Design, fabrication and characterization of high-performance terahertz quantum cascade lasers

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Electromagnetic waves in the terahertz frequency range (1-10 THz, 1THz = 1E12 Hz) have attracted intense interest because of their potential for many important applications: bio-chemical species detection, astronomical spectroscopy, terahertz imaging and optical wireless communication, to name a few. Application progress of terahertz technologies has been hampered by the lack of compact, low-energy-consumption, solid-state based and easily-operational terahertz sources and detectors. The situation has started to change recently, particularly after the invention of the first semiconductor quantum cascade laser working in the terahertz frequency range reported in 2002. The development of terahertz quantum cascade lasers has proceeded rapidly, nevertheless, there are still many technical challenges to further improve device performance. Among them, to achieve room-temperature lasing and high-power operation of terahertz quantum cascade lasers might be the biggest challenge. This proposed project will tackle the technical challenges by means of combined experimental and theoretical approaches. The objectives of the proposal include 1) to develop a comprehensive knowledge base on the underlying physics of intersubband transition and carrier dynamics in the quantum semiconductor heterostructures; 2) to develop a simulation package that can numerically calculate the important parameters of the quantum heterostructures and the overall performance of the quantum cascade lasers for comparison to experimental results; 3) to explore new quantum structures (such as a structure based on double phonon relaxation for carrier injection and extraction) that could outperform the existing quantum active-region designs in order to push higher the operating temperature; 4) to fabricate and characterize quantum cascade lasers with new structures and to apply the devices for practical applications. This research will provide a broad base of new knowledge in the THz frequency range with potential impacts in the areas of telecommunication, biological and medical sciences and security. It also brings in excellent training opportunities for HQPs to acquire strong photonic knowledge and highly-demanded hands-on skills.