JP2002050795A - InGaN LIGHT-EMITTING DIODE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an InGaN light-emitting diode which efficiently emits light in a red color band and moreover with spectrum distribution being relatively broad for emission. SOLUTION: The light-emitting layer of a light-emitting diode, which is represented by a general expression InxGa1-xN (0<x<1) is doped with other V-group atoms as an isoelectron trap formation element substituting for an N atom. As the V group atom substituting for N, P (phosphorus), As (arsenide), Sb (animony), and Bi (bismuth) are used. The substitution factor for the N atom is 1% or less, preferably with 0.5% or less. In short, the light-emitting layer of the light-emitting diode is represented by a general formula InxGa1-xN1-yXy (0<x<1; X=P, As, Ab, Bi; y=0<y<0.01/0<y<0.005). The substitution atom acts as an isoelectron trap. The force of the isoelectron trap attracting an electron or hole is essentially based on the difference in the number of orbits of an inner shell electron, and its affecting range is very short being about the Bohr radius. In this respect, it differs much from a long-range electrostatic potential formed by a donor and acceptor of a mixed crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a light emitting diode (LED).

[0002]

2. Description of the Related Art One of the features of a light emitting diode (LED) is that it has high monochromaticity (that is, the half width of a spectral peak is narrow). Utilizing this feature, red (R)
A full-color display device in which green (G) and blue (B) LED light emitters are arranged vertically and horizontally on a plane has already been widely used. In this case, the display color is arbitrarily controlled by the intensity ratio of each color of RGB.

However, when viewed as an illumination device, not as a display device, LEDs still have many problems. As described above, white light can be obtained by using a device in which RGB LED light emitters are arranged and appropriately setting the intensity ratio of each color of RGB. However, when viewed as a lighting device, a conventional lighting device can be used. Compared with a certain incandescent lamp or fluorescent lamp, there are problems such as (1) the device is large-scale, (2) each color of RGB must be controlled independently, and (3) "color rendering property" is poor.

[0004] Here, "color rendering" refers to the nature of the light source, ie, what color the object looks like when the object is illuminated by the light source. Considering the importance of color rendering in lighting equipment, CIE (Commission Internationale de
l'Eclairage, International Commission on Illumination) established a method for evaluating color rendering in 1964. According to this, a series of reference light sources that can be selected according to the color temperature of a light source to be evaluated is determined, and a color rendering index Ra is determined from a color shift when a specified test color is illuminated between the reference light source and the light source to be evaluated. It has become. The color rendering index Ra takes a value of 0 to 100. When the color rendering index Ra is 100, the light source to be evaluated matches the reference light source in how the color looks. As a reference light source, a color temperature of 500
When the temperature exceeds 0K, a perfect radiator is used. As the test colors, eight colors having a predetermined spectral reflectance are selected for general use, and the color rendering index calculated based on this is called an average color rendering index. In addition, seven colors are selected for special purposes, including the Japanese skin color. The color rendering index calculated in this way is called a special color rendering index. For more details, see "Lighting Engineering"
(Edited by the Institute of Electrical Engineers of Japan, published by Ohmsha, p.36).

[0005] The reason why the light of a perfect radiator is used as a reference in evaluating the color rendering properties is that natural light (sunlight) is close to the light of a perfect radiator. The light emitted by the perfect radiator includes light of each wavelength continuously. Since the tint of the object is determined by the light reflectance (spectral reflectance) for each wavelength of the object, light of each wavelength is continuously included in the spectral distribution of the illumination light (luminous body), and If the intensity distribution is close to that of a perfect radiator, the color appearance of the object will be close to that under natural light. However, even if the LED white light emitter composed of RGB emits white light as a whole by adjusting the intensity ratio of each color, its spectral distribution is not continuous, and R (red), G (green) ) And B (blue) are discontinuous with narrow peaks only at three wavelengths. Due to this discontinuity, the RGB-LED luminous body cannot have sufficient color rendering properties as a lighting device.

As a light source for white illumination using a single LED, a gallium nitride-based blue LED covered (or coated) with a YAG phosphor has been devised at present (see Japanese Patent Application Laid-Open No. 5-152609). ). This is a gallium nitride blue L
The YAG phosphor is photo-excited using blue light (wavelength 460 nm) from the InGaN active layer of the ED, and white light is obtained by mixing the yellow light, which is the fluorescence from the phosphor, and the blue light from the LED. .

[0007] Further, there has recently been proposed a device in which the upper surface of an LED is not covered with a phosphor but the substrate of the LED is a phosphor. For example, JP-A-2000-82845 discloses that an n-type ZnSe single crystal substrate doped with iodine, chlorine, bromine, aluminum, gallium or indium has ZnSe or ZnSe-ZnCdSe.
An active layer and a pn junction are formed by laminating epitaxial thin films of a mixed-crystal system, and the blue and blue-green light from the active layer and the light of the active layer emit SA (Self-Activated) emission (self-excitation light) )) To produce white light by synthesizing the generated yellow light. Also, Japanese Patent Application Laid-Open No. 2000-49374 discloses that Ga doped with oxygen or carbon or having nitrogen vacancies is disclosed.
An NGaN single crystal substrate is laminated with an InGaN-based mixed crystal epitaxial thin film to form an active layer and a pn junction.
GaN excited by blue-green light and blue and blue-green light
There is disclosed a technique of synthesizing yellow fluorescence from a fluorescence emission center of a substrate to obtain white light.

[0008]

A lamp having an average color rendering index Ra = 95 or more is used in places where high color rendering properties are required, such as art museums and printing factories. When medical lighting is considered, it is considered that the height of the special color rendering index including red and skin color is important as well as the height of the average color rendering index Ra.

As described above, white light obtained from a gallium nitride blue LED coated with a YAG phosphor has a wavelength of 460 nm.
Since it is a mixture of blue light of m and yellow fluorescence of the YAG phosphor, its color temperature is high and spectral components in the blue-green and red regions are weak as described later. In general terms, the light is cold white and warm. Therefore, it is considered that the color rendering index of the white light, especially the special color rendering index, is low.

On the other hand, JP-A-2000-82845 and JP-A-2000-4
The light emitting device described in Japanese Patent No. 9374 also has a chromaticity diagram
As disclosed in FIGS. 11 and 17 in JP-A-82845, and FIG. 9 in JP-A-2000-49374, the white component is expressed as a mixed color of blue + yellow or blue-green + orange. Is considered to be insufficient.

In any of the above cases, in order to cover these disadvantages and obtain a white light source having high color rendering properties,
It is necessary to introduce a luminescent center having a relatively broad luminescent band in the red region. At this time, it is better to form a red light emitting layer in the epitaxial light emitting layer of the LED, which is the light emitting side, than to introduce the light emitting center into the substrate, so that the color can be adjusted for each growth, and R (red) G (green) By independently controlling the driving of the B (blue) light-emitting layer, there is an advantage that an arbitrary color tone can be adjusted.

Therefore, Japanese Patent Application Laid-Open Nos.
No. 261108 discloses an LE in which R, G, and B layers are formed by changing the In composition of an InGaN active layer to perform light control.
D device is proposed. However, among these, layer B, G
Although practical levels of light emission intensity and efficiency are obtained for the layer, problems remain for the red light emitting layer (R layer). In other words, at present, red light emission itself can be obtained by increasing the In concentration (40% or more), but the luminous efficiency is poor (external quantum efficiency 1% or less), and it is red in the low current region. Even if it shines, there is a problem that if the current is increased, the color changes so rapidly that the light is emitted in yellow or yellow-green. It is expected that this problem will not be solved for the foreseeable future due to the intrinsic properties of the material.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and provides an LED which efficiently emits light in a red region and has a relatively broad spectrum distribution. The present invention provides a light-emitting device using the light-emitting device, which is easily dimmable.

[0014]

Means and effects for solving the problems The above problems are solved.
The light emitting diode according to the present invention made for
General In _xGa_1-xA source having a light emitting layer represented by N (0 <x <1)
The light emitting layer of the photodiode should be replaced with N atoms, etc.
Doped with other Group V atoms as electron trap-forming elements
It is characterized by the following.

The group V atoms to be substituted for N include P (phosphorus),
As (arsenic), Sb (antimony), and Bi (bismuth) can be used. The substitution rate for the N atom is 1%
Below, it is desirably 0.5% or less. That is, the light emitting layer of the light emitting diode according to the present invention has the general formula In _x Ga _1-x N _1-y X
_y (0 <x <1; X = P, As, Sb, Bi; 0 <y <0.01 / 0 <y <0.005).

Incidentally, for example, Japanese Patent Application Laid-Open No. 11-261170 and
JP 2000-4068 discloses Ga_1-xIn_xN_yAs _1-yAnd Ga_x2In_1-x2N
_z2P_1-z2Having an active layer represented by a similar general formula such as
Although a conductor light emitting device is described, these conventional active layers
In the above, N, P, and As form a mixed crystal.
That is, JP-A-11-261170 discloses that `` composition is 3% or more 9
Contains up to 30% nitrogen, up to 30% in
Ga1-xInxNyAs1-y mixed crystal semiconductor layer '' (paragraph 002).
6), and JP-A-2000-4068 discloses `` GaP
In order to increase the luminous efficiency of indirect transition semiconductors such as
Addition of nitrogen as impurity for so-electronic trap
It is widely known that the direct transition type
The required addition amount (nitrogen concentration) is 3 × 10¹⁹[cm^-3Below
is there. 3 × 10¹⁹[cm^-3If nitrogen is added above the concentration of
The crystal becomes a mixed crystal semiconductor containing nitrogen, conduction band, valence band
The effect of reducing the energy on the side
it can. In the present invention, this point is essentially different from the above-described conventional example.
Are different. It is described.

In the present invention, the N atoms in the In _x Ga _1-x N light emitting layer
It is replaced as an isoelectronic trap by a group V atom such as (phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth). The force that the isoelectronic trap attracts electrons or holes is essentially based on the difference in the number of orbits of the core electrons, so that its reach is very short, on the order of the Bohr radius. This point is significantly different from the long-range electrostatic potential created by donors and acceptors in mixed crystals ("Optophysical Handbook"
Shigeo Shioya, Yutaka Toyosawa, Takao Koda, and Motohiro Hiiragi, published by Asakura Shoten).

Assuming that the average attractive force received when a conduction electron or hole passes through the potential field of the isoelectronic trap is J and the average energy of the electron / hole in the conduction band is <E>, | J | ≧ At <E>, a bound state is formed. As can be seen, the impurity potential is large | J |
The larger the value is, the smaller the curvature of the bottom of the conduction band is, and the narrower the energy band width is, the more easily the bound state can be formed. The electrons / holes are extremely localized in the real space due to such a short-range attractive force, and conversely have a large spread in the k space (wave number / momentum space).

The atomic number is larger than N,
P, As, Sb, Bi with many isoelectronic configurations In _xGa_1-xIntroduce into N
Then, the electron trap formed there contains holes
It will be easier. In other words, isoelectronic traps in real space
In the vicinity, a short-range attractive potential for holes is generated.
And bound near the top of the valence band in wavenumber space
A condition is expected to form. Average of gravity | J |
The number of shell electrons is different (increased) from the parent N atom
Since it is large, J increases in the order of P, As, Sb, and Bi. Obedience
Therefore, the holes are strongly bound in that order.

According to calculations, P, As, and P are added to the In _x Ga _1-x N active layer.
By doping a different group V atom such as Sb or Bi by about 0.1 to 1%, a very strong broad emission band centering on red can be obtained. On the other hand, the In concentration x of the In _x Ga _1-x N mixed crystal is set to 0.1 to 0.1.
By changing in the range of 0.3 (10 to 30%), it is possible to change the peak of this emission band around the red region. Therefore, by combining these two methods,
It is possible to create a broad emission band from yellow to pink, red and near infrared.

[0021]

First Embodiment of the Present Invention As a first embodiment of the present invention, a red monochromatic LED will be described. As shown in FIG. 1, the LED 10 of this embodiment is made of sapphire (Al
₂ O ₃ ) In _x Ga _1-x N _1-y X _y (0 <x <1; X = P, As,
Sb, Bi; 0 <y <0.01 / preferably 0 <y <0.005) n-GaN negative electrode layer 13 and p-GaN positive electrode layer 16 with active layer (light emitting layer) 14 interposed
Are laminated. Between the active layer 14 and the p-GaN layer 16, to suppress the overflow of electrons from the n-GaN layer _{13, p-Al z Ga 1} -z N layer 15 (z is usually about 0.2)
Is often provided. The substrate 11 and the n-GaN negative electrode layer 1
3, a GaN buffer layer 12 for crystal matching is provided.

The red LED of the present embodiment emits light in a relatively wide wavelength range from red to infrared, and emits light stably and efficiently. Accordingly, the light source itself can be used stably as a red (R) light source, and a white light source having high color rendering properties can be obtained by combining with a light emitting device of another color (green (G) and blue (B)). become able to.

[0023]

[Second Embodiment of the Present Invention] As a second embodiment of the present invention, such a white light emitting LED will be described. As shown in FIG. 2, the configuration of the n-GaN negative electrode layer 23 and the p-GaN positive electrode layer 2
6 (or overflow suppressing _{p-Al z Ga 1-z} N layer 15) respectively emitting layer 24 R, G, the three primary colors of B between
a, 24b, and 24c are provided. Here are those R layer 24a is according to the present invention, similarly to the first _{embodiment, In x Ga 1-x N} 1-y X y (0 <x <1; X = P, As, Sb, Bi ; 0 <y <
0.01 / preferably 0 <y <0.005). The G layer 24b is In _x1 Ga _1-x1 N (x1 = 0.25 to 0.35), and the B layer 24c is In _x2 Ga _1-x2 N (x2 = about 0.1 to 0.2).
And

As a result, a white light source having a rich red component and high color rendering properties can be obtained as compared with a conventional white light source of this type.

The LED 20 of the present embodiment is not limited to a simple white light source, but may be a light source of any color. That is, each of the R, G, and B layers 24a, 24b, 24
By setting the emission intensity of c appropriately, the R color (a), the G color (b), and the B color (c) as shown by the dotted line in FIG.
It is possible to emit an arbitrary color in a triangle having the three colors as vertices. In this way, in order to balance the emission colors from the respective layers and provide desired color coordinates, color temperature, and color rendering properties, the thickness of each of the purple to yellow emission layers is adjusted, and the number of layers of each color is simply reduced. It is also effective to use a plurality as appropriate instead of the same.

In order to obtain higher color rendering properties, the number of the light emitting layers 34A to 34E can be increased as shown in FIG. In this case, the purple-yellow red regions 34E-34B are In: Ga
A light emitting layer was formed by adjusting the mixed crystal ratio x (E: In _x1 Ga _1-x1 N;
D: In _x2 Ga _1-x2 N; C: In _x3 Ga _1-x3 N; B: In _x4 Ga _1-x4 N), In: Ga
In the red region, which is difficult only by adjusting the mixed crystal ratio, the light emitting layer 34A is formed by the method according to the present invention (A: In _x5 Ga _1-x5 N _1-y).
X _y ). As a result, as shown in FIG. 5, the LED 30 emits light almost uniformly over the entire range of the visible light region, and by appropriately adjusting the light emission ratio in advance, as shown by the dashed line in FIG. In addition, light emission with higher color rendering properties can be achieved.

For the yellow light, instead of providing a light emitting layer (34D in FIG. 4) in the LED, a YAG fluorescent layer is covered on the entire LED 30 and a blue layer 34 of the LED 30 is provided.
Light from D (D: In _x2 Ga _1-x2 N, wavelength 460 nm) may be used as excitation light to generate yellow fluorescence.

[0028]

[Third Embodiment of the Invention] The luminescent color can be arbitrarily changed at the time of use. In order to obtain such dimming properties, for example, the structure shown in FIG.
Electrodes 69a, 69b, 69c, and 69d for separately injecting current into the respective layers 64a, 64b, and 64c are formed (Japanese Patent Laid-Open No. 7-183576). In this case, the configuration according to the present invention is adopted for the R layer 64a. In this LED 60, each layer 64
The emission color can be arbitrarily controlled by adjusting the amount of current supplied to a, 64b, and 64c.

[Brief description of the drawings]

FIG. 1 shows a red light emitting LE according to a first embodiment of the present invention.
D is a layer configuration diagram.

FIG. 2 is a layer configuration diagram of a white (or arbitrary color) light emitting LED according to a second embodiment of the present invention.

FIG. 3 is a chromaticity diagram showing an effect of the LED according to the second embodiment of the present invention.

FIG. 4 shows a high color rendering LE, which is a modification of the second embodiment.
D is a layer configuration diagram.

FIG. 5 is an emission spectrum diagram of the high color rendering LED of FIG. 4;

FIG. 6 shows a dimming LED according to a third embodiment of the present invention.
FIG.

[Explanation of symbols]

10, 20, 30, 60 ... LED 11, 21, 31, 61 ... substrate 12, 22, 32 ... buffer layer 13, 23, 33, 63, 66 ... negative electrode layer 14, 24a to 24c, 34A to 34E, 64a to 64
c: Active layer (light emitting layer) 15, 25, 35 ... Overflow suppression layer 16, 26, 36, 65, 67 ... Positive electrode layer 17, 18, 27, 28, 37, 38, 69a to 69d
…electrode

Claims (4)

[Claims] 1. A light-emitting diode having a light-emitting layer represented by the general formula In _x Ga ₁ -xN (0 <x <1), wherein another light-emitting layer serving as an isoelectronic trap-forming element to be replaced with N atoms is provided. A light emitting diode doped with group V atoms. 2. The light emitting diode according to claim 1, wherein the group V atom substituted for N is any one of P (phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth). 3. The light emitting diode according to claim 1, wherein the substitution ratio of group V atoms to N atoms is 1% or less. 4. The substitution rate of group V atoms to N atoms is 0.5%.
The light emitting diode according to claim 1, wherein: