JP2003218396A - Ultraviolet-ray emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultraviolet-ray emitting element with higher output by optimizing the structure of the ultraviolet-ray emitting element of which the InGaN is the material of a light emission layer. <P>SOLUTION: On a crystal substrate B, a laminated structure S comprising a GaN-based crystal layer is formed across a buffer layer or directly while including a light emission part. The light emission part is in a multi-quantum well structure and InGaN which can emit ultraviolet rays is used for well layers, the number of the well layers is 2 to 20 and the thickness of a barrier layer is 7 to 30 nm. Consequently, high-output ultraviolet-ray emission is obtained although InGaN is used for a light emission layer. <P>COPYRIGHT: (C)2003,JPO

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 a GaN-based ultraviolet light emitting device in which an InGaN-based material having a composition capable of emitting ultraviolet light is used as a material for a light emitting layer.

[0002]

2. Description of the Related Art GaN-based light emitting diodes (LEDs) and G
Among GaN light emitting devices such as aN semiconductor lasers (LD), those using InGaN for the light emitting layer (in particular, blue / green light emitting devices having a light emitting layer with a high In composition)
It is generally known that highly efficient light emission can be obtained. This is because carriers are localized by fluctuations in the In composition, so that the proportion of the carriers injected into the light-emitting layer that are trapped in the non-radiative centers is small, resulting in highly efficient light emission. It is explained.

In GaN-based LEDs and GaN-based LDs,
In order to emit ultraviolet rays of 420 nm or less, InGaN (In composition of 0.15 or less) is generally used as the material of the light emitting layer. Generally, the upper limit of the wavelength of ultraviolet rays is shorter than the short wavelength end of visible light (380 nm to 400 nm), and the lower limit thereof is around 1 nm (0.2 nm to 2 nm), but in the present specification, the above In composition of 0. 15
The blue-violet light having a wavelength of 420 nm or less emitted from InGaN below is also referred to as ultraviolet light. The wavelength of ultraviolet light that can be generated by GaN is 365 nm. Therefore, In
When GaN is a ternary system that essentially contains an In composition and does not contain an Al composition, the lower limit of the wavelength of ultraviolet rays that can be generated is
The wavelength is longer than 365 nm. Below, InGa
An ultraviolet light emitting device using N as a material for the light emitting layer is
It is called a GaN ultraviolet light emitting device.

However, in comparison with the high In composition of the light emitting layer in the blue / green light emitting device, in the InGaN ultraviolet light emitting device,
Since ultraviolet rays have a short wavelength, it is necessary to reduce the In composition of the light emitting layer. For this reason, the effect of localization due to the above In composition fluctuation is reduced, and the ratio of being trapped in the non-radiative recombination center is increased, resulting in an obstacle to higher output.

On the other hand, in the InGaN ultraviolet light emitting device, the structure of the light emitting portion is a single quantum well (SQW) structure or a multiple quantum well (MQW) structure (so-called DH structure is included in the SQW structure because the active layer is thin). ), A light emitting layer (well layer) is sandwiched between cladding layers (including a barrier layer in a quantum well structure) made of a material having a bandgap larger than that. Literature (written by Hiroo Yonezu, published by Engineering Books Co., Ltd.,
According to "Optical Communication Device Engineering", page 72), the band gap difference between the light emitting layer and the cladding layer is generally "0.3 eV".
There is a guideline for the above.

From the above background, when InGaN is used for the light emitting layer (well layer) to generate ultraviolet rays, AlGaN having a large band gap is used for the clad layer / barrier layer sandwiching the light emitting layer in consideration of carrier confinement. Has been.

FIG. 6 shows In _0.03 Ga _0.97 N (emission wavelength 3
Conventional UV LED using 80 nm) as the material for the light emitting layer
It is a figure which shows an example of the element structure of. As shown in the figure,
The n-type GaN contact layer 101 is formed on the crystal substrate B10 via the buffer layer B20, and the SQW is formed thereon.
Light emitting part of structure (n-type Al _0.1 Ga _0.9 N cladding layer 10
2, In _0.03 Ga _0.97 N well layer (light emitting layer) 103, p-type Al _0.2 Ga _0.8 N cladding layer 104), and p-type GaN contact layer 105 are sequentially stacked by crystal growth. Further, an n-type electrode P10 is provided on the partially exposed n-type GaN contact layer 101, and p-type GaN is formed.
The element structure has a p-type electrode P20 provided on the contact layer 105.

The light emitting portion in the example of FIG. 6 has an SQW structure, but when this has an MQW structure, the barrier layer located between the two well layers must be thick enough to cause a tunnel effect. Generally, it is about 3 to 6 nm.

[0009]

However, even if the structure of various light emitting portions is set as described above, InGaN
In the ultraviolet light emitting device, sufficient output was not obtained due to the low In composition of the light emitting layer. An object of the present invention is to solve the above problems and to use InGaN as a material of a light emitting layer, and even when an InGaN-based material is used.
It is to provide a higher-power ultraviolet light emitting device by optimizing the device structure.

[0010]

The inventors of the present invention have limited the structure of the light emitting portion to the MQW structure even if the material of the light emitting layer is an InGaN-based material having a composition capable of emitting ultraviolet light, and further, the well layer thereof. The inventors have found that the output can be improved by limiting the number of layers and the thickness of the barrier layer to specific values, and have completed the present invention. That is, the ultraviolet light emitting device of the present invention has the following features.

(1) A laminated structure made of a GaN-based crystal layer is formed on a crystal substrate via a buffer layer or directly, and the laminated structure has a p-type layer and an n-type layer. A GaN-based semiconductor light-emitting device including a light-emitting portion configured as described above, wherein the light-emitting portion has a multiple quantum well structure, and
The well layer is made of an InGaN-based material capable of emitting ultraviolet light,
The number of well layers is 2 to 20 and the thickness of barrier layers is 7 nm to 30 n
m is an ultraviolet light emitting element.

(2) The above laminated structure is formed on a crystal substrate via an AlN low temperature growth buffer layer,
Immediately above the AlN low temperature growth buffer layer, Al _x Ga _1-x N
(0 <x ≦ 1) The ultraviolet light emitting element as described in (1) above, wherein an underlayer is formed.

(3) Al _x Ga _{1 -x} N (0 <x ≤ 1) The ultraviolet light emitting device according to the above (2), characterized in that there is no AlGaN layer between the underlayer and the well layer. .

(4) The positional relationship between the p-type layer and the n-type layer in the above laminated structure is such that the p-type layer is on the upper side, and the p-type contact layer is In _Y Ga _{1 -Y} N (0 < Y ≦ 1), the ultraviolet light emitting device as described in any one of (1) to (3) above.

(5) The multiple quantum well structure has a barrier layer in contact with the p-type layer, and the thickness of the barrier layer in contact with the p-type layer is 10 nm to 30 nm. ) To (4), the ultraviolet light emitting device.

(6) The above-mentioned multiple quantum well structure is composed of a well layer made of a non-doped GaN-based crystal and a barrier layer made of a Si-doped GaN-based crystal. The ultraviolet light emitting device according to any one of 5).

(7) The above-mentioned multiple quantum well structure is In _x G
The ultraviolet light emitting device according to any one of (1) to (6) above, which is configured by a well layer made of a _1-x N (0 <x ≦ 1) and a barrier layer made of GaN.

(8) AlG is provided between the crystal substrate and the well layer.
The ultraviolet light emitting device as described in (1) above, which is free of a layer made of aN.

(9) The above-mentioned (1) to (8), wherein the crystal substrate is processed to have irregularities on its surface, and the GaN-based crystal layer covers the irregularities and is vapor-phase grown to have a laminated structure. The ultraviolet light emitting device according to any one of claims.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The GaN system referred to in the present invention means In
_X Ga _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦
1, X + Y + Z = 1), for example, AlN, GaN, AlGaN, InGa
N, InGaAlN and the like are mentioned as important compounds. In addition, InGaN-based means the In _x Ga _y Al _z N
Among them, the In composition and the Ga composition are indispensable, and in addition to InGaN, InGaN may be added with the Al composition.

The ultraviolet light emitting device according to the present invention comprises an ultraviolet light L
The present invention will be described below by taking an ultraviolet LED as an example although it may be an ED or an ultraviolet LD. Further, in the element structure, whichever of the p-type layer and the n-type layer may be on the lower side (the crystal substrate side), it is easy to obtain a high-quality GaN-based semiconductor crystal for manufacturing reasons. , N
The embodiment in which the mold layer is on the lower side is preferable. Hereinafter, the element structure will be described with the n-type layer as the lower side, but the invention is not limited to this.

FIG. 1 is a view showing one structural example (LED element structure) of the ultraviolet light emitting element according to the present invention. As shown in the figure, a laminated structure S composed of a GaN-based crystal layer is grown on a crystal substrate B via a GaN-based low temperature growth buffer layer B1. The laminated structure S includes a p-type layer and an n-type layer. An ultraviolet light emitting device according to the present invention is provided by including a light emitting portion configured with a mold layer and further providing electrodes.

More specifically showing the structure of each layer in the example of FIG. 1, the sapphire crystal substrate B,
GaN low temperature growth buffer layer B1, undoped GaN layer 1, light emitting part [n-type GaN cladding layer (= contact layer)
2, MQW structure 3 (GaN barrier layer / InGaN well layer /
GaN barrier layer / InGaN well layer / GaN barrier layer), p
Type AlGaN clad layer 4] and p type GaN contact layer 5. The n-type GaN contact layer is partially exposed, the n-type electrode P1 is formed on the exposed surface, and the p-type Ga is formed.
A p-type electrode P2 is formed on the upper surface of the N contact layer.

An important feature of the above device structure is that the light emitting portion essentially includes the MQW structure, InGaN having a composition capable of emitting ultraviolet light is used as the material of the well layer of the MQW structure, and the number of well layers is 2 to 20, the thickness of the barrier layer is 7
It is at a point of being set to nm to 30 nm. By limiting the light emitting portion to such a structure, an InGaN-based material,
In particular, although it is an ultraviolet light emitting device using InGaN for the light emitting layer, a higher output than before can be obtained.

The light emitting portion is constituted by including a p-type cladding layer and an n-type cladding layer, and has an MQW structure between them.
Both the n-type and p-type cladding layers may be layers that also serve as both the n-type and p-type contact layers, respectively. Also, LD
In the device structure of 1), a waveguiding layer, a cap layer, or the like may be added inside the clad layer, if necessary.

FIG. 3 is a graph showing the relation between the number of MQW well layers and the light emission output, obtained by the measurement in Example 1 below. As is clear from the graph, the number of well layers should be 2 to 20, and outside this range, the light emission output is a low value as before. Further, the number of well layers is particularly preferably 8 to 15, and the highest light emission output is obtained at this time.

The material for the well layer may be an InGaN-based material, especially In _x Ga _{1 -x} N, as long as it has a composition capable of emitting ultraviolet rays of 420 nm or less. The specific In composition x of In _x Ga _1-x N is 0 ≦ x ≦ 0.11. The material of the well layer does not necessarily have to have the same In composition in all the layers, and may be appropriately selected, for example, by grading. The thickness of the well layer may be the same as that of a known MQW structure, and may be, for example, 2 nm to 10 nm.

The barrier layer does not necessarily have to exist independently as the outermost layer adjacent to both cladding layers.
The following modes 1 to 3 may be used. A mode in which the cladding layer also serves as the outermost barrier layer, such as (n-type cladding layer / well layer / barrier layer / well layer / p-type cladding layer). A mode in which the outermost barrier layer exists separately from the cladding layer, such as (n-type cladding layer / barrier layer / well layer / barrier layer / well layer / barrier layer / p-type cladding layer). (N-type clad layer / well layer / barrier layer / well layer / barrier layer / p-type clad layer), in which the outermost barrier layer exists independently on only one side.

In the present invention, the thickness of all barrier layers of the MQW structure is set to 7 nm to 30 nm. FIG. 4 is a graph showing the relation between the barrier layer thickness and the output of the light emitting device, which is obtained by the measurement in the following examples. As is clear from the graph of the figure, an ultraviolet light emitting device having a high emission output can be obtained when the thickness of the barrier layer is 7 nm to 30 nm, and when the barrier layer is thinner than 7 nm or thicker than 30 nm, The emission output is low as before. Within the range of the thickness of the barrier layer, 8 nm to 15 nm is particularly preferable, and at this time, the light emitting device having the highest output can be obtained.

In the conventional MQW structure, the thickness of the barrier layer was 3 nm to 6 nm, whereas in the present invention, the thickness of the barrier layer is 7 nm to 30 nm. By increasing the thickness of the barrier layer to such a value, overlapping of the wave functions is eliminated, and a state in which SQW structures are stacked in multiple layers rather than an MQW structure is obtained, but a sufficiently high output is achieved. When the thickness of the barrier layer exceeds 30 nm, holes injected from the p-layer are trapped by dislocation defects or the like that are non-radiative centers existing in the GaN barrier layer before reaching the well layer, and the emission efficiency is reduced. Is not preferred.

As a preferred embodiment of the MQW structure in the present invention, the outermost barrier layer is always present on the p-type clad layer side (that is, the above-mentioned or embodiment), and the outermost barrier layer thickness on the p-type side. A mode in which the thickness is 10 to 30 nm is included. As a result, the well layer is less likely to be damaged by heat and gas when the layers after the p-type clad layer are grown, so that the damage is reduced, and the dopant material (Mg or the like) from the p-type layer is removed from the well layer. Diffusion is reduced and the strain applied to the well layer is also reduced, so that not only the output is improved, but also the effect of prolonging the life of the device is obtained.

The material of the barrier layer may be any GaN-based semiconductor material having a bandgap that can serve as a barrier layer for the InGaN well layer, but GaN is recommended as the preferred material in the present invention. In the conventional MQW structure, in consideration of carrier confinement in the well layer, a barrier layer having a band gap sufficiently larger than that of the well layer is used. In particular, in the case of an ultraviolet light emitting element, the band gap of the well layer itself is larger than that of a blue light emitting element, so that it is necessary to use a material having a larger band gap for the barrier layer. For example, when the well layer is InGaN (In composition 0.03), AlGaN is used for the barrier layer and the cladding layer.

On the other hand, in the present invention, attention is paid to the fact that the optimum values of the crystal growth temperatures are greatly different in the combination of the InGaN well layer and the AlGaN barrier layer, and this is taken up as a problem. That is, A which is the composition of AlGaN
1N has a higher melting point than GaN, and InN, which is the composition of InGaN, has a lower melting point than GaN. The specific optimum temperature for crystal growth is 1000 ° C. for GaN, and I
nGaN is 1000 ° C. or lower (preferably 600 to 800)
Almost equal to or higher than GaN. Therefore, I
Combining the nGaN well layer and the AlGaN barrier layer,
Unless the growth temperature is largely changed to the respective preferable values during the growth of the well layer and during the growth of the barrier layer, a layer having a preferable crystal quality cannot be obtained.

However, changing the growth temperature for each well layer / barrier layer provides a growth interruption, and in the case of a well layer which is a thin film of about 3 nm, the thickness varies due to the etching action during the growth interruption. However, problems such as crystal defects on the surface occur. Because of these trade-off relationships,
It is difficult to obtain a high quality product by combining the AlGaN barrier layer and the InGaN well layer. In addition, the barrier layer is made of AlGaN
Therefore, there is a problem that strain is applied to the well layer, which hinders high output.

Therefore, in the present invention, GaN is used as the material of the barrier layer to alleviate the above trade-off problem. This reduces the band gap difference between the barrier layer and the well layer, but improves the crystal quality of both layers,
The output is improved overall. In addition, as the InGaN-based material, AlInGaN in which Al is mixed with InGaN may be used as the well layer, and thereby it is possible to obtain the same effect as that of InGaN.

Further, in the present invention, the InGaN well layer and A
In connection with the solution of the above-mentioned problem regarding the combination with the lGaN barrier layer, between the crystal substrate and the well layer (in a mode in which the AlGaN underlayer is formed directly on the AlN low temperature growth buffer layer described later, the AlGaN underlayer and the well layer are formed). Between) and AlGa
The mode in which the N layer is not present is recommended. This alleviates the above problem caused by the difference in crystal growth temperature. A specific example of the mode is a mode in which a GaN layer is used instead of the AlGaN layer. In the example of FIG. 1, undoped GaN with no impurities added on the GaN low temperature buffer layer.
A crystal layer (thickness 0.1 μm to 2.0 μm) is grown, and an n-type GaN crystal layer (contact layer / cladding layer) is grown on the crystal layer.
Is growing. The undoped GaN crystal layer may be omitted. The n-type GaN crystal layer may be provided separately for the n-type GaN contact layer and the n-type GaN clad layer by changing the carrier concentration.

As another preferred embodiment of the MQW structure,
An example is a mode in which the door layer is not added and Si is added to the barrier layer.
To be FIG. 5 shows the carrier concentration by adding Si to the barrier layer.
6 is a graph showing the relationship between the degree and the light emission output. For measurement
In the sample, the number of well layers was 6, and the thickness of the barrier layer was
Is set to 10 nm, but the same applies to other cases. Same figure
As is clear from the graph of, when Si is not added,
Light emission output is small, and the amount of Si added is 5 x 10 ¹⁸cm
^-3It can be seen that the light emission output is reduced even with the above. Barrier layer
Since addition of Si to Si has the function of increasing the emission intensity
Desirably, if too much is added, the crystallinity will decrease,
On the contrary, the emission intensity decreases. Desirable Si addition amount is 5 × 1
0¹⁶cm^-3~ 5 x 10¹⁸cm^-3Is.

The crystal substrate used for growth may be any one capable of growing GaN-based crystals. Preferred crystal substrates include, for example, sapphire (C plane, A plane, R plane), S
Examples thereof include iC (6H, 4H, 3C), GaN, AlN, Si, spinel, ZnO, GaAs, NGO and the like.
Further, it may be a substrate having these crystals as a surface layer. The plane orientation of the substrate is not particularly limited, and may be a just substrate or a substrate having an off angle.

If desired, a buffer layer may be interposed between the crystal substrate and the GaN-based crystal layer. The buffer layer is not essential when using a substrate made of GaN, AlN crystal, or the like as the crystal substrate. In order to obtain a high quality GaN film with few dislocations, it was found that an AlGaN film having a different lattice constant should be arranged as an underlayer on which the GaN film is grown. When grown on the AlGaN film, compressive stress is applied to GaN. When the growth is performed in such a state, the AlGaN film / GaN film interface (more precisely, the AlG film
It was found that dislocations are bent perpendicularly to the growth direction at the initial growth stage of GaN on the aN film and do not propagate in the growth direction. That is, by doing so, a high quality GaN film can be obtained. To grow this AlGaN underlayer, it is preferable to use a buffer layer as the underlayer. A preferable example of the buffer layer is a GaN-based low temperature growth buffer layer. For the material, forming method, and forming conditions of the buffer layer, known techniques may be referred to, but as the GaN-based low temperature growth buffer layer material, GaN, AlN, InN, etc. are exemplified, and the growth temperature is 300 ° C to 600 ° C. ℃ is mentioned. The thickness of the buffer layer is 10 nm to 50 nm, especially 20 nm.
nm to 40 nm is preferable. A particularly preferable form is an AlN buffer layer. FIG. 2 shows an example of the element structure of this embodiment. As shown in the figure, on the crystal substrate B,
A laminated structure S composed of a GaN-based crystal layer is grown via the AlN low temperature growth buffer layer 10, and Al _x Ga _1-x N (0 <x ≦ 1) is formed directly on the AlN low temperature growth buffer layer 10.
The base layer 11 is formed.

The optimum thickness of the Al _x Ga _1-x N underlayer is Al
It varies depending on the composition (value of x). For example, if the Al composition is 3
In the case of 0% (x = 0.3), the thickness is 10 nm to 5 μm,
Particularly, 50 nm to 1 μm is preferable. If the thickness is less than 10 nm, the above effect is lost, which is not preferable. 5 μm
If it is thicker than this, the crystallinity of the GaN layer is deteriorated, which is not preferable. Further, the Al composition (value of x) of the Al _x Ga _1-x N underlayer may be inclined in the growth direction. The Al composition may be continuously changed or may be changed stepwise in multiple stages. Further, the AlGaN underlayer has a large thickness (for example, when the Al composition is 30%, 500 nm to 500 nm).
In the case of about 0 nm), the light emitting portion may be formed directly thereon.

In the present invention, the p-type contact layer is made of InGa.
Forming with N is one of the preferable embodiments. That is, in the conventional GaN-based light emitting device using the p-type GaN contact layer, the p-type contact resistance is 1 × 10 ⁻³ Ωcm.
^It is as high as about ^2, and even a good one is about 1 × 10 ⁻⁴ Ωcm ² . On the other hand, when InGaN is used as the material for the p-type contact layer, the acceptor level becomes shallow and the hole concentration increases, and the contact resistance is 1 ×.
The advantage is that it is as low as 10 ⁻⁶ Ωcm ² .

The p-type contact layer on which the p-type electrode is to be formed is particularly preferably Mg-doped In _Y Ga _1-Y N (0 <Y ≦ 1). By setting the gas atmosphere during the growth of the InGaN layer to N ₂ + NH ₃ , it is possible to relax the condition of so-called p-type treatment for activating Mg after the growth or omit the treatment itself. This is because if the amount of H _{2 in} the gas atmosphere during growth is small, it is possible to suppress the mixture of H ₂ that inactivates Mg into the film. InGa
The acceptor level formed when Mg is doped into N increases the hole carrier concentration at room temperature due to the shallow acceptor level, so that the condition for the p-type treatment can be relaxed or the treatment itself can be omitted. By applying the p-type InGaN contact layer to the ultraviolet light emitting device, the light emission output can be further improved. This is p
This is because it is possible to suppress the diffusion of the doped impurities into the well layer as a result of relaxing the conditions for the patterning process (in particular, thermal annealing) or omitting the process itself. In particular, when the MQW structure is composed of a well layer made of non-doped GaN-based crystal and a barrier layer made of Si-doped GaN-based crystal, it is not necessary to perform heat treatment, so that a steep impurity profile is obtained. Will be obtained. As a result, it is considered that the light emission output is further improved.

In order to reduce the dislocation density of the GaN-based crystal layer grown on the crystal substrate, a structure for reducing the dislocation density may be appropriately introduced. Along with the introduction of the structure for reducing the dislocation density, a part made of a different material such as SiO ₂ may be included in the laminated structure made of the GaN-based crystal layer.

Examples of the structure for reducing dislocation density include the following. (Ii) A structure in which a mask layer (SiO ₂ or the like is used) is formed as a stripe pattern on a crystal substrate so that a conventionally known selective growth method (ELO method) can be carried out. (B) A structure in which dot-shaped and stripe-shaped irregularities are formed on the crystal substrate so that the GaN-based crystal can undergo lateral growth or facet growth. These structures and the buffer layer may be combined appropriately.

Among the structures for reducing the dislocation density, the above (ro) is a preferable structure without using a mask layer.
This will be described below. As a method of processing unevenness, for example, using a normal photolithography technique,
Examples thereof include a method of patterning according to the mode of the target unevenness and performing etching processing using the RIE technique or the like to obtain the target unevenness.

The uneven pattern is a pattern in which dot-like concave portions (or convex portions) are arranged, or stripes in which linear or curved concave grooves (or convex ridges) are arranged at regular or irregular intervals. Such as a pattern and a concentric pattern. The pattern in which the convex ridges intersect in a grid pattern can be regarded as a pattern in which dot-shaped (square hole-shaped) recesses are regularly arranged. Further, the cross-sectional shape of the unevenness may be rectangular (including trapezoidal) wavy, triangular wave, sine curve, or the like.

Among these various concavo-convex patterns, the stripe-shaped concavo-convex pattern (rectangular wavy section) in which linear concave grooves (or convex ridges) are arranged at regular intervals can simplify the manufacturing process and It is preferable because the pattern can be easily produced.

When the uneven pattern has a stripe shape, the longitudinal direction of the stripe may be arbitrary.
For a GaN-based crystal grown by embedding this, <11
In the case of the −20> direction, lateral growth is suppressed and {1
Oblique facets such as the −101} plane are easily formed. As a result, dislocations propagating in the C-axis direction from the substrate side are bent laterally on this facet surface, and it is difficult to propagate upward, which is particularly preferable in that a low dislocation density region can be formed.

GaN growing in the longitudinal direction of the stripe
In the case of the <1-100> direction for the system crystal, the GaN-based crystal that has started to grow from the upper portion of the convex portion grows laterally at a high speed and becomes a GaN-based crystal layer with the concave portion left as a cavity. However, if the longitudinal direction of the stripe is <1-10
Even in the case of the <0> direction, the same effect as in the case of the <11-20> direction can be obtained by selecting the growth condition in which the facet surface is easily formed.

The preferred dimensions in the case of making the cross section of the unevenness into a rectangular wave shape are as follows. The width of the groove is from 0.1 μm
20 μm, particularly 0.5 μm to 10 μm is preferable. The width of the convex portion is 0.1 μm to 20 μm, particularly 0.5 μm to 10 μm.
μm is preferred. The amplitude of the unevenness (depth of the groove) is
It is sufficient that the projection has a depth of 20% or more of the wide one. These dimensions, the pitch calculated from them, and the like are the same for unevenness of other cross-sectional shapes.

As a method of growing the GaN-based crystal layer, HV is used.
The PE method, MOVPE method, MBE method and the like can be mentioned. The HVPE method is preferable when forming a thick film, but the MOVPE method or MBE method is preferable when forming a thin film.

[0052]

Example 1 In this example, the ultraviolet LED shown in FIG. 1 was manufactured, the thickness of the barrier layer was fixed to 10 nm, and the number of well layers was 1 to 25.
25 kinds of samples were formed, and the output of each was measured. The element forming process is as follows.

For each of the samples, first, a C-plane sapphire substrate was mounted on a MOVPE apparatus, and the sample was placed under a hydrogen atmosphere at 11
The temperature was raised to 00 ° C. and thermal etching was performed. The temperature was lowered to 500 ° C., trimethylgallium (hereinafter referred to as TMG) as a III group raw material, and ammonia as a N raw material were flown to grow a GaN low temperature buffer layer having a thickness of 30 nm.

Then, the temperature is raised to 1000 ° C., TMG and ammonia are flown as raw materials to grow the undoped GaN crystal layer 1 to 2 μm, and then SiH ₄ is flown to the Si-doped n-type GaN crystal layer (contact). Layer and clad layer)
Were grown to 3 μm.

[Quantum Well Structure] After lowering the temperature to 800 ° C., a GaN barrier layer (thickness 10 nm) to which Si is added at 5 × 10 ¹⁷ cm ⁻³ and an InGaN well layer (emission wavelength 38
0 nm, In composition 0.03, thickness 3 nm) was changed for each sample to be 1 to 25. further,
In each sample, the last Ga that contacts the p-layer
N barrier layer (added Si 5 × 10 ¹⁷ cm ⁻³ , thickness 20 n
m) was formed.

The growth temperature of each sample was 1000.
After the temperature was raised to 0 ° C., a p-type AlGaN cladding layer 4 having a thickness of 30 nm and a p-type GaN contact layer having a thickness of 50 nm were sequentially formed to form an ultraviolet LED wafer having an emission wavelength of 380 nm, and further, electrodes were formed and elements were separated. An ultraviolet LED chip was used.

Ultraviolet rays L having different numbers of well layers obtained above
20m each of ED chip samples in bare chip state
When the output at a wavelength of 380 nm was measured by energizing A,
As shown in FIG. 3, a graph showing the relationship between the number of well layers and the output was obtained. As described above, the number of well layers should be 2 to 20 at which an output of 2 mW or more can be obtained, and 6 to 15 in particular has been found to be a preferable number of well layers at which an emission output of 5 mW or more can be obtained. .

Example 2 In this example, the ultraviolet LED shown in FIG. 1 was manufactured by the same process as in Example 1, the number of well layers was fixed at 6, and the thickness of the barrier layer was 3 nm. Samples varied up to -40 nm were formed and the output of each was measured.

The samples of the ultraviolet LED chips having different barrier layer thicknesses obtained in this example were measured for output at a wavelength of 380 nm at a current of 20 mA in a bare chip state. A graph was obtained showing the relationship between thickness and output. As described above, the barrier layer thickness should be 7 nm to 30 nm at which an output of 2 mW or more can be obtained, and particularly 8 nm to 15 nm is a preferable barrier layer thickness at which an emission output of 5 mW or more can be obtained. all right.

Although the thickness of the barrier layer is fixed to one type in the first embodiment and the number of well layers is fixed to one in the second embodiment, the thickness of the barrier layer is the same as in the device forming process. The thickness of the barrier layer was changed in the range of 7 to 30 nm, and the element samples were formed in which the number of well layers was changed in the range of 2 to 20 at each thickness. However, a curve similar to that of FIG. 3 is obtained for the change of the number of well layers, and a curve showing the same tendency as that of FIG. 4 is obtained for the change of the thickness of the barrier layer regardless of the number of wells. I understood.

Example 3 In this example, for all the samples manufactured in Examples 1 and 2, the GaN low temperature buffer layer was an AlN low temperature buffer layer and the undoped GaN crystal layer was AlGaN.
Using the p-type GaN contact layer as a base layer and p-type InGaN
Make a sample of UV LED as a contact layer,
The output of each was measured. The element forming process is as follows.

For each of the samples, first, a C-plane sapphire substrate was mounted on the MOVPE apparatus, and the sample was placed under a hydrogen atmosphere at 11
The temperature was raised to 00 ° C. and thermal etching was performed. The temperature was lowered to 350 ° C., trimethylaluminum (hereinafter referred to as TMA) as a group III raw material and ammonia as a raw material N were flown to grow an AlN low temperature buffer layer having a thickness of 20 nm.

Subsequently, the temperature is raised to 1000 ° C., TMA, TMG, and ammonia are flown as raw materials to obtain an Al composition of 10
% Undoped AlGaN crystal layer (underlayer) 1
After the growth of 0 nm, the supply of TMA was stopped, SiH ₄ was flown, and a Si-doped n-type GaN crystal layer (contact layer / cladding layer) was grown to 4 μm. After that, an MQW structure was formed in the same manner as in Examples 1 and 2.

The growth temperature of each sample was 1000.
After the temperature was raised to 0 ° C., the p-type AlGaN cladding layer 4 having a thickness of 30 nm, the p-type GaN layer having a thickness of 50 nm, and the p-type I having a thickness of 5 nm were formed.
An nGaN contact layer (In composition: 10%) was sequentially formed to form an ultraviolet LED wafer having an emission wavelength of 380 nm, and then electrodes were formed and elements were separated to obtain an ultraviolet LED chip.

Each of the ultraviolet LED chip samples obtained as described above was exposed to a wavelength of 3 at a bare chip state and a current of 20 mA.
When the output at 80 nm was measured, all the samples were 10% to 10% higher than the samples of Examples 1 and 2.
The output was improved by about 30%.

[0066]

As described above, as the MQW structure, the number of well layers is 2 to 20, and the thickness of barrier layers is 7 nm to 30 n.
By setting m, InGaN-based materials, especially InG
Although it is an ultraviolet element using aN as the material of the light emitting layer, it has become possible to obtain a high output that has never been obtained.

[Brief description of drawings]

FIG. 1 is a schematic view showing a structural example of an ultraviolet light emitting device according to the present invention.

FIG. 2 is a schematic view showing another structural example of the ultraviolet light emitting device according to the present invention.

FIG. 3 shows MQW obtained by measurement in Example 1 of the present invention
3 is a graph showing the relationship between the number of well layers and light emission output.

FIG. 4 is an MQW obtained by measurement in Example 2 of the present invention.
5 is a graph showing the relationship between the thickness of the barrier layer and the light emission output.

FIG. 5 is a graph showing a relationship between a barrier layer carrier concentration (unit: cm ⁻³ ) and light emission output due to addition of Si to the barrier layer in the ultraviolet device according to the present invention.

FIG. 6 is a diagram showing an example of an element structure of a conventional ultraviolet LED using In _0.03 Ga _0.97 N as a material for a light emitting layer.

[Explanation of symbols]

B crystal substrate Laminated structure composed of S GaN-based crystal layers 2 n-type clad layer 3 MQW structure 4 p-type clad layer P1 n-type electrode P2 p-type electrode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoichiro Ouchi             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Takashi Tsunekawa             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works F-term (reference) 5F041 AA03 AA11 CA05 CA34 CA40                       CA46 CA49 CA57 CA65                 5F073 AA74 CA07 CB05 CB07 DA05                       DA35

Claims (9)

[Claims] 1. A laminated structure composed of a GaN-based crystal layer is formed on a crystal substrate via a buffer layer or directly, and the laminated structure has a p-type layer and an n-type layer. A GaN-based semiconductor light-emitting device including a configured light-emitting portion, wherein the light-emitting portion has a multiple quantum well structure, and the well layer is made of an InGaN-based material capable of emitting ultraviolet light. Is 2 to 20, and the thickness of the barrier layer is 7 nm to 30 nm. 2. The layered structure is formed on a crystal substrate via an AlN low temperature growth buffer layer, wherein
Immediately above the 1N low temperature growth buffer layer, Al _x Ga _{1 -x} N (0 <
x ≦ 1) The ultraviolet light emitting element according to claim 1, wherein a base layer is formed. 3. The ultraviolet light emitting element according to claim 2, wherein there is no layer made of AlGaN between the Al _x Ga _1-x N (0 <x ≦ 1) underlayer and the well layer. 4. The positional relationship between the p-type layer and the n-type layer in the laminated structure is such that the p-type layer is on the upper side, and the p-type contact layer is In _Y Ga _{1 -Y} N (0 <Y <1) The ultraviolet light emitting element according to any one of claims 1 to 3, wherein 5. The multi-quantum well structure has a barrier layer in contact with the p-type layer, and the thickness of the barrier layer in contact with the p-type layer is 10 nm to 30 nm.
4. The ultraviolet light emitting device according to any one of 4 above. 6. The multi-quantum well structure is an undoped Ga
The ultraviolet light emitting device according to claim 1, wherein the ultraviolet light emitting device comprises a well layer made of an N-based crystal and a barrier layer made of a GaN-based crystal with Si added. 7. The multi-quantum well structure is In _x Ga _1-x.
7. The ultraviolet light emitting device according to claim 1, which is composed of a well layer made of N (0 <x ≦ 1) and a barrier layer made of GaN. 8. AlGaN between the crystal substrate and the well layer
2. The ultraviolet light emitting device according to claim 1, wherein there is no layer formed of. 9. The crystal substrate according to claim 1, wherein the surface of the crystal substrate is processed to have irregularities, and the GaN-based crystal layer is vapor-deposited to cover the irregularities to form a laminated structure. Ultraviolet light emitting element.