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Nitride semiconductor led improved in lighting efficiency and fabrication method thereofRelated Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Incoherent Light Emitter Structure, Active Layer Of Indirect Band Gap SemiconductorNitride semiconductor led improved in lighting efficiency and fabrication method thereof description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060208264, Nitride semiconductor led improved in lighting efficiency and fabrication method thereof. Brief Patent Description - Full Patent Description - Patent Application Claims
CLAIM OF PRIORITY [0001] This application claims the benefit of Korean Patent Application No. 2004-18597 filed on Mar. 18, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a nitride semiconductor Light Emitting Diode (LED) improved in lighting efficiency and a fabrication method thereof. In particular, the present invention relates to a nitride semiconductor LED, which is improved in lighting efficiency by using a reverse bias tunneling junction and/or lateral current spreading, and a fabrication method thereof. [0004] 2. Description of the Related Art [0005] In general, nitride semiconductors are used in LEDs for generating blue or green wavelength light. Such nitride semiconductors may be expressed by an equation of Al.sub.xIn.sub.yGa.sub.(1-x-y)N, wherein 0.gtoreq.x.gtoreq.1, 0.gtoreq.y.gtoreq.1 and 0.gtoreq.x+y.gtoreq.1. [0006] LEDs for generating green light are produced by using GaN semiconductors having a wide band gap of about 3.4 eV. A nitride semiconductor of for example GaN has a wide band gap, which acts as a problem in the formation of electrodes and ohmic contact structures. In more detail, there are problems in that contact resistance increased in a p-electrode region also raises the drive voltage while enhancing the heat generation of a diode. Although various schemes may be proposed as means for forming the ohmic contact structures, actually adoptable means are extremely restrictive because those regions forming ohmic contact structures also function as major light emitting surfaces, thereby bringing a critical requirement of allowing light from the active layer to pass through the major light transmitting surfaces. [0007] As a conventional technique satisfying such requirements, there is proposed U.S. Pat. No. 5,563,422, which is entitled "Gallium Nitride-Based III-V Group Compound Semiconductor Device and Method of Producing the Same" and assigned to Nichia Chemical Industries, Ltd. This document proposes a transparent electrode layer using a Ni/Au double layer, and a structure of a nitride semiconductor LED disclosed in this document is shown in FIG. 1. [0008] As shown in FIG. 1, a conventional nitride semiconductor LED 10 includes an n-doped GaN cladding layer 13, a GaN/InGaN active layer 15 of a Multiple Quantum Well (MQW) structure and a p-doped GaN cladding layer 17 formed in their order on a sapphire (AlO.sub.3) substrate 11, in which the p-doped GaN cladding layer 17 and the GaN/InGaN active layer 15 are removed in part to partially expose the top surface of the n-dope GaN cladding layer 13. The nitride semiconductor LED 10 also includes an n-electrode 19a formed on the n-doped GaN cladding layer 13 and an ohmic contact structure. The ohmic contact structure is constituted of a transparent electrode 18 of Ni/Au formed on the p-doped GaN cladding layer 17 and a p-bonding electrode 19b formed on the transparent electrode 18. The transparent electrode 18 is provided to improve contact resistance while ensuring transparency, and may be obtained via deposition of a Ni/Au double layer and subsequent heat treatment. [0009] However, according to the afore-described technique, the transparent electrode attached on the p-doped semiconductor layer causes relatively poor ohmic contact properties thereby increasing drive voltage. It is also difficult to improve brightness since only relatively low transparency metals such as Ni/Au are attached on the p-doped semiconductor layer owing to weak bonding force of the p-doped semiconductor layer with respect to metal. Furthermore, the n-doped GaN cladding layer shows relatively bad overvoltage resistance when bonded with the n-electrode. SUMMARY OF THE INVENTION [0010] The present invention has been made to solve the foregoing problems of the prior art and it is therefore an object of the present invention to provide a nitride semiconductor LED which is improved in lighting efficiency by using a reverse bias tunneling junction and a fabrication method thereof. [0011] It is another object of the present invention to provide a nitride semiconductor LED which is improved in lighting efficiency by using lateral current spreading and a fabrication method thereof. [0012] According to an aspect of the invention for realizing the object, there is provided a fabrication method of nitride semiconductor Light Emitting Diodes (LEDs), the method comprising the following steps of: [0013] (a) forming an n-doped semiconductor layer on a substrate; [0014] (b) forming an active layer on the n-doped semiconductor layer; [0015] (c) forming a p-doped semiconductor layer on the active layer; [0016] (d) forming a p+-doped semiconductor layer on the p-doped semiconductor layer; [0017] (e) implanting n-dopant ions into the p+-doped semiconductor layer to convert at least a portion of the p+-doped semiconductor layer into an n+-doped semiconductor layer so that the n+-doped semiconductor layer cooperates with a remaining region of the p+-doped semiconductor layer to form a reverse bias tunneling junction; and [0018] (f) mesa-etching a resultant semiconductor structure to the extent of exposing a partial area of the n-doped semiconductor layer. [0019] Preferably, the ion implantation step (e) may comprise: forming a SiO.sub.2 layer on the resultant semiconductor layer; etching the SiO.sub.2 layer to expose at least a portion of the p+-doped semiconductor layer; implanting n-dopant ions through the etched portion of the SiO.sub.2 layer; and removing the SiO.sub.2 layer via heat treatment. [0020] Preferably, the ion implantation step (e) implants n-dopants in high and low energy levels into an upper region of the p+-doped semiconductor layer to form an n+-doped semiconductor layer on the remaining region of the p+-doped semiconductor layer and an upper n-doped semiconductor layer on the n+-doped semiconductor layer, thereby realizing lateral current spreading. [0021] Preferably, the ion implantation step (e) may comprise: implanting n-dopant ions at a first energy level into an upper region of the n+-doped semiconductor layer to form an n+-doped semiconductor layer on the remaining region of the p+-doped semiconductor layer; and implanting n-dopant at a second energy level different from the first energy level into the upper region of the n+-doped semiconductor layer to form an upper n-doped semiconductor layer on the n+-doped semiconductor layer, thereby realizing lateral current spreading. Continue reading about Nitride semiconductor led improved in lighting efficiency and fabrication method thereof... 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