KR100971688B1 - Light Emitting Diode with Self-assembled ZnO Quantum dot - Google Patents

Abstract

The light emitting diode with self-assembled ZnO according to the present invention forms a Zn thin film on a semiconductor or insulator single crystal substrate, and then reacts the Zn thin film with oxygen and adjusts the temperature of the substrate to stress the Zn thin film. a self-forming ZnO quantum dot substrate prepared by controlling a stress to self-assemble ZnO quantum dots on the substrate and simultaneously forming surface roughness of the substrate; An n-type semiconductor layer stacked on the self-forming ZnO quantum dot substrate and having a metal pad to which an external voltage or current is applied; A p-type semiconductor layer on which a metal pad to which an external voltage or current is applied is formed; And an active layer provided between the n-type semiconductor layer and the p-type semiconductor layer to generate light by combining electrons provided from the n-type semiconductor layer with holes provided from the p-type semiconductor layer. The ZnO quantum dot of the self-forming ZnO quantum dot substrate acts as a reflector of light generated in the active layer, and the surface unevenness of the self-formed ZnO quantum dot substrate acts as a reflecting layer to increase self-extraction ZnO. It is characterized by being equipped with a light emitting diode.

Light Emitting Diode, Self-forming, ZnO, Quantum Dot

Description

Light Emitting Diode with Self-assembled ZnO Quantum dot

The present invention relates to a light emitting diode in which surface irregularities are formed on a substrate and self-formed ZnO quantum dots are provided on the substrate to increase external light extraction efficiency.

A light emitting diode (LED) is a light emitting device that emits light when a voltage is applied to a PN junction diode of a compound semiconductor. There is no filament short-circuit phenomenon in general light bulbs, and it has a long life. In addition, it is a high-speed response that responds simultaneously with application of current due to the characteristics of semiconductors, and has become the smallest among optical devices with the spread of integrated LEDs. It is easy to configure large screens such as outdoor billboards, and has excellent temperature and impact durability through epoxy packaging, and it is possible to realize a full color after commercialization of a blue LED.

Due to the characteristics of this LED, it was used as a simple display device in the past, but is now used as a BLU (Back Light Unit) for mobile phones, digital devices, liquid crystal displays (LCDs), It is used for lighting such as dashboard, taillight, traffic signal, landscape lighting and general lighting. In addition, it is widely used in display fields such as indoor and outdoor display boards, and environmental fields and bio fields for measuring water pollution and blood oxygen concentration. In addition, the scope of application of light emitting diodes (LEDs) is increasing every year due to improved product performance and lower costs.

As the application range of light emitting diodes (LEDs) is expanded, power consumption of light emitting diodes (LEDs) is minimized, and high power and high efficiency are required.

Various methods are being studied to meet these demands. The method is largely improved internal quantum efficiency and external extraction efficiency, which improves the probability of recombination of electron-holes emitting light in the active layer of light emitting diodes (LEDs) and reduces the non-light recombination. Can be improved. However, such internal quantum efficiency improvement has already improved the efficiency of 70% in blue light emitting diodes, 80% in UV light emitting diodes, and 99% in AlGaAs, and the method of improving internal quantum efficiency is limited. On the other hand, active research on increasing the external extraction efficiency is being conducted. The key to increasing the external extraction efficiency is the total reflection (TIR) at all interfaces that exist until the light generated inside the light emitting diode (LED) exits the air. By reducing internal refraction, the extraction efficiency of generated light is increased. In the case of a light emitting diode (LED) made of a compound semiconductor, it has a large refractive index, and thus, external extraction efficiency is greatly reduced. For example, in the case of InGaN-based light emitting diodes (LEDs), the external extraction efficiency is only 4%.

Various studies are being conducted to increase the external extraction efficiency. For example, in order to reduce total reflection occurring at the interface between sapphire and nitride in a nitride-based light emitting diode, a method of forming a pattern or giving irregularities to the sapphire substrate is used. A method of separating the sapphire substrate to remove absorption or total reflection has also been attempted. There is also a method of increasing the extraction efficiency by controlling the roughness of the nitride surface to reduce the total reflection due to the difference in refractive index between the nitride and air.

It is an object of the present invention to have a high light extraction efficiency due to the presence of a nano reflector structure and a reflective layer due to substrate surface irregularities on a substrate which is a support of a light emitting diode, and a high efficiency epitaxial semiconductor layer capable of forming a high quality epitaxial semiconductor layer on a substrate having a reflector structure formed thereon. It is to provide a diode, and to provide a high-efficiency light emitting diode that can reduce the manufacturing cost of the reflector is unnecessary, no patterning process or regrowth process.

A light emitting diode having a self-assembled ZnO quantum dot according to the present invention forms a Zn thin film on a semiconductor or non-conductive single crystal substrate, and then reacts the Zn thin film with oxygen and controls the temperature of the Zn thin film. Self-assembled ZnO quantum dot substrate fabricated by controlling stress to self-assemble ZnO quantum dots on the substrate and at the same time to form surface roughness of the substrate ; An n-type semiconductor layer stacked on the self-forming ZnO quantum dot substrate and having a metal pad to which an external voltage or current is applied; A p-type semiconductor layer on which a metal pad to which an external voltage or current is applied is formed; And an active layer provided between the n-type semiconductor layer and the p-type semiconductor layer to generate light by combining electrons provided from the n-type semiconductor layer with holes provided from the p-type semiconductor layer. The ZnO quantum dot of the self-forming ZnO quantum dot substrate acts as a reflector of the light generated in the active layer, and the surface unevenness of the self-formed ZnO quantum dot substrate acts as a reflecting layer to increase self-extraction ZnO. It is characterized by being equipped with a light emitting diode.

In order to self-form ZnO quantum dots on the semiconductor or insulator single crystal substrate, the thickness of the Zn thin film is preferably 0.2 nm to 2 nm. When the thickness of the Zn thin film is less than 0.2 nm, ZnO quantum dots may not self-form due to insufficient stress occurring inside the Zn thin film, such as stress due to lattice constant difference between the substrate and the Zn thin film and stress due to a difference in thermal expansion coefficient. Even if the ZnO quantum dots are self-forming, the ZnO quantum dot size is small and the effect of increasing the surface roughness is insignificant. If the thickness of the Zn thin film is greater than 2 nm, there is a disadvantage in that internal defects of the resulting ZnO quantum dots increase.

As described above, a driving force in which ZnO quantum dots are self-formed on the semiconductor or insulator single crystal substrate is a stress present in the Zn thin film, and an important parameter for controlling the stress of the Zn thin film is Zn described above. The thickness of the thin film and the temperature of the substrate (a semiconductor or non-conducting single crystal substrate having a Zn thin film formed thereon).

In order to effectively form ZnO quantum dots effectively with respect to the thickness of the preferred Zn thin film, the temperature of the substrate is preferably controlled to 250 ° C to 500 ° C. At this time, since the temperature of the substrate has a great influence on the nucleation and growth rate of ZnO, the density, size, shape, or combination thereof of the ZnO quantum dots self-forming on the substrate is controlled by controlling the temperature of the substrate and the thickness of the Zn thin film. Will be controlled.

In detail, when the temperature of the substrate decreases, the density of the self-forming ZnO quantum dots increases and the size of the quantum dots itself decreases.When the temperature of the substrate increases, the density of the self-forming ZnO quantum dots decreases and the size of the quantum dots itself increases. do.

The oxygen reacting with the Zn thin film is preferably in the plasma phase.

The semiconductor or non-conductor single crystal substrate on which the Zn thin film is formed can be used as long as it is a stable material that does not react chemically with Zn. However, the group 4 single crystal substrate can be used in terms of practical application and stress generation due to lattice constant mismatch with the Zn thin film. ; Group 3-5 single crystal substrate; Group 2-6 single crystal substrate; Group 4-6 single crystal substrate; Sapphire single crystal substrate; Silicon oxide single crystal substrate; Or these laminated substrates are preferable, and most sapphire substrate and Si single crystal substrate are the most substantially.

The Group 4 single crystal substrate is selected from Si single crystal, Ge single crystal, or SiGe single crystal, and the Group 3-5 single crystal substrate (Group 3-5 compound single crystal substrate) is a GaAs single crystal, InP single crystal, InAsP single crystal, InGaAs single crystal, AsP single crystal or GaP single crystal is selected, and the Group 2-6 single crystal substrate (Group 2-6 compound single crystal substrate) is selected from CdS single crystal, ZnS single crystal, ZnTe single crystal, CdSe single crystal or ZnSe single crystal.

The density of the self-formed ZnO quantum dot of the self-forming ZnO quantum dot substrate is 10 ⁷ to 10 ¹¹ / cm ² , the average height of the ZnO quantum dot is 1 nm to 10 nm, the average width size of 10 nm to 100 It is characterized by being between nm.

As described above, the size, shape, density, or a combination thereof of the self-forming ZnO quantum dots of the self-forming ZnO quantum dot substrate is determined by the temperature of the substrate for controlling the thickness of the Zn thin film and the stress of the Zn thin film. Adjusted.

In the light emitting diode according to the present invention, the ZnO quantum dots of the self-forming ZnO quantum dot substrate act as a reflector of light generated in the active layer and have an increased external extraction efficiency, and also in the process of self-forming the ZnO quantum dots Surface irregularities formed on the surface acts as a reflective layer of light to increase the external extraction efficiency. In this case, the n-type semiconductor layer and the p-type semiconductor layer are n, respectively, so that the n-type semiconductor layer, the p-type semiconductor layer, and the active layer can be directly grown on the self-forming ZnO quantum dot substrate. It is preferable that they are a type ZnO and a P type ZnO.

The light emitting diode according to the present invention has the advantage that the surface roughness of the ZnO quantum dots self-formed on the semiconductor or non-conductor single crystal substrate and the single crystal substrate itself is increased, thereby increasing the external light extraction efficiency, and the ZnO quantum dots act as a reflector and Surface irregularities act as a reflective layer to minimize the light generated in the active layer within the light emitting diode structure and to emit a lot of light to the upper layer surface has the advantage that the light emitting efficiency of the light emitting diode is increased. In addition, the ZnO quantum dot has the advantage that the n-type ZnO semiconductor layer or p-type ZnO semiconductor layer can be grown to a high quality epitaxial on the self-forming substrate. In addition, in forming ZnO quantum dots acting as a reflector on the substrate, there is no additional process such as optical, chemical, or physical patterning or regrowth process, so it is a light emitting diode having low manufacturing cost and high luminous efficiency. There is an advantage.

Hereinafter, a light emitting diode equipped with self-assembled ZnO according to the present invention will be described in detail with reference to the accompanying drawings. The drawings introduced below are provided by way of example so that the spirit of the invention to those skilled in the art can fully convey. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms. Also, like reference numerals denote like elements throughout the specification.

Hereinafter, the technical and scientific terms used herein will be understood by those skilled in the art without departing from the scope of the present invention. Descriptions of known functions and configurations that may be unnecessarily blurred are omitted.

1 is an example illustrating a method of manufacturing a self-forming ZnO quantum dot on a semiconductor or non-conductor single crystal substrate according to the present invention. After forming the Zn thin film 120 on the semiconductor or non-conductor single crystal substrate 110 as shown in FIG. 1 (a), the temperature of the substrate is adjusted to 250 ° C. to 500 ° C. to form oxygen on the plasma and Zn on the Zn thin film 120. When reacted, the ZnO quantum dots 130 self-form due to the stress present in the Zn thin film 120.

Zn thin film 120 may be formed on the semiconductor or non-conductive substrate using a conventional epitaxial manufacturing apparatus such as CVD, PVD, MOCVD, MBE, etc., wherein the thickness of the Zn thin film is 0.2 nm to 2 nm. desirable.

As shown in FIG. 1, after the Zn thin film 120 is formed, the temperature of the substrate is controlled and oxygen reacts with the Zn thin film in order to self-form ZnO quantum dots. ZnO quantum dots are self-formed by activity and at the same time, irregularities are formed on the surface of the substrate by the substrate surface reaction, thereby increasing the roughness of the substrate surface. In this case, the single crystal substrate is preferably a Si single crystal substrate or a sapphire single crystal substrate.

Accordingly, the self-forming ZnO quantum dot substrate 100 according to the present invention has a feature that the self-forming ZnO quantum dots exist on the surface of the single crystal substrate having the unevenness.

2 illustrates an n-type semiconductor layer 220 in which a self-forming ZnO quantum dot substrate 100 illustrated in FIG. 1 and a metal pad 221 to which an external voltage or current is applied are stacked on the self-forming ZnO quantum dot substrate 100. ), A p-type semiconductor layer 210 on which a metal pad 211 to which an external voltage or current is applied, is provided between the n-type semiconductor layer 220 and the p-type semiconductor layer 210 to form the n-type semiconductor layer. An example of the structure of the light emitting diode of the present invention has a structure including an active layer 230 that combines electrons provided from the 220 and holes provided from the p-type semiconductor layer 210 to generate light. .

In FIG. 2, the n-type semiconductor layer 220, the active layer 230, and the p-type semiconductor layer 210 are sequentially stacked on the self-forming ZnO quantum dot substrate 100, and the n-type semiconductor layer ( Although an example has a structure in which a metal pad 221 is formed on an n-type semiconductor layer etched to a part of 220 and exposed on the surface, the light emitting diode of the present invention is not limited to this structure, and p is formed on the substrate. The semiconductor layer, the active layer, and the n-type semiconductor layer may be a stacked structure sequentially.

The n-type semiconductor layer, the p-type semiconductor layer, and the active layer may be formed on the self-forming ZnO quantum dot substrate 100 using a conventional epitaxial forming apparatus, and the active layer may be a well and a barrier. May be a structure of a multi-qunatum wall in which several layers are stacked.

Light generated by the combination of electrons and holes in the active layer is spread in all directions. The ZnO quantum dot 130 serves as a reflector of light traveling in the direction of the substrate, thereby increasing the external extraction efficiency of the light and at the same time. Unevenness of the surface acts as a reflective layer of light, thereby increasing the light extraction efficiency. At this time, the external extraction efficiency of the light by the ZnO quantum dots may be due to the refractive index of the ZnO quantum dot material itself, and may be due to the unevenness formed by the single crystal substrate and the ZnO quantum dots.

The total reflection at the interface between the single crystal substrate and the semiconductor layer is reduced by the unevenness of the ZnO quantum dot 130 and the substrate surface, thereby increasing the extraction efficiency of the generated light. That is, the light emitting diode according to the present invention not only increases the external light extraction efficiency due to the ZnO quantum dots, but also increases the external light extraction efficiency due to the uneven surface of the substrate formed on the semiconductor or insulator single crystal substrate itself.

Preferably, the n-type semiconductor layer, the p-type semiconductor layer is an n-type ZnO layer, a p-type ZnO layer, the active layer is ZnO or ZnCdO. In addition, the n-type or p-type ZnO layer may be a compound of Zn-Mg-O, Zn-Be-O, Zn-Mg-Be-O. The ZnO semiconductor layer may also be stacked on the self-forming ZnO quantum dot substrate through a known process (for example, Japanese Patent Laid-Open No. 2007-128936, Japanese Patent Laid-Open No. 2007-0115969).

In this case, since a ZnO quantum dot is formed on a single crystal substrate of a semiconductor or a non-conductor, the n-type ZnO layer or the p-type ZnO layer may be formed of a high quality epitaxial layer having few crystal defects such as predecessors or point defects.

Although only the core layer constituting the light emitting diode is illustrated in FIG. 2, a buffer layer and a semiconductor layer doped with impurities may be further provided on the substrate.

FIG. 3 is an AFM image of a substrate on which a ZnO quantum dot is self-formed by forming a 0.5 nm Zn thin film on the (111) plane of a silicon single crystal substrate and then controlling the temperature of the substrate to 350 ° C. and reacting with 300 to 500 W rf plasma oxygen. to be. As can be seen in Figure 3, the ZnO quantum dots are self-forming, it can be seen that the silicon surface also has surface irregularities. The light generated in the light emitting diode active layer minimizes the absorption in the light emitting diode structure through the omnidirectional reflecting mirror of the ZnO quantum dot and the silicon substrate and extracts a lot of light to the outside.

1 is an example showing a self-forming ZnO quantum dot substrate according to the present invention,

2 is an example of a light emitting diode equipped with self-forming ZnO according to the present invention.

3 is an AFM image of a ZnO quantum dot self-forming silicon substrate according to the present invention.

Claims (8)

After forming a Zn thin film on a semiconductor or non-conductor single crystal substrate, the substrate is controlled by controlling the temperature of the substrate for reacting the Zn thin film with plasma phase oxygen and controlling the stress of the Zn thin film to 250 ° C. to 500 ° C. A self-forming ZnO quantum dot substrate prepared by self-assembling a phase ZnO quantum dot and simultaneously forming surface roughness of the substrate; An n-type semiconductor layer stacked on the self-forming ZnO quantum dot substrate and having a metal pad to which an external voltage or current is applied; A p-type semiconductor layer on which a metal pad to which an external voltage or current is applied is formed; And An active layer provided between the n-type semiconductor layer and the p-type semiconductor layer to generate light by combining electrons provided from the n-type semiconductor layer with holes provided from the p-type semiconductor layer; It is configured to include, The ZnO quantum dot of the self-forming ZnO quantum dot substrate acts as a reflector of light generated in the active layer, and the surface unevenness of the self-formed ZnO quantum dot substrate acts as a reflecting layer to increase self-extraction ZnO. Equipped with a light emitting diode. The method of claim 1, The thickness of the Zn thin film is a light emitting diode having a self-forming ZnO, characterized in that 0.2nm to 2nm. delete delete The method according to claim 1 or 2, The semiconductor or nonconducting single crystal substrate may include a Group 4 single crystal substrate; Group 3-5 single crystal substrate; Group 2-6 single crystal substrate; Group 4-6 single crystal substrate; Sapphire single crystal substrate; Silicon oxide single crystal substrate; Or a laminated substrate thereof. A light emitting diode with self-forming ZnO. The method according to claim 1 or 2, The self-forming ZnO quantum dot of the self-forming ZnO quantum dot substrate has a density of 10 ⁷ to 10 ¹¹ / cm ² The light emitting diode with self-forming ZnO characterized in that. delete The method according to claim 1 or 2, The n-type semiconductor layer and the p-type semiconductor layer is a light emitting diode with self-forming ZnO, characterized in that each of the n-type ZnO and P-type ZnO.

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