JP3304782B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly to an improvement of a semiconductor light emitting device having a super lattice structure. This semiconductor light emitting device can be used, for example, as a light emitting diode or a laser diode.

[0002]

2. Description of the Related Art As a light emitting device in the visible light short wavelength region, a device using a compound semiconductor is known. Above all, group III nitride semiconductors have attracted particular attention recently because they are of direct transition type and have high luminous efficiency and emit blue light, which is one of the three primary colors of light. As such a semiconductor light emitting element, a light emitting layer having a superlattice structure in which a quantum well layer and a barrier layer are repeatedly laminated has been proposed in order to enhance luminous efficiency.

[0003] In the conventional superlattice structure, the barrier layer Ga
N was directly grown quantum well layer serving an In _X Ga 1 _{over X} N over. In this case, since there is a difference between the former lattice constant and the latter lattice constant, there is a possibility that a lattice defect occurs at the interface between the two. Therefore, the barrier layer is made of In _Y Ga _1-Y
As N (where Y <X), a technique for reducing the difference in lattice constant between the barrier layer and the quantum well layer has been proposed (see JP-A-6-268257).

[0004]

However, when In is added to the barrier layer as described above, the potential barrier between the quantum well layer and the barrier layer, that is, the offset ΔEc on the conduction band side is reduced. Therefore, the number of electrons and holes trapped in the quantum well decreases, and there is a possibility that a sufficient light emission amount cannot be obtained.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. That is, a semiconductor light emitting device formed of a group III nitride semiconductor, wherein the n-type first semiconductor layer, the p-type second semiconductor layer, and the first and second semiconductor layers A light emitting layer having a superlattice structure provided therebetween, wherein the light emitting layer includes a quantum well layer, a barrier layer, and a buffer layer formed between the quantum well layer and the barrier layer. A potential barrier between the layer and the buffer layer is smaller than a potential barrier between the quantum well layer and the barrier layer, and the lattice constant of the buffer layer is the lattice constant of the quantum well layer and the lattice constant of the barrier layer. And a semiconductor light emitting device.

[0006]

According to the semiconductor device having the above structure, a new buffer layer is introduced between the quantum well layer and the barrier layer in the light emitting layer having the superlattice structure. Since the lattice constant of the buffer layer is between the lattice constant of the quantum well layer and the lattice constant of the barrier layer, the change in the lattice constant of the quantum well layer, the buffer layer, and the barrier layer becomes gentle. Therefore, generation of lattice defects at the interface of each layer can be suppressed. Also, the potential barrier between the quantum well layer and the barrier layer, that is, the offset Δ on the conduction band side
Ec can be freely designed irrespective of the presence of the buffer layer. Therefore, if the height of the barrier between the quantum well layer and the barrier layer is large, the number of electrons or holes trapped in the quantum well becomes sufficient even if the buffer layer exists. Therefore, the light emission amount of the semiconductor light emitting device of the present invention increases. That is, the semiconductor light emitting device of the present invention can secure a sufficiently high potential barrier between the quantum well layer and the barrier layer while preventing generation of lattice defects.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a light emitting layer which is a feature of the present invention will be described below in more detail with reference to the drawings. FIG.
Denotes one unit of the quantum well layer 1, the buffer layer 2 and the barrier layer 3 which constitute the light emitting layer, and the light emitting layer is formed by repeating this unit 1 to 40, preferably 3 to 10.

The quantum well layer 1 is made of In _x Ga ₁ -xN.
Here, X is 0.1 (lattice constant: 0.32232)
nm) to 0.3 (lattice constant: 0.32936 nm). In this specification, the lattice constant is the length of a theoretical unit cell in the a-axis direction in a crystal having no distortion. The thickness of the quantum well layer is not particularly limited, but is preferably 2 to 4 nm.

[0009] The buffer layer 2 is made of In _Y Ga _1-Y N.
Here, when Z of the barrier layer 3 described later is Z = 0, that is, when the barrier layer 3 is made of GaN, Y is 0.05 (lattice constant: 0.32056 nm) to 0.1 (lattice constant: 0). .3
2232 nm). If the compounding amount of Y is less than 0.05, the lattice constant of the buffer layer 2 approaches the lattice constant of the barrier layer 3, and if it exceeds 0.1, the lattice constant of the quantum well layer 1 approaches the lattice constant of the quantum well layer 1. -It is not preferable because the change in the lattice constant of the buffer layer 2-the barrier layer 3 is not smooth.

The composition ratio Y of the buffer layer 2 has a relation of X> Y with respect to the composition ratio X of In in the quantum well layer 1.

(1) When Z of the barrier layer 3 is Z> 0, that is, when the barrier layer is a ternary mixed crystal of AlGaN, Y is preferably set to Y = 0. This is because it is often difficult to grow indium-containing crystals directly on aluminum-containing crystals (and vice versa). When a crystal containing aluminum is grown by metal organic chemical vapor deposition (MOVPE), the amount of ammonia in the gas phase must be reduced. This is because ammonia easily reacts with aluminum. On the other hand, when growing a crystal containing indium by the MOVPE method, it is necessary to increase the amount of ammonia in the gas phase. That is, when the crystal containing aluminum and the crystal containing indium are grown continuously, the amount of ammonia in the gas phase must be largely changed. Therefore, in growing each crystal, the time and the cost of raw materials increase in order to stabilize the gas phase components. In addition, since the environment of the gas phase required for growing one crystal is unfavorable for another crystal, the other crystal serving as a base may be adversely affected. Therefore, the buffer layer is made of Al and I
The use of GaN containing no n facilitates adjustment of the gas phase component. In addition, since another problematic crystal containing Al or In is covered with the buffer layer, the base is not damaged by the gas phase component.

(2) It is a matter of course that a crystal containing indium (aluminum) can be directly grown on a crystal containing aluminum (indium) by sufficiently adjusting the components of the gas phase. At this time, the composition ratio Y of indium is under the above conditions.

It is preferable that the lattice constant irregularities between the quantum well layer 1 and the buffer layer 2 and between the buffer layer 2 and the barrier layer 3 are each 2% or less. Lattice constant is 2
%, Lattice defects may occur at the interface between the layers.

When Y is in the above range, the potential barrier between the quantum well layer 1 and the buffer layer 2 becomes smaller than the potential barrier between the quantum well layer 1 and the barrier layer 3 as shown in FIG. That is, the offset ΔEc _buffer-well on the conduction band side between the quantum well layer 1 and the buffer layer 2 is smaller than the offset ΔEc _barrier-well on the conduction band side between the quantum well layer 1 and the barrier layer 3. . The difference between the two offsets is not particularly limited.

The thickness of the buffer layer is as shown in FIG.
It is preferable that the thickness be 0.5 to 2 nm so that the well portion of the quantum well layer 1 can be sufficiently secured when viewed from the barrier layer 3.
More preferably, it is 0.5 to 1 nm. Buffer layer 2
When the thickness exceeds 2 nm, the buffer layer 2 becomes a substantial barrier layer and the quantum well becomes shallow, which is not preferable. If the buffer layer 2 has a thickness of less than 0.5 nm, the effect of the buffer layer may be lost.

The barrier layer 3 is made of Al _Z Ga _1-Z N. Here, when the buffer layer 2 does not contain indium, that is, when the buffer layer 2 is made of GaN, Z
Is 0.05 (lattice constant: 0.318415 nm) to 0.
03 (lattice constant: 0.318569 nm) is preferable. The thickness of the barrier layer 3 is not particularly limited.
It is preferable to set it to 0 to 40 nm.

Since the aluminum atoms are smaller than Ga, the lattice constant of the barrier layer 3 is smaller than that of the quantum well layer 1 and the buffer layer 2. Accordingly, a compressive stress is applied to the quantum well layer 1 by the barrier layer having a smaller lattice constant than the quantum well layer. As a result, strain occurs in the quantum well layer 1 and its band gap is reduced. Therefore, the wavelength of the generated light shifts to the longer wavelength side. By adjusting the composition ratio of aluminum in this manner, the wavelength of the generated light can be controlled. According to the study of the inventors, even if the composition ratio of indium in the quantum well layer is reduced,
For example, even at 20% or less, light having a wavelength of 500 nm or more could be generated.

(1) When indium is contained in the buffer layer 2, Z is set to Z = 0 due to the limitation of the manufacturing process as described above, that is, the barrier layer is made of GaN.
It is preferable to be composed of -(2) By sufficiently adjusting the components of the gas phase, even when the buffer layer 2 contains indium, Z can be set to the above condition.

The quantum well layer 1, buffer layer 2 and barrier layer 3 may or may not contain intentional dopants.

When the above layers are formed by the MOVPE method,
The layer thickness can be controlled by adjusting the flow rate of the source gas and / or the growth time. Further, the composition ratio of each layer can be controlled by adjusting the flow rate and / or the growth temperature of the source gas.

As described above, the light emitting layer of the present invention is formed of a binary mixed crystal or ternary mixed crystal Group III nitride semiconductor.

[0022]

Embodiments of the present invention will be described below.

Embodiment 1 FIG. 3 is a sectional view of a light emitting diode 10 according to Embodiment 1.
FIG. 4 is an enlarged sectional view of the light emitting layer. In the light emitting diode 10 of the embodiment, a buffer layer 12 made of AlN is formed on a sapphire substrate 11. On this buffer layer 12, a silicon-doped n ⁺ layer having a thickness of about 4,000 nm is sequentially formed.
A GaN layer 13, a silicon-doped n-GaN layer 14 having a layer thickness of about 1,000 nm, a light emitting layer 15 having a superlattice structure, a magnesium-doped AlGaN layer 16 having a layer thickness of about 50 nm,
A magnesium-doped p-GaN layer 17 having a thickness of about 100 nm and a magnesium-doped p ⁺ -GaN layer 18 having a thickness of about 25 nm are laminated. An aluminum electrode pad 21 is connected to the n-conductivity type semiconductor layer 13 with a large silicon doping amount, and a gold transparent electrode 22 is connected to the p-conduction type semiconductor layer 18 (top layer) with a large magnesium doping amount.
Is also connected to the electrode pad 23 made of gold.

As shown in FIG. 4, the light-emitting layer 15 having a superlattice structure is formed by sequentially stacking a barrier layer 153, a buffer layer 152, a quantum well layer 151, a buffer layer 152, and a barrier layer 153. The layers include five quantum well layers 151. The barrier layer 153 is made of non-doped G
aN, and its thickness is about 3.5 nm. The buffer layer 152 is made of non-doped In _0.1 Ga _0.9 N (ie,
Y = 0.1), and its film thickness is about 1.0 nm. The quantum well layer 151 is made of non-doped In _0.2 Ga _0.8 N
(That is, X = 0.2), and the film thickness is about 3.5 n
m.

The lattice constant of the quantum well layer 151 is 0.325.
84 nm. The lattice constant of the buffer layer 152 is 0.3
2232 nm. The lattice constant of the barrier layer 153 is 0.1.
3188 nm. Quantum well layer 151 and buffer layer 1
The offset ΔEc on the side of the conduction band with 52 is 300 meV. Quantum well layer 151 and barrier layer 15
The offset ΔEc on the conduction band side with 3 is 6
00 meV.

The light emitting diode 10 is manufactured by the MOVPE method. The gases used are NH ₃ , H ₂ or N ₂ as a carrier gas, and trimethylgallium (Ga (C
H ₃ ) ₃ ) (hereinafter referred to as “TMG”), trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”), and trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMA”). referred to as "TMI".), silane (SiH ₄₎ and cyclopentadiene magnesium _{(Mg (C 5 H 5)} 2)
(Hereinafter referred to as “CP ₂ Mg”).

First, organic cleaning and heat treatment were performed.
A single-crystal sapphire substrate 11 having an a-plane as a main surface is
It was mounted on a susceptor in the reaction chamber of the OVPE apparatus (for example, see Japanese Patent Publication No. 5-73251). Next, at normal pressure
While flowing H ₂ into the reaction chamber at a flow rate of 2 liter / min, the temperature was 11
The sapphire substrate 11 was subjected to gas phase etching at 00 ° C.

Next, the temperature is lowered to 400 ° C.
₂ 20 liter / min, to form NH ₃ to a thickness of 10 liter / min, about 50nm buffer layer 12 of AlN is supplied at 1.8 X 10 ^{over 5} mol / min to TMA. Then maintaining the temperature of the sapphire substrate 11 to 1150 ° C., the H ₂ or N ₂ 1
0 liter / min, NH ₃ 5 liter / min, TMG 2.0
X ^10-4 mol / min and silane at 4.2 X ^10-8 mol / mi
By introducing n, a high carrier concentration n ⁺ layer 13 made of silicon-doped GaN having a thickness of about 4,000 nm was formed.

Following the formation of the n ⁺ layer 13 having a high carrier concentration, the temperature of the sapphire substrate 11 is maintained at 1150 ° C., H ₂ or N ₂ is 10 liter / min, and NH ₃ is 5 liter / mi.
n, 2.0 x ^10-4 mol / min of TMG and 2.
A low carrier concentration n-layer 14 made of silicon-doped GaN having a thickness of about 10 nm was formed by introducing 0 × 10 ⁻⁸ mol / min.

Subsequently, (Step 1) The temperature of the substrate 11 is maintained at 850 ° C., and H ₂ or N ₂ is supplied at 10 liter / min, NH
₃ 20 liter / min, TMG of 1.5 X 10 ^{over 5} mol / min
Then, a barrier layer 153 made of non-doped GaN having a thickness of about 3.5 nm was formed.

(Step 2) The temperature is maintained at 850 ° C., H ₂ or N ₂ is 10 liter / min, and NH ₃ is 20 liter.
r / min, TMG of 1.5 X 10 ^{over 5} mol / min, TMI was introduced 1.0X 10 ^{over 4} mol / min, buffer layer 15 made of non-doped In _0.05 Ga _0.95 N having a thickness of about 1.0nm
2 was formed.

Subsequently, (step 3) the temperature is set to 650 ° C.
, H ₂ or N ₂ at 10 liter / min, NH ₃ at 20
liter / min, TMG a 4.0 X 10 ^{over 6} mol / min, TMI
Was introduced at 1.0 × 10 ⁻⁵ mol / min, and the film thickness was about 3.5 nm.
Well layer 1 made of non-doped In _0.2 Ga _0.8 N
51 were formed.

Further, Steps 2 and 1 were executed to form one unit indicated by reference numerals in FIG. Then, the light emitting layer 15 having five units, that is, the light emitting layer 15 having five quantum well layers 151 was formed by further performing the steps 2, 3, and 2 and the process.

Next, the temperature of the substrate 11 is maintained at 1000 ° C., H ₂ or N ₂ is 25 liter / min, and NH ₃ is 10 liter / min.
min, 2.0 to TMG X 10 ^{over 5} mol / min, a TMA 1.
0 X ^10-5 mol / min, CP ₂ Mg 3.0 X ^10-7 mol
/ min and magnesium doped A with a layer thickness of about 50 nm
An lGaN layer 16 was formed.

Subsequently, the temperature of the substrate was maintained at 1000 ° C., H ₂ or N ₂ was 10 liter / min, and NH ₃ was 5 liter / mi.
n, TMG was introduced at 2.0 × 10 ⁻⁵ mol / min and CP ₂ Mg was introduced at 7.0 × 10 ⁻⁹ mol / min to form a magnesium-doped p-GaN layer 17 having a thickness of about 100 nm. However, in this state, layer 17 is a high-resistance semi-insulator.

Further, the temperature of the substrate is maintained at 1000 ° C.
H ₂ or N ₂ is 10 liter / min, NH ₃ is 5 liter / min,
TMG and 2 X 10 ^{over 5} mol / min, the CP ₂ Mg 2.1 X
10 ^{@ 8} mol / min was introduced to form a magnesium thickness of about 25nm of doped p ⁺ over GaN layer 18. However, in this state, layer 18 is a high resistance semi-insulator.

Thereafter, the layer 18 is irradiated using an electron beam irradiation apparatus.
And 17 were uniformly irradiated with an electron beam. The irradiation conditions of the electron beam were as follows: acceleration voltage: about 10 kV, sample current: 1 μA, beam moving speed: 0.2 mm / sec, beam diameter: 60 μmΦ, degree of vacuum: 5.0
It is an X 10 ^{over 5} Torr. By such electron beam irradiation, the layers 18 and 17 become the desired p ⁺ conduction type and p conduction type, respectively.

The semiconductor wafer thus formed was etched by a known method to obtain a semiconductor layer structure shown in FIG. Then, a transparent electrode 22 was deposited on the uppermost layer 18 to form electrode pads 21 and 23. Thereafter, the light emitting diode 10 having the configuration shown in FIG. 3 was separated from the semiconductor wafer.

According to the light emitting diode 10 of the embodiment thus obtained, light having a wavelength of 520 nm was able to be generated at a normal temperature and an applied current of 20 mA.

Embodiment 2 The light-emitting diode of this embodiment is different from the light-emitting diode 10 of Embodiment 1 only in the structure of the light-emitting layer, and the other structure is the same, so that the description is omitted.

As shown in FIG. 5, the light emitting layer of this embodiment comprises a barrier layer 253, a buffer layer 252, and a quantum well layer 2
51, a buffer layer 252, and a barrier layer 253 are sequentially stacked, and the light emitting layer includes five quantum well layers 251. The thickness of each layer is the same as in the first embodiment. The barrier layer 253 is made of non-doped Al _0.05 Ga _0.95 N, the buffer layer 252 is made of non-doped GaN,
The quantum well layer 251 is made of non-doped In _0.15 Ga _0.85 N.

The lattice constant of the quantum well layer 251 is 0.324.
08 nm. The lattice constant of the buffer layer 252 is 0.3
188 nm. The lattice constant of the barrier layer 253 is 0.3
18415 nm. Offset ΔEc on the conduction band side between quantum well layer 251 and buffer layer 252
Is 450 meV. Quantum well layer 251 and barrier layer 2
The offset ΔEc on the side of the conduction band with 53 is 600 meV.

According to the light emitting diode 10 of this embodiment, the wavelength of 520 n
m of light could be generated.

The barrier layer 253 made of AlGaN keeps the temperature of the substrate 11 at 1000 ° C. and reduces H ₂ or N ₂ by 25 l.
iter / min, 4 X 10 to the NH ₃ 10 liter / min, TMG
^-5 mol / min, TMA was introduced at 1 × 10 ^-5 mol / min. The buffer layer 252 made of GaN keeps the substrate temperature at 850 ° C., makes H ₂ or N ₂ 10 liter / min, NH
₃ 20 liter / min, TMG of 1.5 X 10 ^{over 5} mol / min
Introduced and formed. The quantum well layer made of In _0.15 Ga _0.85 N keeps the substrate temperature at 650 ° C. and keeps H ₂ or N ₂ at 10
liter / min, NH ₃ 20 liter / min, TMG 4.0
X 10 ^{over 5} mol / min, was formed by introducing 1.0 X 10 ^{over 5} mol / min to TMI.

The present invention is not limited to the description of the above-described embodiment, and it does not depart from the scope of the claims.
It includes various modifications that can be expected by those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a view for explaining a characteristic portion of the present invention;
It is sectional drawing which shows the structure of a light emitting layer.

FIG. 2 is an energy band diagram of the light emitting layer.

FIG. 3 is a sectional view showing a configuration of a light emitting diode according to one embodiment of the present invention.

FIG. 4 is a sectional view showing a configuration of a light emitting layer of a light emitting diode according to one embodiment of the present invention.

FIG. 5 is a sectional view showing a configuration of a light emitting layer of a light emitting diode according to another embodiment of the present invention.

[Explanation of symbols]

 1, 151, 251 Quantum well layer 2, 152, 252, buffer layer 3, 153, 253 barrier layer 10 light emitting diode 13, 14 n-type first semiconductor layer 15 light-emitting layer 17, 18 p-type second semiconductor Semiconductor layer

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Umezaki 1 Ochiai Ochiai, Kasuga-cho, Nishikasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. (56) References JP-A-8-228025 (JP, A) JP-A-7-183614 (JP, A) JP-A-10-65271 (JP, A) JP-A-5-259571 (JP, A) JP-A-7-235730 (JP, A) A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 33/00 H01S 5/00-5/50 H01L 21/28 301 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A semiconductor light emitting device formed of a Group III nitride semiconductor, comprising: an n-type first semiconductor layer; a p-type second semiconductor layer; A light emitting layer having a superlattice structure provided between semiconductor layers, wherein the light emitting layer includes a quantum well layer, a barrier layer and a buffer layer formed between the quantum well layer and the barrier layer, A potential barrier between the quantum well layer and the buffer layer,
The smaller than the potential barrier of the quantum well layer and the barrier layer, in the semiconductor light emitting device which is between the lattice constant of the buffer layer is the quantum well layer lattice constant and the barrier layer of the quantum well layer Is composed of In _x Ga ₁ -xN (0 <X),
The buffer layer is made of In _Y Ga _1-Y N (0 ≦ Y <X).
Ri, the barrier layer is _{Al Z Ga 1-Z N (} Z: 0.05~
0.03) . 2. A semiconductor device formed of a group III nitride semiconductor.
An optical device, comprising: a first semiconductor layer of n-conductivity type; a second semiconductor layer of p-conductivity type; and a superlattice structure provided between the first and second semiconductor layers.
It and a light-emitting layer, the light-emitting layer is a quantum well layer, barrier layer and the quantum well layer
And a buffer layer formed between the barrier layer and a potential barrier between the quantum well layer and the buffer layer,
Smaller than a potential barrier between the quantum well layer and the barrier layer.
And the lattice constant of the buffer layer is the lattice constant of the quantum well layer.
Semiconductor light emitting device between the lattice constant of the barrier layer and
Oite, the quantum well layer is made of _{In X Ga 1-X N (} 0 <X),
The buffer layer is _{In Y Ga 1-Y N (} 0 <Y <X) Tona
Wherein the barrier layer is made of GaN.
Conductive light emitting element. 3. A semiconductor device formed of a group III nitride semiconductor.
An optical device, comprising: a first semiconductor layer of n-conductivity type; a second semiconductor layer of p-conductivity type; and a superlattice structure provided between the first and second semiconductor layers.
It and a light-emitting layer, the light-emitting layer is a quantum well layer, barrier layer and the quantum well layer
And a buffer layer formed between the barrier layer and a potential barrier between the quantum well layer and the buffer layer,
Smaller than a potential barrier between the quantum well layer and the barrier layer.
And the lattice constant of the buffer layer is the lattice constant of the quantum well layer.
Semiconductor light emitting device between the lattice constant of the barrier layer and
Oite, the quantum well layer is made of InGaN, the buffer layer
Is composed of GaN, and the barrier layer is composed of AlGaN
A semiconductor light emitting device characterized by the above-mentioned.