JP2005158955A - Light emitting diode element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To endure a use in a high temperature service condition and suppress the deterioration of a lifetime in a light emitting diode element. <P>SOLUTION: On the surface of an opposite side to an active layer 3 of a second conduction type semiconductor crystal layer 4, a penetrating dislocation defective 11 is exposed, the internal surface of the penetrating dislocation defective 11 and its periphery are covered with a material (a coating portion 13) which has non-ohmic contact nature to a second conduction type semiconductor crystal layer 4. A material of ohmic contact nature is not joined to the second conduction type semiconductor crystal layer 4 in the vicinity of the penetrating dislocation defective 11, so that a current does not flow in the vicinity of the penetrating dislocation defective 11. As a result, an increase in leakage current in the vicinity of the penetrating dislocation defective accompanied by an increase in lighting time duration can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light emitting diode element used for illumination, display, and the like.

  In recent years, light-emitting diode (LED) elements that emit visible light (blue to blue-green) or ultraviolet electromagnetic waves have been developed using gallium nitride (GaN) -based compound semiconductors, and AlInGaP-based compound semiconductors have been conventionally used. In combination with green and red by LED elements such as the above, we realized the realization of three primary color (RGB) emission by LED elements. In addition, by combining a GaN-based compound semiconductor LED element with a phosphor that absorbs at least a part of its emission wavelength and converts it into light of a different wavelength, it has a different hue from the original emission color of the LED element, including white. A light emitting device capable of emitting light has also been developed.

  These LED elements have advantages such as small size, light weight, and power saving, and are used for applications such as signal lights, various display light sources, and large displays. The white LED is widely used as an alternative light source for a small light bulb or a light source for a liquid crystal panel such as a mobile phone.

  Currently, LED elements with a rated current of 20 to 30 mA are the mainstream. However, recently, in order to improve the light output per LED element with the aim of expanding into general lighting applications, Attempts have been made to inject power that is orders of magnitude higher into the device.

  By the way, although it is remarkable especially in a GaN-based compound semiconductor LED element, in general, a dislocation defect exists in the compound semiconductor crystal. This dislocation defect is newly generated in the semiconductor crystal due to the lattice mismatch between the substrate crystal and the compound semiconductor crystal. It is a thing. This dislocation defect does not spontaneously disappear during the process of growing the semiconductor crystal layer, but reaches the outermost surface of the semiconductor crystal layer after the growth and becomes a threading dislocation defect. The inside of the dislocation defect is presumed to have a larger diffusion coefficient of atoms than the non-defect site in the crystal. Usually, a metal layer is formed on the surface of the semiconductor crystal layer to form an electrode part, but such a metal diffuses from the surface of the semiconductor layer into the threading dislocation defect, and the leakage current increases. It is considered to be a major cause of element degradation.

In the current LED element of the rated current 20-30 mA class, the element itself is estimated to have a long life of over 40,000 hours. However, when aiming at general lighting applications and injecting an extremely high power into the element compared to the conventional case, the temperature of the LED element greatly increases unless measures are taken to promote heat dissipation of the LED element. In general, since the diffusion rate of atoms increases with temperature, there is a concern that the diffusion rate of the metal atoms constituting the electrode portion into the threading dislocation defects increases and the leakage current increases early. Therefore, when high power is injected into the LED element as compared with the conventional case and used under a high temperature condition, a reduction in life due to an early increase in leakage current becomes a problem. Thus, it is known to suppress leakage current by providing an oxide insulating layer (see Patent Document 1).
Japanese Patent Laid-Open No. 9-293936

However, even in the technique disclosed in the above publication, prevention of leakage current is still insufficient, and further improvement has been desired.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a light-emitting diode element that can withstand use under a higher temperature condition than in the past and does not cause a decrease in lifetime as compared with the prior art. .

  The invention of claim 1 includes a substrate crystal, a first conductivity type semiconductor crystal layer formed on the substrate crystal, an active layer formed on the first conductivity type semiconductor crystal layer, and the active layer. In a light emitting diode device having a second conductivity type semiconductor crystal layer formed thereon, a threading dislocation defect is exposed on a surface opposite to the active layer of the second conductivity type crystal layer, and the threading dislocation The inner surface of the defect and its periphery were covered with a material having a non-ohmic contact property to the second conductivity type semiconductor crystal layer.

  According to a second aspect of the present invention, in the light emitting diode element according to the first aspect, an insulating material is used as the non-ohmic material.

  According to a third aspect of the present invention, in the light-emitting diode element according to the second aspect, the inner surface of the threading dislocation defect is an etch pit having a size reaching the first conductive type semiconductor layer, and the light is incident on the surface of the etch pit. A light reflection structure is formed by forming a layer of an insulating material having transparency and further forming a metal layer on the insulating material.

  According to a fourth aspect of the present invention, in the light emitting diode element according to the third aspect, a high density region and a low density region of threading dislocation defects are selectively formed, and the light reflecting structure is formed in the high density region. It is characterized by that.

  According to the first aspect of the present invention, since the ohmic contact material is not in contact with the second conductivity type semiconductor crystal layer in the vicinity of the threading dislocation defect, no current flows in the vicinity of the threading dislocation defect. Therefore, an increase in leakage current in the vicinity of threading dislocation defects accompanying an increase in lighting time can be suppressed, and the lifetime of the light emitting element can be improved. In addition, a light-emitting element that can withstand use at a higher temperature than conventional ones can be provided.

  According to the invention of claim 2, since the coating material itself is insulative, even if the insulative material diffuses into threading dislocation defects, the leakage current does not increase. Accordingly, the lifetime of the light emitting element can be improved. Moreover, the LED element which can be used at a higher temperature than before can be provided.

  According to the invention of claim 3, since the light reflecting structure is formed on the etch pit, the light propagating in the direction parallel to the active layer out of the light emitted from the active layer is efficiently light. There is an effect that the light extraction rate of the LED element is improved by being reflected toward the extraction surface.

  According to the fourth aspect of the present invention, the region having a low threading dislocation defect density has a higher light output than the region having a high threading dislocation defect density. Therefore, if a light reflecting structure is formed in a region where the threading dislocation defect density is high, light generated in the region where the threading dislocation defect density is low is efficiently reflected to the light extraction surface side by the light reflecting structure in the vicinity thereof. Therefore, the light efficiency is greatly improved.

<Embodiment 1>
FIG. 1 shows a schematic cross section of a light-emitting diode element (hereinafter referred to as an LED element) according to Embodiment 1. The LED element includes a substrate crystal 1 (such as sapphire), a first conductivity type semiconductor crystal layer 2 (such as Si-doped N-type GaN) formed on the substrate crystal 1, and a first conductivity type semiconductor crystal layer 2. The formed active layer 3, the second conductive type semiconductor crystal layer 4 (P-type GaN doped with Mg, etc.) formed on the active layer 3, the conductive layer 6 (Ti in this embodiment), A non-ohmic contact material for the first electrode portion 7 (only Au layer in this embodiment) made of one or more metal layers formed on the conductive layer 6 and the second conductivity type semiconductor crystal layer 4 Covering portion 13 (here, Al), conductive layer 5 (Ni in this embodiment), and second electrode portion 8 (this embodiment) made of one or more metal layers formed on this conductive layer 5 In the example, the Au layer only).

The active layer 3 has, for example, a multi-quantum well structure in which eight layers of GaN / InGaN are stacked. The conductive layer 6 is formed on the surface of the first conductive semiconductor crystal layer 2 exposed by removing a part of the second conductive semiconductor crystal layer 4 and the underlying active layer 3. Is formed of a material having ohmic contact property. The covering portion 13 is a characteristic feature of the present invention, and covers the inner surface 12 of the threading dislocation defect 11 of the second conductivity type semiconductor crystal layer 4 and the periphery thereof and covers the second conductivity type semiconductor crystal layer 4. It is made of a non-ohmic contact material. The conductive layer 5 is formed on Al and on the second conductive type semiconductor crystal layer 4 not covered with Al, and is made of a material having ohmic contact with the second conductive type semiconductor crystal layer 4.
LED element comprising the above

The LED element can be manufactured as follows.
(1) The GaN-based compound semiconductor layer structure can be manufactured using a MOVPE method by a known means (see, for example, “Group III nitride semiconductor” (Baifukan) written by Isao Akasaki). GaN or AlN is formed on the substrate crystal 1 at a low temperature to form a buffer layer, on which an N-type GaN layer, an active layer, and a P-type GaN layer are stacked in this order.
(2) The second conductive semiconductor crystal layer 4 and a part of the underlying active layer 3 are removed by RIE to expose the surface of the first conductive semiconductor crystal layer 2.
(3) On the exposed surface of the first conductive type semiconductor crystal layer 2, a conductive layer 6 made of a material (Ti in this embodiment) having ohmic contact with the first conductive type semiconductor crystal layer 2 is formed.
(4) An Au layer constituting the first electrode portion 7 is formed on the conductive layer 6 by EB vapor deposition.
(5) An Al layer is formed on the surface of the P-type GaN layer by electron beam (EB) evaporation.
(6) Etch back the surface of the Al layer from an oblique direction by RIE. Since it is difficult for RIE ions to reach the inner surface of the threading dislocation defect 11 and its periphery, the inner surface 12 of the threading dislocation defect 11 and the surrounding Al layer are removed even if the Al layer at all other portions is removed. Remains.
(7) On the surface of the second conductivity type semiconductor crystal layer 4 exposed by removing Al, a new layer of Ni, which is a metal material in ohmic contact with the P-type GaN layer, is formed by EB vapor deposition.
(8) An Au layer constituting the second electrode portion 8 is formed on the Ni layer by EB vapor deposition.
The structure of Embodiment 1 can be manufactured by the above method.

  Next, the effect of Embodiment 1 is demonstrated. Since the ohmic contact material is not in contact with the second conductivity type semiconductor crystal layer 4 in the vicinity of the threading dislocation defect 11, current hardly flows in the vicinity of the threading dislocation defect 11. Therefore, an increase in leakage current in the vicinity of the threading dislocation defect 11 accompanying an increase in the lighting time can be suppressed. As a result, when used under the same LED element temperature conditions as in the past, the lifetime of the element can be improved, and an LED element that can withstand use at a higher temperature than in the past can be provided.

  In this embodiment, Al is used as the non-ohmic contact material. However, the material is not particularly limited to Al, and the same effect can be obtained if the material is non-ohmic contact with the P-type GaN layer.

<Embodiment 2>
The second embodiment has substantially the same structure as that of the first embodiment shown in FIG. 1. The difference from the first embodiment is that in this embodiment, the inner surface 12 of the threading dislocation defect 11 shown in FIG. The non-ohmic contact material for the second conductivity type semiconductor crystal layer 4 is covered with SiO ₂ instead of the insulating material Al.

The manufacturing method of the LED element of the _second embodiment is the same as that of the first embodiment except for the formation of the SiO ₂ layer. That is,
(1) The GaN-based compound semiconductor layer structure is produced using the MOVPE method. GaN or AlN is formed on the substrate crystal at a low temperature to form a buffer layer, on which an N-type GaN layer, an active layer, and a P-type GaN layer are stacked in this order.
(2) An SiO ₂ layer is formed on the surface of the P-type GaN layer by a CVD method.
(3) Etch back the surface of the SiO ₂ layer from an oblique direction by the RIE method. On the inner surface and around the threading dislocation defects, since hardly reach ions RIE, be removed SiO ₂ layer of the other sites are all the inner surface and the SiO ₂ layer surrounding the threading dislocation defects Remain.
(4) On the surface of the second conductivity type semiconductor layer exposed by removing the SiO ₂ layer, a new metal material, Ni, which is in ohmic contact with the P-type GaN layer, is formed by EB vapor deposition.
(5) An Au layer constituting the second electrode portion is formed on the Ni layer by EB vapor deposition.
The structure of Embodiment 2 can be manufactured by the above method.

The operation and effect of the second embodiment will be described. Like the first embodiment, the second conductive type crystal layer near the threading dislocation defect is not in contact with the ohmic contact material, and the SiO ₂ itself is insulated. Therefore, even if SiO ₂ itself diffuses into the threading dislocation defect, the leakage current does not increase. Therefore, the lifetime of the light-emitting element can be further improved as compared with Example 1, and a light-emitting element that can withstand use at a higher temperature than conventional can be provided.
In the present embodiment, SiO ₂ is used as the insulating material. However, the present invention is not particularly limited to this, and the same effect can be obtained even if the insulating material is, for example, Si ₃ N ₄ or the like.

<Embodiment 3>
FIG. 2 shows a partially enlarged cross section of the LED device according to the third embodiment. In the third embodiment, the inner surface of the threading dislocation defect 11 and the surrounding structure in the first embodiment of FIG. 1 are different. In the third embodiment, the inner surface of the threading dislocation defect 11 is an etch pit 14 having a size that reaches the first conductivity type semiconductor crystal layer 2 (N-type GaN layer). SiO ₂ layer 15 of insulating material having transparency is formed, to form a (Al in this embodiment) excellent metal layer 16 to the light reflecting on the SiO ₂ layer 15, covered with the SiO ₂ layer 15 A conductive layer 5 made of a material (Ni in this embodiment) that can be in ohmic contact with the second conductivity type semiconductor layer is formed on a part of the second conductivity type semiconductor crystal layer 4 that has not been formed. A second electrode portion 8 is formed above. Other configurations are the same as those of the first embodiment.

The manufacturing method of Embodiment 3 is as follows.
(1) Similar to the first and second embodiments until P-type GaN is formed on sapphire and the first electrode portion is formed.
(2) Etching the surface of the P-type GaN using the RIE method expands threading dislocation defects on the surface of the P-type GaN layer, and etch pits 14 having a depth until reaching the N-type GaN layer. To form.
(3) The SiO ₂ layer 15 is formed on the surface of the P-type GaN layer.
(4) On the SiO ₂ layer 15, an Al layer 16 which is a metal material having excellent light reflectivity is deposited by EB deposition.
(5) The surface of the Al layer / SiO ₂ layer is etched back from an oblique direction by the RIE method. Since it is difficult for RIE ions to reach the inner surface of the threading dislocation defect and its surroundings, the inner surface of the threading dislocation defect and the surrounding Al are removed even if the Al layer / SiO ₂ layer in all other parts is removed. Layer / SiO ₂ layer remains.
(6) On the exposed surface of the second conductive type semiconductor crystal layer 4, a new layer of Ni (conductive layer 15), which is in ohmic contact with the P-type GaN layer, is formed by EB vapor deposition.
(7) An Au layer constituting the second electrode portion 8 is formed on the Ni layer by EB vapor deposition.

The effect of this Embodiment 3 is demonstrated. On the etch pit 14 expanded to the surface of the active layer 3 on the first conductivity type semiconductor crystal layer 2 side, a SiO ₂ layer 15 that is also a translucent material is used as an insulating material, and further a light reflective property is provided thereon. A light reflecting structure is provided by providing an Al layer 16 that is superior to the above. As a result, among the light emitted from the active layer, the light propagating in a direction parallel to the active layer is efficiently reflected by the light reflecting structure formed on the surface inclined with respect to the active layer. The light extraction rate of the LED element is improved.

<Embodiment 4>
In FIG. 3, the partial expanded cross section of the LED element which concerns on Embodiment 4 is shown. In this LED element, a mask layer (SiO ₂ layer in this embodiment) is formed in a stripe shape on a substrate crystal (sapphire) 1, and a first conductivity type semiconductor crystal layer 2 (Si) is formed on the substrate crystal 1 and the mask layer. N-type GaN doped with GaN), and an active layer 3 (multi-quantum well structure in which eight layers of GaN / InGaN are stacked) is formed on the first conductivity type semiconductor crystal layer 2 and formed on the active layer 3 The second conductive type semiconductor crystal layer 4 (P-type GaN doped with Mg) is formed, and the second conductive type semiconductor crystal layer 4 and a part of the underlying active layer 3 are removed and exposed. A conductive layer 5 made of a material having ohmic contact with the first conductive semiconductor crystal layer 2 (Ti in this embodiment) is formed on the surface of the one conductive semiconductor crystal layer 2, and this conductive layer 5 Single layer or multiple layers of metal forming the first electrode portion 8 on top (In this example Au layer only) is obtained by forming a.

  Although the structure as described above is known, the threading dislocation density above the mask layer 17 can be made smaller than the threading dislocation density in other regions, and therefore, threading dislocation defects are present in the GaN-based compound semiconductor crystal layer. Reference numeral 11 denotes a selectively formed region having a high density and a region having a low density. The above structure is an example of selectively forming a region having a high threading dislocation defect density and a region having a low threading dislocation defect density, and is not particularly limited to the above structure.

  In the fourth embodiment, on the basis of the above structure, the same light reflecting structure as that shown in the third embodiment is formed for each threading dislocation defect in a region where the threading dislocation defect density is high, A conductive layer 5 made of a material having ohmic contact property (Ni in this embodiment) is formed on the N-type GaN layer on the N-type GaN layer where the reflective structure is not formed, and the second electrode portion is formed on the conductive layer 5. A single layer or a plurality of metal layers (only an Au layer in this embodiment) constituting 8 is formed.

The manufacturing method of Embodiment 4 is as follows.
(1) After the SiO ₂ mask layer is formed on the substrate crystal by the MOVPE method, P-type GaN is formed by the method described in the first embodiment and the first electrode portion is further formed.
(2) The surface of the P-type GaN layer above the SiO ₂ mask is covered with an inverted mask pattern for the SiO ₂ mask formed on the substrate crystal.
(3) Similar to the third embodiment, the surface of the P-type GaN layer not covered with the mask is etched using the RIE method to enlarge threading dislocation defects on the surface of the P-type GaN layer, and N Etch pits having a depth to reach the type GaN layer are formed.
(4) An SiO ₂ film is formed on the surface of the P-type GaN layer.
(5) Al, which is a metal material having excellent light reflectivity, is deposited on the SiO ₂ layer by EB deposition.
(6) Etch back the surface of the Al layer / SiO ₂ layer from an oblique direction by the RIE method. Since it is difficult for RIE ions to reach the inner surface of the threading dislocation defect and its surroundings, the inner surface of the threading dislocation defect and the surrounding Al are removed even if the Al layer / SiO ₂ layer in all other parts is removed. Layer / SiO ₂ layer remains.
(7) On the exposed surface of the second conductivity type semiconductor layer, a new layer of Ni, which is a metal material in ohmic contact with the P-type GaN layer, is formed by EB vapor deposition.
(8) An Au layer that constitutes the second electrode portion is formed on the Ni layer by EB vapor deposition.

  By the above method, an LED element in which the same light reflecting structure as that described in Embodiment 3 is selectively formed for threading dislocation defects in a region having a high threading dislocation defect density can be produced.

  The effect of this Embodiment 4 is demonstrated. The region having a low threading dislocation defect density has a higher light output than the region having a high threading dislocation defect density. Therefore, if a light reflecting structure is formed in a region having a high threading dislocation density, light generated in a region having a low threading dislocation density is efficiently reflected to the light extraction surface side by the light reflecting structure in the vicinity thereof. There is an effect that the light efficiency is greatly improved. The present invention is not limited to the configuration of the above embodiment, and various modifications can be made without departing from the spirit of the invention.

(A) is sectional drawing of the light emitting element which concerns on Embodiment 1, 2 of this invention, (b) is the elements on larger scale. FIG. 6 is an enlarged cross-sectional view of the vicinity of the surface of an LED element according to Example 3. FIG. 6 is an enlarged cross-sectional view of a part of an LED element according to Example 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate crystal 2 1st conductivity type semiconductor crystal layer 3 Active layer 4 2nd conductivity type semiconductor crystal layer 5 Conductive layer 6 Conductive layer 7 1st electrode part 8 2nd electrode part 13 Covering part of non-ohmic contact material 14 Etch pit 15 SiO ₂ layer

Claims (4)

A substrate crystal, a first conductivity type semiconductor crystal layer formed on the substrate crystal, an active layer formed on the first conductivity type semiconductor crystal layer, and a first crystal formed on the active layer In a light-emitting diode element having a two-conductivity-type semiconductor crystal layer,
Threading dislocation defects are exposed on the surface of the second conductivity type crystal layer opposite to the active layer;
A light-emitting diode element, wherein the inner surface of the threading dislocation defect and the periphery thereof are covered with a material having a non-ohmic contact property to the second conductivity type semiconductor crystal layer.   The light-emitting diode element according to claim 1, wherein an insulating material is used as the non-ohmic material. The inner surface of the threading dislocation defect is an etch pit having a size reaching the first conductivity type semiconductor layer,
A light-reflective structure is formed by forming a light-transmitting insulating material layer on the surface of the etch pit, and further forming a metal layer on the insulating material. The light emitting diode device according to claim 2.   4. The light emitting diode device according to claim 3, wherein a high density area and a low density area of the threading dislocation defects are selectively formed, and the light reflecting structure is formed in the high density area.

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