Gallium-containing light-emitting semiconductor device and method of fabrication

Abstract

An LED comprising a light-generating semiconductor region having an active layer sandwiched between two confining layers of opposite conductivity types. A cathode is arranged centrally on one of the opposite major surfaces of the semiconductor region from which is emitted the light. An array of discrete gold regions are formed via transition metal regions on the other major surface of the semiconductor region at which is exposed one of the confining layers which is of n-type AlGaInP semiconductor material. The gold is thermally diffused into the confining layer via the transition metal regions at a temperature less than the eutectic point of gold and gallium, thereby creating an array of ohmic contact regions of alloyed or intermingled gold and gallium, which are less absorptive of light than their conventional counterparts, to a thickness of 20 to 1000 angstroms. After removing the transition metal regions and gold regions from the surface of the light-generating semiconductor region, a reflective layer of aluminum is formed so as to cover both the ohmic contact regions and the exposed surface portions of the AlGaInP confining layer. An electroconductive base-plate of doped silicon is then bonded to the reflective layer.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This is a continuation of Application PCT / JP2003 / 014890, filed Nov. 21, 2003, which claims priority to Japanese Patent Application No. 2002-348416 filed Nov. 29, 2002.BACKGROUND OF THE INVENTION [0002] This invention relates to a light-emitting semiconductor device, or light-emitting diode (LED) according to more common parlance, and more particularly to such devices employing gallium-containing compound semiconductors. The invention also concerns a method of making such light-emitting semiconductor devices. [0003] The LED has been known which has a light-generating semiconductor region grown on a substrate of electrically conducting material such as gallium arsenide. Typically, the light-generating semiconductor region has an active layer sandwiched between an n-type cladding or lower confining layer, which overlies the substrate, and a p-type cladding or upper confining layer. An anode is mounted centrally atop the upper confining lay...

AI Technical Summary

Benefits of technology

[0008] The present invention has it as an object to further enhance the efficiency of the light-emitting semiconductor device of the kind incorporating the gold-germanium-gallium ohmic contact regions, or, for a given intensity of light produced, to make the forward voltage of the device lower than hitherto.

[0017] Conversely, for a given output light intensity, the ohmic contact region or regions may be greater in surface area with respect to the area of the second major surface of the semiconductor region, to an extent corresponding to the increased amount of light reflected back through the ohmic contact regions. That is to say that the same output light intensity is obtainable if the ohmic contact region or regions are made greater than hitherto. Such larger ohmic contact region or regions lead to less resistance to current flow through the device, to less forward voltage, to less power loss, and hence to higher efficiency of light production.

Problems solved by technology

This known remedy is objectionable for a relatively high forward voltage required between anode and cathode as a result of additional resistance at the interface between light-generating semiconductor region and transparent baseplate.

The last cited prior art LED proved to possess its own weaknesses, however.

The gold-germanium-gallium ohmic contact regions were rather inconveniently absorptive of light by reasons of their germanium content and thickness in particular.

The total reflectivity of the ohmic contact regions and reflective layer was therefore as low as 30 percent or thereabouts, making it difficult for the LED to gain sufficiently high efficiency.

Another shortcoming concerned the morphology of the gold-germanium-gallium ohmic contact regions: Their surfaces were so uneven that difficulties were experienced in bonding the electroconductive baseplate thereto via the reflective layer.

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