UNIROYAL produces MOCVD epiwafers suitable for use in LED device fabrication. Like all semiconductors, compound semiconductors start with substrates machined from crystaline boules. Such substrates are grown, sliced, thinned and polished by our vendors to UNIROYAL’s specific and exacting requirements. Current substrates utilized by UNIROYAL include: Sapphire for InGaN and Gallium Arsenide (GaAs) for AlInGaP products.

Sapphire For InGaN: Two-inch diameter C-axis surface-oriented (also called 0-degrees) Czochralski (CZ) grown sapphire (Al2O3) sub-strates are used for UNIROYAL InGaN on Sapphire LED production. CZ sapphire substrates provide a very high quality crystaline structure, dielectric isolation, and uniform dielectric constant, in addition to excellent physical and optical properties, which make them the cost-effective choice for the company’s InGaN LED products.

The resulting epiwafers produced on sapphire incorporate proprietary buffer layer(s), specular GaN films (n- and p-type), Multiple-Quantum Well (MQW), a semiconductor structure that exhibits reduced dislocation densities, high conductivity and a homoepitaxial growth surface. Up to this point, the brightest InGaN LEDs are p-n junctions grown on electrically insulating sapphire substrates.

GaAs For AlInGaP: Single-Crystal n-type conducting 3" diameter GaAs substrates are used to produce AlInGaP material system LEDs for lattice matching over the entire Al, Ga, composition range. This enables high quality LEDs from the Red to Yellow-Green hues. With energy gaps greater than approximately 2.25 eV (~560 nm), AlInGaP becomes an indirect gap, separate confinement heterostructure (SCH), light-emitting semiconductor.

The different band gaps of the respective materials localize the electron or hole carriers in specific layers. The resultant EPI and LED die products feature Distributed Bragg Reflector (DBR), Multiple-Quantum Well (MQW), and a Gallium Phosphide window layer composition.

MOCVD growth of crystaline compound semiconductor structures occurs at high temperature (>1000 ºC) via chemical reactions causing the vapor epi-layer substance atoms to be diffused onto the substrate material. The reactions involve “snapping” and/or“ settling” the atoms into their location on the crystal substrate. Deposition occurs between metalorganic precursors and hydride gasses on a hot substrate surface. The result is a uniform distribution of atoms, layer upon layer.

Hetero-Epitaxy is the core competency of UNIROYAL. The technology used by the company has a long history of success and has been reduced to high-volume production practices at its Tampa, Florida facility. Precise particle control is achieved by elimination of gas phase pre-reactions, and the use of thermophoresis, to keep particles from reaching the wafer surface. Wafer-to-wafer, batch-to-batch reproducibility of MOCVD epitaxial growth is constantly monitored with a wide array of test processes and post growth characterization tools to ensure the most consistent results everyday.

UNIROYAL MOCVD epiwafers yield the device fabrication user better results in terms of material quality: Finished epiwafers exhibit high uniformity consistently, as well as end device fabricated LEDs that are not only easier to package but provide better electro-optical performance results.