JPS5945234B2 - 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 analysis, 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 latted Cyochralski method, and an 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 the crystal strain 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. Concentration ND is 2×1017crfL-3
The acceptor concentration NA of the p-type GaP layer 3 is 1×1018 (
V7! -3, the concentration of the substrate 1 is higher than the concentration of the GaP layer 2, and the acceptor concentration of the p-type GaP layer 3 is
and higher than the donor concentration of the n-type GaP layer 2. The energy band structure when this light emitting diode is forward biased is as shown in FIG. 1c.

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, J is the hole current density of the holes injected into the n-type GaP layer 2, and Ln is the electron current density of the holes injected into the p-type GaP layer 3. The diffusion length, L, represents the diffusion length of holes injected into the n-type GaP layer 2. The n-type GaP layer 2 of this light emitting diode has a thickness (width) of 25 μm or more, whereas Lp is about 2 to 3 μm, and the thickness (width) of the n-type GaP layer 2 is approximately 2 to 3 μm. is sufficiently larger than L.

Therefore, all of the holes injected into the n-type GaP layer 2 recombine with electrons and disappear within the n-type GaP layer 2, and J, is substantially It's reaching zero. Note that Jn is also several μm away from the p-n junction 5.
In remote areas, it is virtually zero. By the way, N
By optically exciting a GaP crystal doped with , the luminous efficiency of the bulk (GaP crystal) can be determined.

For example, American InstituteOfPll
Magazine “JournalOfAppli” published by ySiCS
edPhysicsVOl45ro11N0vember
1974,” pages 4920-4930, P. D. Dap
The paper “KineticsO
frecOmbinatiOninnitrOgen-
According to “DOpedGaP”, the excitation intensity is 10A/Cr
When the luminous efficiency reaches its maximum at level A, NA=1X1018C77 for p-type bulk! -3, when ND=1×1017CTL-3 for n-type bulk.
The luminous efficiency at this time is 0.3% for the p-type bulk and 0.052% for the 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, calculations based on the experimental data in the above paper show that the light emitting diode has the highest luminous efficiency when NA = 1 x 1018 cm.
-3, ND-2X1017? -3, the light emitting efficiency of the light emitting diode is 0.086%, and the efficiency of electron injection into the p-type bulk is 18%. In fact, even in the design of an actual GaP light emitting diode, NA-1×101 is used as shown in Figure 1b.
The optimal design is 8 cm-3, ND-2×1017 cm-3, and a luminous efficiency of about 0.08% is obtained in this case. As is clear from the above, in the conventional GaP light emitting diode, although the p-type bulk 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, 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.
It is also conceivable that the light emitting efficiency of the light emitting diode can be increased by increasing the injection efficiency of electrons into 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, and 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 impossible to improve luminous efficiency. 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 GaP green light emitting diodes, it is important to fully utilize the underutilized p-type GaP layer 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 provides high impurity concentration n
a n-type GaP semiconductor epitaxial growth layer with a low impurity concentration adjacent to the n-type GaP semiconductor layer with a high impurity concentration, and a p-type GaP semiconductor layer adjacent to the n-type GaP semiconductor epitaxial growth layer with a low impurity concentration. In the GaP green light emitting diode comprising:
The diffusion length of minority carriers (holes) injected into the GaP type semiconductor epitaxial growth layer is below the diffusion length and 1 μm or more,
The present invention also relates to a GaP green light emitting diode, characterized in that the impurity concentration of the high impurity concentration n-type GaP semiconductor layer is higher than the impurity concentration of the p-type GaP semiconductor layer. According to the above invention, p-type GaP, which has not been fully utilized in the past, can be used in GaP green light emitting diodes.
The injection efficiency of minority carriers (electrons) into the semiconductor layer can be increased.

That is, by setting the thickness of the epitaxially grown n-type GaP semiconductor layer with a low 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 n-type GaP semiconductor layer with a high impurity concentration can be grown. The light emitting efficiency in the p-type GaP semiconductor layer can be increased by effectively utilizing the reflection effect generated by the junction between the n-type GaP semiconductor layer and the n-type epitaxially grown layer with a low impurity concentration. G
High luminous efficiency can also be obtained with an aP semiconductor epitaxial growth layer. Therefore, the luminous efficiency of the GaP green light emitting diode, which has conventionally had extremely poor luminous efficiency, 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, in which, similarly to FIG. 1, a indicates a three-layer semiconductor structure, b indicates an impurity concentration distribution, c indicates an energy band structure at forward bias, d schematically shows the minority carrier current density at the time of forward bias, and in FIGS. 2C and d, the same symbols as in FIGS. 1C and d are given the same reference numerals.

This light emitting diode is a T
n+ type GaP of el-L type, n+ type GaP consisting of crystal
A substrate 11 and an S- and N-doped layer formed on the substrate 11 to a thickness of about 3 μm by LPE. monomorphic GaP layer 12 and L
It consists of a Zn- and N-doped p-type GaP layer 13 formed on an n-type GaP layer 12 to a thickness of about 30 μm by PE method, and an n+-n-junction 14 and a p-n (n-1p) Junction 15
and has. As is clear from FIG. 1b, the respective impurity concentrations are such that the donor concentration ND of the substrate 11 is 1×1018? -3,
The donor concentration ND of the n-type GaP layer 12 is 1×1017C7
r1-3 The acceptor concentration NA of the p-type GaP layer 13 is 5x
It is 1017 cm-3. The SSD law is, for example,
8-20106 and the magazine "Electronic Materials" January 1973 issue, pages 18 to 23, the crystal growth method for compound semiconductors uses component A (such as GaJn) with a relatively low vapor pressure and a relatively high vapor pressure. In a method for producing a crystal of a compound semiconductor AB consisting of a component B (such as P.As) that exhibits pressure, a container containing molten component A is placed in an atmosphere containing vapor of component B, and the molten component A is The part that contacts the vapor of component B is kept at a high temperature lower than the melting point of compound semiconductor AB, the other part is kept at a lower temperature than the high temperature part, the vapor pressure of component B is selected to be higher than the decomposition pressure of compound semiconductor AB, and the high temperature The compound semiconductor AB synthesized in the part is diffused (Synthesis) into the melted component A as a solute (SOlute).
DlffUSlOn) to grow a compound semiconductor crystal from the low temperature part as a crystal of compound semiconductor AB.

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 the red phosphorus is heated to 430°C to generate 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 this example, n+ type Ga
Since the P substrate 11 uses the crystal produced by the above-mentioned SSD method, its crystallinity is good, and therefore the crystallinity of the n-type GaP layer 12 grown on the substrate 11 is also very good.

Therefore, the n-type GaP layer 12 is 1X1017? Thanks in part to the low impurity concentration of −3, it has a very large hole diffusion length L of about 12 μm. Since the crystallinity of the interface between the n+ type GaP substrate 11 and the n-type GaP layer 12 is also much better than that of the conventional one, a good n+-n-type junction 1 with less recombination of carriers in the depletion layer generated at the junction is achieved.
4 is formed. This light emitting diode's n-type Ga
Since the thickness of the P layer 12 is designed to be 3 μm, which is sufficiently p smaller than the hole diffusion length L (approximately 12 μm), most of the holes injected into the n-type GaP layer 12 are n-type. GaP
Diffuses through layer 12 to reach n+-n junction 14.

It is known that an n+-n- or p+-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, since the n+-n junction 14 is a good junction, it effectively acts as a potential barrier, and has the effect of blocking the holes that have diffused up to the n+-n junction 14 (n+-n junction 14).
Since the junction 14 appears to reflect holes, it exhibits a reflection effect (referred to as a reflection effect). Therefore, the injection of holes into the n+ type GaP substrate 11 is restricted, and the hole concentration in the n type GaP layer 12 becomes high. On the other hand, holes (hole current density J) are steadily injected into the n-type GaP layer 12.

, ) is the sum of two components: the hole J,l that recombines and disappears in the n-type GaP layer 12 and the hole J,2 injected into the n+-type GaP substrate 11 (n+ There must also be some holes that recombine and disappear at the -n junction 14, but this is ignored here). J,l does not have a very large p-value due to the size relationship between the thickness, that is, the width, of the n-type GaP layer 12 and L, and J,2 also has a p-value of 1d due to the reflection effect of the n+-n-type junction 14. J.

, is suppressed to a value smaller than . The sum of these is J. , also has a smaller value than JOp in FIG. 1d (when the total current density is the same). n+ type G due to reflection effect
Since injection of holes into the aP substrate 11 is limited, injection of holes into the n-type GaP layer 12 is limited on a regular basis. As a result, the electron injection efficiency [JOn/(JOn+JOp)] into the p-type GaP layer 13 increases, and the n-type GaP layer 13 increases.
This value is close to the injection efficiency calculated for an n+-p junction without the aP layer 12. In this example, the electron injection efficiency into the p-type G&P layer 13 is approximately 35%, compared to the conventional 18%.
% was about twice as high. In this way, the efficiency of electron injection into the p-type GaP layer 13, which has a high luminous efficiency as a bulk, increases, so the luminous efficiency of this light emitting diode increases at a current density of 1.
At 0A/Cd, it is 0.11%, compared to the conventional 0.08%.
%, a significant improvement of approximately 40%.

Note that if an LEC crystal is used as the n+ substrate 6 to carry out the present invention, the crystallinity deteriorates as described above, and the light emitting efficiency of the light emitting diode deteriorates. Although current LEC crystals cannot be used in the above embodiments, this will not apply in the future when the crystallinity of LEC crystals is improved. However, the embodiment of FIG. 3, which will be described below, allows current LEC crystals to be used in the present invention. FIG. 3 shows a GaP green light emitting diode according to a second embodiment of the present invention. The light emitting diode of this example includes a substrate 21 of Te-doped n-type GaP crystal manufactured by the LEC method, and a substrate 21 with a thickness of approximately 30 μm formed by the LPE method on the substrate 21.
an S-doped n+ type GaP layer 22 formed in a thickness of about 3 μm;
and an N-doped n-type GaP layer 23 and a Zn- and N-doped p-type GaP layer 24 formed to a thickness of about 30 μm on the n-type GaP layer 23 by the LPE method, and an n+-n-type junction 25. and a p-n or n-1p junction 26. As is clear from FIG. 3b, the impurity concentration of each layer is equal to the donor concentration N of the substrate 21. Is it 4×1017? -3, n-decade Ga
The donor concentration ND of the P layer 22 is 2X1018c1n+3,n
The donor concentration ND of the monomorphic GaP layer 23 is 1Xh017C11
Acceptor fiber NA of L-3p@GaP layer 24 is 5×10
17C! It is n-3. In this example? The n+ type GaP layer 22 with a high impurity concentration to obtain the radiation effect is formed by the LPE method, and the deterioration of crystallinity due to the high impurity concentration of the n+ type GaP layer 22 can be prevented by providing the n-type GaP layer 23. The p-type GaP layer 24 has relatively good crystallinity.

Therefore, even if the crystallinity of the n+ type GaP layer 22 is not very good, the crystallinity of the p-type GaP layer 24 is improved, and the p-type GaP layer 22 has good crystallinity.
The bulk luminous efficiency of the P layer 24 was kept high, and the injection efficiency increased due to the reflection effect, resulting in a luminous efficiency of 0.11% at a current density of 10 A/Cd. As a modification of the second embodiment, if an n-type GaP substrate manufactured by the SSD method is used instead of the n-type GaP substrate 21 manufactured by the LEC method shown in FIG. 3, the current density is as high as 0.14% at a current density of 10 A/Cd. It was possible to obtain luminous efficiency. In the above two examples, n
Most of the holes injected into the monomorphic GaP layers 12 and 23 are n
The reflection effect does not appear unless the +n junctions 14 and 25 are reached. Therefore, the thickness of the n-type GaP layers 12 and 23 must naturally be equal to or less than the hole diffusion length of the n-type GaP layers 12 and 23, but due to the reflection effect, the thickness of the p-type GaP layer 1
In order to obtain a substantial increase in the efficiency of electron injection into the n-type GaP layers 12 and 24, it is necessary to make the hole diffusion length of the n-type GaP layers 12 and 23 less than one. In the above embodiment, the thickness of the n-type GaP layers 12 and 23 is approximately 3 μm, which is less than the hole diffusion length. Further, it is necessary that the n-type GaP layers 12 and 23 have a thickness that is at least thick enough to obtain the effect of alleviating crystal strain, and it is desirable that this layer has a thickness of 1 μm or more. In addition, the minority carrier injection efficiency in a p-n (n-1p) junction approximates the value calculated for an n+1p junction assuming that there are no n-type GaP layers 12 and 23. , it is meaningless unless the electron injection efficiency into the p-type GaP layer at the n+-p junction is sufficiently high. For this purpose,
The p-type GaP layers 13 and 24 are usually used with 5×1017
~1×1018? When the impurity concentration is about -3, the impurity concentration of the n + type GaP layer 11y22 is changed to the p type GaP layer 13,
It is necessary to select an impurity concentration of 24 or higher. 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, FIG. 2 is an explanatory diagram showing a light emitting diode according to a first embodiment of the present invention, and FIG. 3 is an explanatory diagram showing a light emitting diode according to a second embodiment of the present invention. FIG.

Claims (1)

[Scope of Claims] 1. An n-type GaP semiconductor layer with a high impurity concentration, an n-type GaP semiconductor epitaxial growth layer with a low impurity concentration adjacent to the n-type GaP semiconductor layer with a high impurity concentration, and an n-type GaP semiconductor layer with a low impurity concentration. In a GaP green light emitting diode including a GaP semiconductor epitaxial growth layer and an adjacent p-type GaP semiconductor layer, the thickness of the low impurity concentration n-type GaP semiconductor epitaxial growth layer is changed from the p-type GaP semiconductor layer to the low impurity concentration layer. The impurity concentration of the high impurity concentration n-type GaP semiconductor layer is set to be 2/3 or less of the diffusion length of minority carriers (holes) injected into the n-type GaP semiconductor epitaxial growth layer and 1 μm or more, and the impurity concentration of the high impurity concentration n-type GaP semiconductor layer is
Ga characterized in that the impurity concentration is higher than that of the semiconductor layer.
P green light emitting diode. 2 The high impurity concentration n-type GaP semiconductor layer is an SSD
The GaP green light emitting diode according to claim 1, wherein the GaP green light emitting diode is a substrate of an n-type GaP semiconductor crystal manufactured by a method. 3. The GaP green light emitting diode according to claim 1 or 2, wherein the p-type GaP semiconductor layer is a p-type GaP semiconductor epitaxially grown layer obtained by epitaxially growing a p-type GaP semiconductor. 4 The p-type GaP semiconductor layer has the low impurity concentration n
The GaP green light emitting layer according to claim 1 or 2, which is a p-type diffused GaP semiconductor layer formed by diffusing p-type impurities into an n-type GaP semiconductor epitaxial growth layer for forming a GaP-type GaP semiconductor epitaxial growth layer. diode.