Patterned sapphire substrate, light-emitting diode element and its fabrication method

Abstract

A patterned sapphire substrate, a light-emitting diode (LED) device, and a method for fabricating the same are disclosed. By forming a plurality of trenches spaced apart by platforms on the surface of the epitaxial sapphire substrate, and controlling the width of each platform to be no less than 1.5 times the width of the adjacent trench, the defect density of the epitaxial film layer grown on the patterned sapphire substrate can be effectively reduced, thereby improving luminous efficiency. Furthermore, the LED device of this invention, by forming a current-confining layer on the P-type epitaxial layer corresponding to the orthographic projection range of one of the platforms on the patterned sapphire substrate, allows carriers to be confined to the low-defect-density platform region during injection into the P-type epitaxial layer, further reducing the leakage current of the LED device.

Claims

1. A patterned sapphire substrate, comprising: a sapphire substrate having an m-plane crystal plane and having a top surface and a bottom surface opposite to each other, and a plurality of trenches formed downward from the top surface, the trenches being distributed along a first direction and extending along a second direction orthogonal to the first direction, wherein any two adjacent trenches define a platform, and the width of any platform along the first direction is not less than 1.5 times the width of any trench, wherein... The sapphire substrate also has at least one alignment pattern formed downward from the top surface and having a predetermined alignment relationship with the trenches, and the width of the at least one alignment pattern is between 20 and 1000 µm.

2. The patterned sapphire substrate as described in claim 1, wherein, The width of any platform is 1.5 to 3.5 times the width of any trench.

3. The patterned sapphire substrate as claimed in claim 1 further includes a buffer layer formed on the top surface of the sapphire substrate and filling and covering the trenches and the platforms, wherein the buffer layer is coplanar with the surface opposite to the sapphire substrate.

4. The patterned sapphire substrate as described in claim 1, wherein, The depth of these trenches is between 1 and 2 µm, and the width is between 1.5 and 3 µm.

5. A light-emitting diode (LED) element, comprising: a patterned sapphire substrate as described in claim 1; a light-emitting unit formed on the patterned sapphire substrate, having an N-type gallium nitride (GaN) epitaxial layer, a quantum well layer, and a P-type GaN epitaxial layer sequentially formed from the top surface of the patterned sapphire substrate; an insulating layer covering the surface of the light-emitting unit; and an electrode unit having an N-type electrode and a P-type electrode passing through the insulating layer and respectively contacting and connecting with the N-type GaN epitaxial layer and the P-type GaN epitaxial layer, wherein... The P-type electrode has a current-confining layer that corresponds to the orthographic projection range of one of the platforms of the patterned sapphire substrate and is directly connected to the P-type gallium nitride epitaxial layer, and an extension electrode that extends from the current-confining layer through the insulating layer.

6. The light-emitting diode element as claimed in claim 5, wherein, The N-type gallium nitride epitaxial layer is semi-polar and has a (201) crystal plane.

7. A method for fabricating a light-emitting diode (LED) device, comprising: step a, providing a patterned sapphire substrate as described in claim 1; step b, sequentially epitaxially growing an N-type gallium nitride (GaN) epitaxial layer, a quantum well layer, and a P-type GaN epitaxial layer on the patterned sapphire substrate; step c, depositing a conductive layer made of a transparent conductive material on the surface of the P-type GaN epitaxial layer, removing a portion of the conductive layer by photolithography, and forming a current-limiting layer made of the transparent conductive material on the surface of the P-type GaN epitaxial layer, corresponding to the orthographic projection range of one of the platforms of the sapphire substrate; step d, etching downwards from the surface of the P-type GaN epitaxial layer to expose the N-type GaN epitaxial layer to form a platform region, and depositing metal in the platform region to form an N-type contact pad; step e, depositing an insulating material to form an insulating layer covering the N-type contact pad, the current-limiting layer, and the surface of the P-type GaN epitaxial layer. Step f involves removing a portion of the insulating layer using photolithography to form two openings that expose the N-type contact pad and the current-limiting layer; and step g involves forming an N-type extension electrode and a P-type extension electrode that fill the openings, contact the N-type contact pad and the current-limiting layer, and extend to the top surface of the insulating layer.

8. The method for fabricating a light-emitting diode element as described in claim 7, wherein, The trenches of the patterned sapphire substrate have a width between 1.5 and 3 µm. The patterned sapphire substrate also has at least one alignment pattern formed from the top surface downwards, having a predetermined alignment relationship with the trenches, and a width between 20 and 1000 µm. Step c is based on the alignment of the at least one alignment pattern to form the current confinement layer.

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