JPH0555630A - Light emitting element material and its manufacture - Google Patents

Abstract

PURPOSE:To improve light emitting brightness by growing an indirect transition type GaInP layer of good crystals on a GaP substrate. CONSTITUTION:An indirect transition type GaInP thick film layer 4 of 100mum or larger is grown on a GaP substrate 1 by means of yo-yo salute supply method, and an N-doped indirect transition type GaInP thin film layer 6 is grown on the layer 4. The thick film layer 4 prevents and buffers a defect caused by misalignment of lattices between the GaP substrate 1 and the thick film layer 4. Therefore the thin film layer of good crystals can be grown on the thick film layer 4, resulting in higher brightness of pure green light emission.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a light emitting diode (LE) using a GaInP mixed crystal which is an indirect transition type semiconductor crystal material.
D), a semiconductor laser (LD) and other light emitting device materials, and a method for manufacturing the same.

[0002]

2. Description of the Related Art GaInP mixed crystals, which are compound semiconductor materials of III-V group ternary alloys, have the largest direct transition type band gap among III-V group compound semiconductors except nitrides, and red light emission is Of course, it is the most advantageous material constituting a light emitting element that emits green to red light, and is currently used as a material for red LDs and LEDs.

For example, as a green light emitting element, a direct transition type
Promising use of GaInP mixed crystals, LE emitting green light
To fabricate D, a lattice matching type AlGaInP mixed crystal with a high AlP mixed crystal ratio is formed as a light emitting layer on a GaAs substrate, or a lattice mismatch relaxation layer is introduced on a GaP or GaAs substrate and a high density It is necessary to form a GaInP light emitting layer having a GaP mixed crystal ratio.

However, since the GaAs substrate crystal has a band gap of 1.424 eV and its light absorption property is remarkably increased for light having a wavelength shorter than about 870 nm, when a surface-emitting type visible light LED is manufactured, for example. , Which is an obstacle to high brightness. Further, the AlGaInP mixed crystal having a high AlP mixed crystal ratio is easily oxidized, and the characteristics of the device are likely to be deteriorated. in addition,
The higher the AlP mixed crystal ratio, the more difficult it is to achieve low resistance.

Introducing a lattice misfit relaxation layer not only requires a complicated process such as growing several epitaxial layers having different compositions, but also causes the lattice misfit relaxation layer itself to absorb light to some extent. Therefore, there is a problem that it hinders high brightness and is particularly a source of dislocations, which causes deterioration of device characteristics. Above all, since the mixed crystal ratio of GaP must be set to less than 0.7, green light emission is caused because it approaches the crossover point of direct transition / indirect transition, and DA pair light emission easily occurs. There is a fatal problem that is difficult to obtain.

As an example of the light emitting device material in the green region made of another semiconductor material, there is an indirect transition type GaP doped with nitrogen (N) to form an isoelectronic center. This indirect transition type GaP band
The gap corresponds to the emission wavelength of 555 nm, and green emission is obtained. However, the emission of N-doped GaP is mainly Χ.
It is recombination emission (indirect transition emission) from the (chi) band through nitrogen, and recombination emission (direct transition emission) from the Γ (gamma) band having a high emission transition probability like direct transition type GaInP is small. Therefore, the brightness is at a low level.

[0007]

Therefore, nitrogen (N) is used as a light emitting element material that emits direct and indirect transition light as described above.
Indirect transition GaInP (hereinafter referred to as “N-doped”)
Also referred to as "GaInP". ) Is expected as a green light emitting device material. That is, N-doped GaInP is an indirect transition type,
Further, since the band gap is very close to GaP, green light emission can be obtained by doping with nitrogen (N) for forming an isoelectronic center. Further, N-doped GaInP is mainly used for indirect transition light emission, but since more electrons are involved in direct transition light emission than GaP, higher brightness can be expected than N-doped GaP.

In the growth of N-doped GaInP, it is desirable to directly grow it on a substrate lattice-matched with N-doped GaInP, because it is expected that higher brightness can be expected without interposing a lattice mismatch relaxation layer for the above-mentioned reason. However, the current situation is that no lattice-matched substrate is found.
Even if a GaP substrate having a relatively close lattice constant was used, a good quality crystal could not be obtained due to defects and dislocations due to lattice misalignment (about 2% or less), and as a result, brightness exceeding N-doped GaP could not be obtained. ..

In view of the above circumstances, the present invention is a light emitting element material using GaInP mixed crystal which is an indirect transition type semiconductor crystal material, and prevents light absorption by a substrate crystal or the like to achieve high brightness, Moreover, it is an object of the present invention to provide a light emitting element material which improves element characteristics as compared with the conventional one, particularly a light emitting element material for a green LED, and a method for producing these materials.

[0010]

In the course of research to achieve the above object, the present inventor has grown a GaInP layer by growing a thick indirect transition GaInP layer on the GaP substrate.
It has been found that on the thick film layer, defects and the like due to lattice matching with the GaP substrate are eliminated. As a result of further intensive research based on this finding, the inventors have developed the light emitting device material and the manufacturing method thereof according to the present invention.

That is, the light emitting device material of the present invention comprises an indirect transition type GaInP thick film layer having a thickness of 100 μm or more and an indirect transition type GaInP thin film layer containing a dopant for an isoelectronic center on a GaP substrate. It has a structure formed by sequential growth. The production method of the present invention is a liquid phase epitaxial growth method, particularly preferably yo-yo.
By the solute supply method, an indirect transition type GaInP thick film layer with a film thickness of 100 μm or more and an isoelectronic
Indirect transition type GaInP containing dopant for center
It is characterized in that thin film layers are successively grown.

In the present invention, the GaP substrate means a bulk crystal GaP substrate material. In the indirect transition type GaInP thick film layer (hereinafter also simply referred to as “thick film layer”) grown on the GaP substrate, the mixed crystal ratio (x) of GaP is larger than the mixed crystal ratio at which the crossover point described above is obtained ( Specifically, 0.7 <
x <1) is an epitaxial layer composed of a mixed crystal with a constant composition, and the thickness of this epitaxial layer is 100 μm or more,
Preferably 100-500 μm, more preferably 100-300
μm. The reason is that when the thickness is less than 100 μm, defects due to lattice mismatch with the substrate occur. Therefore, it is desirable that the thickness is 500 μm or less, not only is it costly to grow an excessively thick layer, but also light emission is absorbed. This is because there is a fear.

In the present invention, an indirect transition type GaInP thin film layer (hereinafter also simply referred to as "thin film layer") is grown on the thick film layer. The mixed crystal ratio of the thin film layer is the same as the mixed crystal ratio of the thick film layer so as to be lattice-matched with the thick film layer. Since the mixed crystal of this thin film layer is an indirect transition type, it is necessary to add a dopant for the isoelectronic center. As such a dopant, N, O, Zn-O,
N-Zn or the like is exemplified, and the thick film layer described above can be doped similarly to the thin film layer.

A method of manufacturing a green light emitting element material will be described below as an example of a method of manufacturing a light emitting element material according to the present invention.

[First Step] First, an indirect transition type GaInP thick film layer is grown on a GaP substrate by LPE (liquid phase epitaxial growth method) such as yo-yo solute supply method and temperature difference method. At this time, the mixed crystal ratio x (Ga _x In _1-x P) of the thick film layer is 0.7.
As described above, preferably 0.9 < x <1.

When a thick film layer is grown, in the case of ordinary LPE (slow cooling method, etc.), a single growth is limited to about 30 μm, and the growth process must be repeated many times. On the other hand, in the yo-yo solute supply method, the normal L
It can be grown thicker than PE and is efficient.

Yo-yo solute supply method (Shizuoka University Institute of Electronics Research Report 21, (1986), 119 "Growth of semiconductor crystals by the yo-yo solute supply method", JP-A-63-81989, JP-A-6-1989 1-31
5174 and Japanese Patent Application No. 2-80330) refer to a GaInP-based alloy, which is a raw material for the epitaxial layer, on the lower side,
The substrate is arranged so that the growth surface of the substrate faces downward and faces the GaInP-based alloy as a raw material, and an In solution in which Ga and GaP are saturated dissolved is inserted between the GaInP-based alloy and the GaP substrate to form a solution. It is a method of growing a GaInP thick film layer on the substrate surface by raising or lowering the temperature of. The relationship between the temperature of the solution and the growth of the GaInP thick film layer is as follows. First, the inserted solution is cooled (T is the temperature at this time) to bring it into a supersaturated state. GaInP-based crystal precipitates from the solution, but because it has a lower specific gravity than the solution, it moves upwards, causing more of the GaP substrate surface to move.
GaInP-based crystal grows. Then, after maintaining the temperature T for a predetermined time, the temperature of the solution is raised to T '. The solution gradually becomes unsaturated, but due to the difference in specific gravity, dissolution from the GaInP-based alloy arranged on the lower side mainly occurs. After holding at the temperature T'for a predetermined time, the temperature is cooled to T. Hereinafter, this temperature cycle is repeated several times to grow a GaInP thick film layer having a desired thickness on the substrate. In the present invention, T is usually 700-800.
℃, preferably 740 ~ 780 ℃, T'is usually 750 ~
The temperature is 900 ° C, preferably 770 to 820 ° C. Also, T '° C
The holding time is usually 1 to 100 minutes, preferably 2 to 10 minutes.
Minutes. The temperature cycle is usually 2 to 100 times, preferably 10 to 30 times.

The LPE according to the temperature difference method is to provide a constant temperature difference in the solution when the saturated solution is brought into contact with the substrate, and when the substrate contact side is set at a lower temperature than the other parts, the difference in solubility occurs. A density gradient is generated from this, and the GaInP thick film layer is grown on the substrate by mass transfer of solute using the density gradient as a driving force. In the present invention, the above solution can be used, and a GaInP alloy is arranged on the lower side,
1 to 50 ° C., preferably 4 to 25 ° C., on the substrate and on top of the solution
A temperature difference of ℃ is formed by a known method, and the temperature of the substrate is adjusted to 70
The GaInP thick film layer can be grown by setting the temperature to 0 to 850 ° C, preferably 750 to 820 ° C. The thickness of the growth layer is controlled by the growth time.

A dopant for adjusting the conductivity type may be mixed in the thick film layer. For example, in the case of n type, S, Te,
When Se, etc. are made to be p-type, Zn, Cd, Be, etc. are 5 × 10 ¹⁶
It can be doped at about 1 × 10 ¹⁹ cm ⁻³ . However,
It is necessary to dope so that a pn junction is formed, that is, a conductivity type opposite to that of a GaInP thin film layer described later.

[Second Step] A thin film layer is further grown on the thick film layer grown by the above first step. As a method for growing the thin film layer, LPE is desirable as in the above,
Conventionally known vapor phase growth (chloride method, halide method), M
OVPE (organic metal vapor phase epitaxy), MB
It can also be grown by E (molecular beam epitaxial growth method) or the like.

In the present invention, a pn junction may be formed at the interface between the thin film layer and the thick film layer as shown in FIG. 1, and as shown in FIG. A pn junction may be formed. When a pn junction is formed in the thin film layer, the thin film layer on the GaInP thick film layer side of the pn junction (hereinafter also referred to as “first layer”) is 1 to 45 μm, preferably 1 to 10 μm.
It is suitable to grow the thin film layer (hereinafter also referred to as the "second layer") on the opposite side of the first layer through the pn junction to about 5 to 45 m, preferably about 10 to 30 m.

[Third Step] Since the light emitting element material thus manufactured is grown so thick that the thick film layer on the GaP substrate can serve as a substrate, the light emitting element should be obtained by removing the GaP substrate. You can The GaP substrate is removed by a conventional method such as polishing.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method of manufacturing a light emitting device material according to the present invention will be described in detail with reference to the drawings.

FIG. 3 is a schematic sectional view of a crystal growth apparatus used in the manufacturing method according to the present invention. In the figure, 20 is a boat using an appropriate material, for example, high-purity carbon, and is provided with a cylinder into which a piston 19 can be inserted. Before the growth is started, the material for the In-Ga-P solution 3 is charged in this cylinder.

Reference numerals 14 and 14 'are gas piping systems for introducing a high-pressure atmospheric gas into the quartz tube 16. Flange
13 'is provided with an airtight seal that allows the piston 19 to move at the piston penetration portion of the flange. Reference numeral 24 is a holder for the substrate 1 and also a lid for the growth boat, 22 is a vent for gas, and is an escape passage for the excess solution, and 23 is a saucer for the excess solution. still,
Although not shown in the figure, the carbon boat was impregnated with an inorganic substance and sealed with B ₂ O _{3 so} that the substrate,
The raw alloy and solution are devised so that highly volatile P (phosphorus) is not lost by evaporation. However, g in the figure indicates the direction of gravity.

The raw material 2 used for epitaxial growth is Ga
It may be P or a Ga _z In _1-z P alloy (z> y) having a mole fraction on the GaP side of the target composition (mixed crystal ratio y). For example,
Using a GaInP alloy 2 having a GaP mole fraction of 0.9, the GaP substrate 1 is arranged on the upper side and the GaInP alloy 2 is arranged on the lower side. The GaP substrate used has an area of 1 × 1 cm ² , a crystal plane orientation of (111), (111) B or (111) A, and a carrier concentration of 10
^{It is 17} to 10 ¹⁸ cm ^-3 . The GaInP alloy 2 is doped with S, Si, Te, Se or the like (preferably Te) as a donor impurity. At this time, it goes without saying that the surface of the GaP substrate 1 is polished and the surface is sufficiently cleaned with an appropriate etching solution.

The solution used is prepared so as to precipitate a GaInP mixed crystal having a GaP mole fraction of 0.9 at 800 ° C. Specifically, Ga 42.1 mg, GaP 73.
Use a solution in which 1 mg is dissolved. As a result, the GaP substrate 1, the GaInP alloy 2 and the solution 3 are prepared.

First, the electric furnace 10 shown in FIG.
After reaching 0 ° C., the temperature is maintained there for about 1 to 5 hours to sufficiently homogenize the solution 3 ′ inserted in the cylinder of the boat 20. Of course, the heat treatment for homogenizing this solution
It does not matter if the temperature is higher than 800 ° C. In this case, the heat treatment for homogenization shall be followed by slow cooling to 800 ° C to prepare for the next operation.

After the solution homogenizing treatment is completed as described above, the piston 19 is operated to inject the solution between the GaP substrate 1 and the raw material GaInP alloy 2. Then, after maintaining the temperature for an appropriate time, an appropriate slow cooling rate, for example, 0.1 to 2
Cool to 770 ° C at 10 ° C / min and hold for 10 minutes. next,
The temperature is raised to 800 ° C at a rate of 0.5 ° C / min, the temperature is maintained for an appropriate time, and then cooled in the same manner as above. By this one cycle, the GaInP mixed crystal layer 4 having a GaP mole fraction of 0.9
Grows about 15 μm. In this embodiment, the GaInP mixed crystal (thick film) layer 4 of about 300 μm is grown by 20 cycles.

In this way, the lattice mismatch to the GaP substrate 1
By growing the GaInP mixed crystal layer 4 as a thick film, the surface of the GaInP thick film layer 4 is not affected by the lattice mismatch at the interface with the GaP substrate 1, and a good quality light emitting layer is grown on the GaInP thick film layer 4. be able to.

In this embodiment, as shown in FIG.
N-doped GaInP thin film layer (first layer) 5 on GaInP thick film layer 4
And the N-doped GaInP thin film layer (second layer) 6 is grown. The first and second layers 5 and 6 can be grown by the yo-yo solute supply method subsequent to the growth of the GaInP thick film layer 4 described above, but here, an example in which the slide boat method is applied is shown.

First, the GaP substrate 1'on which the GaInP thick film layer 4 is grown is set on the slider 43 of the crystal growth apparatus as shown in FIG. Then, predetermined amounts of In, InP, and GaP cleaned by chemical etching and cleaning are inserted into the solution reservoir 41a and the solution reservoir 41b of the slide boat 40, respectively. As a material to be inserted into the solution reservoirs 41a and 41b, an In-Ga-P alloy sufficiently mixed by an appropriate method in advance may be used.

To give a concrete example of the charged amount, in the n-type N-doped GaInP thin film layer 5, Ga 25.
3 mg and 43.8 mg of GaP are charged in the p-type N-doped GaInP thin film layer 6, and Ga 4.6 mg and GaP 54.7 mg are added to 3 g of In, respectively. After inserting these materials into the respective solution reservoirs 41a and 41b, a lid 46 is provided to prevent volatilization of phosphorus and the like.
Are attached to the respective solution reservoirs 41a and 41b.

The slide boat 40 is installed in a quartz tube 45 through which ammonia gas for doping is introduced in addition to hydrogen gas. After passing enough hydrogen and ammonia gas so that residual oxygen and water vapor do not exist in the quartz tube 45,
By heating the growth material to a temperature slightly higher than the growth temperature of each layer, for example, about 2 to 20 ° C. by the electric furnace 42, and keeping the temperature for a certain time (for example, 2 to 4 hours), Homogenize the growth solution of.

Thereafter, the growth start temperature of the first layer, for example,
Gradually cool to 820 ° C at an appropriate rate of 0.01 to 2.0 ° C / min. At this time, the In composition for growth of the first layer 5 is prepared such that GaInP is in a saturated or supersaturated state close to saturation. After that, the slider operating rod 47
Is used to move the slider 43 to move the GaP substrate 1'to the solution reservoir 41.
The growth solution in the solution reservoir 41a and the GaP substrate 1'are brought into contact with each other by moving them just below a.

The solution should be at a suitable rate, for example 0.01-2.0 ° C /
Since it is gradually cooled in minutes, GaInP becomes supersaturated in the solution, and it precipitates on the GaP substrate 1'and n-type N-doped.
The GaInP thin film layer 5 grows. When the thin film layer 5 has an appropriate thickness, for example, about 15 μm, the slider 43 is moved to move the GaP substrate 1 ′ directly under the solution reservoir 41 b, and p
A type N-doped GaInP thin film layer 6 is grown. When the thickness reaches a predetermined value, for example, about 35 μm, the slider 43 is restarted.
Is moved to separate the growth solution in the solution reservoir 41b from the surface of the thin film layer 6 so that they do not come into contact with each other, thereby ending the growth.

The light emitting device material grown as described above is a film thick enough to allow the GaInP thick film layer to serve as a substrate. Therefore, the light emitting device can be obtained by removing the GaP substrate.

In the case of manufacturing a green LED, for example, based on the above light emitting element material, as shown in FIG.
200 μm n-type N-doped Ga _0.9 In _0.1 P on P substrate 31
Thick film layer 34, 15 μm n-type N-doped Ga _0.9 In _0.1 P thin film layer (first layer) 35 and 10 μm p-type N-doped Ga _0.9 In _0.1
The P thin film layer (second layer) 36 is sequentially grown by LPE (yo-yo solute feeding method or other LPE). Next, n-type GaP
The substrate 31 is removed by polishing, and a p-side electrode E31 such as AuZn / Au and an n-side electrode E32 such as AuGeNi / Au are provided by means such as vacuum deposition. LE obtained by the above operation
The emission wavelength of D is 565 nm, and it can be seen that green light is emitted.

[0039]

Since the light emitting device material of the present invention is constructed as described above, it has the following effects.
Since GaInP or GaP is used without the need for a GaAs substrate or a lattice mismatch relaxation layer, light emission of a wavelength shorter than about 870 nm,
Especially, it reduces surface absorption of green light, and it is a surface-emitting visible light LE.
Higher brightness of D can be expected. Because Al is excluded,
The characteristics of the device are stabilized, and it is easy to reduce the resistance. Indirect transition type GaInP is a direct transition type GaInP.
Unlike that, its band gap is close to that of indirect transition GaP, and green light emission can be expected. Since indirect transition GaInP has more electrons involved in direct transition light emission than GaP, recombination light emission from the Γ (gamma) band having a high emission transition probability increases, and high brightness can be expected.

Further, the manufacturing method of the present invention has the following effects. Since it is not necessary to grow the lattice mismatch relaxation layer, the manufacturing can be simplified. 100 on GaP substrate
By growing an indirect transition type GaInP thick film layer with a thickness of μm or more, it becomes possible to grow an indirect transition type GaInP thin film layer of good quality crystal on the thick film layer, which contributes to high brightness of a light emitting element, especially a green light emitting element To do. LP is the epitaxial growth method
E, preferably yo-yo solute supply method, so thick GaIn
The P-based layer can be easily grown. Since the epitaxial growth layer is a mixed crystal having the same composition (mixed crystal ratio), continuous growth is possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a light emitting device material according to the present invention.

FIG. 2 is a cross-sectional view showing a modified embodiment of the light emitting device material according to the present invention.

FIG. 3 is a schematic cross-sectional view of a crystal growth apparatus used when performing a yo-yo solute supply method.

FIG. 4 is a schematic cross-sectional view of a crystal growth apparatus used when carrying out the slide boat method.

5 is a cross-sectional view showing an example of an LED using the structure of FIG.

[Explanation of symbols]

 1: GaP substrate 4: GaInP thick film layer 5: N-doped GaInP thin film layer (first layer) 6: N-doped GaInP thin film layer (second layer) 51: n-type GaP substrate 54: n-type N-doped GaInP thick film layer 55: n-type N-doped GaInP thin film layer (first layer) 56: p-type N-doped GaInP thin film layer (second layer) E51: p-side electrode E52: n-side electrode

Claims (4)

[Claims] 1. A structure in which an indirect transition GaInP thick film layer having a thickness of 100 μm or more and an indirect transition GaInP thin film layer containing a dopant for an isoelectronic center are sequentially grown on a GaP substrate. Light emitting device material. 2. A liquid phase epitaxial growth method is used to obtain GaP.
A method for manufacturing a light emitting device material, which comprises sequentially growing an indirect transition type GaInP thick film layer having a film thickness of 100 μm or more and an indirect transition type GaInP thin film layer containing a dopant for an isoelectronic center on a substrate. 3. The liquid phase epitaxial growth method is yo-yo
The method according to claim 2, which is a solute supply method. 4. A method for producing a light emitting device material, which comprises removing the GaP substrate from the light emitting device material obtained by the method according to claim 2.