JP2010109127A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device capable of suppressing a leakage current between a p-type semiconductor layer and an n-type semiconductor layer, and of sufficiently keeping p-n isolation between the p-type semiconductor layer and the n-type semiconductor layer, which improves the emission intensity. <P>SOLUTION: The light emitting device includes a substrate 2 having a recess 2a and insulation characteristics, and a laminate 1 composed of an n-type semiconductor layer 1c, a light emitting layer 1b and a p-type semiconductor layer 1a arranged in the recess 2a, where the light emitting layer 1b touches the inner surface of the recess 1a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light emitting element represented by a light emitting diode (abbreviated as LED).

  In recent years, attention has been paid to light-emitting elements that emit light from the ultraviolet region to blue light, and gallium nitride-based compound semiconductors are known as materials for such light-emitting elements, for example.

  Such a light-emitting element can emit white light when combined with a phosphor, and is considered promising as an alternative to incandescent bulbs and fluorescent lamps because of its energy saving and long life. Has begun. However, since the luminous efficiency of these light emitting elements is lower than that of fluorescent lamps, further higher efficiency is required, and various studies for that purpose are being conducted.

For example, Patent Document 1 has a structure in which a semiconductor layer made of GaAs or the like is provided in a recess provided in a substrate such as SiO _2, and an electrode is planarly separated on the opening plane of the recess to emit light. A light-emitting element with reduced intensity variation is disclosed (see Patent Document 1).
Japanese Patent Laid-Open No. 4-188821

  However, in the light emitting element in Patent Document 1, since the light emitting layer located between the p type semiconductor layer and the n type semiconductor layer is exposed to the outside, the p type semiconductor layer and the n type semiconductor are used in the use of the light emitting element. When conductive dust or the like that conducts between the layers adheres, a leakage current is generated, and there is a tendency that pn separation between the p-type semiconductor layer and the n-type semiconductor layer is not ensured.

  It is an object of the present invention to suppress light leakage between a p-type semiconductor layer and an n-type semiconductor layer, and to secure sufficient pn separation between the p-type semiconductor layer and the n-type semiconductor layer to improve light emission intensity. It is to provide an element.

  The present invention is a laminated body having a recess and having an insulating property and an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer provided in the recess, the light-emitting layer being And a laminate that is in contact with the inner surface of the recess.

  The refractive index of the substrate is preferably lower than the refractive index of the laminate.

  An upper electrode layer is provided on the substrate so as to cover the stacked body and the recess, and is electrically connected to the n-type semiconductor layer or the p-type semiconductor layer, and is formed from the bottom surface of the recess to the back surface of the substrate. A lower electrode layer that is provided in the through hole and is electrically connected to a semiconductor layer that is not electrically connected to the upper electrode layer of the n-type semiconductor layer or the p-type semiconductor layer. Furthermore, it is preferable to comprise.

  Preferably, the substrate is a sapphire substrate, and the stacked body is a group IIIB nitride semiconductor.

  In the light-emitting element of the present invention, since the stacked body is provided in the concave portion of the insulating substrate, the light-emitting layer of the stacked body is covered with the insulator, and thus, between the p-type semiconductor layer and the n-type semiconductor layer. Leakage current can be suppressed, pn separation between the p-type semiconductor layer and the n-type semiconductor layer can be sufficiently secured, and the emission intensity can be improved.

  Since the refractive index of the substrate is lower than the refractive index of the laminated body, the light emitted from the light emitting layer passes through a medium having a lower refractive index as the light travels in the order of the laminated body, the substrate, and air. The relaxation effect is high, and the light extraction efficiency is improved.

  Since the upper electrode layer covers the stacked body, peeling of the stacked body from the substrate can be suppressed.

  Since the substrate is a sapphire substrate having high insulating properties and a refractive index larger than that of the group IIIB nitride semiconductor, the leakage current between the p-type semiconductor layer and the n-type semiconductor layer is sufficiently suppressed, and the p-type semiconductor A sufficient pn separation between the n-type semiconductor layer and the n-type semiconductor layer can be ensured to improve the emission intensity.

  Hereinafter, the light emitting device of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing one light emitting device according to an embodiment of the present invention. Moreover, FIG. 2 is sectional drawing which shows one light emitting element of another embodiment of this invention. FIG. 3 is a cross-sectional view showing an embodiment of the light emitting device of the present invention which is arrayed.

  1 to 3, 1 is a laminate, 2 is a substrate, 3 is a first electrode layer, 4 is a buffer layer, 5 is a first pad electrode, 6 is a second electrode layer, and 7 is a second electrode layer. A pad electrode is shown. In addition, the laminated body 1 includes 1a a p-type semiconductor layer, 1b a light emitting layer, and 1c an n-type semiconductor layer. The substrate 2 has a recess 2a and a through hole 2b.

  The light-emitting element in the present invention includes a substrate 2 having a recess 2a, and a laminate 1 composed of an n-type semiconductor layer 1c, a light-emitting layer 1b, and a p-type semiconductor layer 1a. The substrate 2 has an insulating property.

  In the present invention, the inner surface of the concave portion of the insulating substrate 2 is in contact with the light emitting layer 1b. Thereby, since the light emitting layer 1b is covered with an insulator, the leakage current generated between the p-type semiconductor layer and the n-type semiconductor layer is suppressed, and the pn isolation between the p-type semiconductor layer 1a and the n-type semiconductor layer 1c is achieved. Can be sufficiently secured to improve the light emission intensity.

  In the present invention, the refractive index of the substrate 2 is preferably lower than the refractive index of the laminate 1. Since the refractive index of the substrate 2 is lower than the refractive index of the stacked body 1, the light emitted from the light emitting layer 1b passes from the medium having the higher refractive index to the lower medium in the order of the stacked body 1, the substrate 2, and the air. The effect of reducing the refractive index is high, and the light extraction efficiency is improved.

  The refractive index of the laminate 1 is preferably not more than twice the refractive index of the substrate 2. For example, the case where the laminate 1 is GaN (refractive index: 2.4) and the substrate 2 is sapphire (refractive index: 1.7) is applicable.

  When the refractive index of the laminated body 1 is not more than twice the refractive index of the substrate 2, total reflection that occurs when light passes from the laminated body 1 to the substrate 2 is suppressed, and the light extraction efficiency is improved.

  Hereinafter, each structure of the light emitting element of the present invention will be described.

(substrate)
The substrate 2 has an insulating property. Note that the insulating property in this case means a resistivity of 10 ⁹ Ω · cm or more.

The substrate 2 can be any substrate as long as it can grow the laminate 1 and has an insulating property as described above. Specifically, examples of the substrate 2 include gallate substrates such as sapphire (Al ₂ O ₃ ), spinel (MgAl ₂ O ₄ ), and LiGaO ₂ , ZnO substrates doped with Li and the like to increase resistance, and AlN substrates. It is done.

  Specifically, the recess 2a of the substrate 2 has a depth of 2 to 5 μm.

  The width of the recess 2a may be set to a desired element size, and is not particularly limited. However, if it is too narrow, the source gas is not supplied to the recess and growth does not occur.

  The recess 2a is formed by dry etching such as RIE using a chlorine-based gas.

  The thickness of the substrate 2 is about 100 to 1000 μm.

  In FIG. 1, a through hole 2 b is provided from the bottom surface of the recess 2 a of the substrate 2 to the back surface of the substrate 2. The through hole 2b is provided in order to electrically connect the n-type semiconductor layer 1c side of the stacked body 1 surrounded by the insulating substrate 2 to the outside. The through hole 2b is formed by processing by laser, microblast, wet etching, dry etching or the like. A combination of these techniques may also be used.

  When the shape of the through-hole 2b is a substantially cylindrical diameter, the hole diameter (diameter) of the through-hole 2b is about 50-300 micrometers.

  In FIG. 1, the through-hole 2b is provided on the wall surface side of the recess 2a in the bottom surface of the recess 2a, but there is no particular problem if it is provided on the bottom surface of the recess 2a.

  A reflective metal layer is preferably formed on the outer bottom surface and side surfaces of the substrate 2. Light can be effectively extracted from the upper surface. In particular, when the substrate 2 is highly sapphire, the reflected light propagates through the sapphire, so that the loss is small. In addition, Al, Ag, etc. are mentioned as a reflective metal layer.

(Laminate)
The stacked body 1 includes a p-type semiconductor layer 1a, a light emitting layer 1b, and an n-type semiconductor layer 1c.

The stacked body 1 is a semiconductor formed in the recess 2a of the substrate 2, and is formed of, for example, a nitride semiconductor. Here, the nitride semiconductor means, for example, a semiconductor composed of a nitride of a group IIIB (group 13) element in the periodic table. The group IIIB nitride semiconductor can be represented by the chemical formula Al _x Ga _y In _(1-xy) N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1). Examples of the group IIIB nitride semiconductor include gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), and the like.

  The stacked body 1 has a stacked structure in which an n-type semiconductor layer 1c, a light-emitting layer 1b, and a p-type semiconductor layer 1a are stacked in a recess 2a with a light-emitting layer 1b interposed therebetween. A block layer that suppresses carrier overflow is disposed between at least one of the n-type semiconductor layer 1c and the light-emitting layer 1b and between the p-type semiconductor layer 1a and the light-emitting layer 1b. Also good.

  In order to obtain the n-type semiconductor layer 1c made of a group IIIB nitride semiconductor, Si (silicon), which is an element of group IVB in the periodic table, may be mixed into the layer as a dopant. The n-type semiconductor layer 1c has a thickness of about 1 to 5 μm. Further, in order to obtain the p-type semiconductor layer 1a made of a group IIIB nitride semiconductor, Mg (magnesium), which is an element of group IIA in the periodic table, may be mixed into the layer as a dopant. The thickness of the p-type semiconductor layer 1a is about 150 to 500 nm.

The light emitting layer 1b is provided between the n-type semiconductor layer 1c and the p-type semiconductor layer 1a. The light emitting layer 1b is a multilayer quantum structure in which a quantum well structure composed of a light emitting layer side barrier layer having a wide forbidden band and a light emitting layer side well layer having a narrow forbidden band is regularly stacked a plurality of times (for example, about 3 times). It is good also as a well structure (MQW). The light emitting layer side barrier layer may be an In _0.01 Ga _0.99 N layer. Examples of the light emitting layer side well layer include an In _0.11 Ga _0.89 N layer. The thickness of the light emitting layer side barrier layer is about 5 to 15 nm, and the thickness of the light emitting layer side well layer is about 2 to 10 nm. The thickness of the light emitting layer 1b is about 25 to 150 nm.

  As a growth method of the stacked body 1, a molecular beam epitaxy (MBE) method, an organic metal epitaxy (MOVPE; Metal Organic Vapor Phase Epitaxy) method, a hydride vapor phase epitaxy (HVPE), and a hydride vapor phase laser (HVPE). A deposition (PLD; Pulsed Laser deposition) method or the like is used.

  The depth of the recess 2a of the substrate 2 is 2 to 5 μm as described above, and the thickness of the laminate 1 is the same as the depth of the recess 2a.

  In the light emitting device of the present invention, the light emitting layer 1b is in contact with the inner surface of the recess 2a. This structure can be obtained by rotating the substrate 2 when the laminate 1 is grown.

  Below, the specific example of the laminated body 1 by the metal organic chemical vapor deposition (MOCVD) method for making it grow so that the light emitting layer 1b may contact with the inner surface of the recessed part 2a is shown. At this time, the substrate 1 is always rotated at 5 to 10 rpm.

  First, the n-type semiconductor layer 1c is grown. The temperature of the substrate 2 may be set to 950 to 1150 ° C., and the n-type semiconductor layer 1c may be formed by forming gallium nitride (GaN) with a thickness of about several μm (for example, 1 to 5 μm) as the n-type semiconductor layer 1c. At this time, Si is doped.

The light emitting layer 1b has a temperature of about 700 ° C., a barrier layer made of indium gallium nitride (In _0.01 Ga _0.99 N) having a thickness of about 5 to 50 nm, and a nitride layer having a thickness of about 1 to 20 nm. A well layer made of indium gallium (In _0.11 Ga _0.89 N) may be repeatedly stacked.

The p-type semiconductor layer 1a includes a first p-type cladding layer, a second p-type cladding layer, and a p-type contact layer. In the first p-type cladding layer, the temperature of the substrate 1 is set to about 700 ° C., and an aluminum gallium nitride (Al _0.15 Ga _0.85 N) layer is formed on the barrier layer of the multiple quantum well layer to about 10 to 100 nm. The thickness is formed. In the second p-type cladding layer, the temperature of the substrate 1 is set to about 820 ° C., and an aluminum gallium nitride (Al _0.2 Ga _0.8 N) layer is 50 to 300 nm on the first p-type cladding layer. It is formed with a thickness of about. In the p-type contact layer, the temperature of the substrate 1 is set to about 820 to 1050 ° C., and a gallium nitride (GaN) layer is formed with a thickness of about 5 to 50 nm on the second p-type cladding layer. At this time, magnesium (Mg), zinc (Zn), or the like is added as a p-type impurity element.

  By the above method, the laminated body 1 can be grown so that the light emitting layer 1b may contact the inner surface of the recessed part 2a.

In addition, when forming the laminated body 1 by the above method, a laminated body may be formed besides the inside of the recessed part 2a. In this case, it is preferable to remove the laminate from the viewpoint of reducing the height of the light emitting element. For example, the excess stacked body is removed after growth by covering the recess with a mask and performing dry etching such as RIE. Alternatively, the layered product can be removed by forming a mask with a material that inhibits growth, such as SiO ₂ , and then performing wet etching using hydrofluoric acid.

  Further, by the above method, the semiconductor grows also from the wall surface in the recess 2a, but the thickness is small, and since it is merged with the semiconductor grown from the bottom surface of the recess 2a, the presence may be ignored.

  As shown in FIG. 1, a buffer layer 4 is preferably provided between the stacked body 1 and the substrate 2. The buffer layer 4 is preferably formed in order to relieve stress when stress is generated between the stack 1 and the substrate 2 as in the case where the stack 1 is sapphire and the substrate 2 is GaN. The buffer layer 4 is made of a material such as gallium nitride or aluminum nitride, for example. The thickness of the buffer layer 4 is about 0.01 to 0.2 μm.

  In the case of FIG. 1, the buffer layer 4 is formed by growing gallium nitride and aluminum nitride at a temperature of about 400 ° C. to 700 ° C. before forming the n-type semiconductor layer.

  The light emitting device of the present invention preferably includes the following configuration in addition to the laminate 1 and the substrate 2.

(electrode)
The electrode is composed of a first electrode layer 3 and a second electrode layer 6. The thicknesses of the first electrode layer 3 and the second electrode layer 6 are each 0.1 to 5 μm.

As the first electrode layer 3 and the second electrode layer 6, for example, aluminum (Al), titanium (Ti), nickel (Ni), chromium (Cr), indium (In), tin (Sn), molybdenum ( Mo), silver (Ag), gold (Au), niobium (Nb), tantalum (Ta), vanadium (V), platinum (Pt), lead (Pb), beryllium (Be), tin oxide (SnO ₂ ), Indium oxide (In ₂ O ₃ ), indium tin oxide (ITO), gold-silicon (Au—Si) alloy, gold-germanium (Au—Ge) alloy, gold-zinc (Au—Zn) alloy, gold-beryllium ( A thin film such as an Au—Be) alloy can be preferably used. Further, the first electrode layer 3 and the second electrode layer 6 may be formed by laminating a plurality of layers selected from the above materials.

  The 1st electrode layer 3 and the 2nd electrode layer 6 are produced by methods, such as a vacuum evaporation method and sputtering method.

  In FIG. 1, the first electrode layer 3 is provided on the p-type semiconductor layer 1a and connected to the p-type semiconductor layer 1a (hereinafter referred to as the upper electrode layer). The second electrode layer 6 is provided in a through hole 2b provided from the bottom surface of the recess 2a of the substrate 2 to the back surface of the substrate 2, and is connected to the n-type semiconductor layer 1c (hereinafter referred to as a lower electrode layer). . The second electrode layer 6 is formed, for example, by embedding a conductive paste or the like in the through hole 2b. In order to reduce contact resistance, it is preferable to deposit a metal layer in the through hole 2 before the conductive paste is embedded in the through hole 2b.

  The upper electrode layer is preferably provided on the substrate 2 so as to cover the laminate 1 and the recess 2a. Thereby, since the upper electrode layer covers the stacked body 1, peeling of the stacked body 1 from the substrate 2 can be suppressed. In the case of FIG. 1, the upper electrode layer is electrically connected to the p-type semiconductor layer 1a because the p-type semiconductor layer 1a is located at the upper part, but the n-type semiconductor layer 1c is located at the upper part. And electrically connected to the n-type semiconductor layer 1c.

  When the upper electrode layer is used as described above, the lower electrode layer is provided in the through hole 2b provided from the bottom surface of the recess 2a to the back surface of the substrate 2. In the case of FIG. 1, the lower electrode layer is electrically connected to the n-type semiconductor layer 1 c because the n-type semiconductor layer 1 c is located below, but the p-type semiconductor layer 1 a is located below. Are electrically connected to the p-type semiconductor layer 1a.

  It is preferable that the height of the stacked body 1 and the depth of the recess 2a are substantially the same (the step is within 1 μm) so that no step is generated in the upper electrode layer.

  The first electrode layer 3 and the second electrode layer 6 in the light emitting device of the present invention are not limited to the positions of the upper electrode layer and the lower electrode layer in FIG. 1, and for example, as shown in FIG. Both the electrode layer 3 and the second electrode layer 6 may be provided on the upper side of the light emitting element. In this case, since both the first electrode layer 3 and the second electrode layer 6 are exposed to the outside and can be electrically connected to the outside, the through-hole provided in the substrate 2 of the light-emitting element in FIG. The hole 2b is not necessary. In this respect, it is preferable to the light emitting element of FIG.

  On the other hand, in the case of the light emitting element of FIG. 2, the upper electrode layer cannot be formed on the substrate 2 so as to cover the laminate 1 and the recess 2a so as to suppress the peeling of the laminate 1 from the substrate 2. In terms of the point, the light-emitting element of FIG. 1 is preferable to the light-emitting element of FIG.

  In consideration of connection by wire bonding, both the first electrode layer 3 and the second electrode layer 6 may have a pad electrode.

  The pad electrode 5 is an electrode terminal connected to the upper electrode layer 3, and the pad electrode 7 is an electrode terminal connected to the lower electrode layer 6.

  The pad electrodes 5 and 7 are made of, for example, titanium or a layer in which a gold layer is laminated with titanium as a base layer. The pad electrodes 5 and 7 have a thickness of about 0.5 to 5 μm.

  The pad electrodes 5 and 7 are formed by a method such as a vacuum evaporation method or a sputtering method.

  As described above, a light-emitting element can be manufactured.

  FIG. 3 is a cross-sectional view showing an embodiment of the light-emitting element of the present invention which is arrayed.

  The light emitting device of the present invention may include a substrate 2 having a plurality of recesses 2a, and a laminate 1 provided in each of the plurality of recesses 2a. The light emitting elements thus obtained are arrayed.

  Usually, after a laminated body is grown on a substrate, light-emitting elements having a desired size are cut out one by one to produce light-emitting elements. In this case, it is necessary to dice the light emitting element itself, and the light emitting layer is damaged. However, when arraying is performed as described above, since the substrate 2 can be cut by dicing or the like instead of the stacked body, the active layer is not damaged and the element yield is improved.

  Further, by providing the upper electrode layer 3 that is located on the substrate 2 so as to cover the plurality of stacked bodies 1 and the plurality of recesses 2a and is connected to each of the stacked bodies 1, on the plurality of p-type semiconductor layers 1a, A common electrode is formed on one surface. Thereby, for example, when the light emitting elements are mounted on a package or the like, they can be mounted together without mounting the light emitting elements one by one.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

It is sectional drawing which shows embodiment of the light emitting element of this invention. It is sectional drawing which shows other embodiment of the light emitting element of this invention. It is sectional drawing which shows embodiment of the light emitting element of this invention made into the array.

Explanation of symbols

1: Laminate 1a: p-type semiconductor layer 1b: light-emitting layer 1c: n-type semiconductor layer 2: substrate 2a: recess 2b: through hole 3: first electrode layer 4: buffer layer 5: first pad electrode 6: Second electrode layer 7; second pad electrode

Claims (4)

A substrate having a recess and having an insulating property;
A laminated body provided in the concave portion and composed of an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer, wherein the light emitting layer is in contact with the inner surface of the concave portion;
A light emitting device comprising:   The light emitting device according to claim 1, wherein a refractive index of the substrate is lower than a refractive index of the laminate. An upper electrode layer provided on the substrate so as to cover the stacked body and the recess, and electrically connected to the n-type semiconductor layer or the p-type semiconductor layer;
A semiconductor layer which is provided in a through hole formed from the bottom surface of the recess to the back surface of the substrate and which is not electrically connected to the upper electrode layer among the n-type semiconductor layer or the p-type semiconductor layer. A lower electrode layer electrically connected to
The light emitting device according to claim 1, further comprising: The light emitting device according to any one of claims 1 to 3, wherein the substrate is a sapphire substrate, and the stacked body is a group IIIB nitride semiconductor.

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