At present, localized surface plasmon resonance (LSPR) is considered one of the most promising strategies for controlling surface chemistry with hot charge carriers4,5,6. LSPR is the collective oscillation of metal electrons that can be excited by incident light at the interface between a metal nanoparticle and a dielectric (or semiconductor) environment. During decay, LSPR can generate a significant flux of hot electrons and holes with excess energies of several electron volts. In clean metals, plasmon-induced charge carriers can be injected into the adsorbate to drive a photochemical reaction or they disappear as a result of thermalization (Fig. 1a). To reduce the recombination rate of the hot carriers and thereby increase the efficiency of the metal nanoparticles as catalysts, a Schottky contact can be used, which is created by depositing metal nanoparticles on a semiconductor surface7,8,9,10,11. Much work has been done studying plasmon-induced reactions of various types ranging from the simplest dissociation of molecules4,12 to more complex surface reactions13,14,15,16,17,18,19,20. In particular, a number of studies14,21,22,23,24,25 have shown a significant improvement in the efficiency of different catalysts for the hydrogen evolution reaction (HER) caused by the generation and transfer of hot electrons. A more detailed review of hot-electron-driven chemistry can be found in a recent paper by Wei and co-workers7. However, because of its complexity, the detailed mechanism for energy transfer from a plasmonic nanoparticle to a chemisorbed molecule remains poorly understood15,26. The task is further complicated by the fact that catalysts based on LSPR are often multicomponent core-shell or antenna-like nanostructures containing both plasmonic and catalytic materials15,27. The properties of such nanostructures can change over the course of a photocatalytic reaction because of the presence of adsorbates26,28,29. Therefore, further progress in studying the chemistry of hot-charge carriers requires the development of new research methods that include these factors.
The work described in this paper is part of a systematic study of ohmic contact strategies for GaN-based semiconductors. Gold contacts exhibited ohmic behavior on p-GaN when annealed at high temperature. The specific contact resistivity (ρc) calculated from TLM measurements on Au/p-GaN contacts was 53 Ω cm2 after annealing at 800 C. Multilayer Au/Mg/Au/p-GaN contacts exhibited linear, ohmic current-voltage (I-V) behavior in the as-deposited condition with ρc = 214 Ω cm2. The specific contact resistivity of the multilayer contact increased significantly after rapid thermal annealing (RTA) through 725 C. Cross-sectional microstructural characterization of the Au/p-GaN contact system via high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during high-temperature treatments, which coincided with the improvement of contact performance. In the as-deposited multilayer Au/Mg/Au/p-GaN contact, the initial 32 nm Au layer was found to be continuous. However, Mg metal was found in direct contact with the GaN in many places in the sample after annealing at 725 C for 15 s. The resultant increase in contact resistance is believed to be due to the barrier effect increased by the presence of the low work function Mg metal.
metal semiconductor contacts rhoderick pdf 15
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