Room Temperature GaN Film Growth by UV Surface Plasmon-Mediated N2H4 Decomposition

Siying Peng Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California, USA Matthew Sheldon Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California, USA Wei-Guang Liu Materials and Process Simulation Center, California Institute of Technology, Pasadena, California, USA Andres Jaramillo-Botero Materials and Process Simulation Center, California Institute of Technology, Pasadena, California, USA William Goddard III Materials and Process Simulation Center, California Institute of Technology, Pasadena, California, USA Harry A. Atwater Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California, USA

We report growth of GaN films at room temperature facilitated by UV surface plasmon-mediated N2H4 decomposition to generate reactive nitride growth precursors. Conventional growth methods for GaN include CVD and MBE, which both require high temperatures (> 500 K) to create atomic nitrogen by thermally decomposing nitride precursor molecules. Alternatively, magnetron sputtering can be used to grow GaN at room temperature but the high ion kinetic energy limits the crystalline quality of the growing film. Our study is motivated by the fact that UV radiation can resonantly dissociate nitrogen bonds, through a pathway that neither produces species with high kinetic energy nor requires high temperatures. Ultraviolet surface plasmons are generated at a nanostructured aluminum surface where nitrogen precursors are adsorbed, and the resonantly excited surface plasmons generate dissociated nitrogen species that lead to GaN film growth. Additionally, because film growth can occur at lower temperatures, our method may open doors for new semiconductor materials such as indium-rich InGaN, which is normally hindered due to phase separation into InN and GaN at elevated growth temperatures.

For UV surface plasmon-mediated GaN growth, we identified N2H4 as a promising nitrogen precursor molecule. We have performed full wave simulation to design periodic aluminum nanostructure arrays, yielding a surface field enhancement of 25x at 248 nm which corresponds to the maximum absorption cross section for hydrogen abstraction from N2H4. We fabricated large area (3 mm x 9 mm) Al UV plasmonic nanostructures using nanoimprint lithography printing from a master stamp generated by e-beam lithography. Reflection spectroscopy characterization of these aluminum nanostructures showed enhanced absorption at 248 nm. In high vacuum ambient conditions at cryogenic temperatures, mass spectrometry indicated that UV surface plasmons enhance N2H4 dissociation by an overall factor of 6.2x. The calibrated gallium flux and surface plasmon generated nitrogen flux were introduced sequentially to enable layer by layer growth of GaN on gold. XPS of nitrogen 1s electrons confirms the Ga-N bond formation based similar binding energy distribution compared to that of a bulk GaN crystal. XRD characterization confirms nanocrystalline quality of the GaN film. EDS indicates partial oxidation of the Ga-N bond during film growth. Strategies to improve crystalline quality of the film as well as suppressing oxidation will be discussed.

speng@caltech.edu









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