T-rays, often called terahertz radiation or submillimeter waves, are loosely defined as the wavelengths from 30 µm to 1,000 µm, or the frequencies from 10 THz to 300 GHz. This non-ionizing radiation appears as a harmless alternative to x-rays in medical, biological and security screening. Current solutions in terms of coherent sources of T-rays either require cryogenic temperatures or are relatively bulky equipments based on optically-pumped materials. The solid-state recourse consisting of GaAs-based quantum cascade lasers presents an intrinsic limitation in operation temperature: The low energy of the longitudinal-optical (LO) phonon in arsenide compounds hinders laser emission beyond 180 K at 4 THz, and forces operation below the liquid nitrogen temperature (< 70 K) for frequencies below 1 THz. Overcoming this limitation requires a technology revolution through introduction of a new material system. This project aims at exploring a novel semiconductor technology for high-performance photonic devices operating in the T-ray spectral region. The advanced materials that we will investigate consist of nitride-based [GaN/Al(Ga,In)N] superlattices and nanowires, where we can profit from unique properties of III-nitride semiconductors, namely the large LO-phonon energy and the strong electron-phonon interaction. Our target is to adapt the quantum cascade design and fabrication technology to these new materials, characterized by intense internal polarization fields. Our project aims at pushing intersubband transitions in this material family to unprecendently long wavelengths, in other to cover the whole T-ray spectral gap with coherent solid-state sources operating at room temperature and above.
Fields of science
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