Light emitting semiconductor device and method for manufacturing

Abstract

The light emitting semiconductor device (1) of the present invention is made of nitrides of group III metals and comprises a layer structure comprising an n-type semiconductor layer (2), a p-type semiconductor layer (3), an active region (4) between the n-type semiconductor layer and the p-type semiconductor layer. The layer structure has a contact surface (5) defined by one of the n-type and p-type semiconductor layers and comprises further a reflective contact structure (6) attached to the contact surface. According to the present invention, the reflective contact structure (6) comprises: a first transparent conductive oxide (TCO) contact layer (13), having a poly-crystalline structure, attached to the contact surface (5) of the layer structure; a second transparent conductive oxide (TCO) contact layer (14) having an amorphous structure; and a metallic reflective layer (15) attached to the second TCO layer.

Description

FIELD OF THE INVENTION[0001]The present invention relates generally to light emitting semiconductor structures made of nitrides of group III metals. More precisely, the invention relates to reflective contacts used e.g. in vertical geometry Light Emitting Diodes (LEDs), and manufacturing thereof.BACKGROUND OF THE INVENTION[0002]Light emitting semiconductor devices like LEDs have a continuously growing role in different fields of everyday life. They have a great variety of applications e.g. in telecommunications, lighting, and display technology.[0003]From the material point of view, one dramatically expanding branch of today's LED technology is based on nitrides of group III metals like Gallium Nitride GaN, Aluminum Gallium Nitride AlGaN, Indium Gallium Nitride and the alloys thereof. These materials are found particularly suitable candidates for high brightness LEDs for e.g. lighting applications.[0004]In the intensive development of more and more efficient LED structures, one of t...

AI Technical Summary

Benefits of technology

[0011]Said structure of the reflective metal contact utilizing a two-layer intermediate TCO structure between the metallic reflective layer and the contact surface provides great advantages over the prior art solutions. Each of the two TCO layers has its own purpose. The polycrystalline material structure of the first TCO layer provides high optical transparency and low electrical resistivity. The second TCO layer of amorphous structure, for its turn, enables a strong adhesion to the metallic reflective layer.

[0012]In addition to the different crystal structures, also the accurate chemical compositions of the two layers can be optimized separately according to their different purposes. To take full advantage of this opportunity, in a preferred embodiment of the present invention, the chemical composition of the first TCO contact layer is selected to promote strong adhesion to the contact surface of the layer structure, good transparency, and high electrical conductivity of the first TCO contact layer, and the chemical composition of the second TCO contact layer is selected to promote strong adhesion of the metallic reflective layer to the second TCO contact layer. In other words, in this embodiment the properties of the two TCO layers are optimized separately according to their different purposes.

[0017]The metallic reflective layer can have a thickness of e.g. 20-1000 nm, however preferably at least 200 nm to ensure that no light is penetrated through the layer and thus to maximize the reflectivity of the reflective contact structure.

[0029]The manufacturing process according to the present invention is suitable for cost-effective mass production of light emitting devices in which up to several tens of wafers can be processed simultaneously.

Problems solved by technology

This configuration set up several limitations for the device operation.

In the first case, both adhesion strength and long-term stability of the structure are usually insufficient.

On the other hand, it increases optical losses through light absorption in the adhesion layer.

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