WO2003043097A1

WO2003043097A1 - Ultraviolet emitting device

Info

Publication number: WO2003043097A1
Application number: PCT/JP2002/011770
Authority: WO
Inventors: Hiroaki Okagawa; Kazuyuki Tadatomo; Yoichiro Ouchi; Takashi Tsunekawa
Original assignee: Mitsubishi Cable Industries, Ltd.
Priority date: 2001-11-15
Filing date: 2002-11-12
Publication date: 2003-05-22
Also published as: KR20040062636A; KR100709058B1; CN1586015A; TW567620B; CN100355094C; JP2003218396A; TW200300300A

Abstract

A multilayer structure (S) comprising a GaN crystal layer and an emitting region is built directly on a crystal substrate (B) or on a buffer layer on the crystal substrate (B). The emitting region has a multiple quantum well structure. The well layers are made of InGaN that can emit ultraviolet radiation. The number of well layers is 2 to 20, and the thickness of a barrier layer is 7 to 30 nm. Therefore, a high output power of ultraviolet radiation is achieved though the emitting layer is made of InGaN. To form a high-quality GaN film, an AlGaN underlying layer is preferably formed directly on an AlN low-temperature growth buffer layer. A mode is recommended in which an AlGaN layer is not formed between the crystal substrate and a well layer (between the AlGaN underlying layer and a well layer in the case of the mode where the AlGaN underlying layer is provided.)

Description

Specification

UV light emitting element

Technical field

The present invention relates to a semiconductor light-emitting device, and more particularly to a GaN-based ultraviolet light-emitting device using an InGaN-based material having a composition capable of emitting ultraviolet light as a material of a light-emitting layer.

Background art

Among GaN light-emitting devices such as GaN-based light-emitting diodes (LEDs) and GaN-based semiconductor lasers (LDs), those using InGaN as the light-emitting layer (especially, light-emitting layers with a high In composition) It is generally known that a blue-green light-emitting element having high efficiency can emit light with high efficiency. This is because, due to the localization of carriers due to fluctuations in the In composition, the proportion of carriers injected into the light-emitting layer that is trapped in non-light-emitting centers is reduced, resulting in high-efficiency light emission. Is described.

Even when trying to emit ultraviolet light of 420 nm or less in GaN-based LEDs or GaN-based LDs, InG aN (In composition 0.15 or less) is generally used as the material of the light-emitting layer. Used.

In general, the upper limit of the wavelength of ultraviolet light is shorter than the short wavelength end of visible light (380 η π! ~ 400 nm), and the lower limit is around I nm (0.2 nm ~ 2niii). Ultraviolet light including 420 ηπι or less emitted by InG aN having an Iri composition of 0.15 or less is referred to as ultraviolet light. The wavelength of ultraviolet light that can be generated by G a Ν is 365 nm. Therefore, when InGaN is a ternary system that essentially contains the In composition and does not contain the A1 composition, the lower limit of the wavelength of the ultraviolet light that can be generated is a wavelength longer than 365 nm. . Hereinafter, an ultraviolet light emitting device using InGaN as a material of a light emitting layer is referred to as an InGaN ultraviolet light emitting device.

However, compared to the high In composition of the light emitting layer of the blue-green light emitting element, the InGaN ultraviolet light emitting element needs to reduce the In composition of the light emitting layer because the ultraviolet light has a short wavelength. For this reason, the effect of localization due to the fluctuation of the In composition described above is reduced, and non-light emission is performed. The rate of capture at the recombination center has increased, and as a result, has hindered high output. On the other hand, in the IriGaN ultraviolet light-emitting device, the light-emitting portion has a single quantum well (SQW) structure or a multiple quantum well (MQW) structure (the so-called DH structure is included in the SQW structure because the active layer is thin). ), The light emitting layer (well layer) is sandwiched by cladding layers (including barrier layers in the quantum well structure) made of a material of a larger band gap. According to the literature (Hiroo Yonezu, published by Kogaku Tosho Co., Ltd., “Optical Communication Device Engineering”, page 72), it is generally suggested that the difference in the band gap between the light emitting layer and the cladding layer be 0.3 eV or more. Is out.

From the above background, when ultraviolet light is generated by using InGaN for the light emitting layer (well layer), the cladding layer sandwiching the light emitting layer 障壁 The barrier layer must have a large band gap in consideration of carrier confinement. N is used.

_{_{6, I n 0. 03 G a}} . FIG. 2 is a diagram showing an example of a conventional element structure of a conventional UV LED using ₉₇ N (emission wavelength: 380 nm) as a material of an emission layer. As shown in the figure, an n-type GaN contact layer 101 is formed on a crystal substrate B10 via a buffer layer B20, and a light emitting portion (n-type Aa. . ₉ N cladding layer _{_{102, I ll 0. 03 G}} a .. g7 N well layer (light emitting layer) 103, p-type _{_{_{A l 0. 2 G a ..}}} 8 N cladding layer 10 4), p-type G a N The contact layers 105 are sequentially stacked by crystal growth. Further, an element structure in which an η-type electrode P 10 is provided on the partially exposed η-type Ga contact layer 101 and a p-type electrode P 20 is provided on the ρ-type Ga contact layer 105 It has become.

Although the light emitting part in the example of FIG. 6 has an SQW structure, if this is an MQW structure, the barrier layer located between the two well layers needs to be thick enough to cause a tunnel effect. Is about 3 to 6 nm.

However, even with various light-emitting portions as described above, the InGaN ultraviolet light-emitting device has not been able to obtain a sufficient output due to the low In composition of the light-emitting layer.

Disclosure of the invention The object of the present invention is to solve the above-mentioned problems, and when using InG aN as the material of the light emitting layer, and even when using IiiGaN-based material, by optimizing the element structure, a higher output ultraviolet light can be obtained. It is to provide a light emitting device.

The present inventors 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 capable of emitting ultraviolet light, and furthermore, the number of well layers and the thickness of the barrier layer. It has been found that the output can be improved by limiting the value to a specific value, and the present invention has been completed. That is, the ultraviolet light emitting device of the present invention has the following features. '

(1) A stacked structure composed of a GaN-based crystal layer is formed on a crystal substrate via a buffer layer or directly, and the stacked structure includes a p-type layer and an n-type layer. A GaN-based semiconductor light-emitting device including a light-emitting portion to be formed, wherein the light-emitting portion has a multiple quantum well structure, and the well layer is made of an In GaN-based material capable of emitting ultraviolet light; An ultraviolet light emitting device, wherein the number of well layers is 2 to 20, and the thickness of the barrier layer is 7 nm to 30 nm.

(2) the laminate structure be one that is formed on the crystal substrate through the A 1 N low-temperature growth buffer layer, directly on the A 1 N low-temperature grown buffer layer A 1 _X G a Bok _X N ( 0 ≦ x ≦ 1) The ultraviolet light emitting device according to the above (1), wherein an underlayer is formed.

(3) A 1 _X G a! _ _X N (0 <x≤ 1) The above (2), wherein there is no layer made of A 1 G aN between the underlayer and the well layer. Ultraviolet light emitting element.

(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 n _Y G _ai — _Y N (0 <Υ ≤ 1) The ultraviolet light-emitting device according to the above (1), characterized by the following.

(5) The multiple quantum well structure has a barrier layer in contact with the ρ-type layer, and the thickness of the barrier layer in contact with the ρ-type layer is 10 ηπ! The ultraviolet light emitting device according to the above (1), wherein

(6) The above multiple quantum well structure has a well layer made of an undoped GaN-based crystal, The ultraviolet light-emitting device according to the above (1), comprising an i-added barrier layer made of a GaN-based crystal.

(7) The multi-quantum well structure, I n _x G _ai - those constructed and well layers made of _{x N (0 <x≤ 1)} , by a barrier layer made of GaN, the (1), wherein Ultraviolet light emitting element.

(8) above I n _x G a - _X N of I n the composition x is 0 rather x 0. 1 1, (7) the ultraviolet light emitting device according.

(9) The ultraviolet light emitting device according to the above (1), wherein there is no layer made of A 1 GaN between the crystal substrate and the well layer.

(10) The ultraviolet light-emitting device according to the above (1), wherein the crystal substrate has a surface processed with irregularities, and the GaN-based crystal layer covers the irregularities by vapor phase growth to form a laminated structure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic view showing a structural example of an ultraviolet light emitting device according to the present invention. Each symbol in the figure indicates the following. B: Crystal substrate, S: Laminated structure composed of GaN-based crystal layer, 2: n-type clad layer, 3: MQW structure, 4: p-type clad layer, P1: n-type electrode, P2: p-type electrode.

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

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

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

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

Figure 6 shows In. .. ₃ was G a _0. Of a ₉₇ N-emitting layer material is a diagram illustrating an example of an element structure of a conventional UV LED.

BEST MODE FOR CARRYING OUT THE INVENTION The G a N system in the present invention is represented by In _x Ga _Y A l _z N (0≤X≤1, 0≤Y≤1, 0≤≤≤1, Ζ + Χ + Υ = 1) Among compound semiconductors, for example, A1N, GaN, AlGaN, InGaN, InGaA1N, and the like are important compounds.

Further, the I The InGaN-based, the Among _{_{_{I n x Ga Y A l z}}} N, and comprise a I n compositions and G a composition mandatory, other I The InGaN, is A 1 composition I The InGaN It may be added.

The ultraviolet light emitting device according to the present invention may be an ultraviolet LED, an ultraviolet LD, etc. Force Hereinafter, the present invention will be described using an ultraviolet LED as an example. In addition, during the element structure, the p-type and n-type layers may be formed on either side (the crystal substrate side). For this reason, an embodiment in which the η-type layer is on the lower side is preferable. Hereinafter, the device structure will be described with the η-type layer as the lower side, but the present invention is not limited to this.

FIG. 1 is a view showing one structural example (LED element structure) of an 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 ultraviolet light emitting device according to the present invention includes a light emitting portion including a p-type layer and an n-type layer, and is further provided with electrodes.

The structure of each layer in the example of FIG. 1 is shown more specifically.From the lower layer side, a sapphire crystal substrate B, a GaN low-temperature growth buffer layer B1, an undoped GaN layer 1, a light emitting section (n-type GaN clad layer) (= Contact layer) 2, MQW structure 3 (GaN barrier layer InGaN well layer ZGaN barrier layer / InGaN well layer / GaN barrier layer), p-type A1Ga The N clad layer 4] is a p-type GaN contact layer 5. The n-type GaN contact layer is partially exposed, an η-type electrode P1 is formed on the exposed surface, and a p-type electrode P2 is formed on the upper surface of the ρ-type Ga a contact layer.

An important feature of the above device structure is that the light emitting portion essentially includes an MQW structure, and InGaN having a composition capable of emitting ultraviolet light is used as a material for the well layer of the MQW structure. In addition, the number of well layers is 2 to 20, and the thickness of barrier layers is 7 to 30 nm.

By limiting the light emitting portion to such a configuration, a higher output than before can be obtained even though it is an ultraviolet light emitting device using an InGaN-based material, particularly InGaN as a light emitting layer.

The light emitting section is configured to include a P-type cladding layer and an n-type cladding layer, and has an MQW structure therebetween. The n-type and p-type cladding layers may be layers that also serve as n-type and _P- type contact layers, respectively. In the LD device structure, a waveguide layer, a cap layer, or the like may be added to the inside of the cladding layer, if necessary.

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

The material for the well layer, I nG a N-based materials, in particular I n _x G _ai - is a _{X N (0 <x≤ 1 G} a is rather 0 if required X <1), 420 nm UV light below Any composition that can emit light may be used. A more specific and preferred value of the In composition X of In _x G _{& 1} _ _Χ is 0 <x≤0.11. The material of the well layer does not necessarily need to have the same In composition in all the layers, and may be appropriately selected as needed, for example, by being inclined.

The thickness of the well layer may be similar to a known MQW structure, for example, 2 ηπ! ~ 1 O nm is sufficient.

The barrier layer does not necessarily need to exist independently as the outermost layer adjacent to both cladding layers, and may be in the following modes 1 to 3, for example.

(1) An aspect in which the cladding layer also serves as the outermost barrier layer, as in (n-type cladding layer / well layer / well layer Zp-type cladding layer).

(2) The outermost barrier layer exists separately from the cladding layer, as in (n-type cladding layer Z barrier layer Z well layer no barrier layer Z well layer no barrier layer / P type cladding layer). (3) The outermost barrier layer exists independently on only one side, such as (n-type clad layer / well layer barrier layer / well layer Z barrier layer Zp-type clad layer).

In the present invention, the thickness of the barrier layer of all the MQW structures is 7 nm to 30 nm. FIG. 4 is a graph showing the relationship between the thickness of the barrier layer and the output of the light emitting element, obtained by measurement in the following examples. As is evident from the graph in the same figure, when the thickness of the barrier layer is 7 nm to 30 nm, an ultraviolet light emitting device having a high emission output can be obtained, and when the barrier layer is thinner than 7 nin or more than 30 nm. When the thickness is large, the light emission output is low as before. Among the above ranges of the thickness of the barrier layer, particularly preferred is a thickness of 8 nm to 15 nm. At this time, a light-emitting element having the highest output can be obtained.

While the thickness of the barrier layer in the conventional MQW structure is 3 nm to 6 nm, 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, the wave functions do not overlap, and the SQW structure is more stacked than the MQW structure, but a sufficiently high output is achieved. . If the thickness of the barrier layer exceeds 30 nm, holes injected from the p-layer are trapped by non-emission center dislocation defects existing in the GaN barrier layer before reaching the well layer, and light is emitted. It is not preferable because the efficiency is reduced.

In a preferred embodiment of the MQW structure according to the present invention, the outermost barrier layer is always present on the p-type cladding layer side (that is, the above-described embodiment (1) or (3)), and the outermost barrier layer thickness on the p-type side is as follows. Is set to 10 to 30 ηπι. As a result, the well layer is less likely to be damaged by heat or gas when growing the layers subsequent to the p-type cladding layer, thereby reducing the damage. In addition, the dopant material (such as Mg) from the p-type layer is reduced. Since diffusion into the well layer is reduced and the strain applied to the well layer is also reduced, not only the output is improved, but also the effect of extending the life of the element is obtained.

The material of the barrier layer may be a GaN-based semiconductor material having a band gap that can serve as a barrier layer for the InGaN well layer. In the present invention, GaN is recommended as a preferable material. In the conventional MQW structure, a barrier layer with a sufficiently larger band gap than the well layer is used in consideration of confinement of carriers in the well layer. 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 or the like. Therefore, it is necessary to use a material having a larger band gap for the barrier layer. For example, when the well layer is made of InGaN (In composition 0.03), A 1 GaN is used for the barrier layer and the cladding layer.

On the other hand, in the present invention, the combination of the InGaN well layer and the A1GaN barrier layer focuses on the fact that the optimum values of the crystal growth temperatures are greatly different from each other, and this is taken up as a problem. . That is, A 1 N having a composition of A 1 GaN has a higher melting point than GaN, and InN having a composition of In GaN has a lower melting point than GaN. Specifically, the optimum temperature for crystal growth is 1000 ° C for GaN and 1000 for InGaN. C or less (preferably about 600 to 800; about C), A 1 G aN is G a N or more. Therefore, when the InGaN well layer and the A1GaN barrier layer are combined, the growth temperature must be significantly changed between the growth of the well layer and the growth of the barrier layer to the respective preferable values. In this case, a layer having a preferable crystal quality cannot be obtained.

However, changing the growth temperature for each of the well layers and the Z barrier layers causes a growth interruption, and the thickness of the well layer, which is a thin film of about 3 nm, changes due to the etching action during the growth interruption, or the surface of the surface changes. There is a problem that crystal defects enter the crystal.

Because of these trade-offs, it is difficult to obtain a high-quality product by combining the A1GaN barrier layer and the InGaN well layer. In addition, there is a problem that the well layer is distorted when the barrier layer is made of A 1 GaN, which hinders high output.

Therefore, in the present invention, the above trade-off problem is reduced by using GaN as a material for the barrier layer. This reduces the band gap difference between the barrier layer and the well layer, but improves the crystal quality of both layers, resulting in an overall improvement in output. As an InGaN-based material, A1 InGaN in which A1 is mixed into InGaN may be used as a well layer, thereby obtaining the same effect as that of InGaN. It is possible. Further, according to the present invention, in connection with the solution of the above-mentioned problem relating to the combination of the InGaN well layer and the A1GaN barrier layer, between the crystal substrate and the well layer (the A1N low-temperature growth buffer layer described later) In the embodiment in which the A 1 GaN underlayer is formed immediately above the GaN layer, it is recommended that the A 1 GaN layer is not present between the A 1 GaN underlayer and the well layer. This alleviates the above-mentioned problem caused by the crystal growth temperature difference. As a specific example of an embodiment in which the A 1 GaN layer is not present, there is an embodiment in which a GaN layer is used instead of the A 1 GaN layer. In the example shown in Fig. 1, an undoped GaN crystal layer (0.1111 to 2.0 m thick) without impurities is grown on the GaN low-temperature buffer layer, and an n-type GaN crystal Layer (contact layer / cladding layer) is grown. Note that the undoped GaN crystal layer may be omitted. Further, 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.

Another preferred embodiment of the MQW structure is one in which the well layer is not added and Si is added to the barrier layer.

FIG. 5 is a graph showing the relationship between the carrier concentration due to the addition of Si to the barrier layer and the emission output. In the sample used for the measurement, the number of well layers is 6, and the thickness of the barrier layer is 10 nm, but the same applies to other cases. As is evident from the graph in the same figure, when no Si was added, the luminescence output was small, and the luminescence output decreased even when the amount of Si added was 5 × 10 ¹⁸ cm− ³ or more. . The addition of Si to the barrier layer is desirable because it has the function of increasing the emission intensity. However, if the addition amount is too large, the crystallinity decreases, and conversely, the emission intensity decreases. Desirable Si addition amount is 5 × 10 ²⁶ c π ³ to 5 × 10 ¹⁸ cm— ³ .

The crystal substrate used for the growth may be any as long as the GaN-based crystal can be grown. Preferred crystal substrates include, for example, sapphire (C-plane, A-plane, R-plane), SiC (6H, 4H, 3C), GAN, A1N, Si, spinel, ZnO, G a As and NGOs. Further, a substrate having these crystals as a surface layer may be used. The plane orientation of the substrate is not particularly limited, and may be a just substrate. A substrate having an off angle may be used.

A puffer layer may be interposed between the crystal substrate and the GaN-based crystal layer, if necessary. When a substrate made of GaN, A 1 N crystal, or the like is used as the crystal substrate, the buffer layer is not essential.

To obtain a high-quality GaN film with few dislocations, an A1 GaN film (A1 GaN underlayer) with a different lattice constant from the GaN film is used as the underlayer for growing the GaN film. It turned out that it was good to arrange. When GaN is grown on the A1 GaN film, compressive stress is applied to GaN. When growth is performed in such a state, dislocations are bent perpendicular to the growth direction at the interface between the A 1 GaN film and the GaN film (precisely, the initial stage of GaN growth on the A 1 GaN film). Is no longer propagated. In other words, a high-quality GaN film can be obtained by doing this. In order to grow this AlGaN underlayer, it is preferable to further use a buffer layer as the underlayer. A preferable buffer layer is a GaN-based low-temperature growth buffer layer. The known technology may be referred to for the material, formation method and formation conditions of the buffer layer, but GaN, A1N, InN, etc. are exemplified as the GaN-based low-temperature growth buffer layer material. Is 300. C-600. C is listed. The thickness of the buffer layer is 10 nm to 50 nm, especially 20 ηπ! ~ 40 nm is preferred. A particularly preferred embodiment is an A 1 N buffer layer. FIG. 2 shows an example of the element structure of this embodiment. As shown in the figure, a laminated structure S composed of a GaN-based crystal layer is grown on a crystal substrate B via an A 1 N low-temperature growth buffer layer 10. A l _x G _ai — _X N (0 <x≤ 1) underlayer 11 is formed directly above.

A lxGa - optimal thickness _X N underlayer varies by A 1 Composition (value of x). For example, when the A1 composition is 30% (x = 0.3), the thickness is 10 nm to 5 m, especially 50 ηπ! ~ 1 μπι is preferred. If the thickness is less than 10 nm, the above effect is lost, which is not preferable. On the other hand, if the thickness is more than 5 μπι, the crystallinity of the GaN layer is undesirably reduced.

Further, by applying a gradient A 1 Composition of A 1 _{_X} G a _X N base layer (value of x) in the growth direction Is also good. The A1 composition may be changed continuously or in multiple steps.

Further, when the thickness of the A 1 GaN base layer is large (for example, when the A 1 composition is 30%, about 500 ηπ! To 5000 nm), the light emitting portion may be formed directly thereon. In the present invention, forming the p-type contact layer with InGaN is one of the preferred embodiments.

That is, in the conventional G a N-based light-emitting element using a p-type G a N contactor coat layer, p-type co Ntakuto resistance, 1 X 10- ³ Ω cm ² about the high, but may 1 X 1 (gamma is a ⁴ Omega cm ² approximately. in contrast, when using the I nG a N as the material of the p-type contact layer, and shallow Akuseputa level, and the advantage that the hole concentration is increased, contour transfected resistance 1 advantage down to about X 10- ⁶ Ω cm ² is obtained.

p-type electrode formation p-type contour coat layer to be, it is particularly preferable that the Mg-doped _{I n Y G a wN (0} <Y≤ 1). By the gas atmosphere in the I nG a New layer growth Ν ₂ + ΝΗ _3, it is possible to omit the relaxation or process itself so-called ρ-type processing conditions to activate the Mg after growth. This is because if the amount of H _{2 in} the gas atmosphere during growth is small, the incorporation of H ₂ that inactivates Mg into the film can be suppressed. Also, due to the shallow acceptor level formed when Mg is doped into InGaN, the hole carrier concentration at room temperature becomes high, so that the conditions for the p-type treatment can be relaxed or the treatment itself can be omitted. it can.

By applying the p-type InGaN contact layer to an ultraviolet light emitting device, the light emission output can be further improved. This is because the conditions of the p-type treatment (especially thermal annealing) can be relaxed or the treatment itself can be omitted for the above-mentioned reason, and as a result, diffusion of the doped impurities into the well layer can be suppressed. Because you can.

In particular, when the MQW structure is composed of a well layer made of an GaN-based crystal with no addition and a barrier layer made of a GaN-based crystal with Si added, no heat treatment is required. Thus, a steep impurity profile can 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. With the introduction of a structure for reducing dislocation density, a portion composed of a different material such as SiO ₂ may be included in a laminated structure composed of a GaN-based crystal layer.

As a structure for reducing the dislocation density, for example, the following is mentioned.

(I) A structure in which a mask layer (of which 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 performed.

(B) A structure in which dots and stripes are formed on the crystal substrate so that the GaN-based crystal can grow laterally or facetly.

These structures and the buffer layer may be appropriately combined.

Among the structures for reducing the dislocation density, the above (b) is a preferable structure that does not use a mask layer. Hereinafter, this will be described.

Examples of the method of processing the unevenness include a method of forming a pattern according to the desired unevenness using a normal photolithography technique, and performing an etching process using the RIE technique or the like to obtain the desired unevenness. You.

The arrangement pattern of the irregularities is a pattern in which dot-shaped concave parts (or convex parts) are arranged, a linear or curved concave groove (or convex ridge) is arranged at fixed intervals and irregular intervals, Concentric patterns and the like can be mentioned. A pattern in which convex ridges intersect in a grid pattern can be regarded as a pattern in which dot-shaped (square-hole) concave parts are regularly arranged. The cross-sectional shape of the unevenness includes a rectangular (including trapezoidal) wavy shape, a triangular wavy shape, a sine carp shape, and the like.

Among these various concavo-convex modes, the stripe-shaped concavo-convex pattern '(rectangular wave shape in cross section), in which linear concave grooves (or convex ridges) are arranged at regular intervals, can simplify the manufacturing process and improve the pattern shape. Fabrication is easy and preferable.

When the pattern of concavities and convexities is in the form of a stripe, the longitudinal direction of the stripe may be arbitrary, but for a GaN crystal grown by embedding this, <111-200 ) Direction, lateral growth is suppressed, and oblique facets such as {1-1101} planes are easily formed. As a result, dislocations propagating in the C-axis direction from the substrate side are bent laterally on the facet surface, making it difficult to propagate upwards, and being particularly preferable in that a low dislocation density region can be formed.

If the longitudinal direction of the stripe is the <ϊ−100> direction for the growing GaN crystal, the GaN crystal that started growing from the upper part of the convex part grows at high speed in the lateral direction, and the concave part becomes hollow. A GaN-based crystal layer is formed in the state where it remains. However, even when the longitudinal direction of the stripe is set in the <1-100> direction, the same effect as in the case of the <111> direction can be obtained by selecting growth conditions that easily form the facet plane. Can be.

Preferable dimensions when the cross section of the unevenness is a rectangular wave shape are as follows. The width of the groove is 0.1 π! To 20 / m, particularly preferably 0.5 μm to 10 μm. The width of the convex part is 0.1 l Aim to 20 / im, especially 0.5 μπ! ~ 10 m is preferred. The amplitude of the unevenness (depth of the concave groove) should be at least 20% of the larger of the concave and convex portions. These dimensions and the pitch calculated therefrom are the same for the irregularities of other cross-sectional shapes. .

GaN-based crystal layers can be grown by HVPE, MOVPE, MB, etc. When forming a thick film, the HVP E method is preferable, but when forming a thin film, the MOVPE method or the MBE method is preferable.

. Example

Example 1

In this example, the ultraviolet LED shown in Fig. 1 was manufactured, the thickness of the barrier layer was fixed at 10 nm, and the number of well layers was 1 to 25 to form a total of 25 types of samples. Was measured. The element forming process is as follows.

First, for each sample, a C-plane sapphire substrate was mounted on a MOVPE apparatus, and the temperature was increased to 1100 ° C in a hydrogen atmosphere, and thermal etching was performed. The temperature is 500. C, and trimethylgallium (TMG) as Group III raw material A low-temperature GaN buffer layer with a thickness of 30 nm was grown by flowing ammonia as a feedstock.The temperature was then raised to 1000 ° C, TMG and ammonia were flowed as raw materials, and an undoped GaN crystal layer 1 After growing Si, Si H ₄ was flowed to grow a Si-doped n-type GaN crystal layer ′ (contact layer / cladding layer) at 3 μπι.

(Quantum well structure)

After lowering the temperature to 800 ° C, a GaN barrier layer (10 nm thick) with Si added at 5 × 10 ¹⁷ cm— ³ and an InGaN well layer (emission wavelength 380 nm, In composition (0.03, thickness 3 nm) was changed from 1 to 25 for each sample. In addition, in each of the samples, the last GaN barrier layer (Si added at 5 × 10 ¹⁷ cm— ³ , thickness 20 nm) in contact with the p layer was formed.

After increasing the growth temperature to 1000 ° C for each sample, a 30-nm-thick p-type A1 GaN cladding layer 4 and a 50-nm-thick p-type GaN contact layer were sequentially formed, and the emission wavelength was 380 nm. An ultraviolet LED wafer was used, electrodes were formed, and elements were separated.

Samples of the UV LED chips with different numbers of well layers obtained above were measured at a wavelength of 380 nm by applying a current of 2 OmA in a bare chip state, and as shown in Fig. 3, the number of well layers A graph showing the relationship with the output was obtained. As described above, the number of well layers should be 2 to 20 which can provide an output of 2 mW or more, and especially 6 to 15 is a preferable number of well layers which can provide a light output of 5 mW or more. And power S woratsu 7

Example 2

In this embodiment, the ultraviolet LED shown in Fig. 1 was manufactured by the same process as in the first embodiment, and the number of well layers was fixed at 6, and the thickness of the barrier layer was changed from 3 nm to 40 nm. A sample was prepared and the output of each sample was measured.

When the output of the sample of the UV LED chips having different barrier layer thicknesses obtained in the present example was measured at a wavelength of 380 nm by applying a current of 2 OmA in a bare chip state, As shown in FIG. 4, a graph showing the relationship between the thickness of the barrier layer and the output was obtained. As described above, the barrier layer thickness is 7 ηπ! 3030 nm, especially 8 ηπ! It was found that 15 nm is a preferable thickness of the barrier layer that can obtain a light emission output of 5 mW or more.

In the first embodiment, the thickness of the barrier layer is fixed to one type, and in the second embodiment, the number of the well layers is fixed to one type. Samples with different thicknesses in the range of ~ 30 nm were fabricated, and element samples with the number of well layers varied in the range of 2 to 20 were formed for each thickness. A curve similar to that in Fig. 3 was obtained for the change in the number of well layers, and a curve showing the same tendency as in Fig. 4 was obtained for the change in the thickness of the barrier layer for any number of wells. all right.

Example 3

In this example, for all the samples manufactured in Examples 1 and 2, the GaN low-temperature buffer layer was used as the A1N low-temperature buffer layer, the undoped GaN crystal layer was used as the AI GaN underlayer, and the p-type Ultraviolet LED samples were fabricated using the GaN contact layer as a p-type InGaN contact layer, and the output of each sample was measured. The device formation process is as follows.

First, for each sample, a C-plane sapphire substrate was mounted on a MOVPE apparatus, and the temperature was increased to 1100 ° C in a hydrogen atmosphere to perform thermal etching. The temperature was lowered to 350 ° C, and trimethylaluminum (TMA)

Ammonia was flowed as an N source, and a 20-nm-thick A1N low-temperature buffer layer was grown.

Then the temperature is 1000. The temperature was raised to C, and TMA, TMG, and ammonia were flowed as raw materials. After growing an undoped A 1 GaN crystal layer (underlayer) 1 having a composition of A 1 of 20% by 20 O nm, the supply of TMA was stopped. S i H ₄ flushed, n-type GaN crystal layer S i doped (contact layer and the cladding layer) 4 was μπι growth. Thereafter, an MQW structure was formed in the same manner as in Examples 1 and 2. Each sample has a growth temperature of 1000. After heating to C, p-type AI GaN cladding layer 4 with a thickness of 30 nm, 1) type 0 &] ^ layer with a thickness of 5011111, p-type InGaN contact layer with a thickness of 5 nm (In composition 10 %) In order to form an ultraviolet LED wafer with an emission wavelength of 380 nm, followed by electrode formation and element separation to obtain an ultraviolet LED chip.

When the output of the ultraviolet LED chip samples obtained above was measured at a wavelength of 380 nm by applying a current of 20 mA in a bare chip state, each sample was compared with the samples of Examples 1 and 2 by 10%. Output improvement of about% to 30% was observed.

Industrial applications

As described above, in the MQW structure, the number of well layers is set to 2 to 20, and the thickness of the barrier layer is set to 7 nm to 30 nm, thereby emitting InGaN-based materials, particularly InGaN. Despite being an ultraviolet element used as a material for the layer, a higher output than ever before can be obtained.

This application is based on patent application Nos. 2001-350615 and 2002-073871 filed in Japan, the contents of which are incorporated in full herein.

Claims

The scope of the claims

1. A stacked structure composed of a GaN-based crystal layer is formed on a crystal substrate via a buffer layer or directly, and the stacked structure includes a p-type layer and an n-type layer. A G a N based semiconductor light emitting device including a light emitting portion,

The light emitting section 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 the barrier layer is 7 ηπ! An ultraviolet light emitting device having a wavelength of up to 30 nm.

2. The above laminated structure is formed on a crystal substrate via an A 1 N low-temperature growth buffer layer, and A 1 _X G a (0 <x ≤ 1 2. The ultraviolet light emitting device according to claim 1, wherein an underlayer is formed.

_{_{3. A 1 X G a X.}} X N (0 <x≤ l) between the base layer and the well layer, UV according to claim 2, wherein, wherein there is no A l G aN Tona Ru layer Light emitting element.

4. The positional relationship between the p-type layer and the II-type layer in the above laminated structure is such that the p-type 上側 is on the upper side and the ρ-type contact layer is In n _Y G _{& 1} _ _Υ 0 (0 <Υ≤ 2. The ultraviolet light emitting device according to claim 1, wherein the ultraviolet light emitting device comprises:

5. The method according to claim 1, wherein the multiple quantum well structure has a barrier layer in contact with the ρ-type layer, and the thickness of the barrier layer in contact with the ρ-type layer is 10 nm to 30 nm. The ultraviolet light emitting device of the above.

6. The multiple quantum well structure according to claim 1, wherein the multiple quantum well structure is constituted by a well layer made of a GaN-based crystal with no addition and a barrier layer made of a GaN-based crystal with Si added. The ultraviolet light-emitting device according to the above.

7. the multiple quantum well structure is one that is configured and the well layer made of _{_{_{I n x G ai _ x N}}} (0 <x≤ 1), by a barrier layer consisting of G a N, claims 1 The ultraviolet light emitting device according to the above.

8. The above I n _{_x} G _ai _ _x N of I n composition X is, 0 <x≤0. 1 is a 1, the ultraviolet light-emitting element in the range 7 wherein claims.

9. The ultraviolet light emitting device according to claim 1, wherein there is no layer made of A 1 GaN between the crystal substrate and the well layer.

10. are those crystalline substrate is processed rough surface, GaN-based crystal layer is a laminated structure grown covered connexion gas phase uneven, ultraviolet light emitting devices ₀ according to claim 1, wherein