JPH084151B2 - Epitaxial wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION “Industrial field of application” The present invention relates to a III-V group compound (periodic table No. III) suitable for producing a high-brightness light emitting diode (hereinafter referred to as “LED”).
A compound consisting of b group and V b group elements. The same applies below)
The present invention relates to an epitaxial wafer, particularly an epitaxial wafer having a so-called hetero structure in which different kinds of single crystal layers are stacked.

"Prior Art" Recently, there have been many opportunities for LEDs to be used in display devices used outdoors such as information boards at stations and high mount stop lamps of automobiles. This is because the LED has a long life and can obtain light of various colors, but as the demand increases, further improvement of the light output of the LED has been required.

Further, in such a display device, the breakdown voltage of the LED is required to be 10 V or more for design reasons.

For such applications, the luminous efficiency is high and a large light output can be obtained as compared with an LED having a homostructure using a group III-V compound single crystal layer such as gallium phosphide and gallium arsenide. Conventionally, II with direct transition type band structure
An LED manufactured by using an epitaxial wafer having a hetero structure including a group IV compound single crystal layer and a group III-V compound single crystal layer having an indirect transition type band structure has been used.

"Problems to be solved by the invention" However, in the conventional epitaxial wafer having a heterostructure, the obtained LED has a large variation in the optical output and the breakdown voltage, and the yield of the LED satisfying the above requirements decreases. There was a problem of doing.

“Means for Solving the Problem” The present inventors
As a result of repeated studies aimed at improving the yield and improving the yield of LEDs manufactured using wafers, the epitaxial wafer with a conventional heterostructure has a simple structure that constitutes the heterostructure. The inventors have found that the fact that the interface of the composition of the crystal layer and the pn junction are substantially the same has been a cause of the above-mentioned reduction in yield, and arrived at the present invention.

The above object of the present invention is to provide an epitaxial wafer having a heterostructure including a group III-V compound single crystal layer having a direct transition band structure and a group III-V compound single crystal layer having an indirect transition band structure, This can be achieved by providing a pn junction in the III-V compound single crystal layer having the indirect transition type band structure at a position separated by 0.2 μm or more from the interface between the both single crystal layers.

Examples of the III-V group compound constituting the single crystal layer of the present invention include aluminum, gallium, indium, etc., which are Group IIIb elements of the periodic table, and phosphorus, arsenic, antimony, etc., which are Group Vb elements of the periodic table. And a single compound such as gallium arsenide, gallium phosphide, indium arsenide, or indium phosphide may be selected.
Mixed crystals of aluminum, gallium phosphide / indium, aluminum phosphide / gallium / indium, aluminum arsenide / gallium / indium, gallium arsenide phosphide / indium, etc. change the ratio of their constituent elements, that is, the mixed crystal ratio. It is preferable that both the band structure of the direct transition type and the band structure of the indirect transition type can be selected only by performing the above.

That is, the first method of forming the heterostructure in the present invention is performed by changing the mixed crystal ratio to form both single crystal layers having different band structures. For example, in gallium arsenide aluminum (Ga _1-x Al _x As), the mixed crystal ratio of Al
_x is smaller than 0.45 to form a layer of direct transition band structure,
Also, by making it larger than 0.45, a layer having an indirect transition type band structure can be obtained. Similarly, for gallium indium phosphide (Ga _1-x In _x P), the mixed crystal ratio _x of In is made larger than 0.3 to form a direct transition type layer, and smaller than 0.3 to form an indirect transition type layer. Obtainable.

The second method of forming the heterostructure is performed by combining with a III-V group compound containing different elements. Examples of such a structure include, for example, a layer of aluminum gallium indium phosphide having an indirect transition type band structure and a gallium phosphide layer having a direct transition type band structure.
There is a combination with a layer of indium.

Further, the heterostructure in the present invention is not limited to one layer as long as it includes both crystal layers having different band structures, and it goes without saying that various combinations and arrangements can be adopted depending on the application. . For example, a heterostructure of an epitaxial wafer for LED applications, which will be described in detail below, is a single combination of a single crystal layer having a direct transition band structure and a single crystal layer having an indirect transition band structure. A double hetero type in which one single crystal layer having a hetero type and a direct transition type band structure is sandwiched between two single crystal layers having an indirect transition type band structure is usually used.

The single-hetero structure has a simple structure but low optical output, while the double-hetero structure has a complicated structure but has high optical output.

The epitaxial wafer of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic vertical sectional view of an example of an epitaxial wafer having a double hetero type heterostructure.

In FIG. 1, reference numeral 1 denotes a single crystal substrate. As the substrate 1, a single crystal cut out of gallium arsenide, gallium phosphide, indium phosphide or the like is used. Board 1
It is preferable that the difference in the lattice constant from the single crystal layer 2 provided thereon is small. When gallium arsenide / aluminum is used for the single crystal layer 2, gallium arsenide is preferably used for the substrate 1. The substrate is removed as necessary for the purpose of improving the light output when manufacturing the LED,
Alternatively, it is polished.

Reference numeral 2 is a group III-V compound single crystal layer having an indirect transition type band structure. The thickness of the single crystal layer 2 is usually 20 to 200
μm is suitable. The conductivity type of the single crystal layer 2 is usually p-type.

3 is a III-V group compound single crystal layer having a direct transition band structure.

The thickness of the single crystal layer 3 is usually selected in the range of 0.5 to 5 μm. This is to reduce self-absorption of light and to increase luminous efficiency by confining carriers. The conductivity type of the single crystal layer 3 is usually p-type.

4 is a III-V group compound single crystal layer having an indirect transition type band structure. The thickness of the single crystal layer 4 is usually 20 to 50 μm.
m.

Reference numeral 5 denotes an interface between the single crystal layer 3 having a direct transition band structure and the single crystal layer having an indirect transition band structure.

6 is a pn junction. The pn junction 6 must be provided in the single crystal layer 4 at a position separated from the interface 5 by 0.2 μm or more, preferably within about 5 μm, and more preferably within a range of 0.5 to 3 μm. The position of the pn junction 6 is the interface 5
Is less than 0.2 μm, it is not preferable because variations in light output, breakdown voltage, etc. increase.

The carrier concentration in the single crystal layer 4 between the interface 5 and the pn junction 6 is 1 × 10 ¹⁷ cm ⁻³ or less, more preferably about 1 × 10 ¹⁶ to 8 × 10 ¹⁶ cm ^−3. It is preferable because the output is improved.

In addition, the carrier concentration of the other single crystal layers and the substrate is
It is preferable that it is 1 × 10 ¹⁷ cm ⁻³ or more because the forward voltage of the LED is low.

As mentioned above, an epitaxial layer having a double hetero structure
Although the invention has been described with respect to wafers, the same applies to epitaxial wafers having a single heterostructure. Even in an epitaxial wafer having a single hetero structure, a single crystal layer having a direct transition type band structure is usually p type.

The epitaxial wafer of the present invention is usually grown by a liquid phase epitaxial growth method, but it may be grown by a vapor phase epitaxial growth method, a molecular beam epitaxial growth method or the like. When the vapor phase epitaxial growth method is used, it is preferable to use the metal organic vapor phase growth method, so-called MOCVD method.

"Effect of Invention" The present invention has great industrial utility value because it has the following remarkable effects.

(1) An LED manufactured using the epitaxial wafer of the present invention has a large light output and its variation is small.

(2) Also, the breakdown voltage of the obtained LED is high and its variation is small.

(3) Therefore, the manufacturing yield of LEDs is significantly improved.

[Examples] The present invention will be specifically described based on Examples and Comparative Examples.

In the following examples, the epitaxial wafer is
Using the method and apparatus described in Japanese Patent Application No. 62-273,999, filed by the present applicant, the crystal was grown by the liquid phase epitaxial growth method.

The carrier concentration was measured using "Semiconductor profile plotter" manufactured by Polan, UK. The carrier concentration in the vicinity of the pn junction is C− using a carrier depletion layer generated when a reverse voltage is applied to the pn junction.
It was also measured by the V method.

The mixed crystal ratio was determined by the ZAF correction method from the result of measurement using an X-ray microanalyzer.

The composition boundary was determined from a secondary electron image by an electron beam induced current method or an electron microscope.

LED light output is epoxy coated, current density 12.5A
It was measured under the condition of / cm ² .

Example As a single crystal substrate, a p-type gallium arsenide single crystal substrate doped with zinc having a thickness of 300 μm was used. The plane orientation of the substrate surface was a {100} plane.

The substrate was placed at a predetermined position in the liquid phase epitaxial growth apparatus. In each of the melt baths A to D of the growth apparatus, metal Ga
Each single crystal layer growing melt containing the composition and dopant shown in Table 1 was contained in 100 g.

The growth apparatus is heated to 900 ° C. in a hydrogen stream, and the substrates are sequentially contacted with each single crystal layer growing melt and 750 ° C.
The liquid temperature epitaxial growth was performed by repeating the temperature decrease up to.

The thickness, carrier concentration, mixed crystal ratio, and conductivity type of each single crystal layer were measured using the half surface of the obtained epitaxial wafer. The measured values are shown in Table 2.

The remaining half of the epitaxial wafer is polished to a thickness of approximately 250 μm, and then electrodes are formed to approximately 300 μm x approximately
A 300 μm chip was constructed. This chip was attached to a stem and coated with an epoxy resin to produce an LED lamp.

The peak emission wavelength of the obtained LED lamp is 662 nm on average,
The breakdown voltage was 20 to 25 V, and the optical output was 2.5 cd on average. The light output distribution is shown in FIG.

Comparative Example The same procedure as in Example was repeated except that Melt 3 shown in Table 1 was not used as the melt for growth and the interface between both single crystal layers.
Epitaxial wafers with nearly matched pn junctions were grown. The pn junction of the obtained epitaxial wafer is
It coincided with the composition interface of the single crystal phases 3 and 4 within 0.1 μm.

Using the half surface of this epitaxial wafer, the thickness, carrier concentration, mixed crystal ratio, and conductivity type of each single crystal layer were measured. The measured values are shown in Table 3. In addition, in this comparative example and Table 3, for convenience of explanation, each layer is indicated by using the reference numeral in FIG.

The remaining half of the epitaxial wafer is polished to a thickness of approximately 250 μm, and then electrodes are formed to approximately 300 μm x approximately
A 300 μm chip was constructed. The obtained chip was attached to a stem and coated with an epoxy resin to produce an LED lamp.

The peak emission wavelength of the obtained LED lamp was 662 nm, and the breakdown voltage was 0.5-10V. The optical output was 1.9 cd on average. The light output distribution was as shown in FIG.

As is clear from the examples and comparative examples, when an LED is manufactured using the epitaxial wafer of the present invention, the light output is large and the breakdown voltage is high as compared with the LED using the conventional epitaxial wafer. high. Also,
Since the variations in light output and breakdown voltage are small, the LED yield is also improved.

[Brief description of drawings]

FIG. 1 is a schematic longitudinal sectional view of an example of the epitaxial wafer of the present invention. FIG. 2 is a distribution chart of the light output of the LED lamp manufactured using the epitaxial wafer manufactured in the example. FIG. 3 is a distribution diagram of the light output of the LED lamp manufactured using the epitaxial wafer manufactured in the comparative example. 2 and 3, the vertical axis represents the number of LED lamps, and the horizontal axis represents the light output (unit: cd). 1 ... Substrate 2 ... Single crystal layer having indirect transition type band structure 3 ... Single crystal layer having direct transition type band structure 4 ... Single crystal layer having indirect transition type band structure 5 ... Both single crystal layers Interface 6 …… pn junction

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naonori Fujita 1000 Higashihuinaka-cho, Ushiku-shi, Ibaraki Mitsubishi Monsanto Kasei Co., Ltd. Tsukuba factory (72) Inventor Masahiro Noguchi 1000 Higashi-huinaku-cho, Ushiku, Ibaraki Mitsubishi Mon Santo Kasei Co., Ltd., Tsukuba Plant (56) Reference JP 54-56387 (JP, A) JP 56-24986 (JP, A)

Claims (3)

[Claims] 1. A III-V compound single crystal layer having a direct transition type band structure and III having an indirect transition type band structure.
In an epitaxial wafer having a heterostructure including a group-V compound single crystal layer, a pn layer is formed in the single crystal layer having the indirect transition type band structure and at a position separated by 0.2 μm or more from the interface between the single crystal layers. An epitaxial wafer characterized by having a bond. 2. The epitaxial wafer according to claim 1, wherein the conductivity type of the single crystal layer having a direct transition band structure is p type. 3. The epitaxial wafer according to claim 1 or 2, wherein the III-V compound is gallium aluminum arsenide.