GaN-based light emitting-diode chip and a method for producing same

Abstract

An LED chip comprising an electrically conductive and radioparent substrate, in which the epitaxial layer sequence is provided on substantially the full area of its p-side with a reflective, bondable p-contact layer. The substrate is provided on its main surface facing away from the epitaxial layer sequence with a contact metallization that covers only a portion of said main surface, and the decoupling of light from the chip takes place via a bare region of the main surface of the substrate and via the chip sides. A further LED chip has epitaxial layers only. The p-type epitaxial layer is provided on substantially the full area of the main surface facing away from the n-conductive epitaxial layer with a reflective, bondable p-contact layer, and the n-conductive epitaxial layer is provided on its main surface facing away from the p-conductive epitaxial layer with an n-contact layer that covers only a portion of said main surface. The decoupling of light from the chip takes place via the bare region of the main surface of the n-conductive epitaxial layer and via the chip sides.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] Pursuant to 35 U.S.C. § 120, this application is a continuation application of U.S. application Ser. No. 10 / 258,340, filed on Oct. 22, 2002, which is the U.S. National Phase application of WIPO Application No. PCT / DE01 / 01003, filed on Mar. 16, 2001, which claims the benefit of foreign priority applications filed in Germany, Serial Nos. 100 26 255.4, filed May 26, 2000, and 100 20 464.3, filed on Apr. 26, 2000. The contents of the prior applications are incorporated herein by reference in their entirety.FIELD OF THE INVENTION [0002] The invention concerns a light-emitting diode chip and a method for fabricating the same. BACKGROUND OF THE INVENTION [0003] A fundamental problem in the fabrication of GaN-based light-emitting diode (LED) chips is that the maximum attainable electrical conductivity of p-doped layers, especially of p-doped GaN or AlGaN layers, is not sufficient, in conventional LED chips made of other material systems, to eff...

AI Technical Summary

Benefits of technology

[0008] The object of the invention is, first, to develop an LED chip of the kind described at the beginning hereof that offers improved current spread and whose additional production expenditure is kept to a minimum. A method of fabricating an LED component comprising such a chip is also to be provided.

[0010] The substrate advantageously serves here as a window layer that improves the decoupling of the radiation generated inside the chip. To optimize its thickness, the substrate is advantageously thinned, for example by grinding and / or etching, after the growth of the epitaxial layer sequence.

[0013] The particular advantage of such a so-called thin-film LED chip lies in the reduced, ideally nonexistent, absorption of radiation in the chip and the improved decoupling of radiation from the chip, especially due to the smaller number of interfaces with jumps in the refractive index.

[0014] Both of the LED chips according to the invention have the particular advantage that the lost-heat-producing region (especially the p-doped layer and the p-n junction) of the chip can be situated very close to a heat sink; the epitaxial layer sequence can be thermally coupled to a heat sink practically directly. This enables the chip to be cooled very effectively, thereby increasing the stability of the emitted radiation. The efficiency of the chip is also increased.

[0016] In the LED chip of the invention, the p-contact layer comprises, deposited on the p-side, a transparent first layer, and deposited thereon, a second, reflective layer. The contact layer can thus be optimized in a simple manner with regard to both its electrical and its reflective properties.

[0019] In a further preferred embodiment, the entire bare surface of, or a subarea of, the semiconductor body formed by the layer sequence is roughened. This roughening disrupts the total reflection at the decoupling surface, thereby advantageously further increasing the degree of optical decoupling.

Problems solved by technology

A fundamental problem in the fabrication of GaN-based light-emitting diode (LED) chips is that the maximum attainable electrical conductivity of p-doped layers, especially of p-doped GaN or AlGaN layers, is not sufficient, in conventional LED chips made of other material systems, to effect the spread of current over the entire lateral cross section of the chip, since the front contacts normally used in such chips are made to cover only a fraction of the front of the chip in order to bring about the highest possible decoupling of radiation.

Growing the p-type layer on an electrically conductive substrate, which would make it possible to impress a current over the entire lateral cross section of the p-type layer, does not furnish economically justifiable results.

The reasons for this are that fabricating electrically conductive lattice-matched substrates (e.g. GaN substrates) for the growth of GaN-based layers involves high technical expenditure, and growing p-doped GaN-based layers on non-lattice-matched substrates suitable for undoped and n-doped GaN compounds does not yield adequate crystal quality for an LED.

However, the first-cited proposal has the disadvantage that a substantial portion of the radiation is absorbed in the contact layer.

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