TWI459593B - Structure of light emitting diodes for increase of light emitting efficiency - Google Patents

Description

Light-emitting diode structure for increasing luminous efficiency

The invention relates to a structure in which a light-emitting diode increases luminous efficiency, in particular, a method capable of not only increasing luminous efficiency, but also generating and inducing more photons and increasing the luminous brightness of the light-emitting diode, and performing the whole in its entirety. A structural innovation designer who uses a more practical value-added light-emitting diode to increase luminous efficiency.

According to recent years, the related technologies of light-emitting diodes have sprung up, and the direction of research in all walks of life is nothing more than how to improve the internal quantum efficiency of the light-emitting diodes and the external quantum efficiency [External Quantum Efficiency]. And the light extraction rate [Light Extraction], so some people began to combine the technology of photonic crystals with light-emitting diodes. In addition, some studies in recent years have pointed out that the use of lasers to excite surface electrodes in metal and semiconductor interfaces can enhance the photocurrent effect. The quantum effect, its purpose is nothing more than to improve the external quantum efficiency path and improve luminous efficiency.

The blue light-emitting diode material currently in common use is a gallium nitride (GaN) material, and gallium nitride has a refractive index of about 2.5 at a wavelength of 400 nm, and is a material having a relatively high refractive index. Because of this, most of the light produced by the LEDs is reflected back into the material and eventually absorbed by the material itself, resulting in lower external quantum efficiency. Despite the improvement of the epitaxial technology, the internal volume The sub-efficiency can reach more than 90%, but the external quantum efficiency is low, resulting in poor overall luminous efficiency. Therefore, improving the external quantum efficiency of the light-emitting diode has become one of the important topics in solid-state lighting.

The concept of photonic crystals is proposed by scholars. It is pointed out that electromagnetic waves in a periodically arranged medium will form a band gap similar to that of a semiconductor band structure. Since then, the research of photonic crystals has been developed and explored; the use of photonic crystals to enhance the external quantum efficiency of light-emitting diodes has always been the goal of the photonic crystal team.

If the light-emitting diode is not added with any technology, only the original PN Junction electron hole is combined to form photons, and only about 15% can be converted into light, and others will be refraction, reflection or remain inside the semiconductor. The material absorbs and becomes a heat loss. Therefore, the light-emitting diode industry needs to develop many techniques to reduce reflection, design effective refraction or increase optical coupling or light induction, and try to increase the efficiency of light extraction. Surface photonic crystallization is a quite successful way. Reduce internal reflection and outward scattering of light. With the development of Molecular Beam Epitaxy (MBE) and Metal Organic Chemical Vapor Deposition (MOCVD), the internal quantum efficiency of the LED (Internal Quantum Efficiency) 〕 has achieved quite high efficiency.

Internal quantum efficiency is defined as the ratio of the amount of electrons converted into photon luminescence in the luminescent layer by the forward current injection into the luminescent diode. Although the quantum brightness of the high-brightness light-emitting diodes currently produced is already high, the external quantum efficiency is still very low, even less than 10% in terms of blue light, and there are many reasons for the external quantum efficiency being too low. , such as the non-uniform distribution of current or because of the high refractive index of semiconductor materials and some defects in the semiconductor It is easily emitted to the outside and absorbed by the semiconductor material itself or absorbed by the substrate. Therefore, the true light extraction efficiency (also known as external quantum efficiency; External Quantum Efficiency) is not equal to the internal quantum efficiency, and the external quantum efficiency is defined as the internal quantum efficiency multiplied by the extraction efficiency [Extraction Efficiency].

Photonic crystals modify the material structure of a substance on a wavelength scale, enabling the substance to control the behavior of photons. Photonic crystals mainly load defects in the energy gap structure, forming a local region that destroys the periodic structure. Only photons of certain wavelengths can exist and propagate in this defect region, and in the medium outside this region, the photon energy of those wavelengths It is forbidden.

The atoms inside the crystal are periodic and appear in an ordered arrangement. It is the existence of this periodic potential field that causes the moving electrons to be scattered by the Bragg of the periodic potential field, thus forming an energy band structure, and there may be a band between the energy band and the energy band. Bandgap. If the energy of the electron wave falls in the band gap, it cannot continue to propagate. Whether the electromagnetic wave or the light wave is periodically modulated, there is a band structure, and a band gap may occur, and the wave whose energy falls in the band gap The same cannot be spread.

In other words, the periodic arrangement of ions in the semiconductor creates an energy band structure that in turn controls the movement of carriers in the semiconductor. The same in the photonic crystal is the optical band gap structure caused by the periodic variation of the refractive index of the light, so that the movement of the light in the photonic crystal is controlled by the optical band gap structure.

The structure of a photonic crystal is just like the periodic appearance of a semiconductor material at a lattice junction. A photonic crystal is a material that periodically exhibits a low refractive index at certain locations of a high refractive index material. The high and low refractive index materials are alternately arranged to form a periodic structure to produce a photonic crystal band gap, and the distance between the periodically arranged low refractive index sites is different, resulting in a photonic crystal of a certain distance only generating light waves of a certain frequency. Band effect, that is, only some frequency The rate of light is completely forbidden to propagate in a photonic crystal with a certain period of time.

High brightness is a necessary condition for a light-emitting diode to replace a conventional lighting device, and to achieve high brightness, it is necessary to increase the internal quantum efficiency and external quantum efficiency of the light-emitting diode. Internal quantum efficiency can be achieved by sophisticated epitaxial technology and advanced process technology, while external quantum efficiency is always limited due to total internal reflection.

The use of photonic crystals to enhance the external quantum efficiency of a light-emitting diode is nothing more than overcoming its total internal reflection, resulting in an increase in luminous efficiency. The main mechanisms are:

1. The periodic structure of the surface causes scattering of light, destroying light that would otherwise be totally internally reflected, and allowing more photons to escape the material.

2. The photonic crystal forms a special band structure, and the emission wavelength falls within the photonic crystal, so that the propagation mode in the gallium nitride light-emitting diode material is extracted.

The two mechanism effects have different characteristics. The first mechanism effect enhances the amount of light by means of scattering. The method of overcoming the total reflection is similar to the surface roughening. The second mechanism effect is mainly limited by the energy gap. Propagation mode extraction in the material.

However, although the above-mentioned light-emitting diode structure design can achieve the intended effect of the predetermined light-emitting illumination, it is found that the luminous efficiency of the light-emitting diode is still poor, resulting in a light-emitting diode. There is still room for improvement in the overall structural design.

In view of this, the inventor has been in the process of researching and improving the existing structures and defects by providing rich experience in design and development and actual production of the relevant industries for many years, and providing a structure in which the light-emitting diodes increase luminous efficiency, in order to achieve better practicality. The purpose of value.

The structure of the light-emitting diode of the present invention increases luminous efficiency, which is mainly based on nitriding A gallium-emitting diode epitaxial wafer is formed with a rough surface having a plurality of tapered holes having an opening diameter of less than 2 μm and a tapered hole having a depth of 68.8 nm to 215.5 nm and simultaneously emitting a gallium nitride luminescence dipole The body-expanding wafer is coated with a single-layer nano-metal layer of a particle or a film layer, or a ceramic layer of a particle or a film layer and a nano metal layer; thereby, not only the luminous efficiency but also the luminous efficiency can be increased. Producing, inducing more photons, increasing the brightness of the light-emitting diodes, and increasing the practical value in its overall implementation.

First drawing: the flow chart of the invention

Second drawing: enlarged view of the tapered hole of the present invention

Third: enlarged side view of the tapered hole of the present invention (depth 68.8 nm)

Fourth drawing: enlarged side view of the tapered hole of the present invention (depth 118.5 nm)

Fig. 5 is a side elevational cross-sectional view showing the tapered hole of the present invention (depth 165.6 nm)

Figure 6 is a side elevational cross-sectional view of the tapered hole of the present invention (depth 215.5 nm)

Figure 7: Current and voltage measurement diagram of the light-emitting diode with coarsening of the present invention

Figure 8: Photometric measurement of the light-emitting diode of the present invention with roughening

Ninth diagram: current and voltage measurement diagram of the light-emitting diode with photon inducer of the present invention

Figure 10: Photoluminescence measurement of the light-emitting diode with photon inducer of the present invention

For a more complete and clear disclosure of the technical content, the purpose of the invention and the effects thereof achieved by the present invention, the following is a detailed description, and please refer to the drawings and drawings: First, please refer to The first figure shows the flow chart of the present invention. The present invention mainly uses a positive photoresist as a mask on a gallium nitride light-emitting diode epitaxial wafer, and emits light in gallium nitride by a technique of etching or mechanical processing. A rough surface having a plurality of tapered holes is formed on the diode epitaxial wafer, the opening diameter of the tapered hole is less than 2 μm, and the depth of the tapered hole is 68.8 nm to 215.5 nm, and the particle or film layer is coated. a layer of nano-metal, the single-layer nano-metal layer is a photon inducer, such as gold (Au), or a ceramic layer of a particle or a film layer and a nano metal layer, the ceramic layer A nano metal layer is an inducer of photons, such as cerium oxide (SiO2) and gold (Au), and the particle or film layer has a size of 3 μm or less, and is then brought into the subsequent process of the light-emitting diode element.

The detailed process steps of the tapered hole are described as follows:

First, wafer cleaning (wafer cleanning)

The wafer was immersed in a solvent such as hydrochloric acid (HCL), acetone (ACE), or isopropyl alcohol (IPA) in sequence, and washed with an ultrasonic oscillator for about 3 minutes; this step was repeated twice. After the shock cleaning by the hyper-wave oscillator is completed, the organic liquid remaining on the surface of the wafer is completely washed away by washing with deionized water, and finally dried by low-pressure nitrogen gas to complete the cleaning step.

Second, optical lithography (photolithography) technology defines the hole array structure

(1) Baking: The wafer was soft baked on a hot plate at 100 ° C for 2 minutes to remove moisture on the surface of the wafer.

(2) Photoresist layer coating: using a positive photoresist (EG-516), pre-rotating at 3000 rpm/min for 10 seconds, and then rotating at 5000 rpm/min for 20 seconds.

(3) Soft-baked photoresist: The wafer was placed on a hot plate at 100 ° C for 2 minutes, so that the light was not adhered to the mask when the image was transferred.

(4) Exposure: The sample test piece was placed on a reticle aligner, and 144 mJ of energy was irradiated with a mercury lamp to complete image transfer.

(5) Bake after exposure: The wafer was placed on a hot plate at 100 ° C for 4 minutes to eliminate the standing wave effect.

(6) Development: The exposed wafer was placed in a developing solution, developed for 50 seconds, and then rinsed with deionized water to fix.

(7) Hard baked photoresist: The wafer was baked on a hot plate at 140 ° C for 40 minutes to increase the resistance of the photoresist layer to dry etching.

Inductively Coupled Plasma Etching System (ICP)

Inductively Coupled Plasma Etching System (ICP) is used to pass through N2:5 sccm, Ar:10 sccm, and CL2:20 sccm gas to etch gallium nitride, and the tapered nanopore hole pattern is as follows. The second figure shows a tapered view of the tapered hole of the present invention, and can be formed into different depths according to different use requirements (please refer to the third figure for a side view of the tapered hole of the present invention (a depth of 68.8 nm), 4 is a side elevational cross-sectional view of a tapered hole of the present invention (depth 118.5 nm), a fifth side view of the tapered hole of the present invention, a side view (a depth of 165.6 nm) and a sixth figure of the present invention The enlarged side view of the hole is shown in an enlarged view (depth: 215.5 nm)].

In this way, please refer to the seventh figure, the current and voltage measurement diagram of the light-emitting diode with roughening (ie, tapered holes with different depths on the surface), so that the etching depth is 68.8 nm, 118.5 nm, The forward voltage (Vf) values measured at 165.6 nm and 215.5 nm at a current of 20 mA were 3.079 volts, 3.047 volts, 3.049 volts, and 3.074 volts, respectively, compared to the control group (STD) at 20 mA. The forward voltage (Vf) value of 2.997 volts is about 2.2% higher, with almost no significant increase.

Please also refer to the eighth embodiment of the present invention, as shown in the light intensity measurement diagram of the light-emitting diode of the present invention, forming a rough surface having a plurality of tapered holes on the gallium nitride light-emitting diode. The depth contributes to the light extraction rate, and the average light brightness increases by about 24%, and the depth is 165.6 nm, which is the most increased by 30% compared with the control group (STD).

Please refer to the ninth figure for the luminescence of the photon inducer (that is, the ceramic layer (SiO2) and the nano metal layer in the tapered hole of the roughened gallium nitride light-emitting diode epitaxial wafer). The current and voltage measurements of the diode show that the measured forward voltage (Vf) values are 3.089 volts, 3.076 at etch depths of 68.8 nm, 118.5 nm, 165.6 nm, and 215.5 nm and currents of 20 mA, respectively. Volt, 3.087 volts, and 2.788 volts, the forward voltage (Vf) value measured at 20 mA compared to the control group (STD) was about 2.97 volts, which was about 2.9% higher than the apparent increase.

Please also refer to the tenth figure of the photoluminescence of the photon-inducing body of the present invention, and form a tapered hole having a plurality of different depths on the gallium nitride light-emitting diode. The ceramic layer (SiO2) and the nano-metal layer are covered in the tapered hole, so that the light extraction rate is increased, and the average brightness is increased by about 53%, and the depth is 1700 Å (165.6 nm) and the control group (STD). Compared with the increase of 61%, and because of the rough surface with many tapered holes formed on the gallium nitride light-emitting diode, the injected current is mostly far from the light-emitting layer. Injected, so there will be no leakage current.

As described above, the composition and use of the architecture show that the present invention is compared with the existing architecture, and the present invention is mainly formed on the gallium nitride light-emitting diode epitaxial wafer to form a rough surface having a plurality of tapered holes. And at the same time, on the gallium nitride light-emitting diode epitaxial wafer, a single-layer nano-metal layer coated with a particle or a film layer, or a ceramic layer of a particle or a film layer and a nano metal layer are The photon inducer not only increases the luminous efficiency, but also generates and induces more photons, increases the luminance of the light-emitting diode, and increases the practical value in its overall implementation.

However, the above-described embodiments or drawings are not intended to limit the structure or the use of the present invention, and any suitable variations or modifications of the invention will be apparent to those skilled in the art.

In summary, the embodiments of the present invention can achieve the expected use efficiency, and the specific structure disclosed therein has not been seen in similar products, nor has it been disclosed before the application, and has completely complied with the provisions of the Patent Law. And the request, the application for the invention of a patent in accordance with the law, please forgive the review, and grant the patent, it is really sensible.

Claims (14)

A structure in which a light-emitting diode increases luminous efficiency, and is mainly formed on a gallium nitride light-emitting diode epitaxial wafer to form a rough surface having a plurality of tapered holes having an opening diameter of less than 2 μm and a taper The depth of the hole is 68.8 nm to 215.5 nm, and the metal layer is coated on the gallium nitride light emitting diode. The structure of the light-emitting diode according to claim 1, wherein the tapered surface of the gallium nitride light-emitting diode is formed by etching. The structure of the light-emitting diode according to claim 1, wherein the tapered hole rough surface formed on the gallium nitride light-emitting diode wafer is formed by a mechanical processing method. The structure of the light-emitting diode according to claim 1, wherein the metal layer coated on the gallium nitride light-emitting diode is in the form of particles. The structure of the light-emitting diode according to claim 1 is characterized in that the metal layer coated on the gallium nitride light-emitting diode is a film layer. The structure of the light-emitting diode according to claim 1 is characterized in that the metal layer coated on the gallium nitride light-emitting diode is gold (Au). The structure of the light-emitting diode according to claim 1 is characterized in that the metal layer of the gallium nitride light-emitting diode is over 3 μm . A structure in which a light-emitting diode increases luminous efficiency, which is mainly formed on a gallium nitride light-emitting diode epitaxial wafer to form a rough surface having a plurality of tapered holes having an opening diameter of less than 2 μm , and The tapered hole has a depth of 68.8 nm to 215.5 nm, and a ceramic layer and a metal layer are coated on the gallium nitride light emitting diode. The structure of the light-emitting diode according to claim 8 is characterized in that the tapered hole rough surface formed on the gallium nitride light-emitting diode wafer is etched by etching. The structure of the light-emitting diode according to claim 8 is characterized in that the tapered hole rough surface formed on the gallium nitride light-emitting diode wafer is formed by a mechanical processing method. The light-emitting diode according to claim 8 is characterized in that the GaN light-emitting diode is coated with a ceramic layer and a metal layer in a particulate form. The light-emitting diode according to claim 8 is characterized in that the GaN light-emitting diode is coated with a ceramic layer and a metal layer as a film layer. The structure of the light-emitting diode according to claim 8 is characterized in that the ceramic layer coated on the gallium nitride light-emitting diode is cerium oxide (SiO2) and the metal layer is gold ( Au). The light-emitting diode according to claim 8 is characterized in that the GaN light-emitting diode is coated with a ceramic layer and a metal layer having a size of 3 μm or less.