JPH0550155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a gallium phosphorous light emitting diode in which luminous efficiency is improved by improving crystallinity and lowering the impurity concentration of the n-layer.

Generally, in light-emitting diodes using gallium phosphorus, dislocation density is used as a guideline for determining the quality of crystallinity, and in the case of green light emission, the dislocation density is ¹
If it is less than ^-2 , it is said to be a crystal that provides good luminous efficiency. However, the above values are based on a laboratory level, and for mass production, it is difficult to control crystallinity by dislocation density because the dislocation density is not constant depending on the location within the pulled ingot. For this reason, conventionally, an epitaxial growth layer of the same conductivity type with a certain thickness or more is formed on a substrate obtained by pulling and slicing, taking advantage of the good crystallinity of the epitaxial growth layer, and then forming a Pn junction. was. Although this method certainly improves the crystallinity near the Pn junction, the influence of the substrate transfers to the grown layer, or lattice mismatch occurs between the substrate and the grown layer, resulting in a luminous efficiency of no more than 0.2%.

On the other hand, it has been reported that it is advantageous to use silicon as an impurity in a similar gallium phosphide green light emitting diode. For example, according to Japanese Patent Application Laid-Open No. 56-85879, in a temperature process diagram as shown in Figure 1a,
Immediately before the start of epitaxial production, Si is dissolved in the melt from SiC that has been applied to the boat in advance, and n
When the type is grown and ammonia gas is introduced just before the P type growth, the n layer 24 near the Pn junction 26 in the light emitting diode shown in FIG ^{. -3} , P layer 2
5 is 0.5 when Si is removed and C is doped instead.
~10×10 ¹⁶ cm ^-3 is considered good. Although the luminous efficiency is not explicitly stated in this publication, it was confirmed that the presence of Si near the Pn junction not only significantly reduces the lifetime but also reduces the luminous efficiency itself.

The present invention has been made in consideration of the above points, and
By growing a Si-doped layer on a gallium phosphide substrate, and then growing a layer from which Si has been removed while maintaining the same conductivity type, we can improve the continuity (matching) of the crystal and improve luminous efficiency and lifetime. This invention has been significantly improved, and the present invention will be explained in detail below based on Examples.

FIG. 2 is a temperature process diagram of liquid phase epitaxial growth of a gallium phosphorous green light emitting diode according to an embodiment of the present invention, and FIG. 3 is a diagram of impurity concentration distribution of the green light emitting diode formed thereby.

First, GaP polycrystals and n-type impurities are mixed into the Ga melt, and the semiconductor substrate is separated from the melt and heated. After being maintained at approximately 1030° C. for a while, the melt is placed on the semiconductor substrate at time A to wet the surface of the substrate. After that, epitaxial growth is performed by lowering the temperature at a rate of 2 to 3.5°C per minute. It is preferable that the melt be brought into contact with the atmosphere. Note that if the melt thickness is thin as mentioned above, the growth thickness tends to be thinner, but if the Pn junction is moved away from the substrate, the life will be longer, so the GaP polycrystalline placed in the melt should be
By keeping the weight percent or more in a saturated state, the amount of growth can be increased in a short time.

First, prior to epitaxial growth, a small amount of silicon is added to the melt, and at time B before the temperature is lowered, hydrogen sulfide gas is flowed into the atmosphere at a high concentration of 5.0 cc/min for a short time to increase the impurity concentration of the melt.
Then, the temperature is lowered at a low rate to reduce the impurity concentration of the substrate (1~
An n-layer growth 12 is performed with a concentration 2 of 5 to 8× ¹⁰ 17 cm ⁻³ higher than 3×10 ¹⁷ cm ⁻³ 1. Thereafter, n-layer growth 13 is performed while epitaxial growth is paused for 45 minutes to 120 minutes, and finally n-layer growth 14 is performed in carbon in an ammonia gas atmosphere. The amount of ammonia gas may be about 0.4% by volume relative to the atmospheric gas. Providing a rest time (i.e., constant temperature holding time) lowers the dislocation density in the crystal, but at the same time, the impurity concentration in the melt also decreases, so the n
You get layers. In particular, in the final n-layer growth 14, ammonia gas and Si in the melt react to form Si ₃ N ₄
1/4 to 1/10 of the Si in the melt can be removed, so although nitrogen is included, 10 ¹⁶
An n layer with an extremely low impurity concentration of about 4 cm ^-3 is formed. Incidentally, instead of introducing ammonia gas, if 0.1 to 1.0% by weight of GaN is dropped and mixed into the melt at 1000°C or higher, silicon nitride can be precipitated and the Si concentration can be reduced.

After that, at time D, zinc is introduced into the melt and P grows 1.
Do step 5. Such a P layer is 0.8-1.7× ¹⁰ cm
Although it can be controlled with a high impurity concentration of ^-3 , 5, it is not preferable to make the concentration too high because the crystallinity deteriorates and light absorption occurs.

Usually 10 ¹⁸ cm ^-3 to 10 ¹⁶ cm at Pn junction 6 as mentioned above
If there is a concentration difference of up to ^-3 , the lifetime will be short and switching operation will occur, but as mentioned above, multiple n-layers are formed while adjusting the crystallinity (especially the lattice matching and dislocation density in the area where there is a concentration difference). In addition, by removing Si impurities near the Pn junction in the form of silicon nitride,
By reducing it to 10 ¹⁶ cm ^-3 or less, no switching action occurs. Also, because the current distribution is improved, it is possible to obtain a luminous efficiency of 0.45% (average), which is much higher than the conventional method (0.2%), and a further 80% reduction in brightness.
A device with a long life of over 1,500 hours (overload test using high temperature and large current) was obtained.

As described above, the present invention comprises a first step of epitaxially growing an n-type layer by bringing a melt into contact with an n-type gallium phosphorous substrate, and a second step of bringing the melt into contact with a nitrogen compound to precipitate silicon nitride. process and again n
a third step of epitaxially growing a mold layer;
Since the present invention includes the fourth step of forming a P-type layer, the n-layer concentration near the Pn junction can be made sufficiently low, and a light-emitting diode with good luminous efficiency can be obtained.

As described above, the crystallinity is improved by forming an n-type layer consisting of three layers, including a high impurity concentration layer having a higher impurity concentration than the substrate, with the impurity concentration decreasing in three stepwise steps. As a result, high luminous efficiency and long life can be obtained. Furthermore, in the present invention, a solid phase nitrogen compound is brought into contact with the melt, so if a solid phase nitrogen compound such as GaN is used, it is easy to handle and control the weight.
By bringing the solid phase nitrogen compound into contact with the melt in this manner, the production method having the above-mentioned advantages can be carried out.

[Brief explanation of drawings]

Figure 1 is a temperature process diagram of a conventional light emitting diode.
FIG. 2 is a temperature process diagram of liquid phase epitaxial growth of a gallium phosphorous green light emitting diode according to an example of the present invention, and FIG. 3 is a diagram showing the impurity concentration distribution of the green light emitting diode formed thereby. It is a diagram. 12, 13, 14...N layer growth, 15...P layer growth.

Claims (1)

[Claims] 1. A first step of epitaxially growing an n-type layer with a higher impurity concentration than that substrate and an n-type layer with a lower impurity concentration than that n-type layer by contacting a melt with an n-type gallium phosphorus substrate, and The second step is to bring the liquid into contact with a solid nitrogen compound to precipitate silicon nitride, and again epitaxially grow the n-type layer with the lowest impurity concentration, forming it so that the impurity concentration decreases step by step. A method for manufacturing a gallium phosphorous light emitting diode, comprising a third step and a fourth step of forming a P-type layer.