JP3326261B2 - Gallium phosphide green light emitting diode and method of manufacturing the same - Google Patents

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 that emits high-intensity green light and a method of 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 disclosed in Japanese Patent Application Laid-Open No. 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 laminated. Note that the horizontal axis in the figure indicates the distance of each layer from the bottom surface of the substrate 41. The luminance is improved by lowering the impurity concentration of the second n-layer 43 near the pn junction. As described above, conventionally, in order to obtain high luminance, studies have been made to make the n-layer a multilayer and to find an optimum value of the impurity concentration.

[0003]

However, the above-mentioned light emitting diode is 10 mA in a bare state without resin coating.
Is about 1.1 mcd, and the luminance is still lower than, for example, about 2.3 mcd of a red light emitting diode made of gallium aluminum arsenide, which is considered to have high luminance. Therefore, the inventor of the present invention has focused on the p-layer of the conventional light-emitting diode and has conducted research with a view to further increasing the luminance. As a result, it has been 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 melt is in contact with the second n-layer 43.

That is, when the temperature of the melt gradually decreases during growth, the amount of zinc as an impurity in the melt decreases, and the zinc concentration in the melt increases, as shown in FIG.
The impurity concentration on the surface side of the layer 44 increases. Therefore, p
Since the number of defects on the surface side of the layer 44 increases and the amount of carriers trapped by defects that do not contribute to light emission increases, it has been found that high luminance cannot be obtained. Therefore, the present invention has been made in consideration of such conventional drawbacks, and particularly, focusing on the p-layer, and provides a gallium phosphide green light-emitting diode that emits high-luminance green light and a method of manufacturing the same. .

[0005]

According to a first aspect of the present invention, there is provided an n-type gallium phosphide substrate comprising: an n-type gallium phosphide substrate formed on a substrate and at least near a surface opposite to the substrate; An n-layer containing an impurity at a lower concentration than the substrate; and a p-layer formed on the n-layer, wherein the p-layer has a high-concentration region containing an impurity at a higher concentration near the pn junction than near the surface of the n-layer. has a low density region comprising a lower concentration than the impurity high concentration region at a front surface, a low concentration region of the p layer is the concentration gradient
It is provided so as to be 0.15 / μm or more .

Further, the present invention provides 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 contacting the melt with the high-concentration region to grow a p-type low-concentration region on the high-concentration region.

[0007]

As described above, in the first embodiment of the present invention, a high luminous efficiency can be obtained due to a 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 is missing
Since the light passes through the low-concentration region of the p-layer with few recesses, the luminous efficiency is reduced.
It is emitted as a small amount and high brightness. In particular,
The concentration gradient in the low concentration region of the p layer is 0.15 / μm or more
When, high brightness is obtained compared to below
Was found by experiment.

In the second aspect of the present invention, after growing the high-concentration region, the melt is maintained at a substantially constant temperature and the impurities in the melt are scattered. A low concentration region is continuously formed thereon.

[0009]

Next, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a sectional view of a gallium phosphide green light emitting diode according to the present embodiment. In FIG. 1, a substrate 1 has a thickness of about 2
It is made of 15 μm n-type gallium phosphide 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 and is made of, for example, n-type gallium phosphide having a thickness of about 15 μm, and has a relatively low impurity concentration of about 2 to 5 × 10 ¹⁵ cm ^−3. belongs to. As described above, the n-layer 4 includes the first n-layer 2 and the second n-layer 3, and is provided near the surface on the side opposite to the substrate 1 so as to contain impurities at a lower concentration 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.
The impurity concentration is 10 ¹⁷ cm ⁻³ , and the impurity concentration gradually increases as the surface is closer to 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 2-5 × 10 ¹⁷ cm ⁻³ . The low concentration region 7 is formed on the high concentration region 6 and has a thickness of, for example, 10 to 1.
5 μm p-type gallium phosphide. The low concentration region 7 has a high impurity concentration 6 at the interface side with the high concentration region 6.
0.6 to 1.5 × 10 ¹⁷ c on the surface side
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 impurity concentration than the vicinity of the surface of the n layer 4. The p layer 8 is formed so that the impurity concentration is lower on the surface side than in the high concentration region 6 near the pn junction 9. 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 naked state without resin coating, and the luminance is measured,
The brightness is about 2.2 mcd, about twice as high as that of a conventional light emitting diode, and about the same level of brightness as a red light emitting diode of gallium aluminum arsenide.

As described above, the reason why such a high luminance can be obtained is that the impurity concentration of the high concentration region 6 is 2 to 5 × 10 ¹⁷ cm ⁻³ and the concentration of the surface of the low concentration region 7 is 0.1 μm. 6-1.5
This is because the ratio of non-radiative recombination in the p-layer 8 was reduced due to the reduction to × 10 ¹⁷ cm ⁻³ .

According to experiments performed by the present inventors, it has been found that the concentration gradient of the low concentration region 7 is an important factor in reducing the ratio of non-radiative recombination. The density gradient is obtained by dividing a value obtained by dividing the density at the interface between the low-density region 7 and the high-density region 6 by the density at the surface, and dividing the value by the layer thickness of the low-density region 7. According to an experiment, when the concentration gradient is 0.15 / μm or more, a high luminance of about 2.2 mcd or more is obtained.
When it was less than m, it was found that the brightness was sharply reduced.

Further, it has been found that the density gradient of the rising region 5 is also an important factor for the luminance. This concentration gradient is
The value obtained by dividing the concentration of the rising region 5 at the interface 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 was 1
In the case of 000 / μm or less, a high luminance of about 2.2 mcd or more is obtained, and in the case of exceeding 1000 / μm, the luminance sharply decreases. It is considered that, by reducing the concentration gradient, the amount of light emitted upward from the pn junction 9 is reflected or absorbed in the p layer 8.

Next, a method of manufacturing the gallium phosphide green light emitting diode 12 of this embodiment will be described. First, the manufacturing equipment 13
Will be schematically described with reference to the schematic diagram of FIG. In this figure, a base 15 made of carbon or the like is placed in a reaction furnace 14 made of quartz or the like. A gallium phosphide single crystal substrate 16 is housed in a 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 is the surface of the base 15 and contains a melt 20 for epitaxial growth. In the epitaxial growth process, first, melt 20
Then, the temperature is raised in a state where the single crystal substrate 16 and the single crystal substrate 16 are completely separated, and thereafter 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 a side surface of the reaction furnace 14, and the temperature of the melt 21 is controlled by controlling the current to the heater 22. Zinc powder as a gas and impurities is supplied into the reaction furnace 14 through the gas supply port 23 and the impurity supply port 24, respectively. The 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 the 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 manufactured as described above. First, as shown in step 26, melt 21
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 the hydrogen for about 1 minute to introduce sulfur as the main donor impurity into the melt 21.

Thereafter, as shown in step 27, the temperature of the melt 21 is lowered at a rate of about 2.5 ° C./min, thereby epitaxially growing 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 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 ) precipitates in the melt 21 and the sulfur concentration and the silicon concentration of the melt 21 decrease.

Next, as shown in a step 29, the temperature of the melt 21 is lowered at a rate of about 2.5 ° C./min to obtain a 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. Thereafter, as shown in a second step 31, the melt 2
By lowering the temperature of 1 at a rate of about 2.5 ° C./min, a 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 a third step 32, the melt 21
At about 885 ° C. for about 3 hours. At this time, in the vicinity of the surface of the third n-layer 3a, zinc in the adjacent high concentration region 6 moves and is diffused. As a result, the third n-layer 3a is
N layer 3 and p-type rising region 5 formed thereon
Changes to

That is, the second n-layer 3 is formed on the pn junction, 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 of 2 to 5 × 1 as the second n-layer 3.
From 0 ¹⁵ cm ^-3 , the surface has the same concentration 2 to 5 as the high concentration region 6.
The concentration continuously increases so as to be × 10 ¹⁷ cm ⁻³ .
After the p-type high-concentration region 6 is formed in the second step 31 in this manner, a high temperature (about 885) is formed in the third step 32.
C.) and holding the melt 21 for a long time (about 3 hours) causes the zinc in the melt 21 to be scattered, so that the zinc concentration in the melt 21 gradually decreases.

Thereafter, as shown in a fourth step 33, the melt 21 is heated from about 885 ° C. to about 75 ° C. at a rate of about 2.5 ° C./min.
By lowering the temperature to 0 ° C., a 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. In this manner, the low concentration region 7 is formed such that 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 the concentration of approximately 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 operation in the reaction furnace 14 is completed by stopping the supply of the heater 22 and naturally cooling.

Thereafter, electrodes are formed on the front surface and the back surface of the wafer epitaxially grown on the substrate, and diced, whereby the gallium phosphide green light emitting diode 12 is obtained.

[0030]

As described above, in the first embodiment of the present invention, a high luminous efficiency can be obtained due to a 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
Pass through the low-concentration region of the p-layer with few defects,
The rate is reduced little and emitted as high brightness.
In particular, the concentration gradient in the low concentration region of the p layer is 0.15 / μ.
m, higher brightness can be obtained compared to less than
Experiments have shown that

According to the second aspect of the present invention, since the melt is maintained at a substantially constant temperature after the high-concentration region is grown and impurities in the melt are scattered, the impurity concentration in the melt is reduced, and the high-concentration region is reduced. A low concentration region is continuously formed thereon.

[Brief description of the 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 chart for manufacturing a gallium phosphide green light emitting diode according to an embodiment of the present invention.

FIG. 4 is an impurity concentration diagram 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]

 Reference Signs List 1 substrate 4 n-layer 5 rising region 6 high-concentration region 7 low-concentration region 8 p-layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-209883 (JP, A) JP-A-56-1529 (JP, A) JP-A-59-18688 (JP, A) JP-A-50- 19382 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 33/00 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. An n-type gallium phosphide substrate, an n-layer formed on the substrate and containing impurities at a concentration lower than the substrate at least in the vicinity of a surface opposite to the substrate, and formed on the n-layer. A p-layer having a high-concentration region near the pn junction and containing a higher concentration of impurities than near the surface of the n-layer, and a p-layer having a lower concentration on the surface side than the higher-concentration region. A low-concentration region containing impurities , wherein the p-layer has a low-concentration region;
Is a gallium phosphide green light emitting diode characterized in that the concentration gradient is 0.15 / μm or more . 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 maintaining the melt at a substantially constant temperature and scattering impurities in the melt, and contacting the melt with the high-concentration region to form the high-concentration region. And a fourth step of growing a p-type low-concentration region on the green light-emitting diode.