JP2000091635A - Nitride semiconductor light emitting device - Google Patents

Abstract

(57) Abstract: A light-emitting element such as an LED with high luminance is realized with a minimum laminated structure of a nitride semiconductor. SOLUTION: At least n-type In _a Al _b G is formed on _a substrate.
n consisting of a _1-ab N (0 ≦ a, 0 ≦ b, a + b ≦ 1)
-Type cladding _{layer, In X Al b Ga 1-} X N and the active layer made of (0 ≦ X <1), p -type Al _Y Ga _1-Y N layers (0 having a single quantum well or multiple quantum well structure ≦ Y <1, X ≠
Y = 0) and a p-type contact layer made of p-type GaN.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In).
_X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1).

[0002]

2. Description of the Related Art Conventionally, red LEDs and yellow-green LEDs have been put into practical use as visible LEDs, but recently blue and blue-green LEDs have been developed as nitride semiconductors. , Full color LED displays using R3 colors have emerged.

However, the current green LED has an emission wavelength of 56
The color reproduction area is narrow because it is not a yellowish green area near 0 nm and a pure green LED near 520 nm. In addition, since the brightness of the blue LED and the red LED is only 1/10 or less, the yellow-green L
There was a disadvantage that the number of EDs had to be increased. To solve this, a pure green LED having a luminous intensity of at least 2 cd is required.

[0004] We have developed a high-brightness LED that emits pure green light that can solve this problem, and have already announced it (Jpn.J.Ap.).
pl.Phys. Vol.34 (1995) pp.L797-L799). FIG. 2 shows the structure of the LED. 21 is a substrate made of sapphire,
Reference numeral 22 denotes a buffer layer made of GaN having a thickness of 30 nm.
Is a 4 μm thick Si-doped n-type GaN layer;
m-thick Si-doped n-type Al0.1Ga0.9N layer;
an Si-doped n-type In0.05Ga0.95N layer having a thickness of 2 nm; a non-doped In0.43Ga0.57N active layer having a thickness of 2 nm;
Is a 0.1 μm-thick Mg-doped p-type Al0.1Ga0.9N layer,
Reference numeral 28 denotes a Mg-doped p-type GaN layer having a thickness of 0.5 μm.
This LED has an active layer of a single quantum well (SQW) structure, and has a main emission wavelength of 5 at a forward current of 20 mA.
The luminous intensity when molded with resin having a lens shape of 25 nm, a light output of 1 mW, and a directivity angle of 10 ° is 4 cd.
With the development of this LED, one pixel can be constituted by each of G, B, and R, and a display having a wide color reproduction area can be realized.

[0005]

However, since the LED having the above-mentioned structure has a complicated laminated structure, the growth process of the nitride semiconductor is complicated. Therefore, an object of the present invention is to realize a high-luminance light-emitting element such as an LED with a minimum nitride semiconductor laminated structure.

[0006]

SUMMARY OF THE INVENTION A nitride semiconductor L of the present invention
The ED is a single quantum well including at least an n-type cladding layer made of n-type GaN and a non-doped In _x Ga ₁ -xN (0 <X <1) well layer having a thickness of 7 nm or less on a substrate. A non-doped In _x Ga ₁ -xN (0 <X <1) well layer having a structure or a film thickness of 7 nm or less and a non _- doped I
an active layer having a multiple quantum well structure composed of a barrier layer having a barrier layer of n _Y Ga _1-Y N (including Y <X, Y = 0);
It is characterized by having a laminated structure of a p-type cladding layer made of p-type Al _Y Ga _1-Y N (0 <Y <1) of 5 μm or less and a p _- type contact layer made of p-type GaN. In the present invention, InGaN, AlGaN, GaN and the like do not necessarily refer to a nitride semiconductor of only a ternary mixed crystal or a binary mixed crystal. For example, a trace amount of Al, other It is needless to say that even if impurities are contained within the scope of the present invention.

FIG. 1 is a schematic sectional view showing the structure of the LED element of the present invention. In this figure, 11 is a substrate, 12 denotes a buffer layer, 13 n-type _{In a Al b Ga 1-ab} N (0 ≦
The cladding layer composed of a, 0 ≦ b, a + b ≦ 1) and the n-type contact layer, 16 is composed of In _x Ga ₁ -xN (0 ≦ X <1) having a single quantum well or multiple quantum well structure. An active layer 17 is a p _- type cladding layer made of p-type Al _Y Ga ₁ -YN (0 ≦ Y <1), and 18 is a p-type contact layer made of p-type GaN.

Sapphire (Al ₂ O ₃ , A
Plane, R plane, and C plane), as well as spinel (MgAl
₂ O ₄ ), SiC (including 6H, 4H, 3C), ZnS,
Conventional materials proposed for growing nitride semiconductors such as ZnO, GaAs, and GaN can be used.

The buffer layer 12 is made of, for example, GaN, AlN,
GaAlN, SiC and the like are known, and are usually about 5 n in order to reduce lattice mismatch between the substrate and the nitride semiconductor.
It is grown to a thickness of m to 1 μm. For example,
No. 48794 and Japanese Patent Publication No. 4-15200 disclose AlN
Is described as a buffer layer.
No. 3829 and Japanese Unexamined Patent Publication No.
Is described as a buffer layer. In particular, when a substrate having a lattice constant close to that of a nitride semiconductor or a substrate having the same lattice constant is used, the buffer layer may not be formed in some cases.

Next, a laminated structure which is a feature of the present invention will be described.
State. The n-type cladding layer 13 is made of In _aAl_bGa_1-abN
(0 ≦ a, 0 ≦ b, a + b ≦ 1)
Any composition is acceptable, but particularly preferred
Is GaN, and In value is 0.5 or less._aGa_1-aN or b
Al with a value of 0.5 or less_bGa_1-bIt is desirable to be N
No. This is because, as shown in FIG.
As a contact layer for forming an n-electrode
In this case, a certain thickness is required. The nitride semiconductor
Has good crystallinity even when grown to a thickness of, for example, 1 μm or more.
The contact layer can also be used as an n-electrode
Good ohmic is obtained. And n-type with good crystallinity
The next active layer, p-type cladding layer, etc. are laminated on the cladding layer
Otherwise, it is difficult to obtain high output LED elements
It is. The thickness of the n-type cladding layer is not particularly limited.
No, but as described above, it is also used as a contact layer
Is to be grown to a thickness of about 0.5 μm to 5 μm
Is desirable. In addition, the nitride semiconductor is non-doped and
It has the property of becoming n-type due to the nitrogen vacancies formed therein,
Usually, donor impurities such as Si, Ge, Se, etc. are added during crystal growth.
For doping, it is preferable to use a preferable n type having a high carrier concentration.
Can be

Next, the active layer 16 has a single quantum well (SQW:
Single-Quantum-Well) structure or multiple quantum well (M
In _X Ga _{1 -X} N having a QW (Multi-Quantum-Well) structure
(0 ≦ X <1). With the SQW structure or the MQW structure, a light-emitting element with extremely high output can be obtained. SQW and MQW indicate the structure of an active layer in which light emission between quantum levels by non-doped InGaN is obtained. For example, in SQW, the active layer is formed of a single-composition In _x Ga ₁ -xN (0 ≦
X <1), and strong light emission between quantum levels can be obtained by setting the film thickness of In _x Ga ₁ -xN to 10 nm or less, more preferably 7 nm or less. The MQW is In _x Ga ₁ -xN having different composition ratios (X = 0 and X = 1 in this case).
Is included in the multilayer film. As described above, by using SQW and MQW for the active layer, light emission of about 365 nm to 660 nm can be obtained by light emission between quantum levels. As described above, the thickness of the quantum well layer is 7
nm or less is preferable. In the multiple quantum well structure, the well layer is I
n _X Ga ₁ -XN, and the barrier layer is also In _Y Ga ₁ -YN
(Y <X, including Y = 0 in this case). Particularly preferably, when the well layer and the barrier layer are formed of InGaN, they can be grown at the same temperature, so that an active layer having good crystallinity can be obtained. When the thickness of the barrier layer is 15 nm or less, more preferably 12 nm or less, a high-output light-emitting element can be obtained.

As described above, when the thickness of the well layer of the quantum structure is 7 nm or less, more preferably 5 nm or less, an element having a high light emission output can be realized. This is because this film thickness is I
This indicates that the thickness is less than or equal to the critical thickness of the nGaN active layer. In InGaN, the Bohr radius of electrons is about 3 nm, so that the quantum effect of InGaN appears at 7 nm or less. Similarly, in the case of a multiple quantum well structure, it is desirable that the thickness of the well layer is adjusted to 7 nm or less, while the thickness of the barrier layer is adjusted to 15 nm or less.

Next, the p-type cladding layer 1 in contact with the active layer 16
7 needs to be p-type Al _Y Ga _{1 -Y} N (0 ≦ Y <1), and particularly preferably, when the Y value is 0.05 or more, a high output device can be obtained. Furthermore, AlGaN is easy to obtain a p-type with a high carrier concentration and is hardly decomposed during growth.
This has the effect of suppressing the decomposition of the InGaN active layer 16. In addition, the band offset and the refractive index difference can be made larger than those of the other nitride semiconductors with respect to the InGaN active layer 16, which is the most excellent. In addition, the first p-type cladding layer is made of p-type G
Assuming aN, the emission output is about 1 compared to p-type AlGaN.
/ 3. This is because AlGaN is more likely to be p-type than GaN, or
It is presumed that the GaN active layer has decomposed. Therefore, as the p-type cladding layer, Mg-doped p-type Al _Y Ga _1-Y N having a Y value of 0.05 or more is most preferable.

The thickness of the p-type cladding layer 17 is 1 nm or less.
Above, 2 μm or less, more preferably 5 nm or more, 0.5
It is desirable that the thickness be not more than μm. If it is thinner than 1 nm, p
The state is close to the absence of the mold cladding layer 17 and
The light output tends to decrease.
Cracks easily form in the p-type cladding layer itself during long
Even if the next layer is laminated on a cracked layer,
Good semiconductor layer is not obtained and output tends to decrease
Because. In order to make the nitride semiconductor p-type,
During crystal growth, the action of Mg, Zn, C, Be, Ca, Ba, etc.
Obtained by doping with scepter impurities,
In order to obtain a p-layer having a high carrier concentration, it is necessary to use an acceptor.
After doping with pure substance, atmosphere of inert gas such as nitrogen or argon
It is more desirable to anneal at
(JP-A-5-183189). Annealing
By doing so, it is usually 1 × 10¹⁷~ 1
× 10 ¹⁹/cm^ThreeIs obtained. Again
And an electron beam illuminator disclosed in JP-A-3-218625.
A firing process may be performed.

Next, the p-type contact layer 18 is made of p-type Ga
N, particularly preferably Mg-doped p-type GaN. Since p-type GaN is a layer in contact with an electrode, it is important to obtain ohmic contact in the case of light-emitting elements such as LEDs and LDs. p-type GaN is easy to take ohmic with many metals and is most preferable as a contact layer. An ohmic material can be obtained by using, for example, Ni-Au, Ni-Ti, or the like as the electrode material. Although the thickness of the p-type contact layer is not particularly limited, it is generally preferable that the p-type contact layer is grown to a thickness of about 50 nm to 2 μm.

Nitride semiconductors are prepared by metal organic chemical vapor deposition (MO).
VPE), halide vapor deposition (HDVPE), and molecular beam vapor deposition (MBE). Among them, according to the MOVPE method, a material having good crystallinity can be obtained quickly. In the MOVPE method, TMG (trimethylgallium) and TEG (triethylgallium) are used as a Ga source, TMA (trimethylaluminum) and TEA (triethylaluminum) are used as an Al source, and TMI (trimethylindium) and TEI (triethylaluminum) are used as an In source. Trialkyl metal compounds such as indium) are often used, and gases such as ammonia and hydrazine are used as a nitrogen source. As an impurity source, a gas such as silane gas for Si, germane gas for Ge, Cp2Mg (cyclopentadienylmagnesium) for Mg, and DEZ (diethyl zinc) for Zn is used. In the MOVPE method, these gases are supplied to the surface of a substrate heated to, for example, 600 ° C. or higher, and the gases are decomposed to obtain In _X Al _Y G
a _{1 -XYN} (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) can be epitaxially grown.

[0017]

The light emitting device of the present invention can provide a device having excellent light emission output with a minimum necessary structure. This is because each layer works effectively. First, the n-type cladding layer serves both as a current injection layer and a carrier confinement layer. Since the active layers of SQW and MQW have good crystallinity, they are very efficient layers as light emitting layers. The p-type cladding layer is a layer having a high concentration as a carrier confinement layer, and a high light emission output is obtained because it is a carrier confinement layer. Furthermore, since the p-type contact layer also obtains a favorable ohmic with the electrode material, the forward voltage of the LED element is reduced, and the luminous efficiency is improved.

FIG. 3 is a diagram showing, as relative values, the relationship between the thickness of the active layer having a single quantum well structure and the light emission output according to the light emitting device of the present invention. LED
It shows the structure of the element. As described above, the light-emitting element of the present invention can provide a high-output light-emitting element by setting the thickness of the well layer to 7 nm or less.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an LED device according to the present invention will be described in detail with reference to FIG. The steps described below are based on the MOVPE method.

Example 1 A well-cleaned sapphire substrate 11 was set in a reaction vessel, and after sufficiently replacing the inside of the reaction vessel with hydrogen, the temperature of the substrate was increased to 1050 while flowing hydrogen.
The temperature is raised to ° C. to clean the sapphire substrate.

Subsequently, the temperature is lowered to 510 ° C., and hydrogen is used as a carrier gas, ammonia and TMG (trimethylgallium) are used as source gases, and Ga is deposited on the sapphire substrate 11.
A buffer layer 12 of N is grown to a thickness of 20 nm.

After the growth of the buffer layer, only TMG is stopped, and the temperature is raised to 1030 ° C. When the temperature reaches 1030 ° C., an n-type GaN layer doped with 1 × 10 ²⁰ / cm ^{3 of} Si is grown to 4 μm as the n-type cladding layer 13 using TMG and ammonia gas as the source gas and silane gas as the dopant gas.

After the growth of the n-type GaN layer, the source gas and the dopant gas are stopped, the temperature is set to 800 ° C., and TM is added to the source gas.
Using G, TMI (trimethylindium) and ammonia, the active layer 16 having a single quantum well structure is In0.43Ga.
A 0.57N layer is grown to 3 nm.

Next, the source gas and the dopant gas are stopped,
The temperature was raised again to 1020 ° C.
G, TMA (trimethylaluminum), ammonia,
Using Cp2Mg (cyclopentadienyl magnesium) as a dopant gas, a p-type Al0.1Ga0.9N layer was 2 × 10 ¹⁹ / cm ³ doped with Mg as a p-type cladding layer 17 is 50nm grow.

The TMA gas is stopped, and a p-type GaN layer doped with Mg at 1 × 10 ¹⁹ / cm ³ is grown to a thickness of 1 μm as a p-type contact layer 18.

After the growth of the p-type GaN layer, the substrate is taken out of the reaction vessel, and the substrate is placed in a nitrogen atmosphere by an annealing apparatus.
Annealing at 20 ° C. for 20 minutes to form a p-type clad layer,
The resistance of the mold contact layer is further reduced.

The p-type contact layer 18, the p-type clad layer 17, and the active layer 1 of the wafer obtained as described above
6 is removed by etching to expose the n-type cladding layer 13 and Ni-Au and p-type
GaN layer and an ohmic electrode made of Ti-Al-Au are provided, cut into chips of 350 μm square, installed on a lead frame having a cup shape, molded with epoxy resin, and an LED element having a lens directivity angle of 10 ° It was created.

This LED was caused to emit light at a forward current of 20 mA, and its spectrum was measured.
The device exhibited pure green light emission of 5 nm and a half-value width of 45 nm, a light emission output of 1.5 mW, a quantum efficiency of 2.5%, and a light emission output more than 40 times that of a conventional yellow-green LED made of GaP.

Example 2 In the step of growing the active layer 16, a 3 nm-thick In0.40Ga0.60N layer was used as a well layer at 800 ° C. using TMG, TMI (trimethylindium) and ammonia as source gases. A 6 nm thick In0.2Ga0.4N layer is grown thereon as a barrier layer, and an active layer 16 having a multiple quantum well structure having a five-layer structure (well + barrier + well + barrier + well) is grown thereon. .

After that, when an LED element was prepared in the same manner as in Example 1, the emission peak wavelength was 520 nm and the emission output was 1.9.
An excellent LED with mW and quantum efficiency of 3% was obtained.

Example 3 A green LED device was obtained in the same manner as in Example 1 except that the thickness of the active layer 16 having a single quantum well structure was changed to 7 nm. A green LED having a quantum efficiency of 2.1% was obtained.

Example 4 After growing the buffer layer, the temperature was raised to 1
After the temperature was raised to 030 ° C., TMG and TM
A, ammonia gas and silane gas are used as dopant gas, and Si is used as the n-type cladding layer 13 at 1 × 10 ²⁰ / cm ^3.
Except for growing a doped n-type Al0.05Ga0.95N layer of 4 μm, an LED element was prepared in the same manner as in Example 1. As a result, the same characteristics as those of Example 1 were obtained in both the emission wavelength and the emission output.

Example 5 An LED element was prepared in the same manner as in Example 1 except that the thickness of the p-type cladding layer 17 was changed to 2 μm. The light emitting output was 1.0 mW and the quantum efficiency was 1.7.
% Green LED was obtained.

[Embodiment 6] In the embodiment 1, the active layer 1
A well layer composed of non-doped In0.4Ga0.6N is grown to a thickness of 2.5 nm, and a barrier layer composed of non-doped In0.01Ga0.99N is grown to a thickness of 5 nm. Perform this operation 13
This was repeated twice, and finally, an active layer having a total thickness of 1000 Å was grown by stacking well layers. After that, as in Example 1, an LED element was obtained, which was an excellent green LED having 520 nm, an emission output of 2.5 mW, and a quantum efficiency of 3.2%.
I got

[0035]

As described above, the LED of the present invention can provide a green LED having a very high light emission output with a minimum necessary structure without having a complicated laminated structure. Further, other nitride semiconductor layers disclosed in the present invention may be inserted between or outside the stacked structures without departing from the spirit of the present invention.

As described above, by using the LED of the present invention, in an LED full-color display,
Conventionally, a plurality of GaP LEDs are required to increase the luminous intensity. However, since one pixel can be formed for each of B, G, and R, a high-definition screen can be obtained. Also chip LED
Then, even smaller pixels can be realized, and a wall-mounted TV can also be realized.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of an LED element according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view showing the structure of a conventional LED element.

FIG. 3 is a graph showing the relationship between the thickness of a well layer and the output of the light-emitting element of the present invention.

[Explanation of symbols]

 11 ... substrate 12 ... buffer layer 13 ... n-type cladding layer 16 ... active layer 17 ... p-type cladding layer 18 ... p-type contact layer

Claims (1)

[Claims] 1. A single substrate including at least an n-type cladding layer made of n-type GaN and a non-doped In _x Ga ₁ -xN (0 <X <1) well layer having a thickness of 7 nm or less on a substrate. Including a quantum well structure or a non-doped In _x Ga _1-x N (0 <X <1) well layer and a non-doped In _Y Ga _1-Y N (Y <X, Y = 0) having a thickness of 7 nm or less ) An active layer having a multiple quantum well structure composed of a barrier layer and a p-type Al _Y Ga _1-Y N film having a thickness of 1 nm or more and 0.5 μm or less (0 <Y <
1) and p-type GaN
A nitride semiconductor light emitting device having a laminated structure with a mold contact layer.