JPH07176789A - Gallium phosphide green light emitting diode and its manufacture - Google Patents

Abstract

PURPOSE:To provide a gallium phosphide green light emitting diode that emits green light of high luminance, and a method for its manufacture. CONSTITUTION:The gallium phosphide green light emitting diode consists of a n-type gallium phosphide substrate; a n-layer 4 that is formed on the substrate and that contains in proximity to its surface, positioned on the opposite side to the substrate, impurities of a concentration lower than that of impurities in the substrate; and a p-layer 8 that is formed on the n-layer 4. The p-layer 8 is formed so that it will includes a high concentration region 16 and a low concentration region 7. The high concentration region 6 contains impurities of a higher concentration in proximity to the p-n junction than in proximity to the surface of the n-layer 4. The low concentration region 7 contains impurities of a lower concentration on the side of its surface than that of impurities in the high concentration region 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium phosphide green light emitting diode which emits high brightness green light and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a gallium phosphide green light emitting diode has an impurity concentration characteristic as shown in FIG. 5, for example, as shown in JP-A-59-80981. In this figure, a high-concentration first n-layer 42, a low-concentration second n-layer 43, and a high-concentration p-layer 44 are formed on an n-type gallium phosphide substrate 41.
Are formed by stacking. The horizontal axis of the figure indicates the distance of each layer from the bottom surface of the substrate 41. The luminance is improved by reducing the impurity concentration of the second n layer 43 near the pn junction. As described above, in order to obtain high brightness, it has been studied to make the n-layer a multilayer and to find the optimum value of the impurity concentration.

[0003]

However, the above-mentioned light emitting diode is 10 mA in a bare state without resin coating.
The brightness is about 1.1 mcd when measured by driving at 1, and the brightness is still lower than, for example, about 2.3 mcd of the red light emitting diode made of gallium aluminum arsenide, which is considered to have high brightness. Therefore, the present inventor has conducted research aiming at higher brightness, focusing on the p-layer of the conventional light-emitting diode. As a result, it was found that there is a problem in the manufacturing process of the p layer 44, in which the melt is cooled and epitaxially grown while the second n layer 43 is in contact with the melt.

That is, when the temperature of the melt gradually decreases during growth, the amount of zinc evaporated as an impurity in the melt decreases, so the concentration of zinc in the melt increases, and as shown in FIG.
The impurity concentration on the surface side of the layer 44 is increased. Therefore, p
It was found that high luminance cannot be obtained because defects increase on the surface side of the layer 44 and the amount of carriers trapped in defects that do not contribute to light emission increases. Therefore, the present invention has been made in view of the above-mentioned conventional drawbacks, particularly focusing on the p layer, and provides a gallium phosphide green light emitting diode which emits high brightness green light and a manufacturing method thereof. .

[0005]

In order to solve the above-mentioned problems, a first aspect of the present invention provides an n-type gallium phosphide substrate and a surface formed on the substrate and at least near the surface opposite to the substrate. An n layer containing an impurity at a concentration lower than that of the substrate and a p layer formed on the n layer are provided, and the p layer has a high concentration region containing an impurity at a concentration higher than that near the surface of the n layer near the pn junction. The front surface side is provided with a low-concentration region containing a lower concentration of impurities than the high-concentration region.

The second aspect of the present invention comprises a first step of growing a n-layer by bringing a melt into contact with an n-type gallium phosphide substrate.
A second step of adding a p-type impurity to the melt to grow a p-type high-concentration region on the n-layer, and a third step of keeping the melt at a substantially constant temperature and scattering the impurities in the melt. And a fourth step of bringing the melt into contact with the high concentration region and growing a p-type low concentration region on the high concentration region.

[0007]

As described above, in the first aspect of the present invention, the large energy level difference between the high-concentration region of the p-layer and the vicinity of the low-concentration surface of the n-layer causes a large amount of carriers to be confined in light emission efficiency. High light has a small amount of carriers trapped in defects that do not contribute to light emission and has a low rate of non-radiative recombination.
Since the light passes through the low-concentration region of the p-layer with few defects, the emission efficiency is small and the light is emitted as high brightness.

Further, in the second aspect of the present invention, after the high concentration region is grown, the melt is held at a substantially constant temperature to scatter the impurities in the melt, so that the impurity concentration in the melt is lowered and the high concentration region is increased. A low concentration region is continuously formed on the upper side.

[0009]

EXAMPLE An example of the present invention will be described below with reference to FIG.
FIG. 1 is a sectional view of a gallium phosphide green light emitting diode according to this embodiment. In FIG. 1, the substrate 1 has, for example, a thickness of about 2
It is made of n-type gallium phosphide having a thickness of 15 μm and has an impurity concentration of 1 to 4 × 10 ¹⁷ cm ⁻³ .

The first n-layer 2 is formed on the substrate 1 and is made of, for example, n-type gallium phosphide having a thickness of about 30 μm and has a relatively high impurity concentration of about 10 ¹⁸ cm ^-3 . The second n-layer 3 is formed on the first n-layer 2, is made of, for example, n-type gallium phosphide having a thickness of about 15 μm, and has an impurity concentration of about 2-5 × 10 ¹⁵ cm ^{−3, which} is a relatively low concentration. belongs to. Thus, the n-layer 4 is composed of the first n-layer 2 and the second n-layer 3, and is provided in the vicinity of the surface on the opposite side of the substrate 1 so as to contain a lower concentration impurity than the substrate 1.

The rising region 5 is formed on the second n-layer 3 and is made of, for example, p-type gallium phosphide having a thickness of about 2 μm.
The rising region 5 has the same impurity concentration as that of the second n layer 3 on the interface side with the second n layer 3 and 2 to 5 × on the surface side.
It is 10 ¹⁷ cm ⁻³ , and the impurity concentration is gradually increased toward the surface.

The high concentration region 6 is formed on the rising region 5 and is made of, for example, p-type gallium phosphide having a thickness of about 4 μm,
The impurity concentration is about 2 to 5 × 10 ¹⁷ cm ⁻³ . The low-concentration region 7 is formed on the high-concentration region 6 and has, for example, a thickness of 10 to 1
It is composed of 5 μm of p-type gallium phosphide. The low-concentration region 7 has a high impurity-concentration region 6 on the interface side with the high-concentration region 6.
The same as the above, and 0.6 to 1.5 × 10 ¹⁷ c on the surface side
The concentration is m ^-3 .

As described above, the p-layer 8 is composed of the rising region 5, the high-concentration region 6 and the low-concentration region 7, and the high-concentration region 6 has a higher concentration of impurities than the vicinity of the surface of the n-layer 4. The p layer 8 is formed such that the surface side has a lower impurity concentration than the high concentration region 6 near the pn junction 9. Then, an n-side electrode 10 is formed on the back surface of the substrate 1, and a p-side electrode is formed on the surface of the low-concentration region 7, and these layers constitute the gallium phosphide green light emitting diode 12 of this embodiment.

When the light emitting diode 12 is driven at 10 mA in a bare state without resin coating and the luminance is measured,
The brightness is about 2.2 mcd, which is about twice as high as that of the conventional light emitting diode, and about the same as the brightness of the red light emitting diode of gallium aluminum arsenide.

As described above, the reason why such high brightness is obtained is that the impurity concentration in the high concentration region 6 is 2 to 5 × 10 ¹⁷ cm ⁻³ , and the concentration on the surface side of the low concentration region 7 is 0. 6-1.5
This is because the ratio of non-radiative recombination in the p-layer 8 is reduced because it is as low as × 10 ¹⁷ cm ⁻³ .

According to the experiments of the present inventor, it was found that the concentration gradient in the low concentration region 7 is an important factor in reducing the rate of non-radiative recombination. The concentration gradient is a value obtained by dividing the concentration at the interface between the low concentration region 7 and the high concentration region 6 by the concentration on the surface, divided by the layer thickness of the low concentration region 7. According to the experiment, when the concentration gradient is 0.15 / μm or more, a high brightness of about 2.2 mcd or more can be obtained.
It was found that when it was less than m, the brightness was sharply reduced.

Further, it has been found that the density gradient in the rising region 5 is also an important factor for brightness. What is this concentration gradient?
The value obtained by dividing the concentration at the interface of the rising region 5 with the high concentration region 6 by the concentration at the interface with the second n layer 3 is divided by the layer thickness of the rising region 5. As a result of the experiment, this concentration gradient is 1
When it is 000 / μm or less, a high brightness of about 2.2 mcd or more is obtained, and when it exceeds 1000 / μm, the brightness sharply decreases. It is considered that by making this concentration gradient gentle, the amount of light emitted upward from the pn junction 9 is reflected or absorbed in the p layer 8 is reduced.

Next, a method of manufacturing the gallium phosphide green light emitting diode 12 of this embodiment will be described. First manufacturing equipment 13
Will be briefly described with reference to the schematic diagram of FIG. In this figure, a base 15 made of carbon or the like is arranged in a reaction furnace 14 made of quartz or the like. The gallium phosphide single crystal substrate 16 is housed in the recess 17 of the base 15. A slidable melt reservoir 18 is arranged on the surface of the base 15. Melt reservoir 1
8 is provided with a through hole 19 whose bottom surface is the surface of the base 15, and contains a melt 20 for epitaxial growth. In the process of epitaxial growth, first melt 20
The temperature of the single crystal substrate 16 is raised in a completely separated state, and then the melt reservoir 18 is slid to bring the melt 21 into contact with the single crystal substrate 16.

The heater 22 is provided on the side surface of the reaction furnace 14, and the temperature of the melt 21 is controlled by controlling the current to the heater 22. Gas and zinc powder as impurities are supplied into the reaction furnace 14 through the gas supply port 23 and the impurity supply port 24, respectively. Internal gas is discharged through the gas discharge port 25 as needed.

Further, a method of manufacturing the gallium phosphide green light emitting diode 12 will be described with reference to FIGS. 2, 3 and 4.
FIG. 3 is a temperature step diagram of liquid phase epitaxial growth for explaining the manufacturing method, and FIG. 4 is an impurity concentration diagram of the gallium phosphide green light emitting diode 12 thus manufactured. First, as shown in step 26, about 1 of the melt 21 is added.
While maintaining the temperature at 030 ° C., hydrogen is supplied into the reaction furnace 14, and then hydrogen sulfide (H ₂ S) is mixed with hydrogen for about 1 minute to introduce sulfur as a main donor impurity into the melt 21.

After that, as shown in step 27, the melt 21 is cooled at a rate of about 2.5 ° C./min to epitaxially grow the first n-layer 2 on the n-type gallium phosphide substrate 1. The first n-layer 2 formed at this time has an impurity concentration of about 10 ¹⁸ cm ⁻³ and a thickness of about 30 μm.

Thereafter, as shown in step 28, the melt 21 is held for a long time, but the sulfur introduced in step 26 is scattered in the first half, and the ammonia gas (N
H ₃ ) is introduced into the reaction furnace 14 at a rate of 5 cm ³ / min.
As a result, silicon nitride (Si ₃ N ₄ ) is precipitated in the melt 21, and the sulfur concentration and silicon concentration of the melt 21 are reduced.

Next, as shown in step 29, the melt 21 is cooled at a rate of about 2.5 ° C./min, so that the first n
A third n-layer 3a is epitaxially grown on the layer. The third n layer 3a formed at this time has an impurity concentration of 2 to 5 ×.
At 10 ¹⁵ cm ^-3 , the thickness is about 17 μm. These steps 27, 28 and 29 constitute the first step.

Thereafter, as shown in step 30, the melt 21 is held for a long time while introducing zinc (Zn) powder into the reaction furnace 14. Then, as shown in the second step 31, the melt 2
By lowering the temperature of 1 at a rate of about 2.5 ° C./min, the p-type high concentration region 6 is epitaxially grown on the third n layer 3a. The high concentration region 6 has an impurity concentration of 2 to 5 ×.
At 10 ¹⁷ cm ⁻³ , the thickness is about 4 μm.

Next, as shown in the third step 32, the melt 21
At about 885 ° C for about 3 hours. At this time, zinc in the adjacent high concentration region 6 moves and diffuses inside the surface of the third n-layer 3a. As a result, the third n-layer 3a becomes the second
N layer 3 and a p-type rising region 5 formed thereon
Changes to.

That is, the second n layer 3 is formed on the pn junction and has an impurity concentration of 2 to 5 × 10 ¹⁵ cm ^-3 and a thickness of about 15 μm. And the p-type rising region 5
Is formed on the surface of the second n-layer 3 and has a thickness of about 2
μm and the back surface has the same concentration as that of the second n layer 3 of 2 to 5 × 1.
From 0 ¹⁵ cm ^-3 , the surface has the same density as that of the high-concentration region 6 2-5.
The concentration continuously increases so that the concentration becomes × 10 ¹⁷ cm ^-3 .
Further, after the p-type high concentration region 6 is formed in the second step 31 in this manner, a high temperature (about 885) is set in the third step 32.
By holding the melt 21 for a long time (about 3 hours), zinc in the melt 21 scatters, so that the zinc concentration in the melt 21 gradually decreases.

Thereafter, as shown in the fourth step 33, the melt 21 is melted at a rate of about 2.5 ° C./minute from about 885 ° C. to about 75 ° C.
By decreasing the temperature to 0 ° C., the p-type low concentration region 7 is formed on the high concentration region 6. The low concentration region 7 has a thickness of about 10 to 15 μm. Thus, in the low-concentration region 7, the back surface has the same concentration of 2 to 5 × 10 ¹⁷ cm ⁻³ as the high-concentration region 6, and the front surface has a concentration of about 0.6 to 1.5 × 10 ¹⁷ cm ⁻³ . , The concentration decreases continuously. This completes the epitaxial growth.

Thereafter, as shown in step 34, the supply of zinc is stopped and the hydrogen gas is switched to argon (Ar) gas,
The work in the reaction furnace 14 is completed by stopping the supply of the heater 22 and naturally cooling it.

Thereafter, electrodes are formed on the front surface and the back surface of the wafer epitaxially grown on the above-mentioned substrate, respectively, and dicing is performed to obtain the above-mentioned gallium phosphide green light-emitting diode 12.

[0030]

As described above, in the first aspect of the present invention, due to the large energy level difference between the high-concentration region of the p-layer and the vicinity of the low-concentration surface of the n-layer, light emission in which a large amount of carriers are confined in the light is emitted. Highly efficient light passes through the low concentration region of the p layer with few defects, in which the amount of carriers trapped in defects that do not contribute to light emission is small and the ratio of non-radiative recombination is small. Released as high.

Further, in the second aspect of the present invention, after the high concentration region is grown, the melt is held at a substantially constant temperature to scatter the impurities in the melt, so that the impurity concentration in the melt is lowered and the high concentration region is increased. A low concentration region is continuously formed on the upper side.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a gallium phosphide green light emitting diode according to an embodiment of the present invention.

FIG. 2 is a schematic view of an apparatus for manufacturing a gallium phosphide green light emitting diode according to an embodiment of the present invention.

FIG. 3 is a temperature process diagram for manufacturing a gallium phosphide green light emitting diode according to an embodiment of the present invention.

FIG. 4 is a diagram of impurity concentration in a gallium phosphide green light emitting diode according to an embodiment of the present invention.

FIG. 5 is an impurity concentration diagram of a conventional gallium phosphide green light emitting diode.

[Explanation of symbols]

 1 substrate 4 n layer 5 rising region 6 high concentration region 7 low concentration region 8 p layer

Claims (2)

[Claims] 1. An n-type gallium phosphide substrate, an n layer formed on the substrate and containing an impurity at a concentration lower than that of the substrate at least in the vicinity of the surface opposite to the substrate, and formed on the n layer. A high-concentration region containing impurities of a higher concentration than the vicinity of the surface of the n-layer near the pn junction and a lower concentration than the high-concentration region on the surface side. A gallium phosphide green light-emitting diode characterized by having a low-concentration region containing impurities. 2. A first step of growing a n-layer by bringing a melt into contact with an n-type gallium phosphide substrate, and adding a p-type impurity to the melt to form a p-type high concentration on the n-layer. A second step of growing a region, a third step of keeping the melt at a substantially constant temperature to scatter impurities in the melt, and a step of bringing the melt into contact with the high concentration region and the high concentration region And a fourth step of growing a p-type low-concentration region on the top surface of the gallium phosphide green light emitting diode.