Nanowire heterostructures for intersubband lasers

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The objective of this research is to investigate quantum-dots grown within semiconductor nanowires for terahertz lasers that operate at room-temperature. Semiconductor quantum-dot materials are excellent candidates for intersublevel detectors and emitters because of their dramatic suppression of electronic energy relaxation assisted by optical-phonon scattering. A collaborative research effort will proceed in three stages: (i) rational growth of axial and core/shell heterostructures in nanowires for the formation of coupled-quantum dots, (ii) measurement and characterization of nanowire intersublevel absorption using infrared spectroscopy, and (iii) investigation of nanowire quantum-dot superlattices for electroluminescence and stimulated emission. The intellectual merit is the use of nanowire quantum-dots for intersublevel cascade lasers, which are expected to solve a fundamental limitation of conventional planar THz quantum-cascade lasers, where non-radiative phonon-assisted relaxation prevents room temperature operation. Selective-area MOCVD epitaxy without metal catalysts will be used to grow high-aspect ratio InGaAs/GaAs semiconductor nanowires using lithographically defined oxide growth masks, with embedded axial quantum dots for efficient dot-to-dot tunneling transport. The broader impacts are the development of a class of low-dimensional III-V semiconductor nanomaterials with highly engineerable quantum-electronic properties. This work will advance terahertz materials and technology, where sources and detectors are desired for sensing, imaging, and spectroscopy. The program will also integrate education and research in training of undergraduate/graduate students through laboratory research participation, complementary coursework development, and scientifically focused community K?12 involvement. A plan is in place for focused recruiting of undergraduate student researchers through student underrepresented minority societies and the UCLA Center for Engineering Excellence and Diversity.