JP2976951B2 - Display device with nitride semiconductor light emitting diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Field of the Invention The present invention relates to a display device provided with a nitride semiconductor light emitting diode, in particular, a nitride semiconductor _{(In a Al b Ga 1-} ab N, 0 ≦ a, 0 ≦ b, a + b
≦ 1) The present invention relates to a display device provided with a nitride semiconductor light emitting diode having a semiconductor multilayer structure constituted by ≦ 1).

[0002]

BACKGROUND ART nitride semiconductor _{(In a Al b Ga 1-} ab
N, 0 ≦ a, 0 ≦ b, a + b ≦ 1) are expected as materials for light-emitting elements such as LEDs and LDs that emit ultraviolet to red light. In fact, the present applicant, using this semiconductor material, announced a blue LED with a luminous intensity of 1 cd in November 1993, a blue-green LED with a luminance of 2 cd in April 1994, and a luminous intensity in October 1994. Released 2cd blue LED. These LEDs have all been commercialized and are currently being put to practical use in displays, signals, and the like.

A light emitting chip of such a blue or blue-green LED basically has an n-type GaN on a sapphire substrate.
An n-type contact layer composed of n-type AlGaN, an n-type clad layer composed of n-type AlGaN, and an active layer composed of n-type InGaN.
a p-type cladding layer made of p-type AlGaN and a p-type GaN
And a p-type contact layer made of the same. A buffer layer made of GaN, AlGaN or AlN is formed between the sapphire substrate 11 and the n-type contact layer. N-type InG forming active layer
The aN is doped with a donor impurity such as Si or Ge and / or an acceptor impurity such as Zn or Mg. The emission wavelength of this LED element is determined by the InG of the active layer.
By changing the In content of aN or changing the type of impurities to be doped into the active layer, it is possible to change from the ultraviolet region to red.

[0004]

However, the aforementioned L
The ED element has a problem that the emission output is greatly reduced as the emission wavelength becomes longer. FIG. 4 is a diagram showing the relationship between the peak emission wavelength and the emission output of a conventional LED element.
In this LED, Zn and Si are doped into InGaN of the active layer, and light is emitted through the level of Zn, thereby reducing the emission wavelength by about 0.5 eV in emission energy from the interband emission of InGaN, thereby reducing the emission wavelength. It is long. As shown in FIG. 4, the conventional LED is 3 m at 450 nm.
While the output near W is shown, the output greatly decreases as the emission peak shifts to a longer wavelength, and at 550 nm, the output drops to 0.1 mW or less. For example,
The active layer in an LED emitting at 450 nm is In _0.05 Ga.
The active layer in an LED emitting at _0.95 N and emitting 500 nm is In _0.18 Ga _0.82 N and an LED emitting at 550 nm
The active layer of In is In _0.25 Ga _0.75 N, and each active layer is doped with Zn. Thus, the InGaN active layer doped with impurities, more specifically, IGaN
_{n x Ga 1-x N (} 0 ≦ x <1) active layer, crystallinity and the In content increases the emission output deteriorates decreases significantly.
For this reason, at present, a high-output LED can only be produced with an actually usable In content, that is, an x value of about 0.15 or less, and only a blue LED having a high output has been realized. In addition, since light is emitted by doping Zn, the half width is as wide as about 70 nm, and the blue color purity is inferior.

By the way, at present, when a high-output blue LED is put into practical use, only a green LED has a different color tone and light emission output from other L LEDs.
Inferior to ED. For example, when realizing a full-color LED display with one red LED, one green LED and one blue LED, the green LED must have the highest luminous intensity. However, the luminous intensity of the green LED is still low, and the actual situation is that it cannot be balanced at all with the blue LED and the red LED.

[0006] Since the nitride semiconductor has a band gap energy of 1.95 eV to 6.0 eV, it is theoretically a material that emits light in a wide band from red to ultraviolet. If the output in the long wavelength region of the nitride semiconductor light emitting device can be improved, there is a possibility that light emission at all wavelengths in the visible region can be realized by the nitride semiconductor instead of the conventional GaAs and AlInGaP-based materials.

[0007] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a display device having at least a high-luminance, high-output blue and green light-emitting nitride semiconductor LED. It is in.

[0008]

In the conventional LED, the active layer is formed of InGaN doped with impurities.
When the In composition ratio of InGaN is increased as described above, I
The emission wavelength can be shifted to the longer wavelength side by the nGaN interband emission. However, since the nitride semiconductor tends to deteriorate in crystallinity as the molar ratio of In increases, it is estimated that the light emission output decreases. Therefore, when shifting the emission wavelength of the light emitting element to the longer wavelength side, the present inventors apply stress to the active layer due to the difference in thermal expansion coefficient between the cladding layer and the active layer in the nitride semiconductor structure having the double hetero structure. As a result, it has been newly found that the emission wavelength can be shifted to the longer wavelength side and a light-emitting element having a high emission output can be realized. The present invention is based on this finding.

That is, according to the present invention, at least one
One of the blue light emitting diode, at least one green light-emitting diode, a display device comprising at least one red light emitting diode, the blue light-emitting diodes, and green light emitting diodes, each In _x Ga _1-x N
A first n-type nitride semiconductor layer comprising (0 ≦ x <1);
An active layer having a single quantum well structure or a multiple quantum well structure having a well layer made of a nitride semiconductor containing indium and gallium in contact with one surface of the first n-type nitride semiconductor layer; In contact with the active layer, Al _y Ga _1-y
A light-emitting element having a first p-type nitride semiconductor layer made of N (0 <y <1) and emitting light having energy lower than the band gap energy of the nitride semiconductor constituting the active layer. A display device is provided.

In the present invention, each of the first n-type cladding layers of the blue light emitting nitride semiconductor light emitting diode and the green light emitting nitride semiconductor light emitting diode is formed of an n type In _x G
a _1-x N (0 ≦ x <1).

In the present invention, each of the first p-type cladding layers of the blue light emitting nitride semiconductor light emitting diode and the green light emitting nitride semiconductor light emitting diode has a p-type
It is preferable to be formed of l _y Ga _1-y N (0 ≦ y ≦ 1).

In the present invention, a second n-type nitride semiconductor light emitting diode is formed in contact with each of the first n-type cladding layers of the blue light emitting nitride semiconductor light emitting diode and the green light emitting nitride semiconductor light emitting diode. A mold cladding layer can be provided. Further, the second n-type cladding layer can be formed of n-type Al _a Ga _1-a N (0 ≦ a ≦ 1).

Further, in the present invention, the second p-type nitride semiconductor light-emitting diode made of a p-type nitride semiconductor is in contact with the first p-type clad layer of each of the blue light-emitting nitride semiconductor light-emitting diode and the green light-emitting nitride semiconductor light-emitting diode. A cladding layer can be provided. The second p-type cladding layer may be formed of p-type _{Al b Ga 1-b N (} 0 ≦ b ≦ 1) is preferred.

Further, in the present invention, the respective active layers of the blue light emitting nitride semiconductor light emitting diode and the green light emitting nitride semiconductor light emitting diode are non-doped, or are doped with a donor impurity and / or an acceptor impurity. Is what it is.

In the present invention, the total thickness of the first n-type cladding layer and the active layer of each of the blue light emitting nitride semiconductor light emitting diode and the green light emitting nitride semiconductor light emitting diode may be 300 Å or more. preferable.

In the present invention, preferably, each of the active layers of the blue light emitting nitride semiconductor light emitting diode and the green light emitting nitride semiconductor light emitting diode has a well layer having a thickness of 100 Å or less, more preferably 100 Å or less. Have.

Furthermore, in the present invention, each active layer of the blue light emitting nitride semiconductor light emitting diode and the green light emitting nitride semiconductor light emitting diode is formed of In _x Ga _{1 -x}
A well layer made of N (0 <x <1), or a well layer made of In _x Ga ₁ -xN (0 <x <1);
It can have a multiple quantum well structure composed of Inx'Ga1 _- x'N (0 <x '<1, where x' is different from x) or a combination with a barrier layer made of GaN.

In a preferred embodiment of the present invention, the blue and green light emitting diodes are made of a nitride semiconductor containing indium and gallium, respectively, and the first and second light emitting diodes are made of first and second light emitting diodes.
And an n-type nitride semiconductor layer made of InxGa1-xN (0≤x <1) in contact with a first surface of the active layer, and a second active layer A p-type nitride semiconductor layer made of a nitride semiconductor containing aluminum in contact with the surface, the active layer having a quantum well structure, and light having an energy lower than the original bandgap energy of the nitride semiconductor forming the active layer. , And is constituted by a nitride semiconductor light emitting element. In another preferred embodiment of the present invention, at least the blue and green light-emitting diodes have an n-type nitride semiconductor layer made of GaN and a p-type contact layer made of GaN, respectively. An active layer made of a nitride semiconductor containing indium and gallium between the contact layer and a p-type nitride semiconductor made of a nitride semiconductor containing aluminum in contact with the active layer on the p-type contact layer side; The active layer has a quantum well structure, and is constituted by a nitride semiconductor light emitting element which emits light having an energy lower than the original band gap energy of the nitride semiconductor constituting the active layer.

In still another preferred embodiment of the present invention, at least the blue and green light emitting diodes each include a well layer made of a nitride semiconductor containing indium and gallium, and an active layer having first and second surfaces. And a p-layer made of GaN on the second surface side of the active layer.
An active layer comprising an n-type nitride semiconductor layer having a bandgap energy larger than that of a nitride semiconductor containing indium and gallium, which is in contact with the first surface of the active layer and forms the active layer. A p-type nitride semiconductor layer made of a nitride semiconductor containing aluminum in contact with the second surface of the active layer between the active layer and the p-type contact layer, wherein the active layer has a single quantum well structure or a multiple quantum well structure. Structure and
The active layer is constituted by a nitride semiconductor light emitting device that emits light having an energy lower than the original band gap energy of the nitride semiconductor constituting the active layer.

By the way, when the band gap energy (1.96 eV) of InN is expressed by Eg ₁ and the band gap energy (3.40 eV) of GaN is expressed by Eg ₂ ,
The original bandgap energy Eg of the nitride semiconductor In _x Ga ₁ -xN is expressed by the following formula: Eg = Eg ₁ · x + Eg ₂ · (1-x) −x
It can be calculated by (1-x). The original emission wavelength λ of the active layer corresponds to λ = 1240 / Eg.

The single quantum well structure refers to a structure having a single well layer. That is, the active layer having a single quantum well structure is composed of only a single well layer. The multiple quantum well structure refers to a multilayer structure in which well layers and barrier layers are alternately stacked.

[0022]

Although the present invention is not limited by theory, by providing a difference in the coefficient of thermal expansion between the active layer having the quantum well structure and the cladding layer in contact with the active layer, the interface between the active layer and the cladding layer is provided. It is considered that a stress is applied, thereby emitting light having an energy lower than the band gap energy of the nitride semiconductor (nitride semiconductor containing indium and gallium) constituting the active layer (well layer). is there. That is, in the present invention, each nitride semiconductor LED has a different thermal expansion coefficient (for example, a higher thermal expansion coefficient than those of the first n-type cladding layer and the first p-type cladding layer). It is considered that stress is generated at the interface between the cladding layer and the active layer by forming the active layer. In addition, since the active layer has a single quantum well structure or a multiple quantum well structure, the band gap energy of the active layer is reduced, and the emission wavelength of the active layer is increased. Also, by reducing the well layer and barrier layer of the active layer to the critical thickness,
Even InGaN having a large In composition ratio can be grown with good crystallinity.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention which is a light emitting diode display device including at least one blue light emitting semiconductor diode, at least one green light emitting semiconductor diode, and at least one red light emitting semiconductor diode will be described. First, the nitride semiconductor light emitting device of the present invention will be described.

FIG. 1 is a schematic sectional view showing an example of the structure of a nitride semiconductor light emitting device according to one embodiment of the present invention. FIG.
In the nitride semiconductor device shown in FIG. 1, a buffer layer 2, an n-type contact layer 3, a second n-type cladding layer 4, a first n-type cladding layer 5, an active layer 6, a first p-type It has a structure in which a clad layer 7, a second p-type clad layer 8, and a p-type contact layer 9 are sequentially stacked.

The active layer 6 is formed of a nitride semiconductor containing In and has a single quantum well structure or a multiple quantum well structure. The active layer 6 containing In is made of another AlGaN, G
The emission wavelength can be changed by softening the thickness of the well layer having a single quantum well structure, for example, which is softer than a nitride semiconductor such as aN. Active layer 6 of quantum well structure
May be either n-type or p-type. However, it is particularly preferable to use non-doped (doped with no impurities), since the half-width of the emission wavelength is narrowed by inter-band emission and emission with good color purity can be obtained. Particularly, the composition of the well layer of the active layer 6 is In _z G
It is more preferable that a _{1 -z N} (0 <z <1), since light can be emitted from ultraviolet to red in the inter-band emission. On the other hand, in the case of a multiple quantum well structure, the barrier layer may not be formed of InGaN but may be formed of GaN.

The first n-type cladding layer 5 is formed of a nitride semiconductor having a band gap energy larger than that of the active layer 6, and is particularly preferably n-type In _x Ga ₁ -xN (0
.Ltoreq.x <1). InGaN or GaN
Since the n-type first cladding layer 5 is made of a softer crystal than the nitride semiconductor containing Al, the first cladding layer 5 acts like a buffer layer. That is, since the first cladding layer 5 functions as a buffer layer, no crack is formed in the active layer 6 even when the active layer 6 has a quantum well structure, and the first cladding layer 5 is formed outside the first cladding layers 5 and 7. It is possible to prevent cracks from entering the second n-type clad layer 4 and the second p-type clad layer 8 to be formed.

The first p-type cladding layer 7 is formed of a p-type nitride semiconductor having a band gap energy larger than that of the nitride semiconductor constituting the active layer 6, but is preferably p-type.
It is formed of the type Al _y Ga _1-y N (0 ≦ y ≦ 1). Among them, nitride semiconductors containing Al such as p-type AlGaN are:
Light emission output is improved by being formed in contact with an active layer having a multiple quantum well structure or a single quantum well structure.

Further, the first n-type clad layer 5 and the first p-type
Either of the mold cladding layers 7 can be omitted. When the first n-type cladding layer 5 is omitted, the second n-type cladding layer 4 becomes the first n-type cladding layer 5, and
When the p-type cladding layer 7 is omitted, the second p-type cladding layer becomes the first p-type cladding layer 5. However, it is preferable that the first n-type clad layer 5 made of n-type GaN or n-type InGaN is formed in contact with the active layer.

The device according to the present invention can include a second n-type cladding layer 4 made of an n-type nitride semiconductor in contact with the first n-type cladding layer 5. The second n-type cladding layer 4 is preferably formed of Al _a Ga _1-a N (0 ≦ a ≦ 1). However, when the first n-type cladding layer 5 is In
When formed of GaN, the second n-type cladding layer 4 can be formed of GaN or AlGaN. Since the nitride semiconductor containing Al has a small thermal expansion coefficient and the crystal itself is hard, the second n-type cladding layer 4 is
When the active layer is formed in contact with the n-type cladding layer 5, the emission wavelength can be further shifted to the longer wavelength side in the active layer. However, when the second n-type clad layer 4 containing Al is formed in contact with the active layer 6, a first p-type clad layer also acting as a buffer layer is provided on the opposite main surface of the active layer. 7 is desirably formed of InGaN, GaN, or the like.

The second n-type cladding layer 4 is made of an n-type Al _a G
It is desirable that the film be formed in a thickness of 50 Å to 1 μm by a _1−a N (0 ≦ a <1). Also,
It is desirable that the a value in Al _a Ga _1-a N is 0.6 or less, more preferably 0.4 or less. Because
As described above, the second n-type cladding layer 5
Although the n-type cladding layer 4 is hardly cracked, the crystal of AlGaN is still hard and the a value is 0.6.
This is because if it is larger, cracks tend to occur in the AlGaN layer. In general, the emission wavelength of the active layer 6 tends to become longer as the mixed crystal ratio (a value) of Al increases.

In the device of the present invention, a second p-type cladding layer 8 made of a p-type nitride semiconductor may be provided in contact with the first p-type cladding layer 7. Second p-type cladding layer 8 is preferably formed by _{Al b Ga 1-b N (} 0 ≦ b ≦ 1). However, when the first p-type cladding layer 7 is formed of AlGaN, the second p-type cladding layer 8 can be formed of GaN as a contact layer. When the second p-type cladding layer 8 containing Al is formed in contact with the active layer 6, the main surface (n-layer side) on the opposite side of the active layer 6 is formed of Ga which can also act as a buffer layer.
It is desirable that the first n-type clad layer 5 of N, InGaN or the like be formed in contact with the first n-type clad layer 5.

The operation of the second p-type cladding layer 8 is the same as the operation of the second n-type cladding layer 4,
The mold cladding layer 8 is preferably formed with a thickness of 50 Å to 1 μm. Further, the b value in Al _b Ga ₁ -bN constituting the second p-type cladding layer 8 is desirably 0.6 or less, more preferably 0.4 or less, and generally, the mixed crystal ratio of Al (b As the value (value) increases, the emission wavelength of the active layer tends to become longer.

By using the nitride semiconductor layer or GaN layer containing Al as the second n-type cladding layer 4 and the second p-type cladding layer 8, the active layer 6 containing In and the first Since the band offset with the n-type and p-type cladding layers 5 and 7 can be increased, the luminous efficiency can be increased, and the emission wavelength of the active layer can be shifted to a longer wavelength.

Here, a preferred combination of the active layer and the cladding layer will be described. First, the combination of the active layer 6 and the first cladding layers 5 and 7 is such that the first n-type cladding layer is formed of In _x
Ga _1-x N (0 ≦ x <1), and the active layer is made of In _z G
a _1-z N (0 <z <1)
Is formed of Al _y Ga _1-y N (0 <y <1). However, it goes without saying that in these combinations, the condition of x <z is satisfied from the relation of band gap energy. The active layer 6 has a well layer having a thickness of 100 Å or less in a single quantum well structure, a well layer having a thickness of 100 Å or less in a multiple quantum well structure, and a barrier layer having a thickness of 150 Å or less in a multiple quantum well structure. It is formed to a thickness. In any active layer having a quantum well structure, n-type or non-doped is most preferable because light emission having a small half width due to interband light emission can be obtained.

Next, the most preferable combination is that the second n-type cladding layer 4 is formed of Al _a Ga _1-a N (0 ≦ a ≦ 1), and the first n-type cladding layer 5 is formed of Inx Ga 1−. x N
(0 ≦ x <1), and the active layer 6 is made of In _z Ga _{1 -zN.}
(0 <z <1), the first p-type cladding layer 7 is formed of Al _y Ga _1-y N (0 ≦ y <1), and the second p-type cladding layer 8 is formed of Al _b Ga _1-b N (0 ≦
b ≦ 1). In the case of this combination, the first n-type clad layer 5 and the first p-type clad layer 7
Either one or both may be omitted. When omitted, as described above, the second n-type cladding layer 4 or the second p-type cladding layer 8 respectively acts as the first cladding layer. According to this combination, if sufficient stress cannot be obtained in the active layer 6 only by the first cladding layers 5 and 7 and the active layer 6, the first cladding layers 5 and 7 further include Al outside the first cladding layers 5 and 7. It is considered that the difference between the thermal expansion coefficients of the second cladding layers 4 and 8 and the active layer 6 can be increased by forming the second cladding layer. Therefore,
Since the active layer 6 has a multiple quantum well structure of a well layer and a barrier layer having a small thickness or a single quantum well structure of only a well layer, the band gap of the active layer is reduced due to stress acting on the interface. The emission wavelength can be shifted to the longer wavelength side.

Further, in a preferred embodiment of the device of the present invention, an n-type nitride semiconductor containing indium or an n-type Ga
When forming the first n-type cladding layer 5 with N, the total thickness of the first n-type cladding layer and the active layer 6 is set to 3
Adjust to more than 00 angstrom. This total film thickness is 3
GaN,
InGaN acts as a buffer layer to make the active layer a preferable quantum well structure, and it is possible to prevent cracks from entering the first p-type cladding layer 7 and the second p-type cladding layer 8.

In the present invention, the In _x Ga
_{1-x N, InA In y} Ga 1-y N, and In _z Ga _1-z N, obtained by replacing a part of Ga or In in trace amounts of Al in a range that does not change the effect of the InGaN in the formula
lGaN is also included in the above formula. Similarly, Al
_a Ga _1-a N, InAlGa substituted with Al _b Ga _1-b also in N, traces of some of the Ga or Al in a range that does not change the effect of AlGaN in their formula In
N is also included in the above formula.

Further, the active layer 6 may be doped with a donor impurity and / or an acceptor impurity. If the crystallinity of the active layer doped with the impurity is the same as that of the non-doped, doping with the donor impurity can further increase the interband emission intensity as compared with the non-doped one. When the acceptor impurity is doped, the peak wavelength can be shifted to a lower energy side by about 0.5 eV than the peak wavelength of the interband emission, but the half width becomes wider. When both the acceptor impurity and the donor impurity are doped, the emission intensity can be further increased as compared with the emission intensity of the active layer doped with only the acceptor impurity. In particular, when an active layer doped with an acceptor impurity is formed, the conductivity type of the active layer is preferably n-type by doping also a donor impurity such as Si. However, in the present invention, it is ideal that the active layer emits strong light by inter-band light emission.
It is most preferred to form When the active layer is doped with impurities, the crystallinity tends to be worse than that of the non-doped one. In addition, a light emitting element using non-doped InGaN as an active layer has a Vf higher than that of an impurity doped light emitting element.
(Forward voltage) can be reduced.

The active layer having the multiple quantum well structure is made of, for example, In.
This is a thin film laminated structure in which respective well layers and barrier layers are laminated in a combination of GaN / GaN, InGaN / InGaN (different in composition), and the like. When the active layer has a multiple quantum well structure, the light emission output is improved as compared with the active layer having a single quantum well structure. In the active layer of the multiple quantum well structure, the thickness of the well layer is set to several angstroms to several tens of angstroms, the thickness of the barrier layer is also set to several angstroms to several tens angstroms, and the well layer and the barrier layer are stacked.
It has a multiple quantum well structure. In this case, the well layer preferably has a thickness of 100 Å or less, more preferably 70 Å or less. This range of the thickness of the well layer is the same for an active layer having a single quantum well structure (constituted by a single well layer). On the other hand, the thickness of the barrier layer in the multiple quantum well structure is desirably 150 Å or less, and more desirably, 100 Å or less. Further, a multiple quantum well structure may be formed by doping a well layer and a barrier layer with donor and acceptor impurities. By laminating such thin layers in multiple layers, strain in the crystal can be elastically absorbed by the active layer.

As shown in FIG. 1, an n-type contact layer 3 made of n-type GaN is formed as a layer for forming an electrode in contact with the first n-type cladding layer 5 or the second n-type cladding layer 4. Preferably, a p-type contact layer 9 made of p-type GaN is formed as a layer for forming an electrode in contact with the first p-type cladding layer 7 or the second p-type cladding layer 8. However, this contact layer 3,
9 is not required to be formed as long as the second n-type cladding layer 4 and the second p-type cladding layer 8 are formed of GaN, and the second cladding layers 4 and 8 are used as contact layers. Is also possible. The reason why the contact layers 3 and 9 made of GaN are formed is that a mixed crystal of three or more elements such as the first clad layer and the second clad layer cannot obtain an ohmic contact with the electrode. In particular, it is difficult to obtain an ohmic contact with an electrode of a nitride semiconductor containing Al as in the second cladding layer. Therefore, a light-emitting element with low Vf and high luminous efficiency can be realized by forming GaN, from which an ohmic contact is most easily obtained, in a contact layer with an electrode.

FIG. 2 shows the thickness of an active layer having a single quantum well structure,
That is, it is a diagram showing the relationship between the thickness of the well layer and the emission peak wavelength of the light emitting element. In FIG. 2, a line α indicates a light emitting element whose active layer is made of non-doped In _0.05 Ga _0.95 N, and a line β indicates a light emitting element whose active layer is made of non-doped In _0.3 Ga _0.7 N. In both cases, the structure of the light emitting element has a double clad structure in which a second clad layer, a first n-type clad layer, an active layer, a first p-type clad layer, and a second p-type clad layer are sequentially stacked. It is a terrorist structure. The second n-type cladding layer is 0.1 μm Si-doped n-type Al _0.3 Ga
_0.7 N, the first n-type cladding layer is made of 500 Å In _0.01 Ga _0.99 N, and the first p-type cladding layer is made of 20 Å Mg-doped p-type I-type.
The second p-type cladding layer is made of n _0.01 Ga _0.99 N, and has a double heterostructure of 0.1 μm Mg-doped p-type Al _0.3 Ga _0.7 N. FIG. 2 shows that the emission wavelength changes when the thickness of the active layer is changed.

The In _0.05 Ga _0.95 N active layer indicated by the line α is:
It emits ultraviolet light at around 380 nm at the original band gap energy, but it becomes 420 n
It can emit blue-violet light by increasing the wavelength to near m. The In _0.3 Ga _0.7 N active layer indicated by the line β emits blue-green light at around 480 nm in the original band gap energy, but pure green light at around 520 nm can be obtained by reducing the film thickness. By thus reducing the thickness of the active layer sandwiched between the first n-type cladding layer and the first p-type cladding layer, the emission wavelength can be made longer. In other words, an ordinary thick active layer only emits light corresponding to the bandgap energy of the active layer. However, in the active layer of the single quantum well structure of the present invention, by reducing the thickness of the well layer, As a result, the band gap energy is reduced, and light having a lower energy than the band gap energy of the original well layer, that is, light having a longer wavelength can be emitted. In addition, since it is non-doped, the crystallinity is better than that doped with impurities, so that the output becomes higher, and furthermore, emission between bands is excellent in color purity with a narrow half-value width.

Further, when the active layer is formed of the conventional thick InGaN, the crystallinity of the active layer is poor. For example, when the In composition ratio is 0.3 to 0.5, the crystallinity is poor, and the light emission output is very low. However, by forming a thin film, a large I
There is also an effect that it becomes possible to grow with good crystallinity even at an n composition ratio.

Accordingly, in the present invention, it is desirable that the well layer is formed to have a thickness of 100 Å or less, more preferably 70 Å or less. FIG. 2 shows an example of a light emitting device according to the present invention. The wavelength range in which the emission wavelength shifts to the longer wavelength side is a second cladding layer that applies stress to the active layer due to a difference in thermal expansion coefficient. It also depends on the composition of the first cladding layer,
Also, the preferred thickness of the active layer slightly changes depending on the composition.

In a nitride semiconductor, it is known that the thermal expansion coefficient of AlN is 4.2 × 10 ⁻⁶ / K and that of GaN is 5.59 × 10 ⁻⁶ / K. In
Regarding N, the thermal expansion coefficient is unknown because a perfect crystal has not been obtained. However, assuming that the thermal expansion coefficient of InN is the largest, the order of the thermal expansion coefficient is InN> G.
aN> AlN. On the other hand, looking at the growth temperature of the nitride semiconductor, the growth is usually performed at a high temperature of 500 ° C. in the MBE method and 900 ° C. or more in the MOVPE method. For example, MO
According to the VPE method, the temperature of AlGaN
If it is N, it is grown at 900 ° C. or more. Although the present invention is not limited by theory, after forming a device in which a predetermined active layer is sandwiched by a predetermined cladding layer at a high temperature, and then lowering the temperature to room temperature, a stress due to a difference in thermal expansion coefficient increases. It acts on the active layer, so that the band gap energy of the active layer is reduced, and the emission wavelength is considered to be longer.

In a preferred embodiment of the device of the present invention, an n-type nitride semiconductor containing indium or n-type GaN is provided as a first n-type cladding layer, and in contact with the first n-type cladding layer, indium is added. An active layer made of a nitride semiconductor containing a single quantum well or a multiple quantum well structure to emit light with energy lower than the band gap energy of the active layer. In this device, the total thickness of the first n-type cladding layer and the active layer is more preferably 300 Å or more. In still another embodiment, an active layer having a single quantum well structure or a multiple quantum well structure made of a nitride semiconductor containing indium is provided, and a p-type nitride semiconductor containing aluminum is contacted with the active layer to form a first p-type nitride semiconductor. By providing this active layer as a single quantum well structure or a multiple quantum well structure, the device emits light with energy lower than the band gap energy of the active layer.

As described above, in the conventional nitride semiconductor light emitting device, the active layer mainly composed of InGaN is formed of AlGa.
It has a structure sandwiched between two cladding layers mainly composed of N. In the conventional structure in which the AlGaN cladding layer is sandwiched between the InGaN active layer, as the thickness of the active layer is reduced, the IGaN
Cracks tend to occur in the nGaN active layer and the AlGaN cladding layer. For example, if the thickness of the active layer is less than 200 angstroms, many cracks will be formed, making it difficult to fabricate the device. This is because the cladding layer containing Al has a very hard property due to the crystal nature, and the lattice mismatch generated from the interface with the AlGaN cladding layer and the difference in the coefficient of thermal expansion occur only with the thin InGaN active layer. This indicates that the generated strain cannot be elastically reduced by the InGaN active layer. For this reason, in the past, cracks were formed in the cladding layer and the active layer, so that it was impossible to reduce the thickness of the active layer.

On the other hand, in the present invention, as shown in FIG.
As a layer in contact with the active layer 6 containing
The n-type cladding layer 5 is formed. The first n-type cladding layer 5 functions as a buffer layer between the active layer and the second n-type cladding layer 4 containing Al. That is, the first n
Semiconductor containing In which is the mold cladding layer 5 or G
Since aN has a soft property as a crystalline property, it has a function of absorbing a strain caused by a lattice constant irregularity and a difference in thermal expansion coefficient between the second cladding layer 4 containing Al and the active layer 6. Therefore, even if the active layer is thinned, the active layer 6 and the second n
It is presumed that cracks do not easily enter the mold cladding layer 4.
Since the strain is absorbed by the first cladding layer 5, the active layer tends to be elastically deformed by a stress particularly when the film thickness is 200 Å or less, so that the band gap energy becomes small and the emission wavelength becomes long. is there. Moreover, crystal defects in the active layer are reduced. Therefore, even when the thickness of the active layer is thin, the crystallinity of the active layer is improved, so that the light emission output increases. In order for the first n-type cladding layer 5 to function as a buffer layer in this manner, the total thickness of the active layer 6 and the first n-type cladding layer 5 which are soft crystalline layers is 300 Å or more. Is preferred.

When the first p-type cladding layer is formed of a nitride semiconductor containing aluminum, the output is improved.
This is presumed to be because AlGaN is more likely to become p-type than other nitride semiconductors, or has the effect of suppressing the decomposition of the active layer made of InGaN during the growth of the first p-type cladding layer. It is unknown.

In order to manufacture the light emitting device of the present invention composed of a nitride semiconductor, for example, MOVPE (metal organic chemical vapor deposition), MBE (molecular beam vapor deposition), HDVPE (hydride vapor phase epitaxy), etc. by a vapor deposition method, in on a substrate _{a Al b Ga 1-ab N} (0 ≦ a, 0 ≦ b, a + b
.Ltoreq.1) is obtained by laminating the conductive layers such as n-type and p-type into a double hetero structure. The substrate includes, for example, sapphire (including C-plane, A-plane, and R-plane), SiC (6
H-SiC, including 4H-SiC), spinel (MgA
l ₂ O ₄ , especially its (111) plane), ZnO, Si, G
aAs or another oxide single crystal substrate (such as NGO) can be used. The n-type nitride semiconductor can be obtained in a non-doped state, but can be obtained by introducing donor impurities such as Si, Ge, and S into the semiconductor layer during crystal growth. The p-type nitride semiconductor layer is made of Mg, Zn, Cd,
An acceptor impurity such as Ca, Be, or C is also introduced into the semiconductor layer during crystal growth, or 400 ° C. after the introduction.
The above is obtained by performing annealing.

The light emitting diode display device of the present invention comprises a blue light emitting diode, a green light emitting diode and a red light emitting diode, wherein at least the blue light emitting diode and the green light emitting diode each comprise the nitride semiconductor light emitting device of the present invention. Is what is done.

[0052]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on specific embodiments. The following examples illustrate a method for growing a nitride semiconductor layer by the MOVPE method. Embodiment 1 This embodiment will be described with reference to FIG.

Using TMG (trimethylgallium) and NH ₃ , a buffer layer 2 of GaN was grown at 500 ° C. on the C-plane of the sapphire substrate 1 set in a reaction vessel to a thickness of 500 Å.

Next, the temperature was increased to 1050 ° C., and TMG,
Using SiH ₄ gas in addition to NH ₃ , Si-doped n-type Ga
An n-type contact layer 3 made of N was grown to a thickness of 4 μm.

[0055] Subsequently TMA (trimethylaluminum) as a source gas was added to the second cladding layer 4 made of Si-doped n-type Al _0.3 Ga _0.7 N layer at same 1050 ° C. is grown to a thickness of 0.1 [mu] m.

Next, the temperature was lowered to 800 ° C., and TMG, T
MI (trimethyl indium), NH ₃ and SiH ₄
Was used to grow a first n-type cladding layer 5 made of Si-doped n-type In _0.01 Ga _0.99 N to a thickness of 500 Å.

Subsequently, an active layer 6 (single quantum well structure) made of non-doped In _0.05 Ga _0.95 N was grown at 800 ° C. to a thickness of 30 Å using TMG, TMI and NH ₃ .

Further, in addition to TMG, TMI and NH ₃ , Cp ₂ Mg (cyclopentadienyl magnesium) is newly added.
The first p-type cladding layer 7 made of Mg-doped p-type In _0.01 Ga _0.99 N was grown at 800 ° C. to a thickness of 500 Å.

Next, the temperature was raised to 1050 ° C., and TMG, T
MA, NH ₃ , Cp ₂ Mg, Mg-doped p-type Al
The second p-type cladding layer 8 made of _0.3 Ga _0.7 N is formed in a thickness of 0.
It was grown to a thickness of 1 μm.

Subsequently, at 1050 ° C., using TMG, NH ₃ and Cp ₂ Mg, the p-type
The mold contact layer 9 was grown to a thickness of 0.5 μm. After the above operation was completed, the temperature was lowered to room temperature, the wafer was taken out of the reaction vessel, and the wafer was annealed at 700 ° C. to further reduce the resistance of the p-type layer. Next, a mask having a predetermined shape was formed on the surface of the uppermost p-type contact layer 9, and etching was performed until the surface of the n-type contact layer 3 was exposed. After the etching, the surface of the n-type contact layer 3 has T
A negative electrode made of i and Al and a positive electrode made of Ni and Au were formed on the surface of the p-type contact layer 9. After the electrodes were formed, the wafer was separated into chips of 350 μm square, and LED devices having a directional characteristic of a half-value angle of 15 ° were formed according to a conventional method. This LED element has an If (forward current) of 20 mA and Vf3.
It exhibited blue light emission at 5 V and an emission peak wavelength of 410 nm, and the emission output was 5 mW. Further, the half width of the emission spectrum was 20 nm, and light emission with very good color purity was exhibited.

Example 2 An active layer was formed of In _0.05 Ga _0.95 N, and its thickness was 10
L in the same manner as in Example 1 except that Angstrom was used.
An ED element was manufactured. This LED element has an If 20 mA
Showed blue-violet light emission with a light emission peak wavelength of 425 nm, a very excellent light emission output of 5 mW, and a half-width of the light emission spectrum of 20 nm, showing blue light emission with good color purity.

Example 3 An LED element was manufactured in the same manner as in Example 1 except that the active layer 6 was formed of non-doped In _0.2 Ga _0.8 N. This LED element emits blue light with an emission peak wavelength of 465 nm at If 20 mA, has an extremely excellent emission output of 5 mW, and has a half-width of an emission spectrum of 25 nW.
m and blue light emission with good color purity were exhibited.

Example 4 Example 1 was repeated except that the first p-type cladding layer 7 was not formed.
In the same manner as in the above, an LED element was produced. This LED element has a Vf of 3.5 V at If 20 mA and an emission peak wavelength of 42.
It emitted blue light of 5 nm, and the light emission output was 7 mW. Further, the half width of the emission spectrum was 20 nm. In this light emitting device, the peak wavelength became longer and the light emission output increased.

Embodiment 5 As the first n-type cladding layer 5, Si-doped n-type In _0.01
Ga _0.99 N is grown to a thickness of 300 Å, and then non-doped In _0.3 Ga _0.7 N
Is grown to a thickness of 10 Å, and then Mg-doped In _0.01 Ga _0.99 N is formed as the first p-type cladding layer 7.
An LED element was manufactured in the same manner as in Example 1 except that the layer was grown to a thickness of 300 Å. This LE
The D element emitted green light having a Vf of 3.5 V, an emission peak wavelength of 500 nm, and a half-value width of 40 nm at If 20 mA, and exhibited an extremely excellent light emission output of 3 mW.

Embodiment 6 In the method of Embodiment 1, after the n-type contact layer 3 is grown, the In _{0.4 having a} film thickness of 70 Å is directly applied.
An active layer 6 having a single quantum well structure made of Ga _0.6 N was grown. In this device, the n-type contact layer 3 functions as a first n-type clad layer. Next, a second p-type cladding layer 8 was grown on the active layer 6, and finally a p-type contact layer 9 was grown. Thereafter, the first embodiment
A light-emitting element was manufactured in the same manner as described above. This LED element
At 20 mA If, the device emitted green light having a Vf of 3.5 V, an emission peak wavelength of 525 nm, and a half-value width of 40 nm, and exhibited extremely excellent emission output of 4 mW. Example 7 Si-doped n-type GaN was grown to a thickness of 300 Å as the first n-type cladding layer 5, and non-doped In _0.3 Ga _0.7 N was grown to a thickness of 20 Å as the active layer 6. In the same manner as in Example 1 except that an Mg-doped p-type GaN layer was grown to a thickness of 300 Å as the first p-type cladding layer 7,
An ED element was manufactured. This LED element has an If 20 mA
, Vf 3.5 V, emission peak wavelength 515 nm,
The device exhibited green light emission with a half value width of 40 nm, and the light emission output was 3 mW.

Example 8 The active layer 6 was formed using DEZ (diethyl zinc) as an acceptor impurity source and SiH ₄ as a donor impurity source.
N-type In _0.05 Ga _0.95 N doped with Si and Zn as
An LED element was manufactured in the same manner as in Example 1 except that the layer was formed with a thickness of 50 Å. This LED element has a Vf
3.5V, emission peak wavelength 480nm, half width 80nm
And emitted light of 2 mW.

Example 9 An LED element was manufactured in the same manner as in Example 1 except that the active layer was formed of non-doped In _0.8 Ga _0.2 N. This L
The ED exhibited red light emission with a Vf of 3.5 V and a light emission peak wavelength of 650 nm at If 20 mA, and a light emission output of 0.7 mW.

Embodiment 10 Si-doped n-type In _0.01 as the first n-type cladding layer 5
Ga _0.99 N was formed to a thickness of 500 Å. Next, in order to form the active layer 6, non-doped In _0.15 Ga _0.85 N is formed to a thickness of 10 Å as a well layer, and a non-doped In _0.05 layer is formed thereon as a barrier layer.
Ga _0.95 N is formed to a thickness of 10 angstroms, and this is repeated alternately four times, and finally non-doped In
An active layer having a multiple quantum well structure with a total thickness of 90 Å was formed by forming a _0.15 Ga _0.85 N well layer at 10 Å. Next, Mg-doped p-type In _0.01 Ga _0.99 N was deposited on the active layer as a first p-type cladding layer.
It is formed with a thickness of 0 Å. Other than that, the wafer which laminated | stacked the predetermined | prescribed nitride semiconductor on sapphire like Example 1 was produced.

Thereafter, the nitride semiconductor layer was etched in the same manner as in Example 1, and a mask having a predetermined shape was formed on the surface of the uppermost p-type contact layer 9. , And a positive electrode having a width of 2 μm was formed on the p-type contact layer 9.

Then, the surface of the sapphire substrate on which the nitride semiconductor layer is not formed is polished to reduce the thickness of the substrate to 90 μm.
Then, the M-plane of the sapphire substrate surface (the surface corresponding to the side surface of the hexagonal prism in the hexagonal system) is scribed. After scribing, the wafer was divided into 700 μm square chips.
The laser of the stripe type shown in FIG. In addition,
FIG. 3 is a perspective view of the laser device according to the present embodiment, in which the nitride semiconductor layer surface orthogonal to the stripe-shaped positive electrode is used as an optical resonance surface. Next, after installing this chip on a heat sink and wire bonding each electrode,
When laser oscillation was attempted, laser oscillation with an oscillation wavelength of 415 nm was confirmed at a normal temperature at a threshold current density of 1.5 kA / cm ² .

Embodiment 11 As the first n-type cladding layer 5, Si-doped n-type In _0.01
After forming Ga _0.09 N to a thickness of 500 angstroms, non-doped In _0.15 Ga _0.85 N is formed as a well layer to a thickness of 25 angstroms to form the active layer 6, and a non-doped In _0.05 as a barrier layer is formed thereon. Ga
_The operation of forming _0.95 N to a thickness of 50 angstroms is alternately repeated 13 times, and finally, the non-doped In _0.15 N
Ga _0.85 N was formed to a thickness of 25 angstroms to form an active layer having a multiple quantum well structure with a total thickness of 1000 angstroms. Except for this, the laser element was fabricated in the same manner as in Example 10. This laser device has a threshold current density of 1.0 kA / cm ² at room temperature and 415 nm.
The laser oscillation of the oscillation wavelength of was confirmed.

Embodiment 12 In order to form the active layer 6, non-doped In is used as a well layer.
_0.15 Ga _0.85 N is formed to a thickness of 25 Å, and non-doped In _0.05 Ga _0.95 N is formed thereon as a barrier layer.
The operation of forming N to a thickness of 50 angstroms is alternately repeated 26 times, and finally, the non-doped In _0.15 Ga
_A laser device was fabricated in the same manner as in Example 11, except that _0.85 N was formed to a thickness of 25 angstroms to form an active layer having a multiple quantum well structure having a total thickness of 1975 angstroms. In this laser element, laser oscillation having an oscillation wavelength of 415 nm at a threshold current density of 1.0 kA / cm ² at room temperature was confirmed.

Example 13 The 450 nm blue LED obtained in Example 3, the 515 nm green LED obtained in Example 5, and the conventional GaAs
Each red LED having a light output of 3 mW and 660 nm made of s-based material or AlInGaP-based material is defined as one dot, and these dots are combined into an LED panel by 16 × 16 to form a full-color LED of 320 × 240 pixels. When I made the display,
Surface light emission of 10,000 nits was achieved with white light emission luminance.

[0074]

According to the present invention, there are provided a blue LED and a green light emitting LED having a high light emission output, a high luminance, and a high color purity having a half width of light emission of less than half of the conventional light emission, which could not be achieved by the prior art. A display device is provided. Therefore, according to the present invention, a high-brightness full-color LED display can be realized for the first time.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a nitride semiconductor light emitting device of the present invention.

FIG. 2 is a graph showing the relationship between the thickness of an active layer and the emission peak wavelength of a light-emitting element.

FIG. 3 is a perspective view showing the structure of another nitride semiconductor laser device of the present invention.

FIG. 4 is a graph showing the relationship between the peak emission wavelength and the emission output of a conventional LED element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... Buffer layer 3 ... N-type contact layer 4 ... Second n-type cladding layer 5 ... First n-type cladding layer 6 ... Active layer 7 ... First p-type cladding layer 8 ... Second p-type cladding layer 9 ... p-type contact layer

Continued on the front page (31) Priority claim number Japanese Patent Application No. 6-305259 (32) Priority date Hei 6 (1994) December 9 (33) Priority claim country Japan (JP) (31) Priority claim number Special No. 7-57050 (32) Priority date No. 7 (1995) March 16, (33) Priority claiming country Japan (JP) (31) No. of priority claim No. 7-57051 (32) Priority date No. 7 (1995) March 16 (33) Countries claiming priority Japan (JP) (56) References Appl. Phys. Lett. 64 [13] (1994) p. 1687-1689 (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18 H01L 33/00

Claims (7)

(57) [Claims] 1. A display device comprising at least one blue light emitting diode, at least one green light emitting diode, and at least one red light emitting diode, wherein the blue light emitting diode and the green light emitting diode are:
_{First of} In _x Ga _1-x N (0 ≦ x <1)
A single quantum well structure or a multiple quantum well having a well layer made of a nitride semiconductor containing indium and gallium in contact with one surface of the first n-type nitride semiconductor layer An active layer having a structure, and a first p-type nitride semiconductor layer made of Al _y Ga _1-y N (0 <y <1) in contact with the active layer to form an active layer. A display device comprising a light-emitting element that emits light having energy lower than the band gap energy of a nitride semiconductor. 2. A second n-type nitride semiconductor layer made of n-type Al _a Ga _1-a N (0 ≦ a ≦ 1) in contact with the other surface of the first n-type nitride semiconductor layer The display device according to claim 1, further comprising: 3. A second p-type layer made of p-type Al _b Ga ₁ -bN (0 ≦ b ≦ 1) in contact with the first p-type nitride semiconductor layer.
3. The display device according to claim 1, further comprising a type nitride semiconductor layer. 4. The display device according to claim 1, wherein the active layer is non-doped. 5. The display device according to claim 1, wherein the active layer is doped with a donor impurity and / or an acceptor impurity. 6. The method according to claim 1, wherein said well layer is made of In _c Ga _{1 -cN} (0 <
The display device according to claim 1, wherein c <1). 7. The method according to claim 1, wherein said active layer is made of In _c Ga _{1 -cN} (0 <c
<1) and In _d Ga _1-d N (0 ≦ d <
The display device according to any one of claims 1 to 6, wherein the display device has a multiple quantum well structure composed of a combination with a barrier layer composed of (1).