JP2009152474A - Compound semiconductor light emitting device, lighting device using the same, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable an electrode to be easily formed and improve light derivation efficiency in a compound semiconductor light emitting device yielded by arranging in dispersion a plurality of nanocolumns on a substrate. <P>SOLUTION: A GaN nanocolumn 4 is a laminate of an n-type GaN layer 13, a light-emitting layer 14, and a p-type GaN layer 16. In the GaN nanaocoulumn, an insulating film 3 is formed on side surfaces thereof by anode oxidation, and then a transparent electrode 6 is formed by vapor. Accordingly, for derivation of a p-type electrode, leakage and short circuit are reduced and a simple step only for vaporization enables formation thereof. This ensures very low cost and stable formation and achieves an electrode formation step desired for mass production step. Further, under proper control of the thickness of the transparent electrode 6, it serves as a microlens. Accordingly, total reflection loss at the transparent electrode 6 and atmosphere boundary is suppressed to improve light derivation efficiency. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a compound semiconductor light emitting element such as a III-V group compound semiconductor, a lighting device using the same, and a method for manufacturing the compound semiconductor light emitting element. In particular, the semiconductor element includes a column called a nanocolumn or a nanorod on a substrate. The present invention relates to a structure in which a columnar crystal structure having a nanometer size is formed.

In recent years, compound semiconductor light emitting devices having a light emitting layer made of a nitride semiconductor or an oxide semiconductor have attracted attention. As an example of the structure of this light emitting element, an n-cladding layer and a contact layer composed of an n ⁺ -GaN layer in which a sapphire substrate is used as a growth substrate and silicon (Si) is doped below the light emitting layer, an upper portion of the light emitting layer An electron block layer made of p-Al _x Ga _1-x N doped with magnesium (Mg) and a p-GaN contact layer on the electron block layer are formed. In these light-emitting elements using so-called bulk crystals, the lattice constants of the sapphire substrate and the nitride or oxide semiconductor layer are greatly different and are formed as a thin film on the substrate. Since threading dislocations are included, it is difficult to increase the efficiency of the light emitting element.

Therefore, Patent Document 1 is known as a conventional example of a technique for solving such a problem. In this conventional example, an n-type GaN buffer layer serving as an n-type electrode is formed on a sapphire substrate, and then a large number of the columnar crystal structures (nanocolumns) arranged in an array are formed. A light-emitting element is configured by embedding a transparent insulating layer such as SOG (Spin-on-Glass), SiO _2, or epoxy resin and forming a transparent electrode and an electrode pad to be a p-type electrode. In particular, the blue GaN nanocolumn is composed of an n-type GaN nanocolumn, an InGaN quantum well serving as a light emitting layer, and a p-type GaN nanocolumn.

In this GaN nanocolumn LED, unlike the planar LED, the growth nuclei that were scattered during the growth of the GaN epilayer do not stick together and then grow in a plane, but grow in the vertical direction before the growth nuclei stick together. Dislocations do not exist in principle, and it is expected that the number of point defects generated around threading dislocations is far less than that of the planar type, so that a GaN single crystal with extremely good crystal quality can be obtained compared to the planar type LED. Therefore, the internal quantum efficiency can be expected to improve dramatically.
JP 2005-228936 A

  However, in the nanocolumn LED as described above, the problem of threading dislocation has been solved. However, as a difficulty with the planar type LED, a transparent insulating layer is uniformly embedded in a narrow gap between GaN nanocolumns by spin coating or the like. It is difficult to form a p-type electrode (transparent electrode). In particular, since the p-type GaN layer is very thin, it is difficult to prevent leakage and short circuit between the p-type layer, the light emitting layer, and the n-type layer.

  In addition, since the light emitted from the tip of the nanocolumn is guided and emitted within the nanocolumn, the light emitted from the interface of the nanocolumn tip is concentrated near the vertical axis of the substrate as compared with the angular distribution in the planar LED. However, there is a high possibility of total reflection at the interface between the relatively flat transparent electrode formed on the transparent insulating layer and the atmosphere, and the light extraction efficiency is low.

  An object of the present invention is to provide a compound semiconductor light emitting element capable of preventing leakage and short circuit in a columnar crystal structure and improving light extraction efficiency, an illumination device using the compound semiconductor light emitting element, and a method for manufacturing the semiconductor light emitting element It is to be.

  The compound semiconductor light-emitting device of the present invention is a compound semiconductor light-emitting device in which a plurality of columnar crystal structures formed by sequentially laminating at least an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer are dispersed on a substrate. An insulating film covering at least the side surfaces of the n-type semiconductor layer and the light-emitting layer of the columnar crystal structure, and a transparent conductive film electrically connected to the p-type semiconductor layer, the surface of each columnar crystal The structure formed integrally on the p-type semiconductor layer by vapor deposition so that a convex curved surface whose central axis is a normal line is formed on the structure and a concave curved surface is formed between the columnar crystal structures. It is characterized by comprising such a transparent conductive film.

  The method for producing a compound semiconductor light-emitting device of the present invention comprises a plurality of columnar crystal structures formed by sequentially laminating at least an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer on a substrate. In the method for manufacturing a compound semiconductor light emitting device, a step of anodizing the substrate on which the columnar crystal structure is grown, and at least a tip portion of the columnar crystal structure having an insulating film formed on the surface by the anodization is exposed. Dry etching and integrated on the p-type semiconductor layer, the surface forms a convex curved surface whose central axis is normal on each columnar crystal structure, and between the columnar crystal structures And a step of depositing a transparent conductive film so as to form a concave curved surface.

  According to the above configuration, in a compound semiconductor light-emitting device in which a plurality of nanoscale columnar crystal structures called nanocolumns or nanorods are formed on a substrate, and a method for manufacturing the compound semiconductor light emitting device, at least the columnar crystal structures of the columnar crystal structures are provided. An insulating film is formed by anodic oxidation so as to cover the side surfaces of the n-type semiconductor layer and the light-emitting layer, thereby ensuring insulation between the p-type semiconductor layer and the n-type semiconductor layer and protecting the light-emitting layer. A transparent conductive film that is electrically connected to an external power source is integrally formed on the p-type semiconductor layer by vapor deposition. In this way, leakage and short-circuits can be reduced with respect to p-type electrode extraction, and since it can be created by a simple process of simply vapor deposition, it can be produced at a very low cost and stably. A desirable electrode forming step can be realized. In addition, by forming the insulating film by the anodic oxidation, it is possible to surely perform the insulation as compared with the method of embedding an insulator such as spin coating, and to improve the reliability of the vapor deposition. .

  Then, the thickness of the transparent conductive film is set to a thickness corresponding to the material of the transparent conductive film such as ITO, NiAu, ZnO or the column diameter or pitch of the columnar crystal structure, for example, the column diameter of the columnar crystal structure. The surface of each columnar crystal structure is formed with a convex curved surface whose central axis is a normal line, and a concave curved surface is formed between the columnar crystal structures. Therefore, by using a transparent conductive film, light absorption loss with respect to electrode extraction can be minimized, and light extraction efficiency can be improved. The transparent conductive film is mounted on the tip of the columnar crystal structure by forming a concavo-convex structure on the surface of each columnar crystal structure in a dome shape and continuously between the columnar crystal structures. It functions like a microlens, suppresses total reflection loss between the transparent conductive film and the air interface, and further improves light extraction efficiency.

  In the compound semiconductor light emitting device of the present invention, the formation position and the column diameter of the columnar crystal structure are predetermined by a mask.

  According to the above configuration, the larger the pitch of the columnar crystal structure and the narrower the column diameter, the smaller the R of the convex curved surface and the light extraction efficiency is improved. The light extraction efficiency can be further improved by controlling with a mask.

  Furthermore, in the compound semiconductor light-emitting device of the present invention, the transparent conductive film has a forward voltage with the p-type semiconductor layer lower than 3.5 V when the current value is 20 mA, and has a peak wavelength of light emitted from the light-emitting layer. The transmittance is 50% or more.

  According to said structure, the external quantum efficiency of this compound semiconductor light-emitting device can be improved electrically and optically.

  In the compound semiconductor light emitting device of the present invention, the transparent conductive film is made of ZnO or ITO.

  According to the above configuration, ZnO can be electrically connected to the p-type GaN layer, and the transmittance is high when the wavelength of light generated from the columnar crystal structure is blue. Furthermore, since the refractive index is as high as 2.0, the angle of extraction from the GaN nanocolumn (refractive index 2.5) is wide, and the material is extremely suitable for improving the external quantum efficiency.

  On the other hand, ITO also has high transmittance with respect to blue light emission and excellent electrical conductivity. However, since it is difficult to obtain good electrical connection by direct contact with pGaN, it is necessary to first deposit a Pt thin film or the like to improve the electrical connection. Since the Pt thin film can provide a good electrical connection with a thickness of several nanometers at most, the light absorption loss due to the Pt thin film does not significantly impair the light extraction efficiency, and the overall external quantum efficiency can be improved. Can do.

  Furthermore, the lighting device of the present invention is characterized by using the compound semiconductor light emitting element.

  According to said structure, the illuminating device which can improve light extraction efficiency is realizable.

  As described above, the compound semiconductor light-emitting device and the manufacturing method thereof according to the present invention are compound semiconductors in which a plurality of nanoscale columnar crystal structures called nanocolumns or nanorods are formed on a substrate as described above. In the light-emitting element and the method for manufacturing the same, first, an insulating film is formed by anodic oxidation or the like so as to cover at least the n-type semiconductor layer of the columnar crystal structure and the side surface of the light-emitting layer. A transparent conductive film that is electrically connected to an external power source is integrally formed by vapor deposition on the p-type semiconductor layer while ensuring insulation from the layers and protecting the light emitting layer. Therefore, leakage and short-circuiting can be reduced compared to p-type electrode extraction, and it can be created by a simple process of simply vapor deposition, so that it can be produced at extremely low cost and stably. An electrode forming step desirable for the step can be realized.

  Next, the transparent conductive film is formed to have a thickness corresponding to the material and the column diameter and pitch of the columnar crystal structure, for example, about the column diameter of the columnar crystal structure, A convex curved surface whose central axis is a normal line is formed on each columnar crystal structure, and a concave curved surface is formed between the columnar crystal structures. Therefore, the transparent conductive film functions like a microlens mounted at the tip of the columnar crystal structure, and therefore, the total reflection loss between the transparent conductive film and the air interface is suppressed, and the light extraction efficiency is improved. Can do.

  Furthermore, the lighting device of the present invention uses the compound semiconductor light emitting element as described above.

  Therefore, an illumination device that can improve the light extraction efficiency can be realized.

Hereinafter, an embodiment of the present invention will be described. In this embodiment, an example of a GaN nanocolumn is described as a columnar crystal structure, but the nanocolumn crystal is not limited to GaN, and is an oxide. Needless to say, this also applies to oxynitrides and other materials. Further, although Si is used as the growth substrate, it is not limited to this, and sapphire, SiC, SiO ₂ , ZnO, AlN, or the like can be used. Furthermore, although metal-organic vapor phase epitaxy (MOCVD) is used for the growth of nanocolumn crystals, molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), or the like can also be used.

  FIG. 1 is a cross-sectional view schematically showing the structure of a light-emitting diode 1 which is a compound semiconductor light-emitting element according to an embodiment of the present invention. In the light emitting diode 1, a large number of GaN nanocolumns 4 having an insulating film 3 on the outer peripheral surface thereof are planted on a Si substrate 2, an n-type electrode 5 is formed on the back surface of the Si substrate 2, and the GaN nanocolumns are formed. A transparent electrode 6 and a p-type electrode pad 7 are formed on 4.

  FIG. 2 is a diagram for explaining a method of producing the GaN nanocolumn 4. As shown in FIG. 2A, a silicon oxide film 11 having a thickness of, for example, 50 nm is formed on the Si silicon substrate 2 by a thermal oxidation method. As shown in FIG. 2B, a normal photolithography technique and etching are performed. For example, an opening 12 having a diameter of 100 nm is formed at a location where a GaN nanocolumn 4 will be formed in the future. Subsequently, using the silicon oxide film 11 in which the opening 12 is formed as a mask, a GaN nanocolumn 4 is grown on the opening 12 where the Si substrate 2 is exposed, as shown in FIG.

Since the surface of the Si substrate 2 is a single crystal plane with a plane orientation of (100) or (111), nucleation of the GaN nanocolumns 4 can be easily realized using an MOCVD apparatus. For example, the pressure in the reactor of the MOCVD apparatus is maintained at 76 Torr, the substrate temperature is raised to 1150 ° C., and after the temperature is stabilized, trimethylgallium (TMGa) is used as a Ga source, ammonia (NH ₃ ) is used as an N source, By supplying hydrogen (H ₂ ) as a carrier gas and further supplying tetraethylsilane (TESi), which is a raw material for Si as a dopant, an n-type GaN layer 13 having n-type conductivity is formed to 800 nm. In addition to Si, Ge or the like can be used as a dopant for obtaining the n-type conductivity.

  Next, the light emitting layer 14 is formed. Light having a wavelength of 465 nm emitted from the light emitting layer 14 is absorbed and lost when entering the Si substrate 2. A DBR (Distributed Bragg Reflector) reflecting layer 15 made of an AlGaN / GaN laminated film is formed. This reflective layer 15 is configured by alternately stacking 51 layers of 46.64 nm AlGaN layers and 50.54 nm GaN layers, and is a conductive reflective film having a reflectivity of 99.5% and a stop band width of 14 nm. . When the AlGaN layer is stacked, trimethylaluminum (TMAl) is added to the source gas. After the reflective layer 15 is formed on the Si substrate 2 side (that is, the base side of the GaN nanocolumn 4), the n-type GaN layer 13 is grown for a while (on the free end side), and then the light emitting layer 14 is formed.

  The light emitting layer 14 is laminated by lowering the substrate temperature to 750 ° C. with the reactor pressure kept at 76 Torr. The light emitting layer 14 has a quantum well structure including a well layer (InGaN) and a barrier layer (GaN), and preferably has a multiple quantum well structure (MQW) having a plurality of wells. The In composition in the well layer and the barrier layer is 17% and 0%, and the thicknesses are 2 nm and 5 nm, respectively, and trimethylindium (TMIn) is added to the source gas when the InGaN layer is stacked. As a result, light having a wavelength of 465 nm can be obtained.

Subsequently, the substrate temperature is raised to 1150 ° C. with the reactor pressure kept at 76 Torr, and the p-type GaN layer 16 is deposited. Mg is used as a dopant for obtaining p-type conduction, and bisethylcyclopentadienylmagnesium (Cp ₂ Mg) is used as the Mg raw material instead of the tetraethylsilane (TESi), and the thickness is 200 nm. Only grow. Thus, the GaN nanocolumn 4 has a height of about 1 μm.

  In the Si substrate 2 on which the GaN nanocolumns 4 are thus formed, it should be noted that in the present embodiment, the entire Si substrate 2 on which the GaN nanocolumns 4 are grown is an anode as shown in FIG. The oxidation film formed on the side wall of the GaN nanocolumn 4 is used as the insulating film 3 for protection. The anodizing apparatus 21 is as shown in FIG. 4, and a beaker 22 is filled with an acetic acid solution 23 as an electrolyte, and a sample made of the Si substrate 2 on which the GaN nanocolumns 4 are grown is placed therein. A positive electrode 24 is connected from the outside, and a platinum electrode 26 is immersed in the acetic acid solution 23 with a negative electrode 25 connected from the outside. When a voltage is applied between the external electrodes 24 and 25 and the sample is irradiated with the UV lamp 27, the surface of the GaN nanocolumn 4 is anodized by a photoelectrochemical reaction, and an oxide film grows. The insulating film 3 is as shown in a).

  It should also be noted that the oxide film 3a at the tip of the p-type GaN layer 16 is removed by performing dry etching thereafter. Therefore, the insulating film 3 covers at least the side surfaces of the n-type GaN layer 13 and the light emitting layer 14.

  After securing the insulation between the p-type GaN layer 16 and the n-type GaN layer 13 in this way, it should be noted that the transparent electrode 6 made of a transparent conductive film is deposited by a sputtering apparatus. At this time, since each GaN nanocolumn 4 is isolated at an interval of about 100 nm by patterning of the opening 12 as described above, the transparent layer deposited by laminating to a column diameter of about 100 nm. The electrode 6 does not form a plane, and as shown in FIG. 3B, the surface forms a convex curved surface whose central axis 4 a is a normal line on each GaN nanocolumn 4, and between the GaN nanocolumns 4. A concave curved surface is formed. Finally, as shown in FIG. 1, the p-type pad electrode 7 and the n-type electrode 5 are formed to complete the light-emitting diode 1 of the present invention.

  The transparent electrode 6 is a material whose forward voltage Vf with the p-type GaN layer 16 is lower than 3.5 V when the current value is 20 mA and whose transmittance is 50% or more with respect to the peak wavelength of light emitted from the light emitting layer 14. Chosen. Thereby, the external quantum efficiency of the light emitting diode 1 can be improved electrically and optically.

  Specifically, the transparent electrode 6 is made of ZnO or ITO. ZnO can be electrically connected to the p-type GaN layer 16 and has a high transmittance when the wavelength of light generated from the GaN nanocolumn 4 is blue. Furthermore, since the refractive index is as high as 2.0, the angle of extraction from the GaN nanocolumn 4 (refractive index 2.5) is wide, and the material is extremely suitable for improving the external quantum efficiency. On the other hand, ITO also has high transmittance with respect to blue light emission and excellent electrical conductivity. However, since direct electrical contact with the p-type GaN layer 16 makes it difficult to obtain good electrical connection, it is necessary to first deposit a Pt thin film or the like to improve electrical connection. Since the Pt thin film can provide a good electrical connection with a thickness of several nanometers at most, the light absorption loss due to the Pt thin film does not significantly impair the light extraction efficiency, and the overall external quantum efficiency can be improved. Can do.

  As described above, the light-emitting diode 1 of the present invention is a light-emitting diode in which a plurality of GaN nanocolumns 4 are dispersedly disposed on a Si substrate 2, and the side surfaces of at least the n-type GaN layer 13 and the light-emitting layer 14 of the GaN nanocolumn 4 are arranged. Since the insulating film 3 is formed by anodic oxidation so as to cover, the insulation between the p-type GaN layer 13 and the n-type GaN layer 16 is ensured, and the light-emitting layer 14 is protected, and then the p-type GaN layer 16 is formed on the p-type GaN layer 16. The transparent electrode 6 can be formed by vapor deposition. Therefore, it is possible to reduce leaks and shorts with respect to p-type electrode extraction, and it can be created by a simple process of simply vapor deposition, so that it can be produced at a very low cost and in a stable manner. A desirable electrode forming step can be realized. In addition, by forming the insulating film by the anodic oxidation, it is possible to surely perform the insulation as compared with a method of embedding an insulator such as spin coating, and to improve the reliability of the vapor deposition. .

  Further, by using the transparent electrode 6, it is possible to minimize light absorption loss with respect to electrode extraction and improve light extraction efficiency. Further, by forming the thickness to a thickness corresponding to the material of the transparent electrode 6 (ITO), the diameter of the GaN nanocolumn 4, etc., for example, about 100 nm as described above, the surface is On the GaN nanocolumn 4, a convex curved surface (dome shape) having a central axis 4a as a normal line is formed, and a concave curved surface is formed between the GaN nanocolumns 4 so that the entire transparent electrode 6 has a concavo-convex structure. The electrode 6 functions like a microlens mounted on the tip of the GaN nanocolumn 4, suppresses the total reflection loss between the transparent electrode 6 and the air interface, and further improves the light extraction efficiency.

  Here, if the transparent electrode 6 becomes too thin, the dome in each GaN nanocolumn 4 becomes low (R of the convex curved surface increases), the light extraction efficiency deteriorates, and the conductivity in the surface direction of the transparent electrode 6 decreases. When the thickness becomes too thick, the unevenness approaches the flatness and the light extraction efficiency deteriorates. As described above, each GaN nanocolumn 4 forms a convex curved surface whose central axis 4a is a normal line. In addition, by forming the concave curved surface between the GaN nanocolumns 4 so as to have a thickness approximately equal to the column diameter, for example, the light extraction efficiency can be improved while ensuring conductivity.

  Further, as the pitch of the GaN nanocolumns 4 is increased and the column diameter is reduced, R of the convex curved surface is reduced and the light extraction efficiency is improved. Therefore, the pitch and the column diameter are masked by the silicon oxide film 11. The light extraction efficiency can be further improved by controlling by.

  By using such a light emitting diode 1 for a lighting device, a lighting device capable of improving the light extraction efficiency can be realized.

  Here, in Non-Patent Document 1 (A. Kikuchi, M. Kawai, M. Tada and K. Kishino: Jpn. J. Appl. Phys. 43 (2004) L1524), a p-type electrode is expanded in a champagne glass shape. The transparent electrode is prevented from leaking or short-circuiting by increasing the diameter and growing so as to bond between adjacent nanocolumns. However, even in this prior art, the p-type electrode surface is substantially flat, The problem of light extraction efficiency remains as described in.

It is sectional drawing which shows typically the structure of the light emitting diode which is a compound semiconductor light emitting element concerning one Embodiment of this invention. It is a figure for demonstrating the preparation method of a GaN nanocolumn. It is sectional drawing which shows the preparation method of the said light emitting diode typically. It is a figure which shows the structure of an anodizing apparatus typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting diode 2 Si substrate 3 Insulating film 4 GaN nanocolumn 5 N-type electrode 6 Transparent electrode 7 P-type electrode pad 11 Silicon oxide film 12 Opening part 13 N-type GaN layer 14 Light emitting layer 15 Reflective layer 16 P-type GaN layer 21 Anodization Apparatus 22 Beaker 23 Acetic acid solution 25 Negative electrode 26 Platinum electrode 27 UV lamp

Claims (6)

In a compound semiconductor light-emitting device in which a plurality of columnar crystal structures formed by sequentially laminating at least an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer are disposed on a substrate,
An insulating film covering at least side surfaces of the n-type semiconductor layer and the light emitting layer of the columnar crystal structure;
A transparent conductive film electrically connected to the p-type semiconductor layer, the surface of which forms a convex curved surface whose central axis is a normal line on each columnar crystal structure, and each columnar crystal structure A compound semiconductor light emitting device comprising such a transparent conductive film integrally formed on the p-type semiconductor layer by vapor deposition so as to form a concave curved surface therebetween.   2. The compound semiconductor light emitting device according to claim 1, wherein the formation position and the column diameter of the columnar crystal structure are predetermined by a mask.   The transparent conductive film has a forward voltage with a p-type semiconductor layer lower than 3.5 V at a current value of 20 mA, and has a transmittance of 50% or more with respect to a peak wavelength of light emitted from the light emitting layer. The compound semiconductor light emitting device according to claim 1 or 2.   The compound semiconductor light-emitting element according to claim 1, wherein the transparent conductive film is made of ZnO or ITO.   An illumination device using the compound semiconductor light-emitting element according to claim 1. In a method for manufacturing a compound semiconductor light-emitting element in which a plurality of columnar crystal structures formed by sequentially laminating at least an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer are dispersedly disposed on a substrate,
Anodizing the substrate on which the columnar crystal structure is grown;
Dry etching so that at least a tip portion of the columnar crystal structure having an insulating film formed on the surface by the anodization is exposed;
The surface is integrated on the p-type semiconductor layer so that the surface forms a convex curved surface whose central axis is a normal line on each columnar crystal structure, and a concave curved surface is formed between the columnar crystal structures. And a step of vapor-depositing a transparent conductive film.

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