Kabushiki Kaisha Toshiba

Toshiba Techno Center Inc.

Bridelux, Inc.

Zhen Chen

Yi Fu

Steve Lester

William E Fenwick

A strain release layer adjoining the active layer in a blue LED is bounded on the bottom by a first relatively-highly silicon-doped region and is also bounded on the top by a second relatively-highly silicon-doped region. The second relatively-highly silicon-doped region is a sublayer of the active layer of the LED. The first relatively-highly silicon-doped region is a sublayer of the N-type layer of the LED. The first relatively-highly silicon-doped region is also separated from the remainder of the N-type layer by an intervening sublayer that is only lightly doped with silicon. The silicon doping profile promotes current spreading and high output power (lumens/watt). The LED has a low reverse leakage current and a high ESD breakdown voltage. The strain release layer has a concentration of indium that is between 5&#xd7;10atoms/cmand 5&#xd7;10atoms/cm, and the first and second relatively-highly silicon-doped regions have silicon concentrations that exceed 1&#xd7;10atoms/cm.

LED that has bounding silicon-doped regions on either side of a strain release layer

A vertical GaN-based blue LED has an n-type GaN layer that was grown over a ZnS layer that in turn was grown directly on a silicon substrate. In one example, the ZnS layer is a transitional buffer layer that is 50 nm thick, and the n-type GaN layer is at least 2000 nm thick. Growing the n-type GaN layer on the ZnS buffer layer reduces lattice defect density in the n-type layer. The ZnS buffer layer provides a good lattice constant match with the silicon substrate and provides a compound polar template for subsequent GaN growth. After the epitaxial layers of the LED are formed, a conductive carrier is wafer bonded to the structure. The silicon substrate and the ZnS buffer layer are then removed. Electrodes are added and the structure is singulated to form finished LED devices.

LED on silicon substrate using zinc-sulfide as buffer layer

A vertical GaN-based blue LED has an n-type layer comprising multiple conductive intervening layers. The n-type layer contains a plurality of periods. Each period of the n-type layer includes a gallium-nitride (GaN) sublayer and a thin conductive aluminum-gallium-nitride (AlGaN:Si) intervening sublayer. In one example, each GaN sublayer has a thickness substantially more than 100 nm and less than 1000 nm, and each AlGaN:Si intervening sublayer has a thickness less than 25 nm. The entire n-type layer is at least 2000 nm thick. The AlGaN:Si intervening layer provides compressive strain to the GaN sublayer thereby preventing cracking. After the epitaxial layers of the LED are formed, a conductive carrier is wafer bonded to the structure. The silicon substrate is then removed. Electrodes are added and the structure is singulated to form a finished LED device. Because the AlGaN:Si sublayers are conductive, the entire n-type layer can remain as part of the finished LED device.

N-type gallium-nitride layer having multiple conductive intervening layers

Led that has bounding silicon-doped regions on either side of a strain release layer

A vertical GaN-based blue LED has an n-type GaN layer that was grown directly on Low Resistance Layer (LRL) that in turn was grown over a silicon substrate. In one example, the LRL is a low sheet resistance GaN/AlGaN superlattice having periods that are less than 300 nm thick. Growing the n-type GaN layer on the superlattice reduces lattice defect density in the n-type layer. After the epitaxial layers of the LED are formed, a conductive carrier is wafer bonded to the structure. The silicon substrate is then removed. Electrodes are added and the structure is singulated to form finished LED devices. In some examples, some or all of the LRL remains in the completed LED device such that the LRL also serves a current spreading function. In other examples, the LRL is entirely removed so that no portion of the LRL is present in the completed LED device.

LED having a low defect N-type layer that has grown on a silicon substrate

A buffer layer of zinc telluride (ZnTe) or titanium dioxide (TiO) is formed directly on a silicon substrate. Optionally, a layer of AlN is then formed as a second layer of the buffer layer. A template layer of GaN is then formed over the buffer layer. An epitaxial LED structure for a GaN-based blue LED is formed over the template layer, thereby forming a first multilayer structure. A conductive carrier is then bonded to the first multilayer structure. The silicon substrate and the buffer layer are then removed, thereby forming a second multilayer structure. Electrodes are formed on the second multilayer structure, and the structure is singulated to form blue LED devices.

Buffer layer for GaN-on-Si LED

A strain release layer adjoining the active layer in a blue LED is bounded on the bottom by a first relatively-highly silicon-doped region and is also bounded on the top by a second relatively-highly silicon-doped region. The second relatively-highly silicon-doped region is a sublayer of the active layer of the LED. The first relatively-highly silicon-doped region is a sublayer of the N-type layer of the LED. The first relatively-highly silicon-doped region is also separated from the remainder of the N-type layer by an intervening sublayer that is only lightly doped with silicon. The silicon doping profile promotes current spreading and high output power (lumens/watt). The LED has a low reverse leakage current and a high ESD breakdown voltage. The strain release layer has a concentration of indium that is between 5&#xd7;10atoms/cmand 5&#xd7;10&#xb0; atoms/cm, and the first and second relatively-highly silicon-doped regions have silicon concentrations that exceed 1&#xd7;10atoms/cm.

A laterally contacted blue LED device involves a PAN structure disposed over an insulating substrate. The substrate may be a sapphire substrate that has a template layer of GaN grown on it. The PAN structure includes an n-type GaN layer, a light-emitting active layer involving indium, and a p-type GaN layer. The n-type GaN layer has a thickness of at least 500 nm. A Low Resistance Layer (LRL) is disposed between the substrate and the PAN structure such that the LRL is in contact with the bottom of the n-layer. In one example, the LRL is an AlGaN/GaN superlattice structure whose sheet resistance is lower than the sheet resistance of the n-type GnA layer. The LRL reduces current crowding by conducting current laterally under the n-type GaN layer. The LRL reduces defect density by preventing dislocation threads in the underlying GaN template from extending up into the PAN structure.

Growing community of inventors

Pleasanton, CA, United States of America

Zhen Chen