JP2008091942A - Nitride semiconductor light emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize each structure with respect to the anisotropy, and to further lower the Vf, by clearing up the relation between an anisotropy in current diffusivity of an element in the lateral direction of its n-type layer side and Vf of an LED due to irregularity of a substrate to be processed. <P>SOLUTION: An n-type nitride semiconductor layer (n-type layer) is formed with an n-type impurity doped therein on the substrate having an irregular crystal growth face comprising an insulating material, and a light emitter and an n-type ohmic electrode P1 are formed thereon. When looked from above the substrate, the electrode P1 has a longer distance to a side HE than to any other three sides in a region between the line including the side EF of a rectangle EFGH circumscribing the light emitter and the line including the side GH. In the crystal growth face, its recess extends in the direction orthogonal to the side HE. Accordingly, a current diffusivity is more improved in the lateral direction of the n-type layer than in any other directions, resulting in decrease of Vf. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor light-emitting diode (hereinafter also referred to as a GaN-based LED) in which a main part of a light-emitting element structure is composed of a nitride semiconductor, and particularly relates to a GaN-based LED with a reduced operating voltage.

A nitride semiconductor is a compound semiconductor made of a group III nitride determined by the chemical formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1). For example, those having an arbitrary composition such as GaN, InGaN, AlGaN, AlInGaN, AlN, and InN are exemplified. In the above chemical formula, a part of the group 3 element is substituted with boron (B), thallium (Tl), or the like, and a part of N (nitrogen) is phosphorus (P), arsenic (As), antimony ( Those substituted with Sb) or bismuth (Bi) are also included in the nitride semiconductor.

  In recent years, an n-type nitride semiconductor layer (hereinafter also referred to as “n-type layer”) and a p-type nitride semiconductor layer (hereinafter also referred to as “p-type layer”) are bonded to each other. A GaN-based LED with a light-emitting element structure has been realized, and it is used for a white light source (white LED) using phosphor emission in addition to a colored light source such as a blue LED or a green LED that directly uses light generated in an active layer. It has come into practical use as an excitation light source. Specific applications include LED displays, liquid crystal display backlights, LED lighting, and the like.

In any application, further increase in output and reduction in operating voltage are desired for GaN-based LEDs. Although it is natural that higher output is desired for the LED, the reason why reduction of the operating voltage is desired is mainly for lower power consumption and reduced heat generation.
For example, in portable devices such as mobile phones, it is important to reduce the power consumption of the backlight of the liquid crystal display device to be incorporated. In addition, it is important to reduce power consumption in backlight applications for large liquid crystal display devices and LED lighting applications. In addition, in order to obtain large output, a large number of LEDs are mounted at high density. Since it is used or each element is driven with a large current, it is important to reduce the amount of heat generated. If the heat generation is large, the element temperature during operation becomes high, so that the light emission efficiency decreases, the light emission wavelength fluctuates (in the case of a white LED, the light emission efficiency decreases through a change in the excitation efficiency of the phosphor), Problems such as a reduction in device reliability and lifetime occur.
Note that the operating voltage of a GaN-based LED is generally evaluated by a voltage (forward voltage, also referred to as Vf) required to flow a constant current (generally 20 mA) in the forward direction.

As a method for easily achieving high output of the GaN-based LED, an element is configured using a substrate (hereinafter, also referred to as “processed substrate”) in which the crystal growth surface is processed into an uneven shape by a method such as etching. There is a method for growing a nitride semiconductor layer (Patent Document 1 and Patent Document 2).
When a processed substrate is used, lateral growth of a nitride semiconductor crystal occurs, so that a light-emitting element structure can be formed with a high-quality nitride semiconductor layer having a low dislocation density obtained thereby. A high LED is obtained.
Further, when a processed substrate made of a material having a refractive index different from that of a nitride semiconductor is used, and a nitride semiconductor layer including a light-emitting element structure is grown by embedding unevenness of a crystal growth surface, the substrate and the nitride semiconductor layer As a result of light scattering occurring at the interface with LED, an LED having high external quantum efficiency can be obtained (Patent Document 3).

Hereinafter, in the present specification, for the purpose of simply and clearly explaining the element structure of the conventional and the LED of the present invention, for convenience, the substrate is on the lower side, and the nitride semiconductor layer is stacked thereon, The concept of the vertical direction is introduced into the element structure. A direction perpendicular to the vertical direction (= the nitride semiconductor layer stacking direction or the layer thickness direction) is also referred to as a horizontal direction. The definition of the direction used for the explanation does not limit the posture when the LED is mounted on a lead frame or a mounting substrate.

FIG. 11 is a schematic diagram showing the structure of a conventional GaN-based LED using a processed substrate.
In FIG. 11, 11 is a sapphire single crystal substrate (sapphire processed substrate) whose crystal growth surface is processed into an uneven shape, 12 is an n-type layer, 121 is a layer thickness of 3 μm made of Si-doped GaN ( N-type contact layer (thickness on the convex portion of the substrate 11), 122 is an n-type cladding layer made of undoped AlGaN and having a thickness of 100 nm, and 123 is an undoped In _x Ga _1-x having a thickness of 3 nm. An active layer having an MQW structure in which N (0 <x ≦ 1) well layers and 10-nm-thick Si-doped In _y Ga _1-y N (0 ≦ y <x) barrier layers are alternately stacked. 13 is a p-type layer, 131 is a p-type cladding layer made of Mg-doped AlGaN with a thickness of 30 nm, 132 is a p-type contact layer made of Mg-doped GaN with a thickness of 150 nm, and P11 is An n-type ohmic electrode for injecting current into the n-type layer 2, P12 is a p-type ohmic electrode for injecting current into the p-type layer 3, and P13 is a bonding pad. The p-type ohmic electrode P12 is made of, for example, a stacked body of Ni (nickel) and Au (gold), and is formed in a layer shape so as to spread over the entire upper surface of the p-type layer 13.

In FIG. 11, a striped recess (groove) is formed on the upper surface of the sapphire processed substrate 11 extending in a direction perpendicular to the paper surface (a direction parallel to the cutting line Y <b> 1-Y <b> 1 in FIG. 11A). The concave portion has a depth (a height difference between the concave portion and the convex portion) of 1 μm, a width w of about 3 μm, and a formation period p in the width direction of 6 μm.
The n-type contact layer 121 fills the concave portion on the upper surface of the sapphire processed substrate 11 and grows flat. Therefore, the n-type contact layer 121 has a thick part (layer thickness T1) corresponding to the unevenness of the surface, which is a part having a relatively large layer thickness (that is, a part thicker by entering the concave part of the substrate). In addition, thin portions (layer thickness t1), which are portions having a small layer thickness (that is, portions that are thin because they are positioned on the convex portions of the substrate), are arranged alternately.
On the n-type contact layer 121, a light emitting section in which an active layer 123, a p-type layer 13, and a p-type ohmic electrode P12 are laminated in this order via an n-type cladding layer 122 is shown in FIG. As shown, a corner is cut out from a square, and an n-type ohmic electrode P11 is formed at the cut-out corner. The current injected from the n-type ohmic electrode P11 into the n-type contact layer 121 is diffused in the lateral direction inside the n-type contact layer 121 and supplied to the light emitting portion.
JP 2000-331947 A JP 2002-164296 A JP 2002-280611 A

In the conventional GaN-based LED shown in FIG. 11, the inventors of the present invention have n-type contact layer 121 having a thick portion and a thin portion extending in a direction parallel to the cutting line Y1-Y1, so that n It was noted that the current diffusivity in the lateral direction on the mold layer side is the best in the direction parallel to the cutting line Y1-Y1, and the worst in the direction parallel to the cutting line X1-X1.
Such anisotropy is that, in the n-type contact layer 121, the thick portion having better current diffusivity in the lateral direction than the thin portion is continuous in the direction of the cutting line Y1-Y1, but the cutting line It is caused by not being continuous in the direction of X1-X1.
Note that the n-type cladding layer 122 is a layer having a low electrical conductivity that is not intentionally doped with an n-type impurity, and therefore does not substantially contribute to current diffusion in the lateral direction. Further, since the active layer 3 has a small layer thickness, it does not substantially contribute to current diffusion in the lateral direction.

  As described above, the present inventors have focused on the fact that the GaN-based LED having a processed substrate has anisotropy in the lateral current diffusivity on the n-type layer side of the element. Therefore, it was considered that such anisotropy should have some influence on the Vf of the LED, and the reduction of Vf was examined in consideration of the influence. The relationship between the anisotropy regarding the current diffusivity in the lateral direction on the n-type layer side and the Vf of the LED caused by the unevenness of the processed substrate has not been considered so far.

  An object of the present invention is to provide anisotropy related to current diffusivity in the lateral direction on the n-type layer side of an element, which is caused by unevenness of the processed substrate in the element structure of a GaN-based LED having a processed substrate. To provide a GaN-based LED having a lower Vf than in the past by clarifying the relationship with the Vf of the LED and optimizing the shape and arrangement of the n-type ohmic electrode and the light emitting part against the anisotropy It is in.

The present invention has the following features.
(1) An n-type nitride semiconductor layer doped with an n-type impurity is formed on a substrate having an uneven crystal growth surface made of an insulator, and nitrided on the n-type nitride semiconductor layer. A nitride semiconductor light emitting diode in which an active layer made of a semiconductor, a p-type nitride semiconductor layer, and a p-type ohmic electrode are stacked in this order, and an n-type ohmic electrode are formed in different regions. There,
A rectangle circumscribing the light-emitting portion can be selected so that all four sides are in contact with the outer periphery of the light-emitting portion when viewed from above the substrate, and a set of opposite sides of the rectangle (first side) is selected. , Third side), (second side, fourth side),
The n-type ohmic electrode is
In a region sandwiched between a straight line including the first side and a straight line including the third side, the distance between the n-type ohmic electrode and the fourth side is the distance between the n-type ohmic electrode and the first side and the first side. 80% of the distance when the rectangle is selected so that the distance between the n-type ohmic electrode and the fourth side becomes the maximum so that the distance is greater than any of the distances to the three sides. As above,
Formed,
The n-type nitride semiconductor layer has a portion that enters the recess of the crystal growth surface, and the upper surface thereof is flat, whereby the n-type nitride semiconductor layer includes the crystal growth surface. There is a thick part corresponding to the concave part and a thin part corresponding to the convex part,
In the crystal growth surface, the recess extends in a direction perpendicular to the fourth side, whereby the thick portion of the n-type nitride semiconductor layer extends in the direction, thereby A nitride semiconductor light-emitting diode characterized in that lateral current diffusivity in the n-type nitride semiconductor layer is better in the direction perpendicular to the fourth side than in other directions.
(2) An n-type nitride semiconductor layer doped with an n-type impurity is formed on a substrate having an uneven crystal growth surface made of an insulator, and nitrided on the n-type nitride semiconductor layer. A nitride semiconductor light emitting diode in which an active layer made of a semiconductor, a p-type nitride semiconductor layer, and a p-type ohmic electrode are stacked in this order, and an n-type ohmic electrode are formed in different regions. There,
A rectangle circumscribing the light-emitting portion can be selected so that all four sides are in contact with the outer periphery of the light-emitting portion when viewed from above the substrate, and a set of opposite sides of the rectangle (first side) is selected. , Third side), (second side, fourth side),
The n-type ohmic electrode is
In a region sandwiched between a straight line including the first side and a straight line including the third side, the distance between the n-type ohmic electrode and the fourth side is the distance between the n-type ohmic electrode and the first side and the first side. The maximum width of the n-type ohmic electrode in the extending direction of the first side and the third side is 50% of the total width of the light emitting unit in the same direction so as to be larger than any of the distances to the three sides. As above,
Formed,
The n-type nitride semiconductor layer has a portion that enters the recess of the crystal growth surface, and the upper surface thereof is flat, whereby the n-type nitride semiconductor layer includes the crystal growth surface. There is a thick part corresponding to the concave part and a thin part corresponding to the convex part,
In the crystal growth surface, the recess extends in a direction perpendicular to the fourth side, whereby the thick portion of the n-type nitride semiconductor layer extends in the direction, thereby A nitride semiconductor light-emitting diode characterized in that lateral current diffusivity in the n-type nitride semiconductor layer is better in the direction perpendicular to the fourth side than in other directions.
(3) When viewed from above the substrate, the outer periphery of the light-emitting portion includes all or part of the first side, all or part of the second side, and all or part of the third side. The nitride semiconductor light-emitting diode according to (1) or (2) above, including all or part of the fourth side.
Moreover, the other aspect of this invention has the following characteristics.
An n-type nitride semiconductor layer doped with an n-type impurity is formed on a substrate having an uneven crystal growth surface made of an insulator, and the nitride semiconductor is formed on the n-type nitride semiconductor layer. A light-emitting portion in which an active layer, a p-type nitride semiconductor layer, and a p-type ohmic electrode are stacked in this order and an n-type ohmic electrode are formed in different regions, respectively,
When a pair of opposing sides of a square circumscribing the light emitting portion as viewed from above the substrate is defined as (first side, third side) and (second side, fourth side), respectively, n-type ohmic The electrode has a region sandwiched between a straight line including the first side and a straight line including the third side, and the distance between the n-type ohmic electrode and the fourth side is the distance between the n-type ohmic electrode and the first side. It is formed to be greater than both the distance and the distance to the third side,
The n-type nitride semiconductor layer has a portion that enters the recess of the crystal growth surface, and the upper surface thereof is flat, whereby the n-type nitride semiconductor layer includes the crystal growth surface. There is a thick part corresponding to the concave part and a thin part corresponding to the convex part,
In the crystal growth surface, the recess extends in a direction perpendicular to the fourth side, whereby the thick portion of the n-type nitride semiconductor layer extends in the direction, thereby A nitride semiconductor light emitting diode characterized in that lateral current diffusivity in the n-type nitride semiconductor layer is better in this direction than in other directions.
The preferable aspect in the said other aspect of this invention has the following characteristics.
The ratio of the distance between the n-type ohmic electrode and the first side to the distance between the n-type ohmic electrode and the third side is 0.8 to 1.2.
The distance between the n-type ohmic electrode and the fourth side is 80% or more of the distance when the square is selected so that the distance is maximized.
The light emitting portion is formed in a shape in which one corner portion is cut out from a square when viewed from above the substrate, and an n-type ohmic electrode is formed at the position of the cut out corner portion. The extending direction of the recess is the direction of a diagonal line connecting the apex included in the cut corner of the square and the apex of the diagonal position.
The maximum width of the n-type ohmic electrode in the direction orthogonal to the extending direction of the recess is 50% or more of the total width of the light emitting unit in the same direction.
The concave portion has a stripe shape.
The substrate is a sapphire single crystal substrate in which a stripe-shaped recess is processed on one main surface;
It consists of undoped nitride semiconductor crystals that are three-dimensionally grown on the upper surface of the convex portion and the bottom surface of the concave portion of the main surface.
The p-type ohmic electrode is a reflective electrode or a translucent electrode in which a window is formed in a metal film having a thickness of 0.1 μm or more.
The p-type ohmic electrode is a transparent electrode made of a metal or an oxide semiconductor, and a bonding pad is further formed on the p-type ohmic electrode. A straight line connecting a portion where the pad and the n-type ohmic electrode are closest to each other is parallel to the extending direction of the recess.

  Since the GaN-based LED according to the embodiment of the present invention consumes less power and reduces the amount of heat generated during operation due to the reduction in Vf, the backlight of a liquid crystal display device, LED lighting, etc. It can use suitably for various uses.

FIG. 1 is a diagram showing the structure of a GaN-based LED according to an embodiment of the present invention. Fig.1 (a) is the figure (top view) when the said LED is seen from the top, and FIG.1 (b) has shown sectional drawing in the cutting | disconnection line SS of Fig.1 (a). FIG. 2 is a cross-sectional view taken along a cutting line RR in FIG. The shape of the chip viewed from above the substrate is a square, and A, B, C, and D are the four vertices thereof.
In FIG. 1, 1 is a sapphire processed substrate, 2 is an n-type layer, 21 is an n-type contact layer made of Si-doped GaN and having a layer thickness of 3 μm (thickness on the convex portion of the substrate 1), Reference numeral 22 denotes an n-type cladding layer made of undoped AlGaN with a thickness of 100 nm, and reference numeral 23 denotes an undoped In _x Ga _1-x N (0 <x ≦ 1) well layer with a thickness of 3 nm and Si-doped In _y Ga with a thickness of 10 nm. _1-y N (0 ≦ y <x) barrier layers having 6 layers alternately stacked, an MQW structure active layer, 3 is a p-type layer, and 31 is a Mg-doped AlGaN layer having a thickness of 30 nm. 32 is a p-type contact layer made of Mg-doped GaN with a layer thickness of 150 nm, P1 is an n-type ohmic electrode for injecting current into the n-type layer 2, and P2 is p Inject current into mold layer 3 P3 ohmic electrode, and P3 is a bonding pad. The p-type ohmic electrode P2 is formed in a layer shape so as to spread over the entire upper surface of the p-type layer 3. The n-type ohmic electrode P1 is a laminate of Ti (titanium) and Al (aluminum), the p-type ohmic electrode P2 is a laminate of Ni (nickel) and Au (gold), and the bonding pad P3 is made of Ti and Au. A laminate can be used.

  In the example shown in FIG. 1, the crystal growth surface of the sapphire processed substrate 1 is an uneven surface in which a plurality of stripe-shaped recesses extending in one direction are formed. Hereinafter, when the concave portion provided on the crystal growth surface extends mainly in one direction as described above, the direction is referred to as a “concave extension direction”. As shown in FIG. 1 (a), the recess growth direction is different from the conventional element shown in FIG. The specification of the crystal growth surface is that the depth of the recess is 1 μm, the width w of the recess is about 3 μm, and the period p of the unevenness in the width direction is 6 μm.

The n-type contact layer 21 is formed so as to enter the recess of the sapphire processed substrate 1 and to have a flat upper surface. Therefore, the n-type contact layer 21 has a thick portion (a portion having a layer thickness T) corresponding to the concave portion of the substrate 1 and a thin portion (a portion having a layer thickness t) corresponding to the convex portion of the substrate 1. (In the example of the figure, since the depth of the recess is 1 μm, T = 4 μm and t = 3 μm). Since the unevenness of the substrate 1 is striped, the thick part and the thin part are also striped, and the current diffusivity in the lateral direction in the n-type contact layer 21 is the direction in which the thick part extends, that is, the recess in the substrate 1. It is best in the direction of elongation and worse in the other directions.

On the n-type contact layer 21, a light emitting section in which an active layer 23, a p-type layer 3, and a p-type ohmic electrode P2 are laminated in this order via an n-type cladding layer 22 is shown in FIG. As shown, one corner is cut from the square. In addition, an n-type ohmic electrode P1 is formed at the position of the cut corner. The current injected from the n-type ohmic electrode P1 into the n-type contact layer 21 is diffused in the lateral direction inside the n-type contact layer 21 and supplied to the light emitting portion. In order to make the current diffusivity in the lateral direction sufficient, the carrier concentration of the n-type contact layer 21 is usually set to 1 × 10 ¹⁸ cm ⁻³ or more.

The GaN-based LED shown in FIG. 1 can be manufactured by the following method.
The sapphire processed substrate 1 is processed with a stripe-shaped recess on the main surface of a normal sapphire single crystal substrate (used for growing a nitride semiconductor crystal) by using a general photolithography technique and a dry etching technique. Can be obtained.
Nitride semiconductor layers from the n-type contact layer 21 to the p-type contact layer 32 are nitrides such as MOVPE (organometallic compound vapor phase epitaxy), HVPE (hydride vapor phase epitaxy), and MBE (molecular beam epitaxy). It can be formed by a known vapor phase growth method that can be used for the growth of semiconductor crystals. Although not shown, it is preferable to interpose a buffer layer between the sapphire processed substrate 1 and the n-type contact layer 21.
Further, in this example, the active layer 23 is made n-type conductivity by doping Si, but the conductivity type of the active layer is arbitrary, and various impurity doping methods can be designed with reference to known techniques. .
After the growth of the p-type contact layer 32 is completed, it is desirable to perform a process such as an annealing process or an electron beam irradiation process in order to activate Mg (magnesium) added to the p-type layer 3 as a p-type impurity.

In order to form the n-type ohmic electrode P1, a part of the p-type layer 3, the active layer 23, and the n-type cladding layer 22 is removed by dry etching to form an n-type contact serving as a formation surface of the n-type ohmic electrode P1. The surface of layer 21 is exposed. In the example of FIG. 1, in this step, the regions between the light emitting portions of the respective elements are also subjected to dry etching so that the light emitting portions of the respective elements on the wafer are separated.
The n-type ohmic electrode P1 made of Ti / Al, the p-type ohmic electrode P2 made of Ni / Au, and the bonding pad P3 made of Ti / Au are formed by a known metal thin film forming method such as vapor deposition, sputtering, or CVD. And can be done.
As a method for separating the element formed on the wafer into chips, known chip separation methods such as scribing, dicing, laser fusing, etc. can be used.

As described above, in the GaN-based LED shown in FIG. 1, the light emitting portion has a shape in which one corner portion is cut out from a square when viewed from above the substrate, and the n-type ohmic electrode P <b> 1 is cut out. It is formed at the position of the corner.
FIG. 3 is a top view illustrating the light emitting portion and the n-type ohmic electrode P1 extracted from FIG. 1 for the sake of explanation. In FIG. 3, the hatched part represents the light emitting part, the broken line represents the side of the square EFGH circumscribing the light emitting part, and the alternate long and short dash line L1 represents a straight line including the side EF. A chain line L2 represents a straight line including the side GH. The thick arrow is the direction of recess extension in the crystal growth surface of the substrate 1.
As can be seen from FIG. 3, the n-type ohmic electrode P1 is formed in a region sandwiched between a straight line L1 including the side EF and a straight line L2 including the side GH. The distances between the n-type ohmic electrode P1 and each side of the square EFGH are d1 (distance to the side EF), d2 (distance to the side FG), d3 (distance to the side GH), d4 (side (Distance to HE)), d1, d2, d3 <d4
(Note that d2 = 0).
Accordingly, when viewed from the n-type ohmic electrode P1, the light emitting portion extends farther in the direction perpendicular to the side HE than in the direction parallel to the side HE. Hereinafter, a direction orthogonal to the side having the maximum distance from the n-type ohmic electrode among the four sides of the rectangle circumscribing the light emitting portion is referred to as a “characteristic direction”.

The feature of the GaN-based LED shown in FIG. 1 is that the characteristic direction defined above is coincident with the above-described recess extending direction in the sapphire processed substrate 1, which is the conventional GaN-based LED shown in FIG. This is the biggest difference from LED. Due to this feature, the GaN-based LED shown in FIG. 1 has a lower Vf than the conventional GaN-based LED shown in FIG.
The present inventors consider that the action mechanism is qualitatively as follows.

The conductivity of the p-type nitride semiconductor is considerably lower than that of the n-type nitride semiconductor. Therefore, in the GaN-based LED, the p-type layer is designed to be thin (usually several hundred nm or less). As a result, a current injected from the p-type ohmic electrode into the p-type layer hardly flows in the lateral direction and flows through the p-type layer in the thickness direction.
From this, when the p-type ohmic electrode is virtually divided into fine regions, the current injected from each region into the p-type layer diffuses in the direction immediately below the region and reaches the pn junction. become. Therefore, the effective area of the p-type ohmic electrode, that is, the area of the p-type ohmic electrode that is effectively used for current injection into the p-type layer is affected by the current diffusion range in the n-type layer under the light emitting portion. Will be.
This is because a current (hole current) is injected from one of the subdivided p-type ohmic electrodes into the p-type layer and flows across the p-type layer. This is because a current (electron current) must flow between the layer region and the n-type ohmic electrode. In other words, no current injection from the p-type ohmic electrode to the p-type layer occurs above the region where the current injected from the n-type ohmic electrode does not diffuse on the n-type layer side.
Accordingly, when the lateral current diffusivity in the n-type layer is optimized in the characteristic direction, which is the direction in which the light emitting portion extends farther as viewed from the n-type ohmic electrode, that is, the characteristic direction, When the concave growth direction on the crystal growth surface of the substrate is matched, the current diffusion range in the n-type layer under the light-emitting portion becomes wider, so that the effective area of the p-type ohmic electrode becomes wider. As a result, the contact resistance between the p-type ohmic electrode and the p-type layer is lowered, and the Vf of the LED is reduced.
In particular, since a nitride semiconductor is a wide gap semiconductor, it is difficult to increase the carrier concentration when it is p-type, and therefore, the specific contact resistance between the p-type ohmic electrode and the p-type layer tends to increase. is there. Under these circumstances, it can be said that the method of the present invention that reduces the contact resistance by increasing the effective area of the p-type ohmic electrode is extremely effective in reducing Vf of GaN-based LEDs.

Such an effect of the present invention is that the maximum with respect to the maximum thickness T of the thick portion in an n-type layer doped with an n-type impurity (for example, an n-type contact layer) included on the n-type layer side of the device. The larger the ratio [(T−t) / T] of the difference (T−t) between the thickness T and the minimum thickness t of the thin portion, the more prominent. Specifically, this ratio is 1/5 or more, particularly when it is 1/4 or more.
In addition, in the crystal growth surface of the substrate, the effect of the present invention becomes more remarkable as the recess formation period p in the direction orthogonal to the recess extension direction (stripe width direction) is smaller. Specifically, this period is 20 μm or less, particularly 10 μm or less.
The reason why the effect of the present invention becomes remarkable in each of the above cases is that a larger anisotropy occurs in the lateral current diffusibility on the n-type layer side of the element.

Moreover, the above-mentioned Vf reduction effect becomes more remarkable as the conductivity of the p-type ohmic electrode is higher. Conversely, when the conductivity of the p-type ohmic electrode is low, the effective area tends to be limited by the current diffusion capability of the p-type ohmic electrode itself.
The case where the conductivity of the p-type ohmic electrode is high is specifically a case where, for example, the p-type ohmic electrode is a reflective electrode described later. In addition, when the p-type ohmic electrode is formed of a metal film having a thickness of 0.1 μm or more, not only when the electrode is a reflective electrode but also when the window is formed on the p-type ohmic electrode and the light-transmitting electrode is formed. Since the conductivity is sufficiently high, the effects of the present invention are remarkably exhibited.

By the way, in FIG. 3, when selecting the square EFGH circumscribing the light emitting part having a shape in which one corner is cut out from the square, the vertex included in the cut out corner of the square and the vertex of the diagonal position The square EFGH is selected so that the diagonal connecting the line EF and the side EF is parallel to each other. However, the method of selecting the square EFGH is arbitrary, and the diagonal and the side EF are not parallel as shown in FIG. In this case, a square EFGH may be selected (also in the case shown in FIG. 4, the feature direction is a direction orthogonal to the side HE).
However, when FIG. 4 is compared with FIG. 3, d4 (distance between the n-type ohmic electrode P1 and the side HE) is larger in FIG. 3 (in the case of FIG. 3, the rectangular EFGH so that d4 is maximized). Is selected.). That is, as viewed from the n-type ohmic electrode P1, the light emitting portion extends farther in the characteristic direction. Therefore, the effect of the present invention described above is more remarkable in the case of FIG. 3 than in the case of FIG. Therefore, as shown in FIG. 3, when d4 when d4 is selected so that d4 is maximized is d4max, in the GaN-based LED of the present invention, d4 is 80% or more of d4max, particularly 90% or more. It is preferable to select a rectangular EFGH circumscribing the light emitting portion so that the characteristic direction determined by the EFGH is aligned with the recess extending direction in the substrate.
In FIG. 3, d1 (distance between the n-type ohmic electrode P1 and the side EF) and d3 (distance between the n-type ohmic electrode P1 and the side GH) are the same, whereas in FIG. 4, these distances. Is different. That is, in FIG. 3, when viewed from the n-type ohmic electrode P1, the light-emitting portion is in the direction orthogonal to the characteristic direction (the direction parallel to the side HE. The current diffusion in the n-type layer is poor). In contrast to spreading symmetrically, in FIG. 4, this spreading is biased. If this bias becomes too large, the effect of the present invention based on the effective area expansion of the p-type ohmic electrode may not be obtained on the side where the light emitting portion is small.
Therefore, in the present invention, the rectangular EFGH is selected so that the ratio d1 / d3 of d1 and d3 is 0.8 to 1.2, particularly 0.9 to 1.1, and thereby It is preferable to match the characteristic direction to be determined with the direction in which the recess extends in the substrate. Thus, when the ratio of d1 and d3 is close to 1, the uniformity of current diffusion in the n-type layer under the light emitting portion is also improved, so that the effect of increasing the uniformity of light emission in the light emitting portion is also obtained. .

FIG. 5 is a diagram showing a deformation mode in which the shapes of the light emitting portion and the n-type ohmic electrode P1 in the example of FIG. 1 are deformed, and only the light emitting portion and the n-type ohmic electrode P1 are extracted and drawn. In the drawing, the blacked out portion represents the n-type ohmic electrode P1, and the hatched portion represents the light emitting portion. The recess extending direction in the sapphire processed substrate is a direction indicated by a thick arrow and coincides with the characteristic direction. Although the outline of the chip is not shown, the outline of the chip can be arbitrarily determined regardless of the shape of the light emitting portion.
The shape of the n-type ohmic electrode P1 viewed from above the substrate can be various shapes such as a square shown in FIG. 5A and a right triangle shown in FIG. Further, as shown in FIG. 5C, a shape in which an extending portion P1b for promoting current diffusion protrudes from a bonding portion P1a that secures an area necessary for bonding. In any of these examples, the straight line portion and the corner portion in the upper surface shape of the n-type ohmic electrode P1 can be deformed into a rounded shape.

In the example shown in FIGS. 5B and 5C, the maximum width (W2, W3) of the n-type ohmic electrode in the direction orthogonal to the recess extending direction is the maximum of the n-type ohmic electrode in FIG. Since it is significantly larger than W1, the Vf reduction effect is particularly great. The reason for this is that the direction perpendicular to the recess extension direction is the direction in which the lateral current diffusibility in the n-type layer is the worst, so that the current diffusion in this direction is expanded to the maximum width of the n-type ohmic electrode P1. This is because the current diffusion range in the lateral direction in the n-type layer can be effectively expanded by assisting with the above.
This effect becomes more prominent as the ratio of the maximum width of the n-type ohmic electrode to the full width of the light emitting portion (= the length of the side HE) in the direction orthogonal to the recess extension direction is higher. Therefore, the n-type ohmic electrode is preferably formed so that the ratio is 50% or more, more preferably 70% or more, and particularly preferably 90% or more.
If the n-type ohmic electrode is formed so as to protrude from a region sandwiched between a straight line including the side EF and a straight line including the side GH, the ratio exceeds 100%. In such a case, Further, the size of the n-type ohmic electrode is excessive, and the utilization efficiency of the chip area is lowered.

So far, the present invention has been described by taking an embodiment in which the shape of the light emitting layer is a shape obtained by cutting one corner from a square and an n-type ohmic electrode is provided at the position of the corner. The shape and arrangement of the type ohmic electrode are not limited to this.
In FIG. 6A, the light emitting portion (hatched portion) has a shape in which a portion facing one side is cut out from a square, and the n-type ohmic P1 is circular at the position of the cut out portion. It is an example formed. Moreover, 6 (b) is an example in which the light emitting portion (hatched portion) has an elliptical shape, and the n-type ohmic electrode P1 is formed on the outer side thereof in a rectangular shape.
6A and 6B, a broken line represents a side of the square EFGH circumscribing the light emitting portion. In FIG. 6B, the alternate long and short dash line L1 represents a straight line including the side EF, and the alternate long and short dash line L2 represents a straight line including the side GH. The thick arrow is the direction of recess extension in the crystal growth surface of the substrate.
6 (a) and 6 (b), the n-type ohmic electrode P1 is formed in a region sandwiched between a straight line including the side EF and a straight line including the side GH. Regarding the distance between the type ohmic electrode P1 and each side of the square EFGH, the distance to the side HE is larger than the distance to any of the other three sides. Therefore, the characteristic direction is a direction perpendicular to the side HE, and by matching the recess extending direction of the substrate to this direction, the Vf of the LED can be made lower than when the recess extending direction is orthogonal to this direction. Can do.
Also in these embodiments, when selecting a rectangle circumscribing the light emitting portion, the distance between the n-type ohmic electrode and each of the two sides parallel to the characteristic direction is as equal as possible (the ratio is preferably Is 0.8 to 1.2, more preferably 0.9 to 1.1), and the distance between the n-type ohmic electrode and the side farthest from the n-type ohmic electrode is as large as possible. As described above (preferably, 80% or more of the maximum case), it is preferable to select the rectangle and make the characteristic direction determined thereby coincide with the recess extension direction in the substrate. In addition, it is preferable to form the n-type ohmic electrode so that the ratio of the maximum width of the n-type ohmic electrode to the entire width of the light-emitting portion in the direction orthogonal to the recess extending direction is increased. The ratio is preferably 50% or more, more preferably 70% or more, and particularly preferably 90% or more.

FIG. 7 is a diagram illustrating an arrangement example in the case where a plurality of light emitting units or n-type ohmic electrodes are provided. In FIG. 7, the shaded portion represents the n-type electrode, the hatched portion represents the light emitting portion, the broken line represents the side of the square EFGH circumscribing the light emitting portion, and the thick arrow represents the substrate. It represents the direction of recess extension.
In FIG. 7A, two n-type ohmic electrodes P11 and P12 are provided for one light emitting portion. In such a case, each of the n-type ohmic electrodes P11 and P12 and the feature direction determined by the relationship with the light emitting portion are matched, and the feature direction is matched with the recess extending direction in the substrate. You can do it. In the example of this figure, the light emitting part has a shape in which two corners at diagonal positions are cut off from the square, but this square is selected as a square EFGH circumscribing the light emitting part. The n-type ohmic electrode P11 is provided at the corner corresponding to the square apex F, and the other n-type ohmic electrode P12 is provided at the corner corresponding to the square apex H. The two n-type ohmic electrodes P11 and P12 are both formed in a region sandwiched between the side EF and the side GH. From the relationship between the n-type ohmic electrode P11 and the square EFGH, the feature direction is a direction perpendicular to the side HE, and from the relationship between the n-type ohmic electrode P12 and the square EFGH, the feature direction is a direction perpendicular to the side FG. . That is, these feature directions coincide. The recess extending direction in the substrate coincides with this characteristic direction as indicated by a thick arrow.
In the example of FIG. 7A, the ratio of the maximum width of the two n-type ohmic electrodes P11 and P12 to the entire width of the light emitting portion is less than 100% in the direction orthogonal to the recess extending direction in the substrate. However, in such a case, it is preferable to form the two n-type ohmic electrodes so as to be shifted in the direction orthogonal to the recess extending direction, as in the example of FIG. As described above, this direction is a direction in which the current diffusion in the lateral direction in the n-type layer is poor, but the current diffusion in this direction is assisted by forming the n-type ohmic electrodes so as to be shifted in this way. Because.

  On the other hand, in FIG. 7B, two light emitting portions are provided for one n-type ohmic electrode P1. In this case, it is only necessary that the relationship between the n-type ohmic electrode P1 and each light emitting portion satisfy the relationship defined by the present invention.

As mentioned above, although embodiment of this invention was described concretely using drawing, this invention is not limited to these specific examples.
The concavo-convex shape of the crystal growth surface of the sapphire processed substrate is that, as a result of growing the n-type layer on the crystal growth surface, a thick part extending in a certain direction is formed in the n-type layer, The current diffusion in the lateral direction in the n-type layer is not limited to the stripe shape in the specific example as long as it is better in the direction than in other directions.
For example, FIG. 8A is a view of the concavo-convex crystal growth surface provided with a hexagonal dot-shaped convex portion having a top surface shape, and the hatched portion represents a concave portion. On this crystal growth surface, the concave portions are continuous in the x direction and the y direction, but the convex portions are arranged in the x direction by being densely arranged in the x direction and sparse in the y direction. The width of the continuous recess is wider. That is, this recess extends mainly in the x direction. The n-type layer grown by filling the recesses has a shape in which a wide thick portion extending in the x direction is connected in the y direction via a narrow thick portion. As a result, the lateral direction in the n-type layer The current diffusivity of is better in the x direction than in the y direction.
Further, as shown in FIG. 8B, even when stripe-like recesses (hatched portions) extending in the x direction are intermittently formed on the crystal growth surface, the crystal is grown by filling the recesses. Further, in the n-type layer, the thick portion has a shape extending in the x direction, so that the current diffusibility in the lateral direction is better in the x direction than in the y direction.

The substrate may be any substrate as long as the concavo-convex crystal growth surface is made of an insulator. Typically, a processed substrate in which the main surface of an insulator single crystal substrate is processed into a concavo-convex shape, such as a sapphire processed substrate. Can be mentioned. Such processed substrates can be used for crystal growth of nitride semiconductor such as GaN (undoped) single crystal substrate, AlN single crystal substrate, spinel single crystal substrate, NGO single crystal substrate, LGO single crystal substrate, BN single crystal substrate, etc. It can be produced from various insulating single crystal substrates. In addition, a substrate in which an undoped nitride semiconductor single crystal layer is grown on a single crystal substrate made of an insulator or a semiconductor and irregularities are processed in the single crystal layer portion can also be used as a processed substrate. A mask for selective growth made of an insulator such as SiO2 is formed on a part of the crystal growth surface of these processed substrates (for example, the upper surface of the convex portion in a processed substrate having a convex portion with a flat upper surface). It may be.

The substrate may be one in which the surface of an undoped nitride semiconductor crystal that is three-dimensionally grown is exposed on the crystal growth surface. Hereinafter, such a substrate is referred to as a “faceted growth substrate”. Examples of facet growth substrates include:
(A) An undoped nitride semiconductor crystal is three-dimensionally grown on a main surface of a processed substrate having a main surface with stripe-like irregularities.
(A) A stripe-shaped selective growth mask is formed on a main surface of a substrate having a flat main surface, and undoped nitride semiconductor crystals are three-dimensionally formed from the substrate surface not covered with the mask. What has grown.
FIGS. 9A and 9B are cross-sectional views showing an example of the facet growth substrate of the above (a), and a cross section perpendicular to the direction in which the stripe-shaped unevenness processed on the surface of the processed substrate extends is seen. is there.
In the example of FIG. 9A, the undoped nitride semiconductor crystal 1b grows in an uneven shape covering the entire surface of the processed substrate 1a.
In the example of FIG. 9B, the undoped nitride semiconductor crystal 1b is selectively grown from the bottom surface of the concave portion and the top surface of the convex portion of the surface of the processed substrate 1a. The surface of the processed substrate 1a is exposed at the stepped surface therebetween.
FIGS. 10A and 10B are cross-sectional views showing an example of the facet growth substrate of the above (A), and a cross section perpendicular to the extending direction of the stripe-shaped selective growth mask M is seen.
In the example of FIG. 10A, before the undoped nitride semiconductor crystal 1b is selectively grown from a portion of the upper surface of the substrate 1a that is not covered with the selective growth mask M, and before the mask M is covered. That growth has been stopped. In this case, the mask M can be removed by etching.
In the example of FIG. 10B, an undoped nitride semiconductor crystal 1b is further grown from the state of FIG. 10A and covers the mask M.

  In the above description of the substrate, the undoped nitride semiconductor is treated as an insulator rather than a semiconductor, but this does not affect the lateral current diffusion in the n-type layer doped with the n-type impurity. This is because undoped nitride semiconductor crystals (including those containing impurities which are not intentionally mixed or diffused) having only the above conductivity are substantially regarded as insulators in the present invention.

The n-type ohmic electrode is not limited to Ti / Al, and a known electrode that forms a low contact resistance junction with the n-type nitride semiconductor can be used as appropriate. For example, an electrode made of a material such as Ti, Al, W, a WTi alloy, ITO, or the like that is in contact with the n-type contact layer can be suitably used.
The n-type ohmic electrode can be used as a bonding pad if the layer thickness is about 200 nm or more, but if necessary, an n-side bonding pad is separately provided on the n-type ohmic electrode. It may be formed.

The p-type ohmic electrode is not limited to Ni / Au, and a known electrode that forms a low contact resistance junction with the p-type nitride semiconductor can be used as appropriate. Examples thereof include metal electrodes such as Rh / Au, Pd / Au, and Ir / Pt, and oxide semiconductor electrodes such as ITO (indium tin oxide) and zinc oxide.
If the p-type ohmic electrode is a translucent electrode, light generated in the active layer can be extracted through the p-type ohmic electrode. The translucent electrode has a window portion for making the electrode film transparent by forming a metal electrode film very thin (for example, a film thickness of 20 nm or less) or allowing light to pass through the layered electrode film. Can be obtained. Since the oxide semiconductor electrode is also transparent, it becomes a translucent electrode.
In the case where light generated in the active layer is extracted from the lower surface side of the substrate, it is preferable that the p-type ohmic electrode be a reflective electrode. The reflective electrode may be formed of a metal electrode having a thickness that can reflect light (for example, 50 nm or more), and in particular, Rh (rhodium), Pd (palladium), Pt (platinum), Ir (iridium). It is preferable to use a platinum group metal having a high reflectance such as). The reflective electrode may be formed by laminating a metal film having a thickness capable of reflecting light on the surface of the oxide semiconductor electrode.
When the p-type ohmic electrode is a reflective electrode, if the thickness of the metal electrode film is 200 nm or more, the surface of the metal film can be used for bonding. Can be omitted.

By the way, in the GaN-based LED shown in FIG. 1, when the p-type ohmic electrode P2 is an electrode whose conductivity is not sufficiently high, other than the above-described Vf reduction effect, other contributions to Vf reduction are possible. An additional effect occurs. This is due to the fact that the voltage drop associated with current diffusion in the n-type layer 2 is reduced.
When the conductivity of the p-type ohmic electrode P2 is not sufficiently high, the current flowing inside the n-type layer 2 is closest to the n-type ohmic electrode P1 and the bonding pad P3 when viewed from above the sapphire substrate 1 There is a tendency to concentrate these parts on the route connecting the shortest distances. In the GaN-based LED shown in FIG. 1, the direction of this path coincides with the recess extension direction in the substrate 1, but the recess extension direction is the direction in which the current diffusibility in the n-type layer 2 is the best. Therefore, this GaN-based LED has a lower Vf because the voltage drop caused by the current flowing along the path in the n-type layer 2 is smaller in the GaN-based LED than the other LEDs having the recess extending direction.
This effect appears, for example, when the p-type ohmic electrode is a transparent electrode that is made translucent by forming a thin metal film, or when the oxidation is 1 to 2 orders of magnitude lower than that of metal. This is a case of a transparent electrode made of a physical semiconductor film. In particular, when a transparent electrode made of a metal film is used, when the film thickness is 10 nm or less, or when an electrode film is formed or heat-treated in an atmosphere containing oxygen (light transmission by partial oxidation) However, this effect becomes significant. In addition, when a transparent electrode made of an oxide semiconductor is used, this effect becomes significant when the film thickness is 200 nm or less.

Example 1
The GaN-based LED shown in FIG. 1 was produced by the following procedure.
[Formation of processed substrate]
A striped mask pattern made of a photoresist was formed on one main surface of a C-plane sapphire substrate. The width of the stripe-shaped mask is 3 μm, the period (mask width + substrate exposed portion width) is 6 μm, the longitudinal direction of the stripe is the <1-100> direction of sapphire (the nitride semiconductor crystal grown on the substrate <11-20> direction).
Reactive ion etching was performed on the mask to form a sapphire-processed substrate 1 in which a groove having a depth of 1 μm was formed in the exposed portion of the substrate and a stripe-shaped uneven pattern was formed on the crystal growth surface.

[Formation of laminate 1]
After removing the photoresist, the sapphire processed substrate was mounted on a MOVPE apparatus, and the temperature was raised to 1100 ° C. in a hydrogen atmosphere to clean the surface.
Next, the substrate temperature was lowered to 500 ° C., trimethylgallium (TMG) was supplied as a Group 3 source material, and ammonia was supplied as a Group 5 source material to grow a low temperature growth buffer layer by 30 nm.
Next, the temperature of the substrate was raised to 1000 ° C., TMG, silane, and ammonia were supplied, and the n-type contact layer 21 having a flat upper surface was grown so that the minimum thickness t of the thin portion was 3 μm.
Then, while the supply of silane was stopped, trimethylaluminum (TMA) was supplied, and the n-type cladding layer 22 was grown to 100 nm.

[Formation of laminate 2]
After the growth of the n-type cladding layer 22, the substrate temperature is lowered to 750 ° C., trimethylindium (TMI) is used as an indium raw material, and well layers and barrier layers are alternately grown to form an active layer 23 having an MQW structure. did. During the growth of the well layer, the supply amount of TMI was adjusted so that the emission wavelength was 405 nm.
Next, the temperature of the substrate is raised to 1000 ° C., trimethylaluminum (TMA), TMG, ammonia, biscyclopentadienylmagnesium (Cp ₂ Mg) is supplied, and p-type made of Al _0.2 Ga _0.8 N The cladding layer 31 was grown by 30 nm.
Subsequently, after the supply of TMA was stopped and the p-type contact layer 32 was grown to 150 nm, the substrate temperature was lowered to room temperature in an ammonia atmosphere, and the wafer was taken out of the MOVPE apparatus.

[Electrode formation]
An n-type ohmic electrode forming surface exposed by annealing, reactive ion etching, n-type ohmic electrode P1, p-type ohmic electrode P2, and bonding pad P3 are formed on the wafer obtained in the above process. The electrodes were sequentially heat-treated.
At this time, the shape and arrangement of the n-type ohmic electrode P1, the light emitting portion, and the bonding pad P3 with respect to the extending direction (longitudinal direction) of the stripe-shaped recess on the crystal growth surface of the sapphire processed substrate 1 are the LEDs shown in FIG. These were patterned so as to be as follows. That is, the light emitting portion has a shape in which one corner portion is cut out from a square, and an n-type ohmic electrode is formed at the position of the cut out corner portion. The diagonal direction connecting the vertices contained in the vertices and the vertices at the diagonal positions (hereinafter simply referred to as “diagonal lines”) and the extending direction of the stripe-shaped recesses were matched.
The n-type ohmic electrode P1 was formed by laminating Ti (titanium) with a thickness of 30 nm and Al (aluminum) with a thickness of 300 nm in this order from the side in contact with the n-type contact layer 21 by vapor deposition. The diameter of the n-type ohmic electrode was 100 μm.
The p-type ohmic electrode P2 was formed by laminating Ni (nickel) with a thickness of 20 nm and Au (gold) with a thickness of 100 nm in this order from the side in contact with the p-type contact layer 42 by vapor deposition. In the p-type ohmic electrode P2, square windows of 8 μm × 8 μm are formed in a matrix, and the area ratio of the window to the area of the region where the p-type ohmic electrode P2 spreads on the p-type contact layer 32 is about A 70% translucent electrode was obtained.
The bonding pad P3 was formed by laminating Ti and Au, and its diameter was 100 μm.

[Divide into chips]
After electrode formation, the lower surface of the sapphire substrate 1 is polished to a thickness of 100 μm, and then a scribe line is marked on the polished surface and braking is performed to obtain a 350 μm square chip. It was.
The obtained LED chip (bare chip) was fixed on the lead frame with the sapphire processed substrate 1 side down, and after wire bonding, energization was performed at a current value of 20 mA, and Vf at that time was measured. 3.3V.

Example 2
Rotate the arrangement of the n-type ohmic electrode, light emitting part, and bonding pad by 20 ° with respect to the direction of extension of the stripe-shaped recess on the crystal growth surface of the sapphire substrate (the angle formed by the diagonal line and the extension direction of the stripe-shaped recess) GaN LED chip was fabricated in the same manner as in Example 1 except that these were patterned so as to be arranged like the element shown in FIG.
When Vf of the GaN-based LED was measured, it was 3.4V.

Comparative Example 1
Rotate the arrangement of the n-type ohmic electrode, light emitting part, and bonding pad by 45 ° with respect to the extending direction of the stripe-shaped recess on the crystal growth surface of the sapphire substrate (the angle formed by the diagonal line and the extension direction of the stripe-shaped recess) GaN LED chip was fabricated in the same manner as in Example 1 except that the element shown in FIG. 11 was used.
When Vf of this GaN-based LED was measured, it was 3.5 V, and it was found that Vf was higher than that of the example product.

Example 3
In this example, the maximum width of the n-type ohmic electrode in the direction orthogonal to the extending direction of the stripe-shaped concave portion on the crystal growth surface of the sapphire processed substrate was widened, and the effect was examined.
The area of the light emitting part and the n-type ohmic electrode is kept the same as in Example 1, and the n-type ohmic electrode in the direction perpendicular to the extending direction of the recess is formed as shown in FIG. A GaN-based LED chip was fabricated in the same manner as in Example 1 except that the ratio of the maximum width to the total width of the light emitting portion was 75%.
The Vf of the GaN-based LED was measured and found to be 3.2V.

Example 4
In this example, a facet growth substrate was used as the substrate.
In the above-described step [Formation of laminated body 1], after the growth of the low-temperature buffer layer, undoped GaN is grown instead of Si-doped GaN, and the undoped GaN crystal is as shown in FIG. 9B. In addition, when three-dimensional growth is performed on the top surface of the convex portion and the bottom surface of the concave portion of the sapphire substrate (that is, where the facet growth substrate is formed in the MOVPE apparatus), the supply of silane is started and the n-type contact is started. Growing layers.
The n-type contact layer was grown so that the upper surface thereof was flat and the distance between the upper surface and the upper surface of the convex portion of the sapphire processed substrate was 4 μm. The maximum thickness of the n-type contact layer is about 5 μm (distance from the bottom of the recess of the sapphire substrate to the top surface of the n-type contact layer), and the minimum thickness is about 1.5 μm. (Distance from the upper end of the undoped GaN crystal grown on the convex portion of the sapphire processed substrate to the upper surface of the n-type contact layer).
Regarding the growth process of the nitride semiconductor layer above the n-type contact layer and the subsequent processes, a GaN-based LED chip was fabricated and Vf was measured in the same manner as in Example 1. Met.
The output of the GaN-based LED of Example 4 when the forward current flowed 20 mA was higher than that of the LED of Example 1. This is because the buffer layer is grown on the sapphire substrate, and immediately after that, the Si-doped GaN is not grown, but the undoped GaN is grown first, and then the Si-doped GaN is grown. As a result, the crystallinity of the active layer grown thereon was also improved, and it is considered that the luminous efficiency was improved.

Comparative Example 2
The arrangement of the n-type ohmic electrode, the light emitting part, and the bonding pad is rotated by 45 ° with respect to the extending direction of the striped recess on the crystal growth surface of the sapphire substrate (the angle formed by the diagonal line and the extending direction of the striped recess) GaN LED chip was fabricated in the same manner as in Example 4 except that it was rotated so that the angle was 45 °, and Vf was measured to be 3.6V.

Example 5
In this example, the effect when the current diffusivity of the p-type ohmic electrode is low was examined.
A GaN-based LED chip was fabricated in the same manner as in Example 1 except that the p-type ohmic electrode was a 10 nm thick transparent electrode in which Ni and Au were laminated, and Vf was measured. there were.

Comparative Example 3
A GaN-based LED chip was fabricated in the same manner as in Comparative Example 1 except that the p-type ohmic electrode was a 10 nm thick transparent electrode in which Ni and Au were laminated, and Vf was measured. there were.

  According to the above examples and comparative examples, the Vf of the GaN-based LED according to the present invention is compared with that in which the n-type ohmic electrode and the light emitting portion are arranged without considering the extension direction of the stripe-shaped recess on the crystal growth surface of the processed substrate And found that it was lower.

  In the future, the amount of GaN-based LEDs used in lighting applications is expected to increase, so that low power consumption is extremely important from the viewpoint of energy saving. Further, the reduction in the amount of heat generated during operation increases the durability of the LED itself and peripheral devices, and simplifies the heat dissipation structure, so that it is also important in terms of effective use of resources. Therefore, if the output performance is the same for GaN-based LEDs, it is said that it is better that Vf is as low as 0.1 V. From such circumstances, the industrial value of the present invention is extremely large.

It is a schematic diagram which shows an example of the structure of GaN-type LED of this invention. FIG. 1A is a view (top view) when the LED is viewed from above, and FIG. 1B is a cross-sectional view taken along a cutting line SS in FIG. In FIG. 1A, the device is partially cut out to show a striped uneven pattern on the crystal growth surface. The stripe pattern drawn by the thick black line and the white line schematically shows a state when the striped uneven pattern is viewed from above. It is sectional drawing in the cutting line RR of Fig.1 (a). It is explanatory drawing (top view) which extracted and drew the light emission part and the n-type ohmic electrode from FIG. It is explanatory drawing which extracted and extracted the light emission part and the n-type ohmic electrode from an example of GaN-type LED of this invention. It is a schematic diagram which shows the various formation patterns of a light emission part and an n-type ohmic electrode in GaN-type LED of this invention. It is explanatory drawing which extracted and extracted the light emission part and the n-type ohmic electrode from an example of GaN-type LED of this invention. It is a schematic diagram which shows the various formation patterns of a light emission part and an n-type ohmic electrode in GaN-type LED of this invention. It is the schematic diagram which showed the various aspects of the unevenness | corrugation of the crystal growth surface of a board | substrate. It is sectional drawing which shows an example of the facet growth board | substrate which can be utilized as a board | substrate in this invention. It is sectional drawing which shows the other example of the facet growth board | substrate which can be utilized as a board | substrate in this invention. It is a model which shows an example of the structure of the conventional GaN-type LED using a process board | substrate. 11A is a top view of the LED, FIG. 11B is a cross-sectional view taken along a cutting line X1-X1 in FIG. 11A, and FIG. 11C is a cutting line Y1-Y1 in FIG. 11A. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Process substrate 21 n-type contact layer 22 n-type clad layer 23 Active layer 31 p-type clad layer 32 p-type contact layer P1 n-type ohmic electrode P2 p-type ohmic electrode P3 Bonding pad

Claims (3)

An n-type nitride semiconductor layer doped with an n-type impurity is formed on a substrate having an uneven crystal growth surface made of an insulator, and the nitride semiconductor is formed on the n-type nitride semiconductor layer. A light-emitting portion in which an active layer, a p-type nitride semiconductor layer, and a p-type ohmic electrode are stacked in this order and an n-type ohmic electrode are formed in different regions, respectively,
A rectangle circumscribing the light-emitting portion can be selected so that all four sides are in contact with the outer periphery of the light-emitting portion when viewed from above the substrate, and a set of opposite sides of the rectangle (first side) is selected. , Third side), (second side, fourth side),
The n-type ohmic electrode is
In a region sandwiched between a straight line including the first side and a straight line including the third side, the distance between the n-type ohmic electrode and the fourth side is the distance between the n-type ohmic electrode and the first side and the first side. 80% of the distance when the rectangle is selected so that the distance between the n-type ohmic electrode and the fourth side becomes the maximum so that the distance is greater than any of the distances to the three sides. As above,
Formed,
The n-type nitride semiconductor layer has a portion that enters the recess of the crystal growth surface, and the upper surface thereof is flat, whereby the n-type nitride semiconductor layer includes the crystal growth surface. There is a thick part corresponding to the concave part and a thin part corresponding to the convex part,
In the crystal growth surface, the recess extends in a direction perpendicular to the fourth side, whereby the thick portion of the n-type nitride semiconductor layer extends in the direction, thereby A nitride semiconductor light-emitting diode characterized in that lateral current diffusivity in the n-type nitride semiconductor layer is better in the direction perpendicular to the fourth side than in other directions. An n-type nitride semiconductor layer doped with an n-type impurity is formed on a substrate having an uneven crystal growth surface made of an insulator, and the nitride semiconductor is formed on the n-type nitride semiconductor layer. A light-emitting portion in which an active layer, a p-type nitride semiconductor layer, and a p-type ohmic electrode are stacked in this order and an n-type ohmic electrode are formed in different regions, respectively,
A rectangle circumscribing the light-emitting portion can be selected so that all four sides are in contact with the outer periphery of the light-emitting portion when viewed from above the substrate, and a set of opposite sides of the rectangle (first side) is selected. , Third side), (second side, fourth side),
The n-type ohmic electrode is
In a region sandwiched between a straight line including the first side and a straight line including the third side, the distance between the n-type ohmic electrode and the fourth side is the distance between the n-type ohmic electrode and the first side and the first side. The maximum width of the n-type ohmic electrode in the extending direction of the first side and the third side is 50% of the total width of the light emitting unit in the same direction so as to be larger than any of the distances to the three sides. As above,
Formed,
The n-type nitride semiconductor layer has a portion that enters the recess of the crystal growth surface, and the upper surface thereof is flat, whereby the n-type nitride semiconductor layer includes the crystal growth surface. There is a thick part corresponding to the concave part and a thin part corresponding to the convex part,
In the crystal growth surface, the recess extends in a direction perpendicular to the fourth side, whereby the thick portion of the n-type nitride semiconductor layer extends in the direction, thereby A nitride semiconductor light-emitting diode characterized in that lateral current diffusivity in the n-type nitride semiconductor layer is better in the direction perpendicular to the fourth side than in other directions.   When viewed from above the substrate, the outer periphery of the light-emitting portion includes all or part of the first side, all or part of the second side, all or part of the third side, and the first side. The nitride semiconductor light-emitting diode according to claim 1 or 2, comprising all or part of four sides.

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