JP3087742B2 - White LED - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white color LED which has a long life and is capable of emitting light of various wavelengths, from warm color to cool color, by a method wherein a ZnSe thin film is epitaxially grown on a ZnSe board whose self-excitation emission center is doped. SOLUTION: Leads 12 and 13 and an LED chip 15 are buried in a transparent molded body 11, where the ZnSe LED chip 15 is mounted and fixed on the flat top surface 14 of the L-shaped lead 12. The LED chip 15 is composed of a ZnSe board 16 possessed of a dopant that serves as a self-excitation emission center and a light emission structure (thin film) 17 epitaxially grown on the board 16. The light emission structure 17 is formed of a thin film of ZnSe or ZnCdSe and contains a PN junction. The epitaxial light emitting structure 1 is formed of a laminated thin film whose main component is ZnSe, possessed of a PN junction, and provided with a P electrode ring-shaped or small in area and located on its top. The P electrode is connected to the lead 13 with a wire 18, and an N electrode on the board 16 is connected direct to the lead 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel semiconductor light emitting device capable of emitting white light with a single device. There is a great demand for white light. White light is most suitable as a light source for illumination. The liquid crystal backlight uses white light. The present invention relates to a semiconductor white LED that can be used for lighting, display, a liquid crystal backlight, and the like.

[0002]

2. Description of the Related Art Light-emitting diodes (LEDs) of a single color such as red, yellow, green, and blue have already been manufactured and sold. As a red high-intensity light-emitting diode (LED), one having several Cd (candela) or more is already on the market.
Red L with a light emitting layer of AlGaAs or GaAsP
ED. It is a low-cost LED and is used for a wide range of applications. Green / yellow-green LEDs using GaP as a light emitting layer are also manufactured and sold. Some blue LEDs use SiC as an active layer. Blue and green LEDs include GaInN as an active layer. Orange / yellow elements include AlGaInP as a light emitting layer. Both are inexpensive and practical LEDs. Among them, GaP and SiC are indirect transition type semiconductors, so their efficiency is low, and they have not reached candela-class output.

[0003] Since all of these LEDs utilize electronic transition between bands of a light emitting layer material, they are only monochromatic light.
That's why LEDs were monochromatic. This is natural. Monochromatic LEDs have many uses, such as display LEDs. However, monochromatic LEDs alone cannot replace all light sources. Monochromatic light sources are useless for applications such as lighting, special displays, and liquid crystal backlights. When monochromatic light is used for lighting, all objects appear in that color. When monochromatic light is used for the liquid crystal backlight, only the shaded image of that color can be seen.

A white light source including all colors is absolutely necessary. However, there is no semiconductor light emitting element which emits white light.
Incandescent lamps, fluorescent lamps and the like are still widely used as illumination light sources. Incandescent bulbs are inefficient. Also, the life is short. Fluorescent lamps are not efficient, but have a short life. A heavy object such as a ballast is required. Also the size is too big. There are such difficulties.

It is desired for a white light source to have a small size, a simple peripheral circuit, a long life, a high luminous efficiency, and a low cost.
It seems that only semiconductor light emitting devices can satisfy these requirements. However, as described above, since the semiconductor light emitting device uses an electronic transition between band gaps, it is inevitably only monochromatic light. A semiconductor element alone cannot generate white light.

[0006]

The use of blue, green, and red LEDs, which are the three primary colors, could produce a white LED. Blue LEDs using GaN have also become commercially available, and LEDs of three primary colors are available. However, combining three light emitting elements results in high cost. It requires three times the power as well as the product cost, which is not efficient. It is also necessary to adjust the balance among the three primary colors. The circuit must be complicated. It is also disadvantageous in terms of size. There is little benefit in producing white light by combining a plurality of LEDs in this way. Again, one wants to emit white light with a single LED.

There has been proposed an attempt of a white LED in which a GaN-based LED and a YAG-based phosphor are combined. For example, there is a white semiconductor light emitting device introduced in the following literature.
"Optical Functional Materials Manual", Optical Functional Materials Manual Editing Board, edited by Optoelectronics, p457, 19
June 1997

This device uses GaInN as an active layer.
It has a structure in which an N-based LED chip is embedded in a YAG fluorescent material that emits yellow light. This is shown in FIG. A first lead 2 and a second lead 3 are fixed in a transparent mold 1 made of resin. The upper part of the first lead 2 has a Γ shape, and a depression 4 is formed. A GaN-based LED chip 5 having a GaInN active layer is fixed in the depression 4. The recess 4 is filled with a yellow YAG phosphor 6 so as to completely cover the LED 5. The upper surface of the GaN LED has an anode electrode and a cathode electrode, which are connected to leads 2 and 3 by wires 7 and 8.

Since a normal light emitting element and a light receiving element use a conductive substrate, the chip bottom surface becomes an electrode and is directly attached to a lead.
Therefore, only one wire connecting the other upper electrode and the lead is required. However, a GaN-based blue LED has a GaN or GaInN layer laminated on a sapphire substrate. Since sapphire is an insulator, the bottom surface cannot be used as a cathode.
Therefore, an n-side electrode (cathode) and a p-side electrode (anode) are formed on the upper surface of the chip. So you need two wires.
When current flows from the anode to the cathode, the GaN LED emits blue light. Part of the blue light passes through the YAG phosphor and is emitted to the outside. The rest is absorbed by the phosphor 6 to emit yellow light having a longer wavelength. Blue light and yellow light overlap.
The synthesized light is white. In other words, this is GaNLE
The blue color of D and the fluorescent light excited by the blue color are superimposed to emit white light.

The light emission of the LED is aggressive light emission due to the inter-band transition of electrons. The phosphor absorbs the light and emits light when the electrons inside are excited from the base band to the upper band and the electrons fall into the base band via a level called the emission center. Naturally, in this excitation light emission, light having lower energy than the light of the LED is emitted. Surrounding the LED with a suitable phosphor will emit the intrinsic light of the LED and longer wavelength fluorescence. Since the YAG phosphor emits just yellow light, it is combined with the blue color of the LED to become white. In visible light, blue has a short wavelength and high energy. This is possible because a blue light emitting element is present.

FIG. 2 shows an emission spectrum of the GaN / YAG light emitting device. The horizontal axis represents wavelength, and the vertical axis represents emission intensity (arbitrary scale). The sharp peak at 460nm is GaN LE
This is due to the light of D. The broad peak around 550 nm is the fluorescence from the YAG phosphor. The naked eye does not separate the colors and cannot be observed.

However, the GaN / YAG light emitting device has some disadvantages. An extra YAG phosphor, which is a material completely different from GaN-based LEDs, is required. This is the first difficulty. Since the YAG phosphor having poor transparency is filled on the chip, much of the light from the LED is absorbed. If only the blue GaN LED used for this is used, the brightness is 1 Cd or more,
It has excellent characteristics such as an external quantum efficiency of 5% or more. However, GaN / YAG has a luminance of only 0.5 Cd and an external quantum efficiency of only about 3.5%. The brightness drops Y
This is because the AG phosphor absorbs light. Further, the light conversion efficiency of the YAG phosphor is as low as about 10%. Therefore, in order to obtain a warm white color in which yellow is dominant, the fluorescent material layer must be thicker. Then, absorption is further increased, and both luminance and efficiency are reduced.

[0013]

SUMMARY OF THE INVENTION The present invention proposes a white LED having a simple structure in which a ZnSe substrate and a ZnSe-based blue light emitting element are combined. When a ZnCdSe or ZnSe thin film is grown on a ZnSe substrate, a blue L
Become ED. The present invention takes advantage of this structure to produce a white LED. This is an extremely simple structure, which is a combination of a ZnSe substrate and a ZnSe-based LED lattice-matched thereto. No phosphor is required, and the ZnSe substrate plays the same role as the phosphor. The same material is used for both the light emitter and the phosphor. This is a device which is originally a blue light emitting diode and is converted into a white LED with a little contrivance. A semiconductor crystal substrate is always required for a ZnSe-based blue light emitting element. The originally required substrate is used instead of the phosphor. I have to say that it is a very clever idea.

When a ZnSe substrate is doped with iodine (I), aluminum (Al), chlorine (Cl), bromine (Br), gallium (Ga) or indium (In), n
Be a type. Moreover, they give rise to luminescent centers. 51
By applying light of a wavelength shorter than 0 nm, 550
self-excitation light (self
-activated: SA emission) occurs. Therefore, this emission center is called an SA emission center. Center wavelength of SA emission,
The half width of the emission spectrum depends on the dopant (I, Al, C
(1, Br, Ga, In)) and the doping amount. Since SA emission is widely distributed from yellow to red, there is a case in which this and the blue of ZnSe LED are added. To the naked eye, this is synthesized and it looks like white light.

That is, the device of the present invention is composed of two parts: (1) ZnSe-based LED: blue light emission (460 to 510 nm) due to band-to-band transition (2) ZnSe substrate: yellow to red self-excitation light (SA:
550-650 nm). The advantage of this device lies in its simplicity. In general, a light emitting element has an active layer formed on a substrate, and the substrate is always present. In a normal device, the substrate merely holds the active layer and only allows a current to flow, and is passive. However, in the present invention, the substrate itself is cleverly used as a light emitting layer. Therefore, in the white LED of the present invention, in the ZnSe blue LED, only a dopant for generating an SA emission center is added to the ZnSe substrate, and only one step is added. It does not add a different material.

There are various types of white. When blue is predominant, the color becomes cool white, and when red is predominant, the color tends to warm. If the ZnSe substrate is thicker, the blue color of the LED is absorbed and reduced, and the yellow color of the SA emission prevails. If the ZnSe substrate is thin, the blue of the LED will prevail, and the SA emission will be weak. Z
By changing the thickness of the nSe substrate, the intensity of SA emission can be adjusted. That is, the ratio of the SA light emission to the blue light emission from the LED can be changed depending on the substrate thickness. However, other conditions impose limitations on the substrate thickness. When the thickness is 10 μm or less, the rate of breakage increases in a later step. Yield decreases and costs increase. Conversely, if the substrate thickness is 2 mm or more, the size of the LED becomes too large. In addition, the ratio of yellow light is excessively increased, and the light is not white. Therefore, the thickness of the substrate is about 10 μm to 2 mm.

As described above, the center wavelength of SA emission can be changed by adjusting the kind and concentration of the dopant. The ratio of SA light can be changed by the thickness of the substrate. Therefore, by freely adjusting the three parameters of the dopant type, the concentration, and the substrate thickness, it is possible to obtain any white from warm to cool white.

There are several options for the geometric arrangement. The same arrangement (erect) as a conventional LED in which a substrate is placed below and a thin film is placed above is also possible. Conversely, an inverted arrangement in which a thin film is placed below and a substrate is placed above is also possible. It is also possible to adopt a structure that prevents only blue from being emitted to the outside.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Upright ZnSe White LED FIG. 3 shows an example of the structure of a white LED according to the present invention.
FIG. 3A is a longitudinal sectional view, and FIG. 3B is a sectional view of only a chip. The leads 12 and 13 and the LED chip 15 are embedded in the transparent mold 11. Such a structure is tailored to conventional LEDs. Transparent molds are the cheapest LED packages. Of course, it can also be stored in a metal can type package. Packages and leads can be freely selected depending on the purpose. Γ type lead 12
The top 14 has no depression and is a flat surface. On the flat surface 14, the ZnSe LED 15 is fixed upright.
The LED 15 includes a ZnSe substrate 16 having a dopant serving as a SA emission center, and a light emitting structure (thin film) 17 epitaxially grown thereon.

The light emitting structure 17 is a thin film of ZnSe, ZnCdSe or the like and includes a pn junction. The epitaxial light emitting structure 17 is a laminate of thin films mainly composed of ZnSe,
At the top with the junction is a ring-shaped or small area p-electrode. This is connected to the lead 13 by the wire 18. The n electrode on the substrate side is directly connected to the lead 12.
Only one wire is required. The lead 12 becomes a cathode and the lead 13 becomes an anode. When a current flows through the pn junction, a band gap transition occurs.
m light E is emitted. Part goes down and enters the substrate. Here, SA emission by the ZnSe dopant is promoted. The mixed light of the LED light E and the SA light F, which is reflected by the bottom surface of the SA light F or directly passes through the thin film 17, and exits to the outside, appears to be white. This is an upright structure for bonding the substrate 16 to the lead surface 14. All ordinary LEDs are so. However, in this case, the ratio of the LED light E always exceeds 50%, and the SA light emission is weakened.

(2) Inverted ZnSe White LED FIG. 4 shows an example of the structure of an inverted white LED according to the present invention. FIG. 4A is a longitudinal sectional view, and FIG. 4B is a sectional view of only a chip. The lead 2 is placed inside the transparent mold 21.
2, 23 and the LED chip 25 are embedded. Such a structure is tailored to conventional LEDs. The top 24 of the リ ー ド -shaped lead 22 has no depression. It is a flat surface. The ZnSe LED 25 is fixed on the lead top 24. LE
D25 is ZnS having a dopant serving as a SA emission center
An e-substrate 26 and a light emitting structure (ZnSe-based thin film) 27 epitaxially grown thereon are formed. The epitaxial light emitting structure (thin film) 27 is a thin film of ZnSe, ZnCdSe or the like, and includes a pn junction. The LED is fixed to the lead surface 24 in the opposite direction. There is a p-electrode on the thin film surface, which is directly bonded to the lead surface 24. There is a ring-shaped or small-area n-electrode on the ZnSe substrate side. The n-electrode is connected to the lead 23 by a wire 28. Again, only one wire is required. In this case, the lead 23 becomes a cathode and the lead 22 becomes an anode.

When a current flows through the leads 22 to 23, a band gap transition occurs and the epitaxial thin film 2
7 emits light E of 460 nm to 510 nm. Everything goes up and enters the substrate. The transmitted light goes out to the outside as blue light. Part of the light is absorbed to promote SA emission by the ZnSe dopant. The SA light emission F in the substrate also goes upward. Both the LED light E and the SA light F go upward.
The two dissimilar lights mix to become white. With this structure, SA light increases in proportion to the substrate thickness. 50 SA light
% Or more is easy. Easy to control the color tone of white light. However, care must be taken because the normal LED and the anode and cathode pins are reversed.

(3) Inverted shield type ZnSe white LED FIG. 4 shows blue light emitted from the thin film 27 in parallel with the substrate surface.
Blue-green light cannot be mixed with SA light because it does not pass through the substrate,
It turns blue only. In order to avoid this, the shape of the lead may be devised. FIG. 5 shows an example of the structure of an inverted shielded white LED according to the present invention. FIG. 5A is a longitudinal sectional view, and FIG. 5B is a sectional view of only a chip. Inside the transparent mold 31, the leads 32, 33 and the LED chip 3
5 is embedded. Such a structure is a conventional LED
It is adjusted to. A deep recess 39 is formed in the top 34 of the Γ-shaped lead 32. Deep depression 3 in lead top 34
9 is fixed to the bottom of the ZnSe LED 35. LED35
The area of the upper opening as viewed from above is small, so that light does not exit to the side.

The LED 35 is composed of a ZnSe substrate 36 having a dopant serving as a SA emission center, and a light emitting structure (ZnSe-based thin film) 37 epitaxially grown thereon. The epitaxial light emitting structure (thin film) 37 is made of ZnSe, ZnC
It is a thin film such as dSe and includes a pn junction. The LED is fixed in the opposite direction to the bottom 34 of the depression 39. Thin film 37
There is a p-electrode on the surface, which is directly bonded to the bottom of the recess of the lead 32. There is a ring-shaped or small-area n-electrode on the ZnSe substrate side. The n-electrode is connected to the lead 33 by a wire 38. Again, only one wire is required.
Also in this case, the lead 33 is a cathode and the lead 32 is an anode. The reflector 40 on the ring is joined to the upper surface of the depression.

By passing a current, the epitaxial thin film 37 emits light E of 460 nm to 510 nm. Everything goes up and enters the substrate. The transmitted light goes out to the outside as blue light. Some light is absorbed causing SA emission by the ZnSe dopant. SA emission F (5
(50 nm to 650 nm) also goes upward. LED light emission E
Both SA emission F goes upward. Together, they exhibit a white color. Any light emitted obliquely to the surface is blocked by the hollow wall. Only light that exits perpendicular to the surface can go upward and out of the dent. This is a directional LED
become.

(4) Inverted substrate shield type ZnSe white LE
D Since there is no light emitted to the side in FIG. 5, it always becomes white light. That's good, but it has the drawback of being too directional. An LED with less directivity may be required. 5 also has the disadvantage that the shape of the leads is complicated and it is difficult to mount them on an LED chip. LEDs with low directivity and no blue or blue-green leakage
Will be described with reference to FIG. This is one in which the ZnSe substrate itself is given a concave shape and the light emitting structure is embedded in the substrate.

FIG. 6A is a longitudinal sectional view, and FIG. 6B is a sectional view of only a chip. The leads 42 and 43 and the LED chip 45 are embedded in the transparent mold 41. A unique shape LED is provided on the top 44 of the ＬＥＤ-shaped lead 42.
The chip 45 is bonded in the opposite direction. The center of the LED 45 is a deep depression 49 in which a ZnSe-based epitaxial light emitting structure 47 is formed. That is, the epitaxial thin film 47 has a shape surrounded by the substrate. All the light emitted from the epitaxial thin film 47 is
Must pass through.

An insulating layer 50 and a ZnSe layer 51 are provided at the periphery of the substrate. The LED 45 is bonded to the lead surface 44 by the ZnSe layer 51. However, no current flows from the lead surface 44 to the device because of the insulating layer 50. Lead surface 44
There is a bulge 52 at the center. The ridge 52 is fixed in contact with the p-electrode of the epitaxial light emitting layer. p electrode and lead 4
2 are thereby electrically connected. ZnSe substrate 4
The bottom side of 6 is up. The bottom surface has an n-electrode on a ring or a small area, and the n-electrode is connected to the lead 43 by a wire 48. Lead 42 is anode, lead 4
3 becomes the cathode.

By passing a current, the epitaxial thin film 47 emits light E of 460 nm to 510 nm. Both light traveling upward and light traveling laterally enter the peripheral substrate 46.
The transmitted light goes out to the outside as blue light. Some light is absorbed by the substrate 46 and causes SA emission by the ZnSe dopant. Both the LED light E and the SA light F go upward and to the side. Together, they exhibit a white color. Light emitted not only in the direction perpendicular to the substrate surface but also obliquely or laterally becomes all white light. The resulting LED has no directivity. Use is much wider.

[0030]

Example 1 Example 1 (Iodine transport method ZnSe substrate, multiple
Quantum well active layer, erect)] ZnSe single crystal is chocolate
Skiing and Bridgman cannot grow
No. Here, a method for transporting ZnSe by iodine is described.
Transport method (CVT method: Chemical Vapor Transport)
Therefore, a ZnSe (100) substrate was manufactured. Fig. 13
1 shows an outline of a crystal growth apparatus by an element transport method. Growth room 86
Is placed on the bottom of the ZnSe polycrystalline material 87. Single crystal on top
Is fixed. Iodine in space
Fill it. Higher temperature T at bottom₁To the upper seed crystal 88
Lower temperature T₂To keep. 2ZnSe + 2I at the bottom₂→
2ZnI₂+ Se₂Reaction occurs. Zinc iodide ZnI₂
Is a gas and rises. Se₂Also rises. Seed crystal is low
The opposite reaction occurs here because of the temperature. 2ZnI
₂+ Se₂→ 2ZnSe + 2I₂Becomes This ZnSe
Accumulate on the seed crystal in a uniform orientation. Iodine
It acts like carrying zinc. So it is called iodine transport method
U. Growth temperature T ₂Is about 850 ° C.

The ZnSe single crystal thus obtained was heat-treated with an apparatus as shown in FIG. The ZnSe single crystal 89 was placed in the heat treatment chamber 90 and heated to about 1000 ° C. in a zinc vapor atmosphere to perform heat treatment. The heat treatment time is about 50 hours. Thereafter, cooling was performed at a rate of 60 ° C./min. Chemical transport methods and heat treatment methods are known.

[0032] I do not deliberately put dopant, but transporting material iodine (I ₂₎ becomes n-type semiconductor by heat treatment is doped in the crystal. The electron concentration is 5
It is on the order of × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁸ cm ⁻³ . The substrate thickness was 400 μm.

Next, an epitaxial light emitting structure was formed on a ZnSe substrate by a molecular beam epitaxial growth method. The molecular beam epitaxial growth apparatus will be described with reference to FIG. The molecular beam growth chamber 92 is a chamber that can be evacuated to an ultra-high vacuum. A liquid nitrogen shroud 93 is provided inside. Although an evacuation device is not shown here, an ultra-high vacuum of 10 ⁻⁸ Pa is drawn using a two-stage vacuum pump. At the center is a substrate holder 94, where a ZnSe wafer 95 is mounted. Wafer-95
A plurality of molecular beam cells 96 at the position of the bottom of the cone toward
97 and 98 are provided. ZnCl ₂ molecular beam cell 96,
A Se molecular beam cell 97 and a Zn molecular beam cell 98 are shown here.

In addition, Cd, Mg, S (ZnS), T
A molecular beam cell such as e is provided. ZnCl ₂ is provided for doping chlorine Cl as a dopant into a thin film. Each of the PBN crucibles and the surrounding
Data, supports, thermocouples, shutters, etc. The solid raw material is heated and vaporized by the heater. These materials fly toward the substrate 95 as molecular beams. For nitrogen, a radical cell 99 is used. Nitrogen molecules are gaseous from the beginning, but do not react as they are, so they are nitrogen atoms or molecular radicals. Nitrogen is also required as a dopant. The growth temperature is between 275 ° C and 325 ° C. 6th family / 2
The group ratio is 1-5. Growth rate is 0.4-0.7μm
/ H.

FIG. 7 shows the structure of the epitaxial growth layer 60. On an n-type ZnSe substrate 62, an n-type ZnSe buffer layer 63, an n-type ZnMgSSe cladding layer 64, a ZnS
e / ZnCdSe / multi quantum well active layer 65, p-type Zn
An MgSSe cladding layer 66 and a p-type ZnTe / ZnSe superlattice contact layer 67 are provided. Show the composition more specifically

(1) n-type ZnSe substrate 62 (2) n-type ZnSe buffer layer 63 (3) n-type Zn _0.85 Mg _0.15 S _0.10 Se
_0.90 cladding layer 64 (4) 10 nm ZnSe layer and 5 nm Zn _0.88
A multiple quantum well active layer 65 in which Cd _0.12 Se layers are alternately stacked in a quintuple (5) p-type Zn _0.85 Mg _0.15 S _0.10 Se
_0.90 cladding layer 66 (6) p-type ZnTe / ZnSe laminated superlattice contact layer 67

When a ZnSe thin film is used alone as the active layer, light emission of 460 nm corresponding to the band gap can be obtained. Mixed crystal ZnCdSe containing Cd can emit light with a wavelength longer than 460 nm because the band gap becomes narrower. Since ZnSe and ZnCdSe have different lattice constants and become lattice-mismatched as they are, the active layer has a superlattice structure here. In this example, the ratio of Cd is 0.1
2 which emits light at 490 nm. The structure of the active layer may be other than this as long as the active layer does not cause lattice relaxation. By increasing Cd, light with a longer wavelength can be emitted. The clad layer has a wider band gap than the active layer. This is for carrier confinement. The composition of the cladding layer is defined by the condition that the lattice constant is close to that of the ZnSe substrate and lattice-matched.
In the epitaxial layer, nitrogen (N) is used as a p-type dopant and chlorine (Cl) is used as an n-type dopant.

On the p-type contact layer of this epitaxial wafer, a p-side electrode made of Pd / Au was formed.
An n-side electrode of In was formed on the n-type ZnSe on the back surface.
Ti / Au can also be used for the n-side electrode. Photolithography is used to form the pattern electrodes. 300 μm × 300 μm epitaxial wafer after electrode formation
It was cut into an m-square size and fixed to the stem 14 of the lead 12 as shown in FIG. The n-side electrode was down and the p-side electrode was up. That is, the ZnSe substrate 16 comes into contact with the stem 14. The p-side electrode was attached to another lead 13 by a wire. These were molded with a transparent resin.

This LED was measured in a constant current mode. High intensity white light was emitted. The luminance was 1.5 Cd for a drive current of 20 mA. FIG. 8 shows the emission spectrum of this LED. LED emission from the epitaxial light emitting layer having a sharp peak at 490 nm as designed,
SA emission from a broad ZnSe substrate having a dull peak in nm is combined. The synthesized light is white. The yellow color was a little better than the white color.

Embodiment 2 Grain boundary grown ZnSe, single quantum well or double hetero active layer, upright] Grain
-Zn produced using the Growth method (grain boundary growth method)
An Se substrate was prepared. Also in this growth method, an appropriate heat treatment is performed by doping with aluminum to obtain an n-type 5 × 10 5
The carrier concentration was about ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ . A thin film having the structure shown in FIG. 9 was epitaxially grown on the n-type ZnSe substrate by the molecular beam epitaxial growth apparatus shown in FIG. Epitaxial wafer-70
Are formed on an n-type ZnSe substrate 72, an n-type ZnSe buffer layer 73, an n-type ZnMgSSe cladding layer 74, a ZnC
dSe single quantum well or Te-doped ZnSe double hetero active layer 75, p-type BeZnMgSe cladding layer 76, p-type ZnTe / ZnSe superlattice contact layer 7
7 is formed. The specific composition of the mixed crystal is shown below.

(1) n-type ZnSe substrate 72 (2) n-type ZnSe buffer layer 73 (3) n-type Zn _0.85 Mg _0.15 S _0.10 Se
_0.90 cladding layer 74 (4) Zn _0.92 Cd _0.08 Se single quantum well active layer or Te-doped ZnSe double hetero active layer 75 (5) p-type Be _0.20 Zn _0.60 Mg _0.20 Se
Cladding layer 76 (6) p-type ZnTe / ZnSe superlattice contact layer 7
7

The active layer is made of ZnCd having a Cd ratio of 0.08.
It is a Se layer or a ZnSe layer doped with Te. This produces 477 nm light. In the epitaxial layer, nitrogen (N) is used as a p-type dopant and chlorine (Cl) is used as an n-type dopant. Substrate thickness is 300 μm
Was prepared. Pd / Au was provided on the p-type ZnTe / ZnSe superlattice contact layer 77 as a p-side electrode. On the back surface of the n-type ZnSe substrate 72, In or Ti /
An Au n-side electrode was provided. This was cut out into chips and mounted on a package.

A current was applied to the LED to emit light. It was 1.5 Cd at a current of 20 mA. FIG. 10 shows the emission spectrum of this LED. The emission of the LED with a sharp peak at 477 nm is superimposed on the SA emission of the substrate with a broad and low peak at 590 nm. The emission color was bluish and cool white.

Embodiment 3 ZnSe, Zn by grain boundary growth method
Se active layer, inverted, substrate thickness 3 types] Grain-Gro
A ZnSe substrate having a thickness of 700 μm and a thickness of 300 μm manufactured using the WTH method (grain boundary growth method) was prepared. Doping aluminum and performing appropriate heat treatment, n-type 5 ×
The carrier concentration became about 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ . On the n-type ZnSe substrate, a thin film having the same configuration as that of the first embodiment shown in FIG. 7 was epitaxially grown by a molecular beam epitaxial growth apparatus to obtain an epitaxial wafer-60.

(1) n-type ZnSe substrate 62 (2) n-type ZnSe buffer layer 63 (3) n-type Zn _0.85 Mg _0.15 S _0.10 Se
_0.90 cladding layer 64 (4) 10 nm ZnSe layer and 5 nm Zn _0.88
A multiple quantum well active layer 65 in which Cd _0.12 Se layers are alternately stacked in a quintuple (5) p-type Zn _0.85 Mg _0.15 S _0.10 Se
_0.90 cladding layer 66 (6) p-type ZnTe / ZnSe
Multilayer superlattice contact layer 67

A substrate having a thickness of 300 μm was polished after epitaxial growth to produce a substrate having a thickness of 100 μm. Thus, three types of wafers having a thickness of 100 μm, 300 μm, and 700 μm were completed. A p-side electrode and an n-side electrode were respectively attached, and cut into square chips of 300 μm × 300 μm. As shown in FIG. 4, the stem 2 of the lead 22 is turned upside down with the p-type part facing downward and the n-type part facing upward.
It was fixed to 4. Wire bond to n-side electrode and lead 23
Connected. The whole was covered with a transparent resin.

This LED was made to emit light in a constant current mode.
White light was obtained. In the LEDs of Examples 1 and 2, uneven color tone was observed depending on the angle, but episide down (inverted)
In this embodiment of the mounting, uniform light emission without color tone unevenness was realized when viewed from above. As shown in FIG. 4B, all the light emitted from the epitaxial growth layer passes through the substrate and the absorption is equal in any direction. Typical brightness is 1.5 at 20 mA
２2 Cd.

The 100 μm-thick LED became cold white with a bluish tint, the 300 μm-thick LED became neutral white, and the 700 μm-thick LED became strong yellowish white. This will be described with reference to the chromaticity diagram of FIG.
The chromaticity diagram shows stimulus values for three primary colors, red, green, and blue (a human 3
FIG. 9 is a diagram devised for displaying on a plane coordinate by quantifying a stimulus amount felt by various types of visual sensory organs).
In the emission spectrum of a certain light source, when the stimulus amount corresponding to red is x, the stimulus amount corresponding to green is y, and the stimulus amount corresponding to blue is z, these are normalized by the total stimulus amount, X = x
FIG. 11 is a chromaticity diagram showing the plane coordinates defined by / (x + y + z) and Y = y / (x + y + z). In this coordinate system, a color having any spectrum is represented as one point on the coordinates. Of these, monochromatic light in the range from 400 nm to 675 nm draws a C-shaped curve in the figure. All other colors are composite lights of these monochromatic lights, and can be represented by points in a portion surrounded by a C-shaped curve in the figure. The white light is a portion surrounded by a broken line near the center. It is assumed that two colors P and Q are set to these two-dimensional coordinates. These arbitrary ratios of mixed colors are represented as points on a line connecting two points PQ.

Point A is emission at 490 nm, which is the original emission of the ZnSe epitaxial layer. Since it is monochromatic, it is on the C-shaped curve. Point B is ZnSe centered at 630 nm.
4 shows broad SA emission from a substrate. Since the light itself is a composite color light having a wide spectral half width, it is located inside the C-shaped curve. The mixture of these two colors is on line AB. Since the line segment AB crosses the white area (broken line), the mixed color may be white.

Point C indicates light emission from a 100 μm thick LED, point D indicates light emission from a 300 μm thick LED, and point E indicates light emission from a 700 μm thick LED. All are white, but there are differences from cold to warm colors depending on the ratio of blue. When expressed in terms of color tone temperature, those having a thickness of 100 μm are cool white and have a color tone temperature of about 8000K. Those having a thickness of 300 μm are neutral white and have a color tone temperature of about 5000K. 700
Those having a thickness of μm are warm white with a strong yellow proportion and have a color tone temperature of 3000K.

When the thickness of the substrate is increased, the center of SA increases, so that the ratio of yellow increases. This is the above three different thicknesses of L
Confirmed by ED. However, even if the thickness is kept constant, the ratio of SA emission can be increased or decreased by changing the amount of the dopant.

Embodiment 4 Inverted Reflector] In the third embodiment, the LED is mounted on the stem in an inverted manner. As a result, the color is uniform and white as seen from above. However, when viewed from the side of the chip, there is an angle at which only blue light is emitted. Therefore, a depression was provided in the stem, and a chip was mounted in the depression. This is shown in FIG. The chip was inverted and mounted deep inside the recess 39. In this case, all the light emitted to the side is blocked by the wall surface of the depression 39 and is not outside. The opening is further narrowed by the reflection plate 40. Light comes only upward. The light emitted from the epitaxial thin film must pass through the ZnSe substrate 36 in order to be emitted upward. The blue light is always mixed with the yellow SA light. Thus, an LED emitting uniform white light was obtained. The mounting surface 34 of the stem is mirror-finished, and a thin aluminum plate is used as a reflection plate. Since the blue light is reflected and enters the ZnSe substrate, the reflection increases the yellow-orange intensity. Directivity is improved due to the reflector and the concave structure. The luminance reached 1.8 to 2.5 Cd due to reflection.

Embodiment 5 FIG. Inversion, Reflector] In the fourth embodiment, a recess is formed in the stem, and the LED is mounted in the recess in an inverted manner. Light comes out only upwards. High directivity and high brightness. However, it is difficult to form such a deep recess in the stem. Boost stem costs. Rather, it is better to provide the chip with anisotropy. This is because the chip can be easily given shape anisotropy by a wafer process.

Thus, a chip stem having a shape as shown in FIG. 6 was manufactured. The manufacturing method will be described with reference to FIGS. Z
Grid-like SiN mask pattern 8 on nSe wafer 78
0 was formed. FIG. 12A is a sectional view of a part of the wafer. FIG. 12D shows a plan view. The white portion of the square is the exposed portion 79 of ZnSe. The square portion will later become the light emitting portion. Approximately 3μm other than the mask
Etched to a depth of. As shown in FIG.
3 is formed. The portion immediately below the mask 80 is an inverted mesa 81
Remains in the form of The exposed portion becomes a plane 82.

The epitaxial layer of FIG. 7 was grown on the wafer having the concave portions 83 by the molecular beam epitaxial growth method in the same manner as in Example 1. Recess 83
The epitaxial layer 84 is laminated. The material also rides on the mask 80 to form the laminated body 85, but is not epitaxial growth. No light emitting structure. This is an unnecessary part. An electrode or the like is provided on the epitaxial layer (epitaxial light emitting structure) 84 inside the concave portion 83, and the electrode is also 300 μm ×
It was cut into 300 μm chips. The mask portion becomes the cutting line. An LED chip having a recess at the center is manufactured. The stem 44 of the lead 42 itself has an irregular shape having the convex portion 52.

The chip was inverted and the p-type layer was fixed so as to contact the stem ridge 52. FIGS. 6A and 6B
become that way. The n-side electrode is connected to another lead 43 by a wire 48.
Connected to. This is because the epitaxial light emitting structure 47 is Zn
Since it is embedded in the Se substrate, there is no blue or blue-green leakage light. The LED emits white light uniformly for all viewing angles. This is designed to emit uniform light by devising the shape of the chip. The stem needs to be devised, but this does not increase the cost due to slight deformation. In addition, this embodiment, in which an epitaxial layer is embedded in a chip, has a low directivity and is a full-field type. It emits light at a wide angle and is suitable for display.

Example 6 (Iodine transport method ZnSe substrate, single
One quantum well active layer, erect, substrate thickness 3)] iodine transport method
300 μm thick, n-type fabricated using (CVT method)
5 × 10 ¹⁷~ 1 × 10¹⁸cm^-3Of carrier concentration
A ZnSe substrate was prepared. On this n-type ZnSe substrate,
As shown in FIG. 16 by a molecular beam epitaxial growth apparatus.
A thin film having such a structure was epitaxially grown. (1) n-type ZnSe substrate 102 (2) n-type ZnSe buffer layer 103 (3) n-type Zn_0.85Mg_0.15S_0.10Se_0.90Cladding layer
 104 (4) Zn_0.90Cd_0.10Se single quantum well active layer 10
5 (5) p-type Zn_0.85Mg_0.15S_0.10Se_0.90Cladding layer
 106 (6) p-type ZnTe / ZnSe laminated super lattice contact layer
 107

The active layer is made of ZnCd having a Cd ratio of 0.10.
This is a single quantum well layer composed of a Se layer,
emits m light. A substrate having a thickness of 300 μm is polished on the back side after epitaxial growth to obtain a substrate having a thickness of 30 μm, 100 μm, or 250 μm.
Three types of epiwafers having a thickness of μm were obtained. By subjecting these wafers to the same device processing as in Example 1,
An LED was fabricated. When this LED was caused to emit light in a constant current mode, white light was obtained. Typical brightness is 1.5
２．０2.0 Cd. The 30 μm thick LED emitted a bluish cool white. A 100 μm thick LED also produced a slightly bluish white. The 250 μm thick LED was neutral white. The chromaticity of the emission color of each LED is shown in the chromaticity diagram of FIG. In the figure, point A indicates the chromaticity of light emission from the 480 nm epitaxial layer. Point B is 580n which is photoexcited by light emission from the epitaxial layer.
The chromaticity of SA emission from a CVT ZnSe substrate centered at m is shown.

The colors emitted from the LEDs are all on the line AB connecting these two points. The emission color of the 30 μm thick LED is point C, the emission color of the 100 μm thick LED is point D, 25
The emission color of the 0 μm thick LED is represented by point E. These light emitting points are all present in a white area surrounded by a broken line. The thinner the substrate, the higher the ratio of blue light emission,
You can see how the color becomes cooler. As the color tone temperature, those having a thickness of 30 μm (point C) are about 20,000K, 10
The one with a thickness of 0 μm (point D) was about 9000K, and the one with a thickness of 250 μm (point E) was about 6000K.

[0060]

According to the present invention, Z doped with SA emission center is used.
A ZnSe-based thin film is epitaxially grown on an nSe substrate, and the thin film emits blue light as an LED, emits yellow or yellow-green SA light when blue passes through the substrate, and emits white light in combination. Since the conductive ZnSe substrate is a single crystal, it has higher transparency than a conventional YAG fluorescent material. So little absorption. Further, the efficiency of the ZnSe substrate to convert blue, blue, and green light into yellow light is high. So Ga
It becomes a white LED with higher brightness than N / YAG.

Since the main component is a ZnSe LED, it has a long life. Various white colors from warm to cool can be generated depending on the kind and concentration of the dopant of the ZnSe substrate.
Further, the color tone can be changed from a warm color system to a cool color system simply by changing the thickness of the substrate. No extra phosphor is required. The substrate itself is effectively used as a SA light emitter. A semiconductor element requires a substrate, but it is used as a yellow light emitter, so that the structure is simple and easy to manufacture.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a white LED according to a conventional example in which a GaN-based LED and a YAG phosphor are combined. (A) is the whole longitudinal section including a package. (B) is an enlarged sectional view near the LED chip.

FIG. 2 shows a GaI comprising a GaN-based LED and a YAG phosphor
FIG. 3 is an emission spectrum diagram of an nN / YAG white LED. The horizontal axis represents wavelength, and the vertical axis represents light intensity (arbitrary scale).

FIG. 3 is a diagram showing an example of a white LED according to Examples 1 and 2 of the present invention in which an LED combining a ZnSe substrate and a ZnSe-based thin film light emitting structure is fixed upright to a stem. (A) is the whole longitudinal section including a package. (B) is an enlarged sectional view near the LED chip.

FIG. 4 is a diagram showing an example of a white LED according to a third embodiment of the present invention in which an LED in which a ZnSe substrate and a ZnSe-based thin film light emitting structure are combined is invertedly fixed to a stem. (A) is the whole longitudinal section including a package. (B) is an enlarged sectional view near the LED chip.

FIG. 5 is a diagram illustrating an example of a white LED according to a fourth embodiment of the present invention in which an LED in which a ZnSe substrate and a ZnSe-based thin film light emitting structure are combined is inverted between valleys of a stem having a concave portion. (A) is the whole longitudinal section including a package. (B) is an enlarged sectional view near the LED chip.

FIG. 6 is a diagram showing an example of a white LED according to a fifth embodiment of the present invention in which an LED having a structure in which a ZnSe-based thin film light emitting structure is embedded in a ZnSe substrate is invertedly fixed to a stem having a convex portion.
(A) is the whole longitudinal section including a package. (B) is LE
FIG. 4 is an enlarged cross-sectional view near a D chip.

FIG. 7 is a diagram showing a layer structure of an epitaxial wafer of the LED of Example 1 having a ZnSe / ZnCdSe multiple quantum well structure as an active layer.

FIG. 8 is an emission spectrum diagram of the LED of Example 1 having a ZnSe / ZnCdSe multiple quantum well structure as an active layer.

FIG. 9: LE of Example 2 having a ZnCdSe single quantum well active layer or a Te-doped ZnSe double hetero active layer
The figure which shows the layer structure of the epitaxial wafer of D.

FIG. 10: ZnCdSe single quantum well active layer or Te
Example 2 having a doped ZnSe double hetero active layer
FIG. 3 is an emission spectrum of ED.

FIG. 11 is a diagram showing, as C, D, and E, light emitting points of three types of LEDs having different thicknesses in Example 3 in a chromaticity coordinate system indicating chromaticity. The horizontal axis is X and the vertical axis is Y.

FIG. 12 is a view for explaining a wafer process for manufacturing an LED chip of Example 5 in which a concave portion is formed in a central portion of a chip, an epitaxial light emitting structure is formed in the concave portion, and the light emitting structure is surrounded by a substrate. .

FIG. 13 is a schematic cross-sectional view of an apparatus for manufacturing a ZnSe single crystal substrate by a chemical transport method.

FIG. 14 is a cross-sectional view illustrating a state in which a ZnSe single crystal manufactured by a chemical transport method is subjected to a heat treatment.

FIG. 15 is a schematic sectional view of a molecular beam epitaxy apparatus for producing a ZnSe-based epitaxial structure on a ZnSe substrate.

FIG. 16 shows a sixth embodiment having a ZnSe single quantum well active layer.
The figure which shows the layer structure of the epitaxial wafer of LED of FIG.

FIG. 17 shows that the chromaticity of the emission color of the three types of LEDs having different thicknesses of the sixth embodiment is changed to the point C (30 μ
m), chromaticity diagrams shown as point D (100 μm) and point E (250 μm).

[Explanation of symbols]

1 Transparent Mold 2 First Lead 3 Second Lead 4 Depression 5 GaN LED 6 YAG Phosphor 7 Wire 8 Wire 11 Transparent Mold 12 Lead 13 Lead 14 Top 15 ZnSeLED 16 ZnSe Substrate 17 Epitaxial Light Emitting Structure (Thin Film) 18 Wire 21 Transparent Mold 22 Lead 23 Lead 24 lead top surface 25 ZnSe LED 26 ZnSe substrate 27 epitaxial light emitting structure (thin film) 28 wire 31 transparent mold 32 lead 33 lead 34 lead top surface 35 ZnSe LED 36 ZnSe substrate 37 epitaxial light emitting structure (thin film) 38 wire 39 depression 40 reflector 41 transparent mold 42 lead 43 Lead 44 Lead top surface 45 ZnSe LED 46 ZnSe substrate 47 Epitaxial light emitting structure (thin film) 48 Wire 49 Depression 50 Insulating layer 51Z Se layer 52 Lead ridge 60 ZnSe LED chip 62 n-type ZnSe substrate 63 n-type ZnSe buffer layer 64 n-type ZnMgSSe cladding layer 65 ZnSe / ZnCdSe multiple quantum well active layer 66 p-type ZnMgSSe cladding layer 67 p-type ZnTe / ZnSe superlattice contact layer 70 ZnSe LED chip 72 nZn LED chip 73n-type ZnSe buffer layer 74n-type ZnMgSSe cladding layer 75ZnCdSe single quantum well active layer or Te-doped ZnSe double hetero-active layer 76p-type BeZnMgSe cladding layer 77p-type ZnTe / ZnSe superlattice contact layer 78ZnSe substrate 79 substrate surface 80 mask 81 convex portion 82 bottom surface 83 depression 84 epitaxial light emitting structure 85 epitaxial layer 86 growth chamber 87 ZnSe polycrystalline material 88 Zn e seed crystal 89ZnSe single crystal 90 heat treatment chamber 92 molecular beam epitaxy chamber 93 liquid nitrogen shroud 94 substrate holder - 95ZnSe substrate 96ZnCl ₂ molecular beam cell 97Se molecular beam cell 98Zn molecular beam cell 99 radical nitrogen source 100ZnSeLED chip 102n-type ZnSe substrate 103n-type ZnSe Buffer layer 104 n-type ZnMgSSe cladding layer 105 ZnCdSe single quantum well active layer 106 p-type ZnMgSSe cladding layer 107 p-type ZnTe / ZnSe superlattice contact layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-21847 (JP, A) JP-A-51-28784 (JP, A) JP-A-9-205228 (JP, A) (58) Investigation Field (Int. Cl. ⁷ , DB name) H01L 33/00

Claims (6)

(57) [Claims] 1. An n-type Z doped with iodine, bromine, chlorine, gallium, indium or aluminum as a luminescent center.
an nSe single crystal substrate, a blue-blue-green light-emitting structure of ZnSe or a mixed crystal compound mainly composed of ZnSe provided by epitaxial growth so as to include a pn junction on the ZnSe single crystal substrate, and a bottom surface of the n-type ZnSe substrate And the p-side electrode provided on the p-type semiconductor in the upper layer of the light-emitting structure.
A side electrode, a support mechanism for supporting the ZnSe substrate or the light emitting structure, a lead for flowing a current to the electrode, and a package surrounding the ZnSe substrate, the light emitting structure, and the support mechanism. By the light of Zn
Exciting the emission center of the Se substrate to emit yellow or orange light, and obtaining white light by combining both blue-blue green light from the emission structure and yellow-orange light from the ZnSe substrate emission center. Characteristic white LED. 2. The light-emitting structure is ZnSe or ZnS
e and Zn_1-xCd _xConsisting of a multilayer structure containing Se
The wavelength of light emitted from the optical structure is in the range of 460 nm to 510 nm.
And 550n excited light emission from the ZnSe substrate
self-excitation (SA) emission having a wavelength of m to 650 nm
The white LED according to claim 1, wherein: 3. The ZnSe substrate has a thickness of 10 μm to 2 m.
The color tone of the obtained white light can be changed from a cool color system to a warm color system by adjusting within the range of m and by changing the emission wavelength from the light emitting structure. 3. The white LED according to 2. 4. The support mechanism has a flat stem at the top.
4. The white LED according to claim 3, wherein the lead of the mold has a substrate side opposite to the stem and a surface having a light emitting structure fixed to the stem surface. 5. A リ ー ド -shaped lead in which a support mechanism has a stem including a concave portion at a top portion, wherein a substrate side is opposite to the stem and a surface having a light emitting structure is fixed to the concave portion of the stem, and is provided at an upper end of the concave portion. 4. The white LED according to claim 3, wherein the white LED has a reflector to reflect a part of the blue, blue and green light from the light emitting structure and irradiate the ZnSe substrate. 6. The ZnSe substrate has a concave portion, a ZnSe, ZnSe + Zn _1-x Cd _x Se light emitting structure is formed at the bottom of the concave portion, the light emitting structure is surrounded by the ZnSe substrate, and the substrate side is opposite to the stem. 4. The white LED according to claim 3, wherein the surface of the light emitting structure is fixed so as to contact the stem.