TWI394293B - Light emitting diode - Google Patents

Description

Light-emitting diode

The present invention relates to a light-emitting diode, and more particularly to a light-emitting diode having higher light extraction efficiency.

High-efficiency blue, green and white light-emitting diodes (LEDs) made of gallium nitride-based (GaN) semiconductor materials have longevity, energy saving, green environmental protection, etc., and have been widely used in large-screen color displays and automobiles. In the fields of lighting, traffic signal, multimedia display and optical communication, it has broad development potential especially in the field of lighting. The prior LED generally includes an N-type semiconductor layer, a P-type semiconductor layer, an active layer disposed between the N-type semiconductor layer and the P-type semiconductor layer, a positive electrode (usually a transparent electrode) disposed on the P-type semiconductor layer, and A negative electrode on the N-type semiconductor layer. When the LED is in operation, positive and negative voltages are applied to the P-type semiconductor layer and the N-type semiconductor layer, respectively, so that holes existing in the P-type semiconductor layer and electrons existing in the N-type semiconductor layer are adjacent to each other. Into the active layer; and recombination occurs in the active layer to generate light waves, which are emitted from the LED through the transparent electrode. However, previous LED extraction efficiencies (extraction efficiency generally refers to the efficiency with which light waves generated in the active layer are released from the interior of the LED) are low due to total reflection and material absorption of light waves. The total reflection phenomenon occurs because the refractive index of the semiconductor is greater than the refractive index of the air. The light from the active layer is totally reflected at the interface between the semiconductor and the air, so that most of the light is confined to the inside of the LED until it is completely absorbed by the material inside the LED.

In view of this, it is necessary to provide an LED with high extraction efficiency.

Hereinafter, a light-emitting diode will be described by way of examples.

A light emitting diode includes a substrate, a reflective layer, an active layer, a transparent electrode, a first photonic crystal structure, and a second photonic crystal structure. The reflective layer is formed on the substrate, the active layer is formed on the reflective layer, and the transparent electrode is formed on the active layer. The transparent electrode includes an upper surface and a lower surface, and the lower surface of the transparent electrode is combined with the active layer. The first photonic crystal structure is disposed on an upper surface of the transparent electrode, and the second photonic crystal structure is formed in the active layer.

A light emitting diode comprising a substrate, a reflective layer, a first semiconductor layer, an active layer, a second semiconductor layer, a transparent electrode, a first photonic crystal structure, and a second photonic crystal structure. The reflective layer is disposed on the substrate, the first semiconductor layer is disposed on the reflective layer, the second semiconductor layer is disposed on the first semiconductor layer, and the active layer is disposed on the first semiconductor layer The transparent electrode is disposed on the second semiconductor layer between the second semiconductor layers. The active layer includes a bottom surface coupled to the first semiconductor layer, and the second photonic crystal structure is formed on a bottom surface of the active layer. The transparent electrode includes an upper surface and a lower surface, the lower surface of the transparent electrode is combined with the second semiconductor layer, and the first photonic crystal structure is disposed on the upper surface of the transparent electrode.

Compared with the prior art, the light-emitting diode has a first photonic crystal structure and a second photonic crystal structure, and the light-emitting diode generates light waves during operation, and the first photonic crystal structure can be used for light waves with a small incident angle. The light is incident on the outer space of the light-emitting diode; and the light wave with a larger incident angle is reflected back into the active layer, and the second photonic crystal structure can diffract it into a light wave with a smaller incident angle and then pass through the first photonic crystal structure. Diffraction to the outer space of the light-emitting diode. In this way, the second photonic crystal structure is combined with the first photonic crystal structure to diffract the light wave, so that the light wave is emitted to the external space relatively quickly, thereby reducing the multiple reflection of the reflected light in the active layer, thereby avoiding the active layer material and The absorption of the light wave by the material of the reflective layer, etc., so that the light-emitting diode has a higher light extraction efficiency.

The illuminating diode of the present technical solution will be further described in detail below with reference to the accompanying drawings and embodiments.

Referring to FIG. 1 , an embodiment of the present invention provides a light emitting diode 100 including a substrate 110 , a reflective layer 120 , and a light emitting diode substrate 10 formed on the reflective layer 120 . The light emitting diode body 10 includes an active layer 11 and a transparent electrode 160 formed on the active layer 11. The active layer 11 includes a first semiconductor layer 130, an active layer 140, and a second semiconductor layer 150. The first semiconductor layer 130, the active layer 140, and the second semiconductor layer 150 are sequentially formed on the reflective layer 120.

The transparent electrode 160 has an upper surface 161 and a lower surface 162. The lower surface 162 is combined with the second semiconductor layer 150. A first photonic crystal structure 170 is formed on the upper surface 161.

A second photonic crystal structure 180 is formed in the active layer 11. Optionally, the second photonic crystal structure 180 may be formed at the interface between the active layer 140 and the first semiconductor layer 130, and may be formed on the active layer 140. The lower surface (the surface of the active layer 140 in contact with the first semiconductor layer 130) may also be formed On the upper surface of the first semiconductor layer 130 (the surface on which the first semiconductor layer 130 is in contact with the active layer 140). In addition, the second photonic crystal structure 180 may also be formed on the bottom surface of the first semiconductor layer 130 (the surface of the first semiconductor layer 130 near the reflective layer 120). In this embodiment, the second photonic crystal structure 180 is formed on the bottom surface of the first semiconductor layer 130, that is, on the bottom surface of the active layer 11.

Preferably, a bonding layer 190 may be disposed between the first semiconductor layer 130 and the reflective layer 120 for combining the active layer 11 having the second photonic crystal structure 180 on the bottom surface and the reflective layer 120.

As shown in FIG. 2, the structural features of the photonic crystal can generally be characterized by the following three parameters, namely, lattice constant (a), aperture (d), and hole depth (h). The a is the center distance of adjacent holes in the photonic crystal structure. The first photonic crystal structure 170 and the second photonic crystal structure 180 have the same range of a, d, and h, that is, a is about 0.5 to 2.0 micrometers, d is about 0.5a to 0.9a, and h is greater than zero and less than or equal to 0.5 micron. When the first photonic crystal structure 170 is the same as a, d, and h of the second photonic crystal structure 180, the first photonic crystal structure 170 is identical in structure to the second photonic crystal structure 180. Of course, the structures of the first photonic crystal structure 170 and the second photonic crystal structure 180 may also be different, that is, the values of a, d, and h of the two are different.

The material of the substrate 110 is sapphire, and may also be a material such as gallium arsenide, indium phosphide, antimony, antimony carbide or tantalum nitride. The reflective layer 120 is formed of a metallic material such as metallic silver or aluminum. The first semiconductor layer 130 is an N-type semiconductor layer made of N-type gallium nitride (GaN) or N-type gallium arsenide or N-type phosphide. The material of the active layer 140 is indium gallium nitride (InGaN). The second semiconductor layer 150 is a P-type semiconductor layer made of P-type GaN, and may also be P-type gallium arsenide or P-type phosphide. The material of the transparent electrode layer 160 is indium tin oxide (ITO) ). The bonding layer 190 may be an epoxy resin adhesive, an ultraviolet curing adhesive, or the like.

The method of fabricating the above-described light emitting diode 100 will be described in detail below. In a first step, a light-emitting diode substrate 10 formed on a substrate 110 is provided. The light emitting diode substrate 10 includes a first semiconductor layer 130, an active layer 140, a second semiconductor layer 150, and a transparent electrode 160. The active layer 140 is disposed between the first semiconductor layer 130 and the second semiconductor layer 150, and the transparent electrode 160 is formed on the second semiconductor layer 150.

The light-emitting diode substrate 10 is the simplest light-emitting diode structure of the prior art and is typically formed on the substrate 110 by a series of physical or chemical deposition methods. In the embodiment, the substrate 110 is made of sapphire, the first semiconductor layer 130 is made of N-type gallium nitride, the second semiconductor layer 150 is made of P-type gallium nitride, the active layer 140 is made of indium gallium nitride, and the transparent electrode 160 is Indium tin oxide material.

In the second step, the substrate 110 is separated from the light-emitting diode substrate 10. The substrate 110 and the light-emitting diode substrate 10 are separated along the interface of the substrate 110 and the first semiconductor layer 130 by a prior art method such as laser lift-off. Thus, a separate substrate 110, and a light-emitting diode substrate 10 composed of the first semiconductor layer 130, the active layer 140, the second semiconductor layer 150, and the transparent electrode 160 are obtained.

In the third step, a second photonic crystal structure 180 is formed on the first semiconductor layer 130.

First, the first semiconductor layer 130 of the light-emitting diode substrate 10 was washed with acetone, isopropyl alcohol, deionized water and ultrasonic waves in advance before the specific production, and then blown dry with nitrogen.

Next, a film having a strong etching resistance such as a hafnium oxide film is formed on the first semiconductor layer 130 by plasma-assisted chemical vapor deposition. Since the subsequent electronic resist to be formed has poor etching resistance, the ruthenium dioxide film formed in this step can protect the first semiconductor layer 130 from being damaged during the plasma etching process.

Again, an electron resistive layer, such as polymethyl methacrylate (PMMA), is formed on the hafnium oxide film. Before the formation of the PMMA layer, it is necessary to clean the surface obtained after the completion of the second step, in particular, the surface of the ruthenium oxide film layer, and blow dry with nitrogen. Since the presence of moisture on the surface of the cerium oxide layer affects the bonding effect of the PMMA layer and the cerium oxide layer, it can be heated at a low temperature to ensure that the surface of the cerium oxide layer is anhydrous. Then, a PMMA layer was formed on the ceria layer by a spin coating method. Finally, a predetermined pattern of the second photonic crystal structure 180 is formed on the PMMA layer by electron beam lithography.

Again, the pattern of PMMA is transferred to the cerium oxide layer by reactive ion reaction in combination with dry etching. The etching depth is the thickness of the hafnium oxide layer to expose the pattern to the surface of the first semiconductor layer 130. Subsequently, it is washed successively with acetone, isopropanol, deionized water and ultrasonic waves for a period of time, such as about 5 minutes, and then the PMMA layer is removed by washing with an ultraviolet ozone cleaner.

Finally, the first semiconductor layer 130 is etched by active ion reaction to transfer the pattern in the ceria layer to the first semiconductor layer 130. In the active ion reaction, boron trichloride (BCl ₃ ) gas may be used. After the first semiconductor layer 130 is etched into a pattern, the cerium oxide layer is removed by using hydrofluoric acid and deionized water, thereby forming the first semiconductor layer. A desired second photonic crystal structure 180 is obtained at 130.

In the fourth step, a first photonic crystal structure 170 is formed on the transparent electrode 160 in a manner similar to the above method of fabricating the second photonic crystal structure 180 on the first semiconductor layer 130.

In the fifth step, the metal reflective layer 120 is formed on the surface of the substrate 110 by physical or chemical vapor deposition.

In the sixth step, the substrate 110 having the metal reflective layer 120 and the LED substrate 10 having the first photonic crystal structure 170 and the second photonic crystal structure 180 are assembled such that the first semiconductor layer 130 and the metal reflective layer 120 are disposed. The phosphor layers 190 are bonded together to obtain the light-emitting diode 100 of the present technical solution. The specific assembly method can be glued with an adhesive material, or a conventional and feasible method can be used.

When the light-emitting diode 100 prepared above is in operation, a negative electrode may be disposed on the substrate 110, and a positive voltage and a negative voltage are applied to the negative electrode of the transparent electrode 160 (usually the positive electrode) and the substrate 110, respectively, so that under the electric field The hole carriers in the second semiconductor layer 150 move toward the first semiconductor layer 130 while the electron carrier fluid in the first semiconductor layer 130 moves toward the second semiconductor layer 150, so that the hole carriers are The electron carriers will recombine in the active layer 140 and release energy, and the released energy will be released in the form of light energy, that is, light waves are generated. The generated light wave is emitted from the inside of the light emitting diode 100 through the transparent electrode 160.

The light waves generated in the active layer 140 are incident into the transparent electrode 160 at different angles for the first photonic crystal structure formed on the transparent electrode 160. In 170, it produces a better diffractive effect on a light wave having a smaller incident angle, that is, a light wave having a smaller incident angle is diffracted by the first photonic crystal structure 170 and can enter the external free space. The light wave having a large incident angle is reflected by the interface between the transparent electrode 160 and the second semiconductor layer 150, and is returned to the active layer 11. When the reflected light returning to the active layer 11 is incident on the second photonic crystal structure 180, the second photonic crystal structure 180 diffracts the reflected light into a light wave having a smaller incident angle to the reflective layer 120, and the incident angle is smaller. The light wave is reflected by the reflective layer 120 and then reaches the second photonic crystal structure 180, and then diffracted by the second photonic crystal structure 180 to the transparent electrode 160. In this process, the light wave having a larger incident angle is converted into a light wave having a smaller incident angle according to the diffraction condition of the first photonic crystal structure 170, and reaches the transparent electrode 160, and then diffracted by the first photonic crystal structure 170 to enter the light-emitting diode. In the outer space of the polar body 100. In this embodiment, the second photonic crystal structure 180 disposed in the active layer 11 combines the diffracting effect of the first photonic crystal structure 170 disposed on the transparent electrode 160 on the optical wave, and the reflected light is greatly reduced in the active layer 11. The number of times of reflection is performed, thereby avoiding absorption of light waves by the material of the active layer 11 and the material of the reflective layer 120, so that the light-emitting diode 100 of the present embodiment has higher light extraction efficiency.

The illuminating effect of the light-emitting diode 100 of the above embodiment was verified by experiments. A gallium nitride material having a wavelength of 450 nm is used as the active layer 11 material of the light-emitting diode 100, and a model of the light-emitting diode 100 is established: an average of the reflective layer 120, the adhesive layer 190, the active layer 11, and the transparent electrode 160. The thicknesses are 0.1 micron, 0.1 micron, 2.5 micron, and 0.3 micron in order; the refractive indices of the transparent electrode 160 and the adhesive layer 190 are about 2.0 and 1.5, respectively; and the complex refractive indices of the active layer 11 and the reflective layer 120 are 2.5+i0, respectively. .02 and 0.1+i5.6; the first photonic crystal structure 170 and the second photonic crystal structure 180 have the same a and d, specifically, a is equal to 0.8 micron and d is equal to 0.8a; the aperture of the first photonic crystal structure 170 The depth is calculated as h ₁ and h ₁ is equal to 0.2 μm; the depth of the second photonic crystal structure 180 is h ₂ , and h _{2 is} varied from zero micron to 0.5 μm.

According to the parameters of the above-mentioned light-emitting diode 100, the luminous efficiency of the light-emitting diode 100 is analogically calculated by the finite-difference time-domain method, and the normalized luminous efficiency of various parameter structures changes with time as shown in FIG. 3, FIG. 3 The abscissa of the middle represents the simulation time; the ordinate represents the change of the hole depth of the second photonic crystal structure 180, the luminous efficiency of the light emitting diode 100 and the light emitting diode of the first photonic crystal structure 170 and the second photonic crystal structure are not provided. The change in the ratio of bulk luminescence efficiency. As shown in FIG. 3, the curve A indicates that when the first photonic crystal structure 170 and the second photonic crystal structure are not disposed in the light emitting diode 100, the light emitting diode is called M-LED at this time, and the luminous efficiency is normalized. 1 is used as a reference curve; when h _{2 is} taken to be zero micrometers, that is, the light-emitting diode 100 is only provided with the first photonic crystal structure 170, and the light-emitting diode is usually referred to as SPC-LED, which can be seen from FIG. The luminous efficiency of the SPC-LED is about twice that of the M-LED; when h ₂ is equal to 0.3 micron, the luminous efficiency of the LED 100 is 3.2 times that of the M-LED. Therefore, the test results show that the light-emitting diode 100 of the present embodiment has higher light extraction efficiency than the light-emitting diode having no photonic crystal structure, and can be further improved than the light-emitting diode having a photonic crystal structure. Improve light extraction efficiency.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above is only a preferred embodiment of the present invention. It is not possible to limit the scope of the patent application in this case. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the present invention are intended to be included in the scope of the following claims.

100‧‧‧Lighting diode

110‧‧‧Base

120‧‧‧reflective layer

130‧‧‧First semiconductor layer

140‧‧‧Active layer

150‧‧‧Second Semiconductor

11‧‧‧Active layer

160‧‧‧Transparent electrode

170‧‧‧First photonic crystal structure

180‧‧‧Second photonic crystal structure

10‧‧‧Light-emitting diode substrate

190‧‧‧bonded layer

161‧‧‧ upper surface

162‧‧‧ lower surface

1 is a schematic cross-sectional view of a light emitting diode according to an embodiment of the present technical solution.

2 is a schematic perspective view of a light emitting diode according to an embodiment of the present technical solution.

FIG. 3 is a graph showing the luminous efficiency as a function of time in the simulation calculation of the light-emitting diode of the above embodiment by the finite difference time domain method.

100‧‧‧Lighting diode

110‧‧‧Base

120‧‧‧reflective layer

130‧‧‧First semiconductor layer

140‧‧‧Active layer

150‧‧‧Second Semiconductor

11‧‧‧Active layer

160‧‧‧Transparent electrode

170‧‧‧First photonic crystal structure

180‧‧‧Second photonic crystal structure

10‧‧‧Light-emitting diode substrate

190‧‧‧bonded layer

161‧‧‧ upper surface

162‧‧‧ lower surface

Claims (9)

A light emitting diode comprising: a substrate; a reflective layer disposed on the substrate; a first semiconductor layer disposed on the reflective layer; a second semiconductor layer disposed on the first semiconductor layer; an active layer And disposed between the first semiconductor layer and the second semiconductor layer, the active layer includes a bottom surface coupled to the first semiconductor layer; and a transparent electrode disposed on the second semiconductor layer, the transparent electrode including an upper surface And a lower surface, the lower surface of the transparent electrode is combined with the second semiconductor layer; and the improvement is that the light emitting diode further comprises a first photonic crystal structure and a second photonic crystal structure, the first photonic crystal structure is disposed On the upper surface of the transparent electrode, the second photonic crystal structure is formed only on the bottom surface of the first semiconductor layer on the bottom surface of the active layer. The light-emitting diode according to claim 1, wherein the first photonic crystal structure has a lattice constant of 0.5 to 2.0 μm, a pore size of 0.5 to 0.9 times a lattice constant, and a pore depth of less than or equal to 0.5 micron. The light-emitting diode according to claim 2, wherein the second photonic crystal structure has a lattice constant of 0.5 to 2.0 μm, a pore size of 0.5 to 0.9 times a lattice constant, and a pore depth of less than or equal to 0.5 micron. The light-emitting diode according to claim 3, wherein a lattice constant, a pore diameter, and a hole depth of the first photonic crystal structure are equal to a lattice constant, a pore diameter, and a hole depth of the second photonic crystal structure. The light-emitting diode according to claim 1, wherein the hair The photodiode further includes a bonding layer formed between the first semiconductor layer and the reflective layer. A light emitting diode comprising: a substrate; a reflective layer formed on the substrate; an active layer formed on the reflective layer; and a transparent electrode formed on the active layer, the transparent electrode including an upper surface a surface and a lower surface, the lower surface of the transparent electrode is combined with the active layer; the active layer includes a first semiconductor layer, a second semiconductor layer, and is formed between the first semiconductor layer and the second semiconductor layer An active layer having a lower bottom surface in contact with the first semiconductor layer, the first semiconductor layer having an upper bottom surface combined with a lower bottom surface of the active layer; The pole body further includes a first photonic crystal structure disposed on an upper surface of the transparent electrode, and a second photonic crystal structure formed on the first semiconductor layer and active in the active layer At the interface of the layer. The light-emitting diode according to claim 6, wherein the second photonic crystal structure is formed on a bottom surface of the active layer. The light-emitting diode according to claim 6, wherein the second photonic crystal structure is formed on a bottom surface of the first semiconductor layer. The light-emitting diode of claim 6, wherein the light-emitting diode further comprises a bonding layer formed between the first semiconductor layer and the reflective layer.