JPS5945235B2 - GaP light emitting diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a highly luminous efficient G
Regarding an aP light emitting diode.

A conventional GaP light emitting diode is generally constructed as shown in FIG. In this figure, a is a three-layer semiconductor structure, and b is a three-layer semiconductor structure.
is the impurity concentration distribution, c is the energy band structure at forward bias, and d is the minority carrier current density at forward bias.
A Te-doped n-type GaP substrate 1 manufactured by a high-pressure melt-pulling method using a liquid capsule called the 2000 (Lated Cyochralski) method, and s and N-doped n-type GaP layer 2 and L on top of n-type GaP layer 2.
It consists of a Zn- and N-doped p-type GaP layer 3 formed by PE method, and has an n-n junction 4 and a p-n or n--p junction 5.
and has. Incidentally, although the crystal growth technology using the LEC method has made remarkable progress and it has recently become possible to obtain GaP substrates of considerably high quality, the reality is that they still have an order of magnitude more crystal defects than Si.

Therefore, in the above-mentioned conventional GaP light emitting diode, an n-type GaP layer 2 is formed by the LPE method in order to alleviate crystal distortion caused by crystal defects in the GaP substrate 1, and this n-
The impurity concentration of the n-type GaP layer 2 is lower than that of the substrate 1 to improve crystallinity, and
The thickness of layer 2 is set to 2 to obtain a sufficient effect of alleviating crystal strain.
The thickness is set at 5 to 50 μm. As a result, the crystallinity of the p-type GaP layer 3 formed to a thickness of 20 to 30 μm becomes relatively good, and a practical light emitting diode can be obtained. Figure 1a
The impurity concentration (assumed to be approximately equal to the carrier concentration) in each region of the light emitting diode shown in FIG. 1B is equal to the donor concentration N of the substrate 1, as shown in FIG. is 3 x 1017 cm-3, the donor concentration ND of n-type GaP layer 2 is 2 x 1017 x I-3, p
The acceptor concentration NA of the GaP layer 3 is 1×1018c!
n-3, the concentration of substrate 1 is higher than the concentration of GaP layer 2, and the acceptor concentration of p-type GaP layer 3 is higher than that of substrate 1 and n-3.
It is higher than the donor concentration of the monomorphic GaP layer 2. When this light emitting diode is forward biased, the energy band structure is the first
It looks like Figure c.

In this band structure diagram, Ec is the lower limit energy level of the conduction band, Ev is the upper limit energy level of the valence band, EF is the Fermi level, 6 is an electron, and 7 is a hole. are injected as minority carriers through the pn junction 5, respectively. This injection state of minority carriers is explained by the current density of minority carriers in FIG. 1d. However, in this figure, the minority carriers existing in the thermal equilibrium state and the depletion layer formed at the junctions 4 and 5 are ignored. Furthermore, the injected minority carriers decrease exponentially as they move away from the pn junction 5, but here they are approximately represented by a straight line. Jn is the electron current density of the electrons injected into the p-type GaP layer 3, Jp is the hole current density of the holes injected into the n-type GaP layer 2, and Ln is the diffusion of the electrons injected into the p-type GaP layer 3. The length Lp indicates the diffusion length of holes injected into the n-type GaP layer 2. This light emitting diode's n-type G
The aP layer 2 has a thickness (width) of 25 μm or more, whereas Lp is about 2 to 3 μm, and the n-type GaP layer 2 has a thickness (width) of 25 μm or more.
The thickness (width) of is sufficiently larger than Lp.

Therefore, the holes injected into the n-type GaP layer 2 are all recombined with electrons in the n-type GaP layer 2 and disappear, and Jp
becomes substantially zero at a distance of several μm from the pn junction 5. Note that Jn is also several μ from the p-n junction 5.
It becomes essentially zero at a distance of m. by the way,
By optically exciting a GaP crystal doped with N, the luminous efficiency of the bulk (GaP crystal) can be determined.

For example, Anlerican InstituteOfPh
Magazine “JournalOfAppll” published by ysics
edPkgsiCs,. Vol. 45, Waterfall 11, NOv
page 4920-4930 of "emberl974"
．． D. The paper “Kin
eticsOfrecOmbinatiOninnit
rOgen-DOpedGaP”, the excitation intensity is 10A/c! At the level of 1i, the luminous efficiency is highest when NA=1×1018 儂−3 for p-type bulk and N for n-type bulk. = 1×10 17 crIL-3. The luminous efficiency at this time is 0.3% for p-type bulk.
, 0.052% in n-type bulk. However, the luminous efficiency of a light emitting diode, which is a p-n junction element, is determined by multiplying the luminous efficiency of the p-type bulk by the electron injection efficiency and the luminous efficiency of the n-type bulk multiplied by the hole injection efficiency. Become peace. Therefore, according to calculations based on the experimental data in the above paper, the light emitting diode with the highest luminous efficiency is NA = 1 x 101
8cm-3, ND=2×1017cr! At L-3, the light emitting efficiency of the light emitting diode is 0.086%, and the electron injection efficiency into the p-type bulk is 18%. Fact, actual G
Even in the design of aP light emitting diode, NA
=1×1018crrL-3, ND=2×1017cm
-3 is the optimal design, and in this case, a luminous efficiency of about 0.08% is obtained. As is clear from the above, although the &ζ p-type bulk of the conventional GaP light emitting diode has high luminous efficiency, the luminous efficiency is low due to the use of a pn junction element.
In the structure shown in FIG. 1, if the impurity concentration of the n-type GaP layer 2 is increased to make it an n+ layer, and the p-n junction 5 is made an n+-p junction to increase the efficiency of electron injection into the p-type GaP layer 3,
It is also possible to improve the luminous efficiency of the light emitting diode. However, in reality, by increasing the impurity concentration of the GaP layer 2, the crystallinity of the GaP layer 2 deteriorates.
Furthermore, the crystallinity of the p-type GaP layer 3 also deteriorates. As a result, the luminous efficiency of the essential p-type GaP layer 3 as a bulk decreases, non-radiative recombination at the p-n junction 5 increases, and minority carriers contributing to light emission are not sufficiently injected.
It is not possible to increase the luminous efficiency of a light emitting diode. Note that the luminous efficiency of the GaAs infrared light emitting diode that emits direct transition type light is high, but the luminous efficiency of the GaP green light emitting diode that emits pseudo direct transition type light is low.

Therefore, in order to increase the luminous efficiency of the GaP green light emitting diode, it is important to fully utilize the p-type GaP layer, which has not been fully utilized in the past, as a light emitting region and to improve the crystallinity of GaP. Therefore, an object of the present invention is to provide a GaP green light emitting diode with high luminous efficiency.

In order to achieve the above object, the present invention includes an n-type GaP semiconductor substrate having a first impurity concentration, and an n-type GaP semiconductor substrate having a first impurity concentration formed on the n-type GaP semiconductor substrate by a liquid phase epitaxial growth method. an n-type GaP semiconductor epitaxial growth layer having a high second impurity concentration;
an n-type GaP semiconductor epitaxial growth layer having a third impurity concentration smaller than the second impurity concentration formed by a liquid phase epitaxial growth method on the n-type GaP semiconductor epitaxial growth layer having an impurity concentration of a p-type GaP semiconductor layer having an impurity concentration equal to or lower than the second impurity concentration formed by a liquid phase epitaxial growth method on the n-type GaP semiconductor epitaxial growth layer having an impurity concentration of 3; The thickness of the n-type GaP semiconductor epitaxial growth layer with the impurity concentration is determined by the minority carriers (holes) injected from the p-type GaP semiconductor layer into the n-type GaP semiconductor epitaxial growth layer with the third impurity concentration.
The present invention relates to a GaP green light emitting diode characterized in that the diffusion length is less than ÷ the diffusion length of and greater than or equal to 1 μm. According to the above invention, in a GaP green light emitting diode, it is possible to increase the injection efficiency of minority carriers (electrons) into the p-type GaP epitaxial layer, which has not been sufficiently utilized in the past.

That is, by setting the thickness of the n-type GaP epitaxial growth layer with the third impurity concentration to 1 μm or more and making it less than or equal to the diffusion length of minority carriers (holes) in this layer, the second impurity concentration can be increased. The light emitting efficiency in the p-type GaP layer can be increased by effectively utilizing the reflection effect caused by the junction between the n-type GaP epitaxial layer of the third impurity concentration and the n-type GaP epitaxial layer of the third impurity concentration. Impurity concentration n-type G
High luminous efficiency can be obtained even with an aP epitaxial growth layer. Therefore, conventionally, G
The luminous efficiency of the aP green light emitting diode can be greatly improved. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a GaP green light emitting diode to which the present invention is applied, and similarly to FIG. The energy band structure at the time of forward bias, d schematically shows the minority carrier current density at the time of forward bias of the n+-n-1p layer. Common elements are given the same reference numerals.

This light emitting diode includes a substrate 11 of Te-doped n-type GaP crystal manufactured by the LEC method, and an S-doped n+-type GaP layer 1 formed on the substrate 11 to a thickness of about 30 μm by the LPE method.
2 and the n+ type GaP layer 12 to a thickness of about 3. μ
an S- and N-doped n-type GaP layer 13 formed in m,
It consists of a Zn- and N-doped p-type GaP layer 14 formed to a thickness of about 30 μm by LPE on an n-type GaP layer 13, and has an n+-n-type junction 15 and a p-n or n-p junction 16. .

As is clear from Figure 2b, the impurity concentration of each layer is as follows:
Donor concentration N of the substrate 11. (first impurity concentration) is 4×1
017Cr! l-3, donor concentration N of n+ type GaP layer 12
Is D (second impurity concentration) 2×1018? −3, donor concentration N of the n-type GaP layer 13; (third impurity concentration) is 1
×1017? -3, the acceptor concentration NA of the p-type GaP layer 14 is 5×10 17 CTrL−3. In this light emitting diode, the n + -type GaP layer 12 is formed by the LPE method which produces crystals with good crystallinity, so it has fairly good crystallinity and alleviates the poor crystallinity of the substrate 11 .

Therefore, the crystallinity of the n-type GaP layer 13 and the p-type GaP layer 2, which are sequentially formed on the n+-type GaP layer 12 by the LPE method, is further improved. The p-type GaP layer 2 is made of n-type GaP, which has very good crystallinity, in addition to the very good crystallinity of the n+-type GaP layer 12, and also because of the low impurity concentration.
In addition to the effect of relaxing the crystal strain of the layer 12, the crystal becomes a good crystal with high luminous efficiency as a bulk. n-type GaP
Since the layer 13 has good crystallinity, the hole diffusion length Lp of the n-type layer 13 is approximately 12 μm, which is very large. Furthermore, since the crystallinity of the interface between the n+ type GaP layer 12 and the n-type GaP layer 13 is good, a good n+-n-type junction 15 is formed in which carrier recombination in the depletion layer generated at the junction is small. . n-type GaP layer 13 of this light emitting diode
Since the thickness of is designed to be approximately 3 μm, which is sufficiently smaller than the hole diffusion length Lp (approximately 12 μm), most of the holes injected into the n-type GaP layer 13 are is diffused to reach the n+-n junction 15.

It is known that an n+-n- or n++p- junction consisting of a high impurity concentration layer and a low impurity concentration layer of the same conductivity type acts as a potential barrier against minority carriers. In this case as well, the n+-n junction 15 is a good junction, so
It acts effectively as a potential barrier and has the effect of blocking the holes that have diffused up to the n+-n junction 15 (called a reflection effect because the n+-n junction 15 appears to reflect the holes). do. Therefore, the injection of holes into the n+ type GaP layer 12 is restricted, and the hole concentration in the n-type GaP layer 13 becomes high. On the other hand, holes (hole current density JOp) that are steadily injected into the n-type GaP layer 13 are
It is the sum of two components: the holes that recombine and disappear in the n+-n junction 15 (Jpl) and the holes that are injected into the n+-type GaP layer 12 (Jp2). There must also be some holes that disappear due to this, but this is ignored here).

JPl does not take a very large value due to the size relationship between the thickness, that is, the width, of the n-type GaP layer 13 and Lp, and JP2 also does not take n+
J in FIG. 1d due to the reflection effect of the -n junction 15
The value is suppressed to be smaller than Op. JOp, which is the sum of these, also has a smaller value than JOp in FIG. 1d (when the total current density is the same). Since the injection of holes into the n+ type GaP layer 12 is limited by the reflection effect, the injection of holes into the n-type GaP layer 13 is normally limited. As a result, the electron injection efficiency [JOn/(JOn+JOp)] into the p-type GaP layer 14 increases, and the n-type GaP layer 14 increases.
This value is close to the injection efficiency calculated for an n+-p junction without the aP layer 13. In this example, p-type GaP layer 1
The electron injection efficiency into 4 is approximately 35%, compared to the conventional 18%.
It has become about twice as much. In this way, the efficiency of electron injection into the p-type GaP layer 14, which has high luminous efficiency as a bulk, increases, so that the luminous efficiency of this light emitting diode increases at a current density of 10
A/Cil is 0.11%, compared to the conventional 0.08
%, a significant improvement of approximately 40%.

As is clear from the above, according to this embodiment, even if it is impossible to obtain a crystal with high impurity concentration and good crystallinity by the LEC method, the thickness of the n+ type GaP layer 12 and Lp is equal to or less than ÷ of Lp. By providing the n-type GaP layer 13, a light emitting diode with high luminous efficiency can be obtained. As a modification of the first embodiment described above, instead of the n-type GaP substrate 11 manufactured by the LEC method in FIG. 2, an n-type GaP substrate 11 manufactured by the SSD method is used.
If you use a substrate of
We were able to obtain a high luminous efficiency of 4%.

The above-mentioned SSD method is a compound semiconductor crystal growth method disclosed in, for example, Japanese Patent Publication No. 48-20106 and the magazine "Electronic Materials" January 1973 issue, pages 18-23. In a method for producing a crystal of a compound semiconductor AB consisting of a component B (such as In) and a component B (P, As, etc.) exhibiting a relatively high vapor pressure, a container containing molten component A is placed in an atmosphere containing the vapor of component B. The part of the molten component A that comes into contact with the vapor of component B is a compound semiconductor AB.
The vapor pressure of component B is selected to be higher than the decomposition pressure of compound semiconductor AB.
is) compound semiconductor AB is a solute (SOlute)
Diffusion into component A melted as (DiffusiOn)
This method of manufacturing a compound semiconductor is characterized in that the compound semiconductor AB is grown as a crystal from the low-temperature part.

For example, a Ga solution is placed in a cylindrical crucible with a conically pointed bottom, and the crucible is sealed in a vacuum container. Red phosphorus is placed at the bottom of the vacuum vessel and heated to 4300 °C to create a P vapor pressure of approximately 1 atmosphere within the vacuum vessel. Further, a temperature gradient is applied to the Ga solution so that the temperature is 1200° C. at the surface of the Ga solution and 1150° C. at the bottom of the crucible.
In this way, GaP is synthesized on the surface of the Ga solution, this GaP diffuses as a solute in the Ga solution toward the bottom of the crucible, and crystal growth begins at the bottom of the crucible. GaP crystals produced by this SSD method have very good crystallinity and are suitable for light-emitting devices because they can be grown at lower temperatures and lower pressures than those produced by the LEC method. In the above embodiment, most of the holes injected into the n-type GaP layer 13 are n+
The reflection effect does not appear until the -n junction 15 is reached.

Therefore, although the n-type GaP layer 13 must naturally have a hole diffusion length equal to or less than the n-type GaP layer, the electron injection efficiency into the p-type GaP layer 14 can be substantially increased due to the reflection effect. It was confirmed that in order to obtain this, the length must be equal to or less than the diffusion length of holes in the n-type GaP layer 13. In the above embodiment, the thickness of the n-type GaP layer 13 is about 3 μm,
It is equal to or less than the hole diffusion length ÷. Further, the n-type GaP layer 13 needs to have a thickness that is at least as thick as possible to obtain the effect of relaxing crystal strain, and it is desirable that this layer has a thickness of 1 μm or more. In addition, since the injection efficiency of minority carriers in a p-n (n-1p) junction approximates the value calculated for an n+-p junction assuming that there is no n-type GaP layer 13, It is meaningless unless the injection efficiency of electrons into the p-type GaP layer at the -p junction is sufficiently high. For this purpose, the p-type GaP layer 14 must be
1×1018? When the impurity concentration is about -3, n+ type G
It is necessary to select the impurity concentration of the aP layer 12 to be higher than the impurity concentration of the p-type GaP layer 14. Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and can be further modified.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional light emitting diode, and FIG. 2 is an explanatory diagram showing a light emitting diode according to a first embodiment of the present invention. In addition, in the symbols used in the drawings, 11 is the substrate, 1
2 is an n+ type GaP layer, 13 is an n-type GaP layer, and 14 is a p type GaP layer.
It is a GaP layer.

Claims (1)

[Scope of Claims] 1. An n-type GaP semiconductor substrate having a first impurity concentration, and a second impurity having a higher impurity concentration than the first impurity concentration formed on the n-type GaP semiconductor substrate by a liquid phase epitaxial growth method. a third impurity concentration lower than the second impurity concentration formed on the n-type GaP semiconductor epitaxial growth layer having the second impurity concentration by a liquid phase epitaxial growth method; an n-type GaP semiconductor epitaxial growth layer; and a p-type GaP semiconductor layer having an impurity concentration equal to or lower than the second impurity concentration formed by a liquid phase epitaxial growth method on the n-type GaP semiconductor epitaxial growth layer having the third impurity concentration. and the thickness of the n-type GaP semiconductor epitaxial growth layer having the third impurity concentration is such that minority carriers (positive 2/3 or less of the diffusion length of the hole) and 1 μm
A GaP green light emitting diode characterized by the above. 2. The GaP green light emitting diode according to claim 1, wherein the n-type GaP semiconductor substrate having the first impurity concentration is an n-type GaP semiconductor crystal substrate manufactured by an LEC method. 3. The GaP green light emitting diode according to claim 1, wherein the n-type GaP semiconductor substrate having the first impurity concentration is an n-type GaP semiconductor crystal substrate manufactured by an SSD method.