This disclosure relates to a light-emitting diode and a manufacturing method thereof, and more particularly to a light-emitting diode which exhibits a reduced degree of bow, and a manufacturing method thereof.
A light-emitting diode (LED) is a solid-state lighting device, which is first introduced in 1962, and which is made of semiconductor materials. At that time, LEDs could only emit red light having a relatively low luminance, and were only used in simple applications, such as signal lights and display panels. With advancement of technology, LEDs which can emit monochromatic lights having different colors have been developed. Until now, LEDs capable of emitting lights that have wavelengths within the visible light range, the infrared light range, and the ultraviolet (UV) light range and that have a significantly improved luminance, are widely used in various complicated applications, such as liquid crystal displays, decoration lights for televisions, lighting devices, and so on.
Among the currently available LEDs, an ultraviolet LED (UV LED) is capable of transforming electrical power directly into UV light. With the advancement of technology, UV LEDs have bright prospects in the biomedical field, identification of counterfeits, air or water purification, computer data storage, military, etc. In addition, UV LEDs have attracted increasing interest in the field of lighting, since the UV LEDs can excite phosphors having RGB colors to emit lights having different colors that are mixable with one another to form white light.
In recent years, the UV LEDs have replaced mercury lamps due to advantages such as increased power, elongated service life, and smaller size. In addition, the Minamata Convention on Mercury becomes effective in 2020, which may speed up large-scale application of the UV LEDs.
Referring to
As shown in
Therefore, there is still a need to develop a UV LED which is free of the convex bow, and a method for manufacturing the same.
Therefore, an object of the disclosure is to provide a light-emitting diode (LED) and a method for manufacturing the same that can alleviate or eliminate at least one of the drawbacks of the prior art.
According to the disclosure, the LED includes a substrate, an epitaxial layered structure, and a strain tuning layer. The epitaxial layered structure includes a buffer layer, an N-type cladding layer, an active layer, and a P-type cladding layer formed on the substrate in such order. The active layer includes a multiple quantum well structure. The strain tuning layer is disposed between the N-type cladding layer and the active layer, and has a lattice constant that is smaller than that of the N-type cladding layer.
According to the disclosure, the method for manufacturing the abovementioned LED includes the steps of:
Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiments with reference to the accompanying drawings, in which:
Before the disclosure is described in greater detail, it should be noted that where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics.
Referring to
The substrate 201 may be a flat substrate or a patterned substrate, and may be made of a material including, for example, but is not limited to, sapphire, silicon, silicon carbide (SiC), and gallium nitride (GaN). In this embodiment, the substrate 201 is a sapphire substrate.
The epitaxial layered structure 20 includes a buffer layer 202, an N-type cladding layer 203, an active layer 205, and a P-type cladding layer 207 formed on the substrate 201 in such order.
The buffer layer 202 may be made of an aluminum nitride (AlN)-based material. The N-type cladding layer 203 is configured to provide electrons for radiative recombination in the active layer 205, and may be made of an aluminum gallium nitride (AlGaN)-based material. The P-type cladding layer 207 is configured to provide electron holes. The active layer 205 is the main region in which electrons from the N-type cladding layer 203 and holes from the P-type cladding layer 207 undergo radiative recombination to emit light. For example, the active layer 205 is configured to emit light having an emission wavelength ranging from 210 nm to 320 nm (i.e., violet light).
When the lattice-mismatch-induced strain between the buffer layer 202 and the N-type cladding layer 203 is not relaxed, such strain may cause formation of a bow, which might result in a great deviation of surface temperature of the active layer 205, thereby lowering uniformity of light emitted from the resultant LED.
Therefore, the strain tuning layer 204 is disposed between the N-type cladding layer 203 and the active layer 205, and has a lattice constant that is smaller than that of the N-type cladding layer 203, so as to reduce the lattice-mismatch-induced strain, thereby improving light uniformity. In certain embodiments, the lattice constant of the strain tuning layer 204 is also smaller than those of the active layer 205 and the P-type cladding layer 206.
In this embodiment, the strain tuning layer 204 as made of a single material represented by AlxGayIn(1−x−y)N, in which 0.7≤x≤1, 0≤y≤0.3, and 0.7≤(x+y)≤1, and has a thickness ranging from one atomic layer (e.g., 0.1 nm) to 100 nm. By formation of the strain tuning layer 204 made from a single material, the lattice-mismatch-induced strain can be reduced, while uniformity of electric current in the LED may also be improved.
Alternatively, the strain tuning layer 204 may be made of a plurality of materials represented by the chemical formula of AlxGayIn(1−x−y)N, in which 0.70≤x≤1, 0≤y≤0.3, and 0.7≤(x+y)≤1, and the materials are different in at least one of x and y. In certain embodiments, x≥0.95. Example of the materials may include, but are not limited to, Al0.7Ga0.3In0.1N, Al0.75Ga0.3In0.05N, Al0.8Ga0.15In0.05N, Al0.85Ga0.1In0.05N, Al0.9Ga0.05In0.05N, Al0.98Ga0.01In0.03N, and combinations thereof. By flexibly controlling aluminum contents (i.e., x) and gallium contents (i.e., y) or the materials for making the strain tuning layer 204, a different degree of the bow can be reduced.
In certain embodiments, the strain tuning layer 204 is doped with an N-type dopant in a doping concentration ranging from 1×1017 cm−3 to 5×1016 cm−3. With such doping, a contact resistance between the strain tuning layer 204 and the N-type cladding layer 203 and that between the strain tuning layer 204 and the active layer 205 may be further lowered, thereby reducing heat generation of the epitaxial structure and reducing an amount of electric current required to be applied.
In certain embodiments, the strain tuning layer 204 directly contacts the N-type cladding layer 203 and the active layer 205, so as to more effectively tune and relax the strain between the N-type cladding layer 203 and the active layer 205, thereby reducing a degree of the bow.
The LED may further include an electron blocking layer 206 which is disposed between the active layer 205 and the P-type cladding layer (207). The electron-blocking layer 206 is configured to prevent the electrons in the active layer 205 from leaking into the P-type cladding layer 207, so as to improve a light extraction efficiency of the LED.
Referring to
Referring to
In step S11, referring to
To be specific, the buffer layer 202 made of an AlN-based material is formed on the substrate 201 using a metal organic chemical vapor deposition (MOCVD) process. As shown in
In step 612, referring to
In step S13, referring to
In step S14, referring to
Referring to
In sum, by formation of the strain tuning layer 204, which is made of AlxGayIn(1−x−y)N and which has an aluminum content of at least 70 mol %, be the N-type cladding layer 203 and the active layer 205, the degree of bow formed due to the lattice-mismatch-induced strain between the buffer layer 203 and the N-type cladding layer 205 may be greatly reduced, so as to prevent deviation of the surface temperature of the active layer 205 (i.e., achieving an even temperature distribution), thereby improving the wavelength uniformity of light emitted from the LED according to this disclosure
In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent, however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details.
It should also be appreciated that reference throughout this specification to “one embodiment,” “an embodiment,” an embodiment with an indication of an ordinal number and so forth means that a particular feature, structure, or characteristic may be included in the practice of the disclosure. It should be further appreciated that in the description, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects, and that one or more features or specific details from one embodiment may be practiced together with one or more features or specific details from another embodiment, where appropriate, in the practice of the disclosure.
While the disclosure has been described in connection with what are considered the exemplary embodiments, it is understood that this disclosure is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.
Number | Date | Country | Kind |
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201810144122.6 | Feb 2018 | CN | national |
This application is a bypass continuation-in-part (CIP) application of PCT International Application No. PCT/CN2019/073485, filed on Jan. 28, 2019, which claims priority of Chinese Invention Patent Application No. 201310144122.6, filed on Feb. 12, 2018. The entire content of each of the International and Chinese patent applications is incorporated herein by reference.
Number | Date | Country | |
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Parent | PCT/CN2019/073485 | Jan 2019 | US |
Child | 16986563 | US |