ABSTRACT

The scientific objective of this proposal is to develop and test artificial semiconductor nonlinear optical materials and semiconductor quantum cascade lasers based on indium-aluminum-gallium-nitride materials. The indium-aluminum-gallium-nitride materials system has fundamental advantages over the materials that were previously used for making quantum cascade lasers and artificial semiconductor nonlinear optical materials. In particular, indium-aluminum-gallium-nitride semiconductor lasers operating in the terahertz spectral range (frequencies in the range of 1-10 THz) are expected to be able to operate at room temperature, unlike semiconductor lasers previously demonstrated in other materials systems. Room-temperature terahertz semiconductor lasers will have a major transformative impact on the instrumentation operating in this frequency range. Indium-aluminum-gallium-nitride materials are also expected to enable the creation of a novel kind of nonlinear metamaterials for operation at the wavelengths used by fiber-optics telecommunication equipment with sub-1-picosecond response time. Two graduate students will be trained during the course of the program. The two principal investigators will also continue their annual participation in the National Science Foundation research experience for undergraduate program and in various K-12 outreach activities at their institutions.

Technical Description.
The objective of this proposal is to develop intersubband optoelectronic devices based on strain-compensated InGaN/AlGaN/GaN heterostructures grown on non-polar m-plane GaN substrates for operation in the short-wavelength infrared (wavelengths in the range 1.4-3 microns) and terahertz (wavelengths in the range 30-300 microns) regions of the electromagnetic spectrum. Current intersubband devices rely on materials with relatively low conduction band offsets (<1 eV) and low longitudinal optical phonon energies (~30-40 meV) that, respectively, prevent intersubband devices from operating in the short-wavelength infrared and limit the operation of terahertz quantum cascade lasers to cryogenic temperatures. GaN/AlGaN heterostructures grown on c-plane substrates have been previously investigated to overcome the abovementioned problems. GaN-based materials system offers conduction band offsets over 2 eV and have optical phonon energies of ~90 meV. However, strain-dependent piezo-electric fields make it virtually impossible to produce desired intersubband bandstructure in practical devices grown on c-plane substrates. Additionally, relatively small heterostructure thickness, limited by strain, and poor optical field confinement in the heterostructure prevented efficient light-matter interaction in devices reported previously. The proposed AlInGaN heterostructures on m-plane GaN substrates are free from strain-induced fields making reliable intersubband bandstructure design possible. Strain-compensation will be used to overcome critical thickness constrains in materials growth. The heterostructures will be further processed into double-metal plasmonic cavities using photoelectrochemical etching for substrate removal to enable efficient light-matter integration. Two types of intersubband devices will be investigated: double-metal waveguide THz QCLs and intersubband nonlinear metasurfaces for operation in the telecommunication spectral range. The former devices represent a viable path towards developing the first room-temperature electrically pumped semiconductor lasers in the THz spectral range, while the latter devices offer a path for developing intersubband metasurfaces with a giant nonlinear response for short-wavelength infrared.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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