JP2004134787A - Group iii nitride compound semiconductor light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group III nitride compound semiconductor light-emitting device capable of emitting light of short wavelength at a high output. <P>SOLUTION: In a group III nitride compound semiconductor light-emitting device provided with a quantum well structure, having a well layer comprising AlGaInN having Al and In as essential constituent elements and a barrier layer comprising AlGaInN which has Al as the essential constituent element, the composition of Al of the barrier layer is made the same as or lower than the composition of Al of the well layer. <P>COPYRIGHT: (C)2004,JPO

Description

(4) The present invention relates to a group III nitride compound semiconductor light emitting device. More specifically, the present invention relates to an improvement of a group III nitride compound semiconductor light emitting device having a quantum well structure and emitting light in an ultraviolet region.

Technology background

発 光 A light emitting element in which Al having a large band gap energy is included in a well layer in order to realize a shorter wavelength has been proposed (for example, see Patent Document 1). In this light-emitting element, both the well layer and the barrier layer contain Al, and the Al composition of the barrier layer is made larger than the Al composition of the well layer. Thus, the difference in lattice constant between the well layer and the barrier layer is reduced, and the piezoelectric field is suppressed to achieve high luminous efficiency. The well layer in the example of Patent Document 1 is a ternary mixed crystal of AlGaN.

On the other hand, it has been proposed to use a quaternary mixed crystal of AlGaInN as a group III nitride-based compound semiconductor constituting a high-output short-wavelength light-emitting element (see Non-Patent Document 1).
FIG. 8 of Non-Patent Document 1 discloses an AlGaInN active layer sandwiched between AlGaN layers, in which the latter has a smaller Al composition than the former. However, since the light emitting device of FIG. 8 does not have a quantum well structure, it is a type different from the present invention.

JP-A-2000-294884 “300 nm band high-brightness ultraviolet LED using InAlGaN quaternary mixed crystal”, Monthly Display August 2001, separate volume, August 2001, FIG.

According to the light emitting device described in Patent Document 1, by introducing Al into both the well layer and the barrier layer, the difference between the lattice constants of the two is reduced. However, according to the study of the present inventors, there are the following problems to be solved.
As described in Non-Patent Document 1, it is preferable to use a quaternary mixed crystal of AlGaInN when emitting short-wavelength light with high output. This is because, by balancing Al and In as a quaternary mixed crystal of AlGaInN, it is possible to control the lattice constant and to match the lattice constant between the underlying layer and the well layer of the quantum well structure. Because you can. Normally, the underlayer made of GaN is formed in a thick film, and if there is a mismatch in the lattice constant between the underlayer and the well layer, the influence of the piezo electric field occurs. However, Patent Literature 1 does not consider such mismatch in lattice constant between the underlayer and the well layer.

In the invention described in Patent Document 1, the Al composition of the barrier layer is made larger than the Al composition of the well layer. The composition is even larger. In such a barrier layer, a crystal defect is generated therein, and an electric resistance is increased.

The present invention has been made to solve the above-mentioned problem, and the configuration thereof is as follows.
_{Al x1 Ga y1 In 1-x1} -y1 N (0 <x1,0 ≦ y1, x1 + y1 <1) well layers made of, _Al was an essential constituent element _{Al x2 Ga y2 In 1-x2} -y2 N (0 A group III nitride-based compound semiconductor light emitting device having a quantum well structure having a barrier layer composed of <x2, 0 ≦ y2, x2 + y2 <1);
A group III nitride-based compound semiconductor light emitting device, wherein the Al composition of the barrier layer is the same as or smaller than the Al composition of the well layer.

According to the light emitting device configured as described above, light having a short wavelength can be emitted with a high output because the ternary mixed crystal of AlInN or the quaternary mixed crystal of AlGaInN is employed in the well layer. Further, since the Al composition of the barrier layer is the same or smaller than that of the well layer, it is possible to prevent the Al composition of the barrier layer from further increasing even if the Al composition of the well layer is increased. Therefore, it is possible to prevent lattice defects from being generated in the barrier layer and prevent the electrical resistance of the barrier layer from becoming unnecessarily large.

Hereinafter, each component of the present invention will be described.
(Group III nitride compound semiconductor light emitting device)
Group III nitride compound semiconductor is represented by the general formula _{Al X Ga Y In 1-X} -Y N (0 ≦ X ≦ 1,0 ≦ Y ≦ 1,0 ≦ X + Y ≦ 1), AlN, GaN and so-called binary system of _InN, including so-called ternary _{Al x Ga 1-x N,} Al x in 1-x N and _Ga x _{in 1-x} N (or more in 0 <x <1). At least a part of the group III element may be replaced by boron (B), thallium (Tl), or the like, and at least a part of nitrogen (N) may be replaced by phosphorus (P), arsenic (As), antimony (Sb) , Bismuth (Bi) or the like.

The group III nitride compound semiconductor may contain any dopant. Silicon (Si), germanium (Ge), selenium (Se), tellurium (Te), carbon (C), or the like can be used as the n-type impurity. As the p-type impurity, magnesium (Mg), zinc (Zn), beryllium (Be), calcium (Ca), strontium (Sr), barium (Ba), or the like can be used. Note that, after doping with a p-type impurity, the group III nitride compound semiconductor can be exposed to electron beam irradiation, plasma irradiation, or heating by a furnace, but is not essential.
Group III nitride-based compound semiconductors include, in addition to metalorganic chemical vapor deposition (MOCVD), well-known molecular beam crystal growth (MBE), halide vapor deposition (HVPE), sputtering, and ion plating. It can also be formed by a singing method or the like.

The material of the substrate on which the group III nitride-based compound semiconductor layer is grown is not particularly limited as long as it can grow the group III nitride-based compound semiconductor layer.For example, sapphire, gallium nitride, spinel, silicon, silicon carbide, Examples of the material of the substrate include zinc oxide, gallium phosphide, gallium arsenide, magnesium oxide, manganese oxide, and group III nitride compound semiconductor single crystals. Among them, it is preferable to use a sapphire substrate, and it is more preferable to use the a-plane or the c-plane of the sapphire substrate.

The light emitting element is formed by laminating such group III nitride compound semiconductor layers. In the present invention, a quantum well structure (a multiple quantum well structure or a single quantum well structure) of a group III nitride compound semiconductor is adopted as a layer structure for light emission.
Here, the well layer is made of AlGaInN containing Al and In as essential constituent elements. _{That, Al x1 Ga y1 In 1-} x1-y1 N (0 <x1,0 ≦ y1, x1 + y1 <1) 4 mixed crystal or the well layer from the ternary mixed crystal of AlInN of is formed. x1 and y1 are appropriately selected according to the lattice constant of the underlayer and the wavelength required for the light emitting element. When the underlayer is made of GaN, it is preferable that x1 is approximately 2.5 times y1.
In order to form a quantum well structure, the thickness of the well layer is preferably 10 nm or less, more preferably 1 to 8 nm, and still more preferably 2 to 4 nm.

The barrier layer is made of AlGaInN containing Al as an essential constituent element. _{That, Al x2 Ga y2 In 1-} x2-y2 N (0 <x2,0 ≦ y2, x2 + y2 <1) barrier layer ternary mixed crystal of quaternary mixed crystal or AlInN of is formed.
Here, the Al composition x2 of the barrier layer is equal to or smaller than the Al composition x1 of the well layer. More specifically, it is preferable that the relationship x2 ≦ x1 ≦ 1.5 × x2 is satisfied.
The thickness of the barrier layer constituting the quantum well structure is preferably 100 nm or less, more preferably 3 to 30 nm, and still more preferably 5 to 20 nm.

The well layer contains In, and the barrier layer also contains In as necessary. Since In has a small bandgap energy, the bandgap energy of each of the well layer and the barrier layer can be adjusted by adjusting the compounding amount and the compounding amount of Al which is an essential element of the present invention.

Next, an embodiment of the present invention will be described.
(Example 1)
FIG. 1 shows a schematic cross-sectional view of a light emitting device 10 of the embodiment. The specifications of each layer of the light emitting element 10 are as follows.
Layer: Composition p-type layer 15: p-GaN: Mg
Quantum well structure 14 (2 pairs): Al _0.15 Ga _0.79 In _0.06 N (well layer)
Al _0.15 Ga _0.85 N (barrier layer)
n-type layer 13: n-GaN: Si
Buffer layer 12: AlN
Substrate 11: Sapphire

An n-type layer 13 made of GaN doped with Si as an n-type impurity is formed on a substrate 11 via a buffer layer 12. Here, sapphire was used for the substrate 11, but it is not limited to this, and sapphire, spinel, gallium nitride, silicon, silicon carbide, zinc oxide, gallium phosphide, gallium arsenide, magnesium oxide, manganese oxide , Zirconium boride, a group III nitride compound semiconductor single crystal, or the like. Further, the buffer layer is formed by MOCVD using AlN, but the present invention is not limited to this. For example, GaN, InN, AlGaN, GaInN, AlGaInN, or the like can be used as a material. Method (MBE method), a halide vapor phase epitaxy method (HVPE method), a sputtering method, an ion plating method, or the like can be used. When a group III nitride compound semiconductor is used as the substrate, the buffer layer can be omitted.
Further, the substrate and the buffer layer can be removed if necessary after the formation of the semiconductor element.

Here, the n-type layer 13 is formed of GaN, but AlGaN, GaInN, or AlGaInN can be used.
Further, the n-type layer 13 is doped with Si as an n-type impurity, but Ge, Se, Te, C, or the like may be used as the n-type impurity.
As the quantum well structure 14, a multiple quantum well structure or a single quantum well structure can be adopted. The number of repetitions when the multiple quantum well structure is employed is not particularly limited, but is preferably 2 to 15.
It is not limited whether or not the AlGaN barrier layer exists between the well layer (the well layer closest to the n-type layer 13 when a plurality of well layers exist) and the n-type layer 13. Similarly, whether or not an AlGaN barrier layer exists between the well layer (the well layer closest to the p-type layer 15 when a plurality of well layers exist) and the p-type layer 15 is not limited.
The quantum well structure 14 may include a group III nitride compound semiconductor layer with a wide band gap doped with Mg or the like on the p-type layer 15 side. This is to effectively prevent electrons injected into the quantum well structure 14 from diffusing into the p-type layer 15.
A p-type layer 15 made of GaN doped with Mg as a p-type impurity is formed on the quantum well structure 14. The p-type layer can be made of AlGaN, GaInN or AlGaInN. Zn, Be, Ca, Sr, and Ba can be used as the p-type impurity. After the introduction of the p-type impurity, the resistance can be reduced by a known method such as electron beam irradiation, heating in a furnace, or plasma irradiation, but this is not essential.
In the light emitting diode having the above structure, each group III nitride compound semiconductor layer is formed by performing MOCVD under general conditions, or a molecular beam crystal growth method (MBE method), a halide gas phase growth method (HVPE method). ), A sputtering method, an ion plating method or the like.

The n-electrode 19 is composed of two layers of Al and V. After forming the p-type layer 15, a part of the p-type layer 15, the quantum well structure 14, and the n-type layer 13 are removed by etching, and the n-type It is formed on the mold layer 13.
The translucent electrode 17 is a thin film containing gold, and is laminated on the p-type layer 15. The p-electrode 18 is also made of a material containing gold, and is formed on the translucent electrode 17 by vapor deposition.

FIG. 2 is a chart showing the composition distribution of Al and In in the quantum well structure 14 of the light emitting diode 10 of the example. As can be seen from the figure, in the present embodiment, the Al composition is the same in the well layer and the barrier layer. In the well layer, the bandgap energy of the entire layer is reduced by increasing the composition of In.
For comparison, the composition distribution of Al and In of the light emitting diode described in Patent Document 1 is shown in FIG.

発 光 The light emitting diode of the above example had a light emission peak near 350 nm when a forward current of 20 mA was applied, and the light emission output was 0.5 mW. This was a light emission output about twice that of the light emitting device having a light emission peak in the same wavelength band in the prior art shown in FIG.

(Example 2)
Next, a light emitting diode according to a second embodiment of the present invention will be described. This light emitting diode has the layer structure shown in FIG. 1, and the specifications of each layer are as follows. The same elements as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
Layer: Composition p-type layer 15: p-GaN: Mg
Quantum well structure 24 (3 pairs): Al _0.15 Ga _0.79 In _0.06 N (well layer)
Al _0.14 Ga _0.85 In _0.01 N (barrier layer)
n-type layer 13: n-GaN: Si
Buffer layer 12: AlN
Substrate 11: Sapphire

FIG. 4 is a chart showing the composition distribution of Al and In in the quantum well structure 24 of the light emitting diode of this embodiment. As can be seen from the drawing, in this embodiment, the Al composition of the barrier layer is smaller than the Al composition of the well layer.
The light emitting diode of the above example had a light emission peak near 350 nm when a forward current of 20 mA was applied, and the light emission output was 0.5 mW. This was a light emission output about twice that of the light emitting device having a light emission peak in the same wavelength band in the prior art shown in FIG.

The present invention is not limited to the description of the above-described embodiments and examples. Various modifications are included in the present invention without departing from the scope of the claims and within the scope of those skilled in the art.

FIG. 1 is a sectional view schematically showing a layer structure of a light emitting device according to an embodiment of the present invention. FIG. 2 is a chart showing the composition of Al and In in the quantum well structure of the light emitting device of the example. FIG. 3 is a chart showing the composition of Al and In in the quantum well structure of the conventional light emitting device. FIG. 4 is a chart showing the composition of Al and In in the quantum well structure of the light emitting device of another embodiment.

Explanation of reference numerals

REFERENCE SIGNS LIST 10 light emitting diode 11 substrate 12 buffer layer 13 n-type layer 14 quantum well structure 15 p-type layer

Claims (4)

_{Al x1 Ga y1 In 1-x1} -y1 N (0 <x1,0 ≦ y1, x1 + y1 <1) well layers made of, _Al was an essential constituent element _{Al x2 Ga y2 In 1-x2} -y2 N (0 A group III nitride-based compound semiconductor light emitting device having a quantum well structure having a barrier layer composed of <x2, 0 ≦ y2, x2 + y2 <1);
A group III nitride-based compound semiconductor light emitting device, wherein the Al composition of the barrier layer is the same as or smaller than the Al composition of the well layer. Claim 1 wherein the barrier layer is made of _Al was an essential constituent elements Al and _{In x2 Ga y2 In 1-x2} -y2 N (0 <x2,0 <y2, x2 + y2 <1), characterized in that Group III nitride compound semiconductor light emitting device. 3. The group III nitride compound semiconductor light emitting device according to claim 1, wherein a relationship of x2 ≦ x1 ≦ 1.5 × x2 is satisfied between the well layer and the barrier layer. 4. 4. The group III nitride compound semiconductor light emitting device according to claim 1, wherein said well layer has a lattice constant substantially equal to that of a GaN layer serving as a base of said quantum well structure.

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