JP2003133589A - GaN BASED SEMICONDUCTOR LIGHT EMITTING DIODE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaN based LED provided with an upper electrode capable of passing more light to the outside than a conventional upper electrode. SOLUTION: The upper electrode P2 is subdivided and formed so as to be provided with light transmissivity. At a subdivided part P22, the electrode is subdivided so as to present a net shape or a branched shape and turned to a part spread on the top surface 4a of an element structure and the top surface is exposed between the subdivided electrodes. As for the degree of subdivision, when the division is performed in a matrix shape with a square whose one side is 50 μm as a constitution unit, an electrode part and an exposed part are similarly present within each constituting unit and it is preferable that the ratio of an area of the electrode part occupying in each constitution unit is 30%-80%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaN-based semiconductor light emitting diode (hereinafter, also referred to as "GaN-based LED").

[0002]

2. Description of the Related Art A GaN-based LED is a light-emitting diode having at least a light-emitting layer made of a GaN-based semiconductor and capable of emitting light having a short wavelength ranging from blue to ultraviolet depending on the composition of the light-emitting layer. . The GaN-based semiconductor here means In _X Ga _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0
≦ Z ≦ 1, X + Y + Z = 1).

As a simple element structure of a GaN-based LED, as shown in FIG.
N-based crystal layer (n-type GaN contact layer 22, In _1-x G
An a _x N (0 <x ≦ 1) light emitting layer 23 and a p-type GaN contact layer 24 are sequentially stacked by crystal growth, and a lower electrode (usually an n-type electrode) 25 and an upper electrode (usually a p-type electrode) are stacked thereon. ) 26 is provided as an example. Here, it is assumed that the crystal substrate is mounted so that the light is emitted upward.

Since the upper electrode 26 is provided on the uppermost surface of the laminated structure and is located above the light emitting layer 23, it becomes an obstacle to the light emitted upward from the light emitting layer. In particular, G
In the case of an aN-based material, current diffusion is difficult and light is emitted only directly under the electrode, so that the problem that the upper electrode becomes an obstacle for light emission is more remarkable than that of LEDs of other material systems. Further, if the area of the upper electrode is too small, the light emitting area is reduced and the brightness is lowered.

As a mode of the upper electrode which can cope with these problems, a mode is known in which a transparent electrode 26a is provided so as to cover the entire top surface of the laminated structure as shown in FIG. 4 (a). In this mode, an electric current is supplied to the light emitting layer in a wide range to cause light to be emitted, and the transparent electrode tries to output the light to the outside without blocking it.

[0006]

However, when the inventors of the present invention examined the above-mentioned conventional upper electrode mode, optimization was considered in both cases regarding the current density and the amount of light that can pass through the upper electrode. No, there was room for further improvement.

An object of the present invention is to solve the above problems and to provide a GaN-based LED having an upper electrode which allows more light to pass to the outside than the conventional upper electrode.

The present invention has the following features. (1) A light emitting diode having a laminated structure including a light emitting layer made of a GaN-based semiconductor, wherein one of both p-type and n-type electrodes provided on the light emitting diode is provided on the uppermost surface of the laminated structure. The upper electrode is provided as an upper electrode, and the upper electrode has a subdivided portion, and the subdivided portion is a portion that is subdivided and spreads on the uppermost surface so that the electrode has a mesh shape or a branched shape. The uppermost surface is exposed between the patterned electrodes, and the electrode of the subdivided portion is formed to have a light-transmitting property with respect to light emitted from the light-emitting layer. GaN-based semiconductor light emitting diode.

(2) The area of the subdivided portion consisting of the electrode portion and the exposed portion of the uppermost surface is 30% to 80% of the entire uppermost surface.
%, The subdivided portion is exposed in the same proportion as the electrode portion and the electrode portion when the subdivided portions are divided into a matrix along the uppermost surface with a square having a side of 50 μm as the constitutional unit. The GaN-based semiconductor according to (1) above, which has subdivided electrodes so as to have a portion and the area ratio of the electrode portion to each constituent unit is 20% to 80%. Light emitting diode.

(3) The GaN-based semiconductor light-emitting diode according to the above (2), wherein the constituent units have an electrode portion and an exposed portion in the same arrangement pattern as each other.

(4) The subdivided portion has a width of 1 μm to 10 μm
The GaN-based semiconductor light emission according to any one of (1) to (3) above, which has a portion in which strip-shaped electrode portions of 1) and strip-shaped exposed uppermost surfaces having a width of 1 μm to 40 μm are alternately arranged. diode.

(5) The GaN-based semiconductor light-emitting diode as described in (1) above, wherein the electrode of the subdivided portion has a light transmittance of 20% to 80% with respect to the light emitted from the light emitting layer.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below by taking a simple device structure as an example. In the following description, a structure in which the upper electrode is a p-type electrode and an insulating substrate is used (a structure in which both electrodes are provided on the upper surface side) will be described, but the element structure is not limited to these, and a conductive type The top and bottom may be reversed, and any element structure using a crystal substrate having conductivity such as a SiC substrate or a GaN substrate may be used.

The GaN-based LED according to the present invention is shown in FIG.
As shown in (b), Al _a Ga _{1 -a} N (0) is formed on the sapphire substrate 1 so as to include a light emitting layer made of a GaN-based semiconductor.
≦ a ≦ 1) n-type Al via the low temperature growth buffer layer 1b
_b Ga _1-b N (0 <b ≦ 1) contact layer 2, In _1-x G
a _x N (0 <x ≦ 1) light emitting layer 3, p-type Al _c Ga _1-c N
(0 <c ≦ 1) The contact layers 4 are sequentially stacked by crystal growth to form a laminated structure. The laminated structure is locally removed to form the n-type Al _b Ga _1-b N contact layer 2
Is partially exposed, a lower electrode (n-type electrode) P1 is formed on the exposed portion, and an upper electrode (p-type electrode) P2 is provided on the uppermost surface 4a of the laminated structure.

The upper electrode 6 is, as shown in FIG.
It has a bonding terminal P21 for connecting to the outside and a subdivided portion P22 extending from there to the entire uppermost surface. In the subdivided portion P22, the electrode is subdivided so as to have a mesh shape or a branched shape and spreads over the entire uppermost surface 4a, and the electrode portion where the electrode material covers the uppermost surface (FIG. 1).
In (a), P23 and P25) and the exposed portion P24 with the uppermost surface exposed therebetween are arranged adjacent to each other in an arrangement pattern. The electrode portions P23 and P25 are formed to have a light-transmitting property with respect to the light emitted from the light emitting layer. With the above structure, compared to the case where the uppermost surface is covered with the transparent electrode, the light of higher output can be extracted even when the same electric power is applied.

As described above, in the GaN-based LED, G
Unlike LEDs made of other materials such as aAs, it is difficult for the current flowing from the upper electrode to the light emitting layer to diffuse. for that reason,
In the light emitting layer, a portion corresponding to immediately below the portion where the upper electrode material is present emits light intensively. In the mode where the transparent electrode is covered with the light-emitting layer, the entire surface of the light-emitting layer can emit light, but on the other hand, a high current density cannot be obtained, and the transmittance of the transparent electrode is not 100%. It is not possible to emit enough upward light to the outside world.

On the other hand, one of the modes of the upper electrode is a so-called "comb-shaped electrode" in which the electrode material is formed in a comb-shaped pattern. Conventionally, the comb-shaped electrode has been used exclusively in the field of light-receiving elements to cause light to be received to enter the element, and the electrode portion is opaque. When such an opaque comb-shaped electrode is simply applied to a GaN-based light-emitting device, it emits light only just under the electrode due to the unique property of the GaN-based material that only a small amount of current diffuses as described above. There arises a problem that the electrode portion blocks light emitted upward.

On the other hand, in the present invention, the upper electrode is made into a subdivided electrode pattern like a comb-shaped electrode, and the subdivided electrode itself is provided with light transmittance. As a result, first, as shown in FIG. 1B, the light L2 traveling directly upward from the light emitting portion can pass through the electrode and go out to the outside while generating intense light emission directly under the electrode. Yes, the loss is reduced. Next, since the current diffuses even if the amount is very small, the light emitting portion is not only directly below the comb-shaped electrode, but is slightly protruded from the portion directly below the comb-shaped electrode to the surroundings. Although each of the protruding portions is minute, since the electrode pattern is a pattern elongated and elongated so as to exhibit a comb shape, the total amount of the protruding portions in the entire pattern contributes to an increase in emission intensity. You will get the amount.
That is, compared with the case where the electrodes having the same area as the comb-shaped electrode are concentrated in one place, there is an advantage that the total area of the light emitting portion is large. Due to these actions and effects, it is possible to extract light with a higher output than the conventional electrode even when the same electric power is applied.

On the uppermost surface, in addition to the area occupied by the bonding terminals and the area of the subdivided portion (electrode portion + exposed portion), as shown in FIG. 1A, on the outer peripheral edge of the uppermost surface,
There is a case where the processing width 4b having a minute width is present as an exposed portion. In the following description, the area of these bonding terminals and the area of only the subdivided portion excluding the processing white on the outer peripheral edge will be described.

The electrode pattern of the subdivided portion may be in a state in which the electrode is spread on the uppermost surface so as to have a mesh shape or a branched shape, and the electrode portion and the exposed portion are adjacently combined with each other. , Irregular, or a mixture of these.
It can be linear, curved, or dot-shaped.

A typical electrode pattern is illustrated below. However, there are numerous electrode patterns as described above, and the present invention is not limited to these examples. The example of FIG. 1A is a comb-shaped pattern in which a strip-shaped electrode P23 branches off from the comb back portion P25 as a trunk line to form a stripe shape. The example of FIG. 2A is a grid pattern, and the electrodes have a mesh shape. The example of FIG. 2B is a pattern in which the exposed portions in the form of circular dots are arranged in a close-packed manner, and is a kind of mesh pattern when attention is paid to the electrodes. In these mesh patterns, the shape of the exposed portion is arbitrary and may be any quadrangle, ellipse, irregular shape, etc., and the orientation and array pattern of the exposed portion may be regular or random. The examples of FIGS. 2C and 3A are patterns in which strip-shaped electrode portions and strip-shaped exposed portions are alternately combined, and can be said to be a kind of comb-shaped pattern or a kind of mesh-shaped pattern. In FIG. 2C, linear strip electrodes are bent and combined, and in FIG. 3A, the strip electrodes are arranged concentrically. The example of FIG. 3B is a pattern in which the subdivided electrodes branch like a maze without regularity. These various patterns may be freely combined, and for example, an irregular capillary pattern may be branched from a regular branch pattern such as a comb shape.

The subdivided portion of the upper electrode is 30% to 80% of the uppermost surface including the electrode portion and the exposed portion sandwiched by the electrode portion.
%, More preferably 40% to 70%. This is not a mode in which the subdivided portions are concentrated in one place in a lump shape, but restricts that they should be dispersed more widely.

The current density is greatly related to the intensity of light emission in the light emitting layer. When the current density is low, the ratio of carriers trapped in the non-emissive component is high, and the emission intensity is low. As the current density is increased, the rate of trapping in the non-emissive component becomes smaller, and the trapped amount is saturated from a certain value, so that the emission intensity becomes stronger. The current density is to reduce the area of each part of the subdivided electrode part (for example,
In the comb-shaped pattern, it is increased by narrowing the electrode band width. If the current density increases, the internal quantum efficiency increases and the output improves. However, if the electrode area is simply reduced without limitation, increase in applied voltage required for sufficient light emission and increase in non-radiative transition ratio due to thermal relaxation by increasing current density, that is, decrease in output can be considered. From this point, the area of the electrode portion and its pitch are important.

On the other hand, even if the electrode is subdivided and formed as a transparent electrode, the transparent electrode cannot pass 100% of the light from the light emitting layer, so that light loss occurs at the electrode portion. In addition, if the electrode has a large area, in order for the light emitted directly under the center of the electrode to go out from the nearest exposed portion to the outside, it has to rise obliquely at a large angle from the direction directly above. At the interface between the upper surface and the outside world, the amount of light reflected inside the element increases, which causes a loss. From this point as well, the area of the electrode portion and its pitch are important.

Therefore, the internal quantum efficiency is further increased, and
In order to take out the generated light to the outside world without loss,
In the present invention, it is recommended that the degree of subdivision of the electrode in the subdivided portion be further limited as described below. Thereby, the object of the invention is achieved to a higher degree.

The degree of subdivision of the electrode is such that, even if the subdivided portion is divided into a matrix having a square having a side of 50 μm as a constitutional unit, no matter which position the constitutional unit is applied to, the constitutional unit is divided into each constitutional unit. It is preferable that the electrode is subdivided so that the electrode portion and the exposed portion always exist in the same ratio. One side of the square of the structural unit is from 2 μm to
It is more preferably 12 μm. Further, in an embodiment in which the electrodes are finely subdivided, the constitutional unit is 2 μm to 4 μm on each side.
It is preferable that the section is divided into squares so that the electrode section and the exposed section are always present in the section even if the section is applied to any position of the section.

Further, a preferable ratio of the area of the electrode portion in each of the above structural units is 20% to 80%, more preferably 20% to 60%, and a particularly preferable ratio is 40%.
~ 60%.

By defining these subdivisions, the internal quantum efficiency is optimized, and the light emitted directly under the electrode can go out from the exposed portion to the outside world at an angle closer to the direct upward direction. The reflection inside the element at the interface between the upper surface and the outside air is suppressed. Also, most of the light that hits the transparent electrode passes through this and goes out to the outside world, so the GaN-based LED seen from the outside emits stronger light than the conventional product when the same amount of power is applied. Becomes

In the case of division into a matrix, a semi-partition that does not become a square may occur in the outer peripheral portion of the subdivided portion. In addition, like the comb-shaped pattern shown in FIG.
In addition to the stripes that are uniformly subdivided, the main line P
When a unique portion such as 25 exists, the definition of the matrix division is applied only to the uniformly subdivided portion.

When the subdivided portions are divided into a matrix, it is sufficient that the electrode portion and the exposed portion are the same in each constituent unit in each constituent unit, and they need not be the same. This is because, in the irregular pattern as shown in FIG. 3B, the ratio of the electrode portion to the exposed portion may vary within a specific width for each structural unit. Further, for the densest electrode pattern as shown in FIG. 2B, since the basic shape of the repeated pattern is an equilateral triangle or a regular hexagon, as shown by a thick solid line in FIG. How to
It may be specified by shifting from [perfect square matrix] to [matrix according to the close-packed pattern]. Further, the subdivided portion may be formed by combining subdivided portions having different unit areas.

The comb-shaped pattern shown in FIG.
The grid pattern shown in (a) includes a regular portion formed by regularly combining the electrode portion and the exposed portion. For example, in a comb pattern, the tooth part of the comb is
The strip-shaped electrode portions P23 and the strip-shaped exposed portions P24 are regularly and alternately arranged to form a stripe shape. When these regular parts are divided into a matrix, the electrode parts and the exposed parts are present in the same arrangement pattern in each square structural unit. The subdivided pattern having such regular portions is preferable because it has an optimal structure for providing more exposed portions (light extraction portions), and among them, the comb-shaped pattern is particularly preferable.

According to the above-mentioned regulation of subdivision, strip-shaped electrode portions and strip-shaped exposed portions are regularly alternated like a comb-shaped pattern or the patterns shown in FIGS. 2 (c) and 3 (a). The striped pattern is preferably a stripe in which the width of the strip-shaped electrode portion is 1 μm to 10 μm and the width of the strip-shaped exposed portion is 1 μm to 40 μm.
In this case, one side of the square of the structural unit is at least 2 (electrode width 1
+ Exposure width 1) μm, maximum 50 (= electrode width 10 + exposure width 4
0) μm. From these widths, it is preferable to select a numerical value such that the ratio of the area of the electrode portion in the constitutional unit is 20% to 80%. A more preferable range is a stripe having a strip-shaped electrode portion having a width of 1 μm to 8 μm and a strip-shaped exposed portion having a width of 1 μm to 20 μm (squares each side is 2 μm to 28 μm), and the ratio of the area of the electrode portion to the constitutional unit is 30. % To 60%, and
The most preferable range is a stripe having a strip-shaped electrode portion having a width of 2 μm to 4 μm and a strip-shaped exposed portion having a width of 4 μm to 8 μm (a square has a side of 6 μm to 12 μm).
The ratio of the area of the electrode portion to the structural unit is 40% to 60
It may be set to%.

As described above, the electrode of the subdivided portion is formed so as to have a light-transmitting property with respect to the light emitted from the light emitting layer. The light emitted from the light emitting layer depends on the composition of the GaN-based semiconductor used for the light emitting layer and is approximately 350 n.
The light is about m to 550 nm. The translucency of the electrode is preferably such that light of these wavelengths has a transmittance of 30% to 60%.

The transparent electrode may be formed by a known transparent electrode forming technique. For example, Al and Ni are used as materials, and the thickness is 10 nm and 1 nm, respectively.
And a mode of a two-layer structure.

In the example of FIG. 1, the laminated structure of GaN-based crystal layers is a three-layer structure of (n-type contact layer, active layer, p-type contact layer), but the light emitting layer has multiple quantum well structures and quantum well structures. Various element structures such as a dot structure may be used. The position of the lower electrode may be changed by using a conductive substrate such as a SiC substrate or a GaN substrate as the crystal substrate. Other parts of the GaN-based LED other than the upper electrode are described, for example, in International Publication WO
Structures and manufacturing methods used for publicly known GaN-based LEDs, such as the element structure described in 99/30373 and the manufacturing method for GaN-based crystals, a crystal growth method for GaN-based semiconductors, a method for reducing dislocation density, etc. May be referred to.

[0036]

EXAMPLES As an example of a GaN-based LED according to the present invention,
A device having the element structure shown in FIG. 1 (the comb-shaped pattern in the subdivided portion) was manufactured as an example product and compared with the conventional product. Regarding the example products according to the present invention, the specifications for subdividing the comb-shaped pattern were changed stepwise, and those within the range recommended by the present invention and those outside the range were manufactured. As for the conventional products, one having an opaque electrode having a comb-shaped pattern and one having a transparent electrode uniformly covering the entire surface were manufactured. The example product and the comparative example product are all the same except for the structure of the upper electrode.

[Production of Example Product] As shown in FIG. 1B, a C-plane sapphire substrate was used as the crystal substrate 1. The substrate was placed in a MOCVD apparatus, heated to 1100 ° C. in a hydrogen atmosphere, and subjected to thermal etching. After that, the atmosphere is switched to nitrogen, the temperature is lowered to 500 ° C., and trimethylgallium (TM) is used as a source gas.
G), NH ₃ is flowed, and GaN low temperature growth buffer layer 1b
Has grown up.

Next, the temperature is raised to 1000 ° C., TMG and NH ₃ as raw materials, and silane as a dopant are flown,
An n-type GaN layer 2 having a thickness of 3 μm was grown. Next, TMG, trimethylindium (TMI), NH as raw materials
₃ is poured onto the layer 2 to form an InGaN layer having a thickness of 0.1 μm.
The active layer (light emitting layer) 3 was grown. Next, as a raw material, T
MG, NH ₃ , and biscyclopentadienyl magnesium (Cp ₂ Mg) as a dopant are flown to obtain a thickness of 0.15.
A μm p-type GaN layer 4 was grown. Then, the atmosphere gas was switched to nitrogen and gradually cooled to room temperature to obtain a laminated structure.

The obtained laminated structure is partially dry-etched to partially remove the p-type GaN layer 4 and the InGaN active layer 3 to expose the n-type GaN layer 2 and to remove the material T.
An n-type ohmic electrode P1 made of i and Al was formed.

Next, on the uppermost surface of the laminated structure, resist coating, pre-baking (baking), exposure (transfer), development,
A transparent electrode having a comb-shaped pattern as schematically shown in FIG. 1A was formed by a processing procedure of vapor deposition and lift-off.

The material composition of the electrode is as follows: lower layer (material Ni, thickness 1.0 nm), upper layer (material Au, thickness 10.0 nm)
2 is a light-transmitting electrode having a two-layer structure. This light transmittance is I
50 nm wavelength light emitted from the nGaN light emitting layer is emitted.
% Could be permeated. The dimensional specifications of the striped portion of the comb-shaped pattern (the tooth of the comb), which is the subdivided portion, are such that the width of the electrode is 2.0 μm and the width of the exposed portion between the electrodes is 8.0 μm.

The device structure is completed by the above process.
After cutting, it is cut into 1 chip of 350mm × 350mm,
The GaN-based LED according to the present invention is used. In one chip state
The total area of the top surface is about 0.12mm²And bondin
Area of terminal for cutting, subdivided part excluding processing white on outer periphery
The area of the minute is about 0.06mm ²Met.

The above LED chip was mounted on a To-18 stem base and the output was measured. The wavelength was 460n.
It was 12 mW at m, 20 mA, and it was found that the output at the same current was improved by 25% as compared with the average output of the conventional light-emitting device using a fully transparent electrode.

[0044]

As described above, by subdividing the upper electrode and making it transparent, the upper electrode is
It has become possible to provide a GaN-based LED capable of increasing internal quantum efficiency and allowing more light to pass from the uppermost surface to the outside world. Further, among the GaN-based LEDs, the internal quantum efficiency and the amount of light passing through the uppermost surface were optimized by limiting the degree of subdivision of the upper electrode.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of the structure of a GaN-based LED according to the present invention. Only the electrodes are hatched to distinguish the regions. 1A is a side view of the element, and FIG. 1B is a top view of the element of FIG. 1A.

FIG. 2 is a diagram showing an example of an electrode pattern of a subdivided portion in the present invention. In the figure, only a part of the pattern is shown.

FIG. 3 is a diagram showing another example of an electrode pattern of a subdivided portion in the present invention. Similar to FIG. 2, the figure shows only a part of the pattern.

FIG. 4 is a schematic diagram showing an example of the structure of a conventional GaN-based LED. 4 (a) is a side view of the device, FIG.
4B is a view of the element of FIG. 4A as viewed from above.

[Explanation of symbols]

1 Crystal substrate 2 n-type GaN-based crystal layer 3 Light-emitting layer made of GaN-based crystal 4 p-type GaN-based crystal layer 4a Top surface of laminated structure P1 lower electrode P2 upper electrode P22 subdivision part

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroaki Okakawa             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works (72) Inventor Yoichiro Ouchi             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works F-term (reference) 5F041 AA03 AA04 CA40 CA65 CA82                       CA88 CA93

Claims (5)

[Claims] 1. A light emitting diode having a laminated structure including a light emitting layer made of a GaN-based semiconductor, wherein the uppermost surface of the laminated structure is one of p-type and n-type electrodes provided in the light emitting diode. One of the electrodes is provided as an upper electrode, and the upper electrode has a subdivided portion, and the subdivided portion is a portion that is subdivided into a net-like or branched shape and spreads on the uppermost surface. The uppermost surface is exposed between the subdivided electrodes, and the electrodes of the subdivided portions are formed to have a light-transmitting property with respect to light emitted from the light emitting layer. And a GaN-based semiconductor light emitting diode. 2. The area of the subdivided portion consisting of the electrode portion and the exposed portion of the uppermost surface occupies 30% to 80% of the entire uppermost surface, and the subdivided portion has this as the uppermost surface. Along the way, when a square having a side of 50 μm is divided into a matrix as a constituent unit, each constituent unit has an electrode portion and an exposed portion at the same ratio, and the area of the electrode portion occupying each constituent unit is The GaN-based semiconductor light-emitting diode according to claim 1, which has a subdivided electrode so that the ratio is 20% to 80%. 3. The GaN-based semiconductor light-emitting diode according to claim 2, wherein the constituent units have an electrode portion and an exposed portion in the same arrangement pattern as each other. 4. The subdivided portion has a portion in which strip-shaped electrode portions having a width of 1 μm to 10 μm and strip-shaped exposed top surfaces having a width of 1 μm to 40 μm are alternately arranged.
The GaN-based semiconductor light-emitting diode according to claim 1. 5. The GaN-based semiconductor light-emitting diode according to claim 1, wherein the translucency of the electrode of the subdivided portion with respect to the light emitted from the light emitting layer has a transmittance of 20% to 80%.