| Research Abstract |
In this project, aiming at the realization of a novel electron device we proposed for a possibility of ultra-high frequency amplifier utilizing the photon-assisted transition and beating of electron waves, we have done (i) establishment of the epitaxial growth of insulator/semiconductor heterostructures and thier application to resonant tunneling structure which is a part of the proposed device, and (ii) detailed observation of the photon-assisted tunneling which is one of the principles of the proposed device.
For the epitaxial growth, we chose CaF_2/Si and CaF_2/CdF_2 heterostructures with large band offsets, and established the growth condition of resonant tunneling structure with the ionization beam epitaxial technique. The quality of the epitaxial layers was then optimized and greatly improved by a selective growth method in which the epitaxial layers were formed in windows with a few hundred-nanometer size made on Si substrates with SiO_2 masks. Resonant tunneling diodes with hish
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reproducibility and large peak-to-valley ratio, at least 10, in the negative differential resistance were obtained at room temperature.
For the observation of the photon-assisted tunneling effect, we fabricated small area GaInAs/InAlAs triple-barrier resonant tunneling diodes integrated with patch antennas, and irradiated terahertz electromagnetic wave onto them. The antenna loss was considerably reduced by an optimized structure, and thus, clear photon-assisted tunneling with large incident power was achieved. The observed results were well explained by the photon-assisted tunneling with multi-photon process of stimulated emission and absorption The terahertz optical gain was deduced from the observed stimulated emission rate. Using these results, we performed theoretical analysis of amplification characteristics of the proposed three-terminal device, and showed that power amplification up to several terahertz is possible. Necessary structures for these characteristics were also designed. Less
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