EAGER: A New Approach to Realize (ZnSe)x(GaAs)1-x Alloys for Light Emission and Other Photonics Applications

University Of California-Davis, Davis CA

Investigators

Abstract

Title: EAGER: A Single Materials System that Could Finally Realize Light Emitting Devices with Optimal Chromaticity Abstract Nontechnical Description: In spite of the tremendous progress made in the last 55 years in developing visible Light Emitting Diodes (LEDs) for applications that require red, green, and blue emitters, at least two different materials systems are still required to realize systems having only the approximate hue and colorfulness properties (chromaticity) that is required. This is a major problem because having to use two different materials technologies adds a large cost to the production of displays that have red, green, and blue elements (pixels), such as scoreboards at public arenas. Furthermore, the current technology does not produce optimal chromaticity in the display systems. Neither of these systems can efficiently produce the required "true" green color. Thus, the combination of high cost and non-optimal chromaticity has prevented the use of pixelated displays for color images for TV systems; modern TV systems use inexpensive white emitting LEDs as the light source to visualize the liquid crystal pixelated TV image. Therefore, it is the goal of this research to perform both fundamental materials science and construct exploratory devices that will realize a unified technology to reduce the manufacturing production costs and improve chromaticity for visible display applications. The broader implications of a successful outcome of this project are threefold. First, it will increase the breadth of the application markets for visible displays, especially advanced pixelated display systems, including TV systems. Second, it will add to the fundamental materials science and device engineering knowledge of a relatively unexplored materials system. Finally, low cost LEDs with optimal chromaticity will enable "tuned" white light sources without the current need to coat blue-emitting LEDs with phosphors and filtering. Technical Description: The goal of this proposal is to develop a lattice-matched, heterovalent compound semiconductor materials system and epitaxy technology to realize efficient and integrated LEDs that will cover the entire spectrum from near IR to blue wavelengths, especially "true green" (555 nm wavelength). The targeted materials system and epi-technology is (ZnSe)x(GaAs)1-x epilayers on ZnSe or GaAs substrates and Molecular Beam Epitaxy (MBE), respectively, and employs a novel method to develop homogeneous epilayers. The specific aims of this research are to 1) develop a recipe for the growth of ZnSe on GaAs based on the configuration of our MBE system, 2) identify the optimal epitaxial growth procedure of quaternary alloys of (ZnSe)x(GaAs)1-x, and 3) fabricate Double-Heterojunction (DH) devices with (ZnSe)x(GaAs)1-x composition tuned for "true green" LEDs. With the knowledge gained in this research, a single commercial materials system and a unified fabrication technology that can produce a wide spectral range of light emitting devices, laser, and solar concentrator chips can be realized. Equally important, the results are expected to have a positive translational impact because it is probable that success in unifying light emitters using a (ZnSe)x(GaAs)1-x system would have a huge impact on the photonics community both in industry and academia, especially those who would produce multi-colored pixel arrays. This in turn will open up new avenues for the community to explore both new heterovalent epitaxy principles and new applications that take advantage of integration of lattice-matched heterovalent direct band gap materials systems.