CN1532953A

CN1532953A - White light-emitting diode element

Info

Publication number: CN1532953A
Application number: CNA031079237A
Authority: CN
Inventors: 赖穆人; 刘家呈; 章烱煜
Original assignee: WEIKAI SCIENCE AND TECHNOLOGY Co Ltd
Current assignee: WEIKAI SCIENCE AND TECHNOLOGY Co Ltd
Priority date: 2003-03-25
Filing date: 2003-03-25
Publication date: 2004-09-29

Abstract

This invention discloses a white light emitting diode taking ZnTe or ZnSe as the substrate and setting a monocrystal BP buffer layer on the substrate to make a cubic crystal blue light diode to epitaxially grow on the said BP buffer layer directly. When the blue light diode emits blue lights of 50nm-470nm wavelength, ZnTe or ZnSe substrate emits a green-yellow light of 550nm after absorbing part of the blue light. The green-yellow light then is mixed with the blue light to generate white light.

Description

White light LED element

Technical Field

The invention relates to a white light diode element, in particular to a boron phosphide buffer layer with a single crystal structure arranged on a substrate of zinc telluride or zinc selenide, so that a blue light diode with a cubic crystal structure can be directly epitaxially grown on the boron phosphide buffer layer.

Background

Because Light Emitting Diodes (LEDs) have the advantages of small size, light weight, high efficiency, long lifetime, etc., they are applied to backlights of special displays based on the development of monochromatic LEDs such as red, blue, green, etc., for example: background light of mobile phone and LCD. In addition, due to the advent of the blue light emitting diode, the industry has been working on developing white light emitting diodes as lighting devices capable of replacing electric bulbs or fluorescent lamps.

In the prior art, fig. 1 shows a cross-sectional view of a light emitting diode with a lateral electrode as a design structure. A first confinement layer, such as an N-type gallium nitride (GaN) layer 11, is disposed on a substrate, such as a sapphire (sapphire) layer 10 (typically including a buffer layer (not shown) between the substrate and the first confinement layer). In the figure, another active layer, such as a GaInN layer 12, is located above the first confinement layer. Furthermore, a second confinement layer, such as a P-type gallium nitride (GaN) layer 13, is disposed on the active layer. In the figure, the reference numeral 14 on the first confinement layer and the reference numeral 15 on the second confinement layer respectively refer to two electrode layers with different polarities, such as an n-electrode 14 and a p-electrode 15. In the prior art, as disclosed in U.S. patent No. 5998925, a conventional white light emitting diode is disclosed, that is, when the above-mentioned stacked structure is packaged, a phosphor-containing body, such as a ytterbium aluminum garnet layer 16(YAG phosphor), is encapsulated in the package cap, so as to partially convert the light emitted from the above-mentioned stacked active layers, such as blue light, into light of different wavelengths, such as yellow light, and then the two lights are mixed to form a white light.

However, the phosphor-ytterbium aluminum garnet layer 16 absorbs part of the blue light source and then converts the blue light source into yellow light, which causes the difference between the yellow light source intensity and the blue light source intensity, and thus the white light generated by the mixing is not ideal. In addition, when the stacked structure is packaged, the phosphor should be coated additionally, which significantly increases the cost of packaging. Furthermore, since the substrate 10 made of sapphire is an insulator, an additional etching process is required to fabricate the lateral electrode, so that the electrode is fabricated on the surface of the first confinement layer, which also increases the process cost.

For this reason, as compared with the lateral electrode led, the prior art led using the vertical electrode as the design structure by replacing the substrate with the non-insulator has been proposed, and a substrate capable of converting the light source wavelength is proposed, as shown in fig. 2. In the figure, the substrate is, for example, an N-type zinc selenide substrate 22. An N-type ZnSe buffer layer 23, an N-type SeSMgZn confinement layer 24, a ZnCdSe active layer 25, a P-type SeSMgZn confinement layer 26 and a P-type contact layer 27 are sequentially formed on the substrate. The primary purpose of the N-type ZnSe buffer layer 23 is to increase the Lattice matching (Lattice Mismatch) between the substrate and the confinement layer 24. The N-type and P-type SeSMgZn confinement layers 24 and 26 on both sides of the ZnCdSe layer 25 have wider band gap than the ZnCdSe layer 25, and can limit the electrons in the ZnCdSe layer 25 to react only therein without escaping outside.

An n-electrode 21 and a p-electrode 28 are also provided on the upper and lower sides of the laminated structure. When the P-electrode 21 and the N-electrode 28 are supplied with appropriate voltages, the ZnCdSe active layer 25 on the P-N junction will generate blue light. A portion of the blue light is absorbed by the doped zinc N-selenide substrate 22 to produce yellow light. By mixing the blue light and the yellow light, white light is generated.

Compared with the former process of lateral electrode, the latter process of vertical electrode light emitting diode has simpler process (without etching for electrode position), and avoids the extra cost of phosphor coating in the former package. However, in the latter process, the efficiency of the white light emitted by the white light emitting device is not as good as that of the former process. In view of the above, the present invention proposes another structure of a vertical electrode led, in which a p-type zinc telluride or zinc selenide is used as a substrate, and a boron phosphide buffer layer with a single crystal structure is further disposed on the substrate, so that a more matched lattice structure is generated when a cubic blue led is epitaxially grown on the boron phosphide buffer layer, thereby effectively solving the white light emitting efficiency. In addition, in the invention, the adoption of p-type zinc telluride or zinc selenide as the substrate can maintain the wavelength of yellow light absorbed and converted by the substrate to be 550nm by doping p-type impurities, and can actually generate purer white light by continuously controlling the wavelength of blue light emitted by the cubic crystal blue light diode which is extended on the substrate to be 450nm to 470 nm.

Disclosure of Invention

As mentioned above, one of the objectives of the present invention is to provide a light emitting diode structure with vertical electrode arrangement.

The invention aims to provide a white light emitting diode structure, which takes p-type zinc telluride or zinc selenide as a substrate, and then a boron phosphide buffer layer with a single crystal structure is arranged, so that a more matched lattice structure is generated when a blue light diode of a cubic crystal is epitaxially grown on the boron phosphide buffer layer.

The white light emitting diode of the invention uses a p-type zinc telluride or zinc selenide as a substrate, a Boron Phosphide (BP) buffer layer, a first type gallium nitride (GaN) binding layer, an active layer and a second type gallium nitride binding layer with single crystal structures are sequentially arranged on the substrate, and a first type electrode and a second type electrode are respectively arranged below the zinc telluride substrate and above the second type gallium nitride binding layer, wherein the first type gallium nitride binding layer and the second type gallium nitride binding layer have opposite conductive types, the second type electrode and the first type electrode are also the same, and the zinc telluride substrate, the boron phosphide buffer layer, the first type electrode and the first type gallium nitride binding layer have the same conductive type.

Drawings

In order to make the aforementioned and other objects, features and advantages of the invention more comprehensible, preferred embodiments accompanied with figures are described in detail below:

FIG. 1 is a schematic cross-sectional view of a white LED with a lateral electrode structure;

FIG. 2 is a schematic cross-sectional view of a white LED with a vertical electrode as a design structure; and

fig. 3 shows a cross-sectional view of a light emitting diode 30 according to the present invention.

The reference numerals in the drawings are explained below:

10 sapphire (sapphire) layer 11N-type gallium nitride (GaN) layer

12 GaInN active layer 13P-type gallium nitride (GaN) layer

14 n-pole electrode and 15 p-pole electrode

16P-Yb aluminium garnet layer 21 n pole electrode

23N type ZnSe buffer layer of 22N type zinc selenide substrate

24N type SeSMgZn bound layer 25 ZnCdSe layer

26P type SeSMgZn bound layer 27P type contact layer

28P electrode 300 substrate

302 boron phosphide buffer layer 304 gallium nitride confinement layer of type one

306 active layer 308 gallium nitride confinement layer of a second type

312 first type electrode 310 second type electrode

Detailed Description

Fig. 3 shows a cross-sectional view of the structure of the led 30 of the present invention. In the figure, it has vertically arranged electrodes 310 and 312. In addition, a substrate 300 is illustrated, and the present invention employs a p-type zinc telluride as the substrate 300, and then a boron phosphide buffer layer 302 with a single crystal structure is grown on the substrate 300 at a high temperature and a low temperature. Then, a first type GaN confinement layer 304, an active layer 306, a second type GaN confinement layer 308, a first type electrode 312 and a second type electrode 310 are sequentially grown on the single-crystal structure boron phosphide buffer layer 302.

In the present invention, p-type zinc telluride is used as the substrate 300, so that the first-type electrode 312 can be formed on one side of the substrate 300 to form a vertical-electrode light emitting device. In addition, the p-type zinc telluride can convert and emit yellow-green light with the wavelength of about 550nm after absorbing part of the blue light emitted by the active layer 306, and the yellow-green light and the blue light with the wavelength of about 450nm to 470nm emitted by the active layer 306 are mixed to generate the white light required by the invention.

In addition, the p-type zinc telluride substrate of the present invention can utilize a reaction chamber with Vertical Gradient Freeze (VGF), pure zinc and pure tellurium are mixed in a crucible, and nitrogen gas of about 20 atm is filled in the reaction chamber; thereafter, to form the p-type zinc telluride substrate 300, at least one more precursor is added to the crucible, e.g., ZnP is added₂. Then, the temperature of the reaction chamber is slowly increased to be higher than the melting point (1295 ℃) of the zinc telluride, and after homogenization (homogenetic transformation) of the pure zinc and the pure tellurium, the temperature is slowly reduced by a gradient less than 10K/cm, and the zinc telluride substrate can be obtained.

Furthermore, the substrate 300 of the present invention can also be formed by using p-type zinc selenide (ZnSe) as a material, using a Chemical Vapor Transport (CVT) method or a technique called iodine transport (iodine transport method), first, placing a polycrystalline zinc selenide (polycrystalline) in the bottom of the reaction chamber, and a zinc selenide seed crystal in the top of the reaction chamber, and filling the entire reaction chamber with iodine vapor; the bottom of the reaction chamber was then heated to a temperature T1 and the top to a temperature T2, T2 being about 850 deg.C, wherein T1 is less than T2, at which time the bottom would react as follows

When the product of the above reaction is ZnI₂And Se₂The vapor rises to the top and is cooled by the zinc selenide seed crystal at the top of the reaction chamber to carry out the reverse reaction of the reaction, so that the zinc telluride continues to accumulate and grow on the zinc selenide seed crystal in the same crystallization direction with the zinc selenide seed crystal. And steam I₂Will be recycled to the bottom and continue the reaction described above. In the process, zinc selenide at the bottom is brought to the top to form crystallized vapor I₂It is naturally absorbed by the zinc selenide at the top, so that the zinc selenide is naturally converted into n-type zinc selenide, except I₂Alternatively, zinc selenide can be converted to p-type zinc selenide by doping the p-type precursor,other doping, such as Al, Cl, Br, Ga, In, can convert the zinc selenide to n-type zinc selenide. The impurities can be used for controlling the wavelength of yellow light emitted after the impurities absorb blue light.

Finally, the tempering step is carried out to repair the vacant part of the selenium. Firstly, heating zinc selenide crystals to about 1000 ℃ in a zinc vapor environment for about 50 hours; and then, cooling the zinc selenide seed crystal at the speed of 60 ℃/min to obtain the zinc selenide crystal with better quality.

In the present invention, the boron phosphide buffer layer 302 of a single-crystal structure can be formed on the crystal plane of the above-mentioned substrate. The substrate 300 may be first chemically cleaned in a suitable solution, followed by a second cleaning step at H₂The substrate 300 is heated to about 900 deg.C under an atmosphere, and the oxide on the upper surface of the substrate 300 is removed, followed by H by a halide vapor phase epitaxy (HALIDE VAPOR PHASE EPITAXY)₂As carrier gas, boron chloride (BCl) is used₃) With phosphorus chloride (PCl)₃) Or boron chloride (BCl)₃) With Phosphine (PH)₃) As a precursor, firstly, the low-temperature boron phosphide layer epitaxy is carried out at about 300 ℃ or lower, the thickness of the boron phosphide layer epitaxy is about 400nm, then, the temperature is raised to about 1000 ℃ or higher, the high-temperature boron phosphide layer epitaxy is carried out, the reaction lasts for about 60 minutes, and the thickness of the boron phosphide layer epitaxy is about 4560 nm.

Boron phosphide is a zinc blend structure (zinc blend structure) with a lattice constant of about 4.538 Å, and gallium nitride of the boron phosphide layer and the zinc blend structure has a lattice constant of about 4.51 Å and a lattice difference of about 0.6%, so that the subsequent epitaxial layer has a perfect crystal structure to improve the luminous efficiency and the service life of the device.

The first type GaN confinement layer 304 of the present invention has a cubic crystal structure, and can be formed by adding other elements according to the requirement to form Al_xIn_yGa_1-x-yN (0 < x < 1, 0 < y < 1, x + y ═ 1) or Al_xGa_yN_1-x-yP (0 < x < 1, 0 < y < 1, x + y ═ 1), such as gallium nitride (GaN), indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN), or gallium phosphonitride (GaNP), and the precursors used are typically methyl diamine or ammonia(NH₃) (ii) a For example, gallium nitride (GaN) precursors including MMH and TMG may be used to form the first type gallium nitride confinement layer 304 on the boron phosphide buffer layer 302 by Metal Organic Vapor Phase Epitaxy (MOVPE).

The active layer 306 of the present invention has a cubic crystal structure, is provided on the first type GaN confinement layer 304, and may be made of a GaN-based semiconductor, such as In_yGaN, 0 < y < 1, and further includes trimethyl indium (TMIn), trimethyl gallium (TMG) and NH by MOCVD method₃Is formed as a precursor. When y is equal to 0.1, the prepared element can emit ultraviolet light with the wavelength of about 405 nm; when y is equal to 0.2, the device can emit blue light having a wavelength of about 470 nm.

The second type GaN confinement layer 308 on the active layer 306 also has a cubic crystal structure, and is formed in the same manner as the first type GaN confinement layer 304.

The first-type electrode 312 of the present invention is disposed on the lower surface of the substrate 300, and the second-type electrode 310 is disposed on the upper surface of the second-type GaN confinement layer 308.

In order to increase the conductivity inside the light emitting device 30 and to make the current uniformly distributed, the first type gan confinement layer 304 may be doped to reduce the resistance and increase the conductivity, for example: these materials are doped with group IIA elements (e.g., Mg) to form P-type conductivity, or group VIA elements (e.g., Si) to form n-type conductivity, and the boron phosphide buffer layer 302 can form P-type conductivity or n-type conductivity by controlling the multi-phosphorus structure (P-Rich) or the multi-boron structure (B-Rich). It should be noted that the substrate 300, the boron phosphide buffer layer 302 and the gan confinement layer 304 of the present invention all need to have the same conductivity type as the first-type electrode 312.

Of course, the second type GaN confinement layer 308 may also be doped to increase conductivity, such as: group IIA elements (e.g., Mg) are doped to make it p-type conductive, or group VIA elements (e.g., Si) are doped to make it n-type conductive. The second type GaN confinement layer 308 and the second type electrode 310 must have the same conductivity type. The conductivity types of the materials of the substrate 300, the boron phosphide buffer layer 302, the first-type gallium nitride confinement layer 306 and the first-type electrode 312 of the present invention are opposite to those of the second-type gallium nitride confinement layer 308 and the second-type electrode 310.

Preferably, the first type electrode 312 is of p-type conductivity, so the substrate 300, the boron phosphide buffer layer 302 and the first type gallium nitride confinement layer 306 are all of p-type conductivity, and the second type electrode 310 is of n-type conductivity and the second gallium nitride confinement layer 308 is of p-type conductivity.

In summary, when a proper voltage difference is formed between the first type electrode and the second type electrode, the active layer 306 on the P-N junction emits blue light with a wavelength of 450nm to 470 nm; then, the zinc telluride substrate or the zinc selenide substrate can emit yellow-green light with the wavelength of about 550nm after absorbing the blue light, and white light can be generated after the blue light and the yellow-green light in a proper proportion are mixed.

The invention abandons the traditional limitations of using III-V group and IV group as substrates, such as: sapphire, GaP, InP, gaas, etc., while group II-VI semiconductor elements are used as substrates for light emitting diodes, such as zinc telluride or zinc selenide; moreover, the phosphorus boride buffer layer utilized by the invention can ensure that the better lattice matching degree is achieved between the II-VI group zinc telluride or zinc selenide substrate and the subsequently formed III-V group gallium nitride binding layer, and a light-emitting element with good quality and long service life can be provided.

While the invention has been described with respect to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A white light emitting diode device comprising:

a zinc telluride (TeZn) substrate;

a Boron Phosphide (BP) buffer layer of a single crystal structure on the substrate;

a first type gallium nitride (GaN) confinement layer of cubic crystal structure on the boron phosphide buffer layer;

an active layer on the first type GaN confinement layer; and

a second type gallium nitride binding layer with cubic crystal structure on the active layer, wherein the second type gallium nitride binding layer and the first type gallium nitride binding layer have opposite conductive type, the active layer emits a light source with a first wavelength, the substrate absorbs the light source and then emits a light source with a second wavelength, and the light source with the first wavelength and the light source with the second wavelength are mixed to generate a light source with a third wavelength.

2. The white light emitting diode device of claim 1, further comprising:

a first type electrode located under the zinc telluride substrate; and

a second type electrode on the second type confinement layer, the second type electrode and the first type electrode having opposite conductivity types.

3. The white light emitting diode device of claim 1, wherein the substrate, the boron phosphide buffer layer, the first-type electrode and the first-type gallium nitride (GaN) confinement layer have the same conductivity type.

4. The white light emitting diode device of claim 3, wherein the substrate has n-type or p-type conductivity.

5. The white light emitting diode device of claim 4, wherein the boron phosphide buffer layer can form an n-or p-type conductivity by controlling a polyboron structure (B-Rich).

6. A white light emitting diode device comprising:

a zinc selenide (SeZn) substrate;

an active layer on the first type GaN confinement layer; and

7. The white light emitting diode device of claim 6, further comprising:

a first type electrode located under the substrate; and

8. The white light emitting diode device of claim 6, wherein the substrate, the boron phosphide buffer layer, the first-type electrode and the first-type gallium nitride (GaN) confinement layer have the same conductivity type.

9. The white light emitting diode device of claim 8, wherein the substrate has n-type or p-type conductivity.

10. The white light emitting diode device of claim 6, wherein the boron phosphide buffer layer can form an n-or p-type conductivity by controlling a polyboron structure (B-Rich).