outdoor information transmission and information transmission between buildings. In addition, this applies not only to the infrared LED but also to the red LED, and the reliability is greatly improved, so that it can be used from the indoor display application to the outdoor display application.

As described above, according to the second embodiment,
For the interface reflection type LED, a growth solution for growing the sacrificial layer is used.
A high emission output and high reliability can be obtained at the same time by only inserting a type dopant and stopping the sacrifice layer etching in the middle, and even in that case, a large increase in the number of steps is not required. Further, when the sacrifice layer is completely removed, the other epitaxial layers are also etched. On the other hand, in the second embodiment, only the periphery where the etching is fast is etched, so that the other epitaxial layers can be removed in a short time. It is possible to work without etching.

Here, since the sacrificial layer may be of the conductivity type opposite to that of the substrate, the sacrificial layer does not necessarily have to be of the n type, but particularly when the sacrificial layer is of the n type as in the second embodiment. As described in Example 1, etching of other epitaxial layers can be effectively avoided, and etching can be performed more easily.

Further, by leaving a part of the sacrificial layer, it is possible to greatly improve the low temperature reliability, which is a particularly problematic point of view in reliability, without causing a significant decrease in light emission output. In addition, the interface reflection type L of the type that completely removes the sacrificial layer
In the ED, the substrate and the epitaxial layer were only connected by the mesa portion, so the heat escape was bad, but in the case of Example 2, the sacrifice layer was left, so the heat escape increased and the current increased. Even if it goes, the forward voltage does not increase much and the response speed does not decrease.

[0064]

According to the first and second aspects of the present invention, since the sacrificial layer filling the concave portion of the substrate is an n-type layer which can be easily etched, only the sacrificial layer can be effectively removed by etching. LED with high dimensional accuracy can be manufactured with high yield,
Higher output can be realized.

According to the third aspect of the present invention, the sacrificial layer for filling the concave portion of the substrate is partially left, and the remaining sacrificial layer is of a conductivity type opposite to that of the substrate. The reliability can be greatly improved while maintaining. Further, since the light emitting layer is also connected to the remaining sacrificial layer, heat can be effectively dissipated, and the LED characteristics can be significantly improved.

According to the invention described in claims 4 and 5, since the sacrifice layer is made to remain in a predetermined size, it is possible to obtain a high light emission output and a high relative intensity at the same time.

According to the sixth aspect of the invention, since the sacrificial layer can be made n-type only by adding the n-type dopant to the growth solution for the sacrificial layer, the number of steps is not increased and the LED can be easily manufactured. You can do it.

[Brief description of drawings]

FIG. 1 is a sectional view of an LED epitaxial wafer for explaining Example 1 of the LED manufacturing method of the present invention.

FIG. 2 is a cross-sectional view of a final structure in which all sacrificial layers of the LED epitaxial wafer manufactured according to Example 1 are removed.

FIG. 3 is a diagram showing the dependency of the etching amount on the sacrifice layer carrier concentration according to the first embodiment.

FIG. 4 is a sectional view of an LED epitaxial wafer for explaining a second embodiment.

FIG. 5 is a diagram showing the diameter dependence of the remaining sacrificial layer of the light emission output and relative intensity according to Example 2.

[Explanation of symbols]

 1 n-type GaGaAs clad layer 2 p-type AlGaAs active layer 3 p-type AlGaAs clad layer 4 n-type AlGaAs sacrificial layer 5 p-type GaAs substrate 6 mesa part 7 n-side electrode 8 p-side electrode 9 cavity part

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masatoshi Watanabe 3550 Kidayomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Ltd. Advanced Research Center

Claims (6)

[Claims] 1. A plurality of recesses formed on the surface of a semiconductor substrate are filled with a semiconductor layer serving as a sacrifice layer, a light emitting layer is formed on a substrate including the semiconductor layer, and the semiconductor layer filling the recesses is removed by etching. In a method of manufacturing a light emitting diode in which a cavity is formed and light is reflected at an interface between the cavity and the light emitting layer, a semiconductor layer that fills the recess has a conductivity type of n-type. Method of manufacturing light emitting diode. 2. A plurality of recesses formed on the surface of a p-type GaAs substrate are filled with an AlGaAs layer having a high AlAs mixed crystal ratio to serve as a sacrificial layer, and G is formed on the GaAs substrate including the AlGaAs layer.
Forming a homojunction, single heterojunction or double heterojunction light emitting layer made of aAs or AlGaAs,
A method for manufacturing a light-emitting diode, wherein a cavity is formed by removing an AlGaAs layer having a high AlAs mixed crystal ratio that fills the cavity, and light is reflected at an interface between the cavity and the light emitting layer, High AlAs mixed crystal ratio Al to fill
A method for manufacturing a light emitting diode, characterized in that the conductivity type of the GaAs layer is n type. 3. A plurality of recesses formed on the surface of a semiconductor substrate are filled with a semiconductor layer serving as a sacrificial layer, a light emitting layer is formed on a substrate including the semiconductor layer, and the semiconductor layer filling the recesses is removed by etching. In a method of manufacturing a light emitting diode, wherein a cavity is formed and light is reflected at an interface between the cavity and the light emitting layer, a semiconductor layer that fills the recess has a conductivity type opposite to that of the semiconductor substrate. A method for manufacturing a light-emitting diode, wherein the semiconductor layer is partially left when the semiconductor layer filling the recess is removed by etching. 4. An epitaxial wafer in which a plurality of recesses formed on the surface of a semiconductor substrate are filled with a semiconductor layer serving as a sacrifice layer, and a light emitting layer is formed on a substrate including the semiconductor layer, and a portion is formed on the surface of the wafer. Manufacture of a light emitting diode in which an electrode is formed on the entire surface, a semiconductor layer filling the recess is removed to form a cavity, and light is reflected at an interface between the cavity and the light emitting layer. In the method, the semiconductor layer that fills the recess has a conductivity type opposite to that of the semiconductor substrate, and when the semiconductor layer that fills the recess is removed, the semiconductor layer partially remains, and the diameter of the remaining region Is set to 50% to 150% of the partial electrode. 5. A plurality of recesses formed on the surface of a p-type GaAs substrate are filled with an AlGaAs layer having a high AlAs mixed crystal ratio to serve as a sacrificial layer, and G is formed on the GaAs substrate including the AlGaAs layer.
An epitaxial wafer on which a homojunction, single heterojunction or double heterojunction light emitting layer made of aAs or AlGaAs is formed is formed. A partial electrode is formed on the front surface of this wafer and a full surface electrode is formed on the back surface thereof to fill the recess. A method of manufacturing a light-emitting diode, wherein an AlGaAs layer having an AlAs mixed crystal ratio is removed to form a cavity, and light is reflected at an interface between the cavity and the light emitting layer, a high AlAs mixed crystal filling the recess. Ratio of AlGaAs
The conductivity type of the layer is n-type, the AlGaAs layer having a high AlAs mixed crystal ratio for filling the recess is partially left, and the diameter of the remaining region is set to 50% to 150% of the partial electrode. Method of manufacturing light emitting diode. 6. An n-type dopant having an n-type conductivity type as the AlGaAs layer having a high AlAs mixed crystal ratio is Te, Sn,
The method for manufacturing a light emitting diode according to claim 2, wherein the light emitting diode is S or Se.