N131-068 TITLE: Materials Development of Periodically Oriented Gallium Nitride (PO-GaN)

TECHNOLOGY AREAS: Information Systems, Materials/Processes, Electronics

OBJECTIVE: Develop growth of Gallium Nitride (GaN) wafers for periodically oriented, quasi-phase matched, nonlinear frequency conversion.

DESCRIPTION: Periodically Oriented Gallium Nitride (PO-GaN) has recently been developed for nonlinear frequency conversion of laser systems. PO-GaN offers a broader transparency range (0.39 - 6 �m) and better thermo-optic properties than any other nonlinear optical (NLO) material. Current laser technology is fundamentally limited by the useful transmission range of nonlinear optic materials. Nonlinear crystals such as BBO, KTP, and LiNbO3 have long been the standards from the ultraviolet (UV) to the near-infrared (IR) but their useful transparency range ends below 4�m. For longer wavelength sources NLO materials like ZGP, AgGaSe, and GaAs have been developed but these are incompatible with mature 1.0 and 1.5�m laser system. No current material will support conversion from UV to the mid-IR.

The potential for PO-GaN nonlinear optic devices is enabled by wafers grown on c-axis material with micron wide inversion domains between the gallium and nitride polarity. Currently, simultaneous growth of both polarities is a challenge that restricts overall thickness and quality. Growth of transparent high optical quality PO-GaN in thickness of several millimeters is desired for integration into advanced frequency agile laser systems. Goals for the PO-GaN growth would be for: low optical absorption and scattering (< 0.1 cm^-1), high-fidelity reproduction of pattern domains, and rapid growth of 1 millimeter thickness on centimeter scale wafers. Hydride vapor phase epitaxy (HVPE) has been demonstrated as a leading growth technique to deliver high growth rate epitaxial films needed to achieve millimeter thick films with acceptable optical quality.

PHASE I: Determine dependency of growth rate, defect generation, and impurity incorporation into periodically oriented growth of gallium nitride in a high growth rate process such as HVPE. Determine technical feasibility of dual-polarity c-axis gallium nitride growth. Develop approaches for balanced polarity growth rates leading to millimeter thickness of periodically oriented gallium nitride. Characterize materials properties to establish potential for utility in nonlinear optic devices.

PHASE II: Develop processes for extended millimeter growth of dual-polarity gallium nitride with low free carrier densities. Fabricate PO-GaN wafers with periodic polarity reversal for quasi-phase matched nonlinear frequency conversion. Then, conduct an evaluation of wafer optical quality and test nonlinear conversion of near-infrared laser system. Develop prototype PO-GaN devices for nonlinear conversion and quantify device efficiency and bandwidths.

PHASE III: Develop growth processes for commercializing PO-GaN wafer material for high power, broadband frequency conversion. Process improvements should target increase wafer diameter, growth rate, and compatibility with production process. Develop a partnership with the laser system integrator to make high quality PO-GaN material for DoD and commercial applications.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Broadband nonlinear optical devices enabling frequency conversion over the targeted range (0.39 - 6 �m) offer the potential for broad impact across several commercial applications. High interest applications include replacing the LiNbO3 devices in imaging devices, medical illumination, gas sensors and biochemical detectors.

REFERENCES:
1. Abe, Makoto, Hiroaki Sato, Ichiro Shoji, Jun Suda, Masashi Yoshimura, Yasuo Kitaoka, Yusuke Mori, and Takashi Kondo. 2010. "Accurate Measurement of Quadratic Nonlinear-Optical Coefficients of Gallium Nitride," Journal of the Optical Society of America" B 27, 2026-2034. http://dx.doi.org/10.1364/JOSAB.27.002026

2. Chowdhury, Aref, Hock M. Ng, Manish Bhardwaj, and Nils G. Weimann. 2003. "Second-Harmonic Generation in Periodically Poled GaN," Applied Physics Letters" 83, 1077. http://dx.doi.org/10.1063/1.1599044.

3. Hite, J.K., N.D. Bassim, M.E. Twigg, M.A. Mastro, F.J. Kub, C.R. Eddy, Jr. 2011. "GaN Vertical and Lateral Polarity Heterostructures on GaN Substrates." Journal of Crystal Growth." 332, 43-47.
DOI: 10.1016/j.jcrysgro.2011.08.002.

4. Katayama, Ryuji, Yujiro Fukuhara, Masahiro Kakuda, Shigeyuki Kuboya, Kentaro Onabe, Syusai Kurakawa, Naoto Fujii, and Takashi Matsuoka. 2012. "Optical Properties of the Periodic-Inverted GaN Waveguides." SPIE Quantum Sensing and Nanophotonic Devices, Ed. M. Razeghi, E. Turnie, and G. Brown, Vol. 8268. DOI: 10.1117/12.909831.

5. S. R. Bowman, S. O'Connor, N. Condon, J. R. Meyer, I. Vurgaftman, C. Eddy, J. Hite, F. Kub, and J. Freitas, "Nonlinear Optical Devices Based on Gallium Nitride," SPIE Defense, Security and Sensing, April 2012. http://spie.org/app/program/index.cfm?fuseaction=conferencedetail&conference=8381

6. Hite, Jennifer K., Mark E. Twigg, Nabil D. Bassim, Michael A. Mastro, Jaime A. Freitas, Jr., Jerry R. Meyer, Igor Vurgaftman, Shawn O'Conner, Nicholas J. Condon, Francis J. Kub, Charles R. Eddy, Jr., and Steven R. Bowman. 2012. "Development of Periodically Oriented Gallium Nitride." Paper Presented at Conference of Lasersand Electro-Optics, San Jose, CA., May 6, 2012.

7. Hite, Jennifer K., Mark Twigg, Michael Mastro, Jaime Freitas, Jr., Jerry Meyer, Igor Vurgaftman, Shawn O'Connor, Nicholas Condon, Fritz Kub, Steven Bowman, and Charles Eddy, Jr. 2012. "Development of Periodically Oriented Galliumnitride for Non-Linear Optics" to appear in Optical Materials Express Vol. 2 (2012).

KEYWORDS: Gallium Nitride, Periodically Poled, Nonlinear Optics, Frequency Conversion

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