Abstract:
A light emitting device comprising a first semiconductor layer, a second semiconductor layer and a quantum well layer, wherein the first semiconductor layer and the second semiconductor layer are disposed on the opposite sides of the quantum well layer, the quantum well layer comprising a plurality of quantum well rods which are separated from each other, and each of the quantum well rods has only one quantum well.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The application relates to a light emitting device with a single quantum well rod and the manufacturing method thereof. 
         [0003]    2. Related Application Data 
         [0004]    The features of LED mainly include small size, high efficiency, long life, quick reaction, high reliability, and fine color. So far, LED has been applied to electronic devices, vehicles, signboards, and traffic signs. Along with the launch of the full-color LED, LED has gradually replaced traditional lighting apparatus such as fluorescent lights and incandescent lamps. 
         [0005]    There are several important factors to influence the light-emitting efficiency of LED, and the external quantum efficiency (EQE) is one of them. EQE is defined as the ratio of the number of photons generated by the active region of the light-emitting diode and the number of electrons injected into the active area per unit time. In the ideal case, each electron injected into the active region should be combined with a hole to generate a photon. However, in the actual operation, the LED can hardly achieve this result. In a worse situation, when the operating current is increased to produce more light, the external quantum efficiency is decreased, which is also known as the external quantum efficiency droop (EQE droop), that limits the performance of light-emitting diodes at high current operation. Therefore, the EQE droop effect needs to be solved. 
       SUMMARY 
       [0006]    The present disclosure provides a novel structure and the manufacturing method thereof for increasing the light extraction efficiency. 
         [0007]    One aspect of the present disclosure provides an light emitting device comprising: a first semiconductor layer of first conductivity-type; a second semiconductor layer of second conductivity-type; a quantum well layer, wherein the first semiconductor layer and the second semiconductor layer are disposed on the opposite sides of the quantum well layer, the quantum well layer comprising a plurality of quantum well rods which are separated from each other, and each of the quantum well rod has only one quantum well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIGS. 1A to 1E  illustrate the corresponding structures fabricated by the manufacturing method step-by-step according to one embodiment of the present disclosure. 
           [0009]      FIG. 1F  illustrates quantum well rods according to one embodiment of the present disclosure. 
           [0010]      FIG. 2  illustrates a light emitting device in accordance with the present disclosure with an x-axis direction. 
           [0011]      FIGS. 3A-3E  illustrate the corresponding structures fabricated by the manufacturing method step-by-step according to one embodiment of the present disclosure. 
           [0012]      FIG. 4  illustrates a light emitting device with a wavelength conversion material according to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0013]    The disclosure discloses a light-emitting diode structure with a single quantum well rod and its manufacturing method.  FIG. 1  shows a manufacturing process of the first embodiment. In  FIG. 1A , a first semiconductor layer  101  is formed on a substrate  100  by epitaxial growth. Then, as shown in  FIG. 1B , a dielectric layer  110  is formed on the first semiconductor layer  101 .  FIG. 1C  shows that the dielectric layer  110  is etched to form a plurality of holes  112  by lithography and etching techniques. Then, as shown in  FIG. 1D , using the MOCVD process to form a quantum well layer  103  through holes  112 . As shown in  FIG. 1E , a second semiconductor layer  102  is formed on the top of the quantum well layer  103 . The quantum well layer  103  includes a plurality of the quantum well rods  1031 , wherein each quantum well rod  1031  has a single quantum well. As shown in  FIG. 1F , a quantum well rod  1031  with a maximum width a (for example, if the quantum well rod is cylinder, the maximum width is the diameter of its circular cross-section) and a height b. The quantum well rod  1031  with only one single quantum well has no potential energy barrier to block the charged carriers. Therefore, electrons and holes can be evenly distributed in the quantum well rod  1031 , and the recombination efficiency is increased and thus the EQE droop is relieved. 
         [0014]    The disclosure discloses another embodiment of the present application. In addition to the above mentioned description, the maximum width a of the quantum well rods  1031  is less than or equal to 1 μm, and better to be less than or equal to 500 nm. The height b of the quantum well rods  1031  is greater than or equal to 50 nm, and better to be greater than or equal to 100 nm. Thus, in addition to improve the hole injection efficiency with the quantum well having no potential energy barrier, the geometry characteristics of quantum well rods  1031  also limit the movement of charged carriers (electrons and holes) along the axis (growth direction) of quantum well rods. When the first semiconductor layer  101  and the second semiconductor layer  102  has a voltage difference between them, the first semiconductor layer  101  and the second semiconductor layer generates a flow of electrons and holes between them. The electrons and holes flow in opposite directions to each other, for example, when the electron flows from the first semiconductor layer  101  to the second semiconductor layer  102 , the hole flows from the second semiconductor layer  102  to the first semiconductor layer  101 . The recombination of electrons and holes  102  in the rod generate photons. Because the geometry limitation of the quantum well rod  1031 , electrons and holes without potential energy barrier are restrained to the Z-axis (growth direction), as shown in  FIG. 2 . Therefore, the recombination efficiency of electrons and holes is greatly improved, thereby increasing the EQE. 
         [0015]    The material of the first semiconductor layer  101  and the second semiconductor layer  102  includes III-nitride compounds which includes but is not limited to aluminum gallium indium nitride (AlGaInN) series material, such as aluminum gallium nitride (AlGaN), gallium nitride (GaN) or indium gallium nitride (GaInN); aluminum gallium arsenide (AlGaAs) series material, such as arsenic gallium (GaAs), indium gallium aluminum phosphide; or (AlGaInP) series of materials such as gallium aluminum phosphide (AlGaP) or gallium phosphide (GaP). The material of quantum well rods  1031  includes III-nitride compounds which includes but is not limited to InGaN , GaN, AlGaInN, AlGaN, GaN), or GaInN. In another embodiment, the material is aluminum gallium arsenide (AlGaAs) series material, such as gallium arsenide (GaAs). 
         [0016]      FIG. 3  represents a manufacturing process of another embodiment. In  FIG. 3A , a substrate  100  is provided. Then forming a first semiconductor layer  101  above the substrate  100  by epitaxial growth. Then, as shown in  FIG. 3B , forming a quantum well layer  103  on the first semiconductor flayer  101 . As shown in  FIG. 3C , forming a mask layer  120  above the quantum well layer  103  by lithography technology, followed by etching technology to form a plurality of quantum well rods  1031  as shown in  FIG. 3D . Then, as shown in  FIG. 3E , forming a second semiconductor layer  102  on the quantum well layer  103  by MOCVD, MVPE, and so on. In this embodiment, the maximum width of quantum well rods  1031  may be less than or equal to 1 μm, or less than or equal to 500 nm. In this embodiment, the height b of quantum well rod  1031  can be greater than or equal to 50 nm, or greater than or equal to 100 nm. 
         [0017]      FIG. 4  represents another embodiment of the disclosure. A light-emitting diode  40  includes a first semiconductor layer  101 , a second semiconductor layer  102 , and a quantum well layer  103 , wherein the quantum well layers  103  includes a plurality of quantum well rods  1031 . The quantum well rods  1031  are surrounded by a wavelength conversion material  104 . The wavelength conversion material  104  fills the gap between the quantum well rods  1031  by electrophoretic deposition approach. The material of wavelength conversion material  104  can be II-VI group elements which in the form of particles or powder. When the electron and hole are combined in the quantum well rods  1031  and generate a light with first wavelength, the light with first wavelength further excites the wavelength conversion material  104  and converts partial of the light with first wavelength to a light with second wavelength. The light with first and second wavelength generates a mixture of light with third wavelength. The wavelength conversion material  104  can be a blue phosphor, yellow phosphor, green phosphor, or red phosphor. The material of wavelength conversion material  104  includes but is not limited to zinc selenide, zinc cadmium selenide, III-phosphide, III-arsenide, and III-nitride, and the combination thereof. 
         [0018]    It will be apparent to those having ordinary skill in the art that various modifications and variations can be made to the devices in accordance with the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure covers modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents. 
         [0019]    Although the drawings and the illustrations above are corresponding to the specific embodiments individually, the element, the practicing method, the designing principle, and the technical theory can be referred, exchanged, incorporated, collocated, coordinated except they are conflicted, incompatible, or hard to be put into practice together. 
         [0020]    Although the present application has been explained above, it is not the limitation of the range, the sequence in practice, the material in practice, or the method in practice. Any modification or decoration for present application is not detached from the spirit and the range of such.