Gallium nitride (GaN)-based wide bandgap semiconductors are very important material systems for fabrication of photon emitters in a wide range of wavelengths. In particular, the light emitters in ultraviolet (UV), blue, and green wavelengths have been developed and demonstrated in recent years. Besides these UV and visible light emitters, the unique properties of a GaN material system such as large exciton energy and large LO phonon energy, have been proposed as a very suitable material candidate for realization of various photon emitters such as single-photon emitters, LEDs, vertical cavity surface emitting lasers (VCSELs), and quantum cascade lasers (QCL) at room temperature.

GaN-based quantum confined structures and nanostructures for control of photon emission have been developed, as well as various blue and UV emitters including the high-efficiency blue LEDs and blue VCSELs. In addition, a GaN-based quantum cascade device has been developed for generation of THz emission. All of these GaN-based photon-emitting devices are mostly grown on a foreign substrate such as sapphire, which has large lattice mismatched with GaN. As a result, there are defects in the grown nanostructures such as multiple quantum-well (MQW) structure for devices such as QCLs, LEDs, and VCSELs when the structures are grown by conventional MOCVD epitaxial growth method.

This work resulted in the development of a new epitaxial growth approach to reduce the defect density, improve epi-layer quality, and achieve better thickness control by using atomic layer deposition technique to grow MQW and various nanostructures for application in QCLs, LEDs, and VCSELs.

A viable new epitaxial growth technique was established with better thickness control, low defect density, and high-quality epitaxial film for use in growth of photonic emitters. The precision control of epitaxial layer thickness and composition are critical to GaN-based photon-emitter device performance. The understanding of the optical characteristics and structural properties of the grown structures is important for refinement and optimization of device design and growth techniques for fabrication of functional photon-emitting devices.

This work was done by Shing-Chung Wang of National Chiao Tung University for the Asian Office of Aerospace Research and Development. For more information, download the Technical Support Package (free white paper) at under the Photonics category. AFRL-0152

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Development of GaN-Based Nanostructure Photon Emitters

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This article first appeared in the June, 2010 issue of Defense Tech Briefs Magazine.

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