Princeton University

School of Engineering & Applied Science

Novel Layered Semiconductor Quantum Structures in New Material Systems

Yu Song
Engineering Quadrangle J401
Thursday, July 10, 2014 - 2:30pm to 4:00pm

The dissertation focuses on the theory and the experimental implementation of novel phenomena and devices related to thin layered semiconductor quantum structures, especially in new material systems.
Non-equilibrium Green's function theory is employed for a profound understanding of the subband structure in layered semiconductors. A general model for handling the effects of the interface roughness in thin layered semiconductors is developed, which explains the experimentally observed energy shift and unusual broadening in the ISB transitions in III-nitride superlattices.
Based on quantitative theoretical knowledge, we explore quantum cascade (QC) structures in III-nitride material systems with large conduction band offsets and high longitudinal optical (LO) phonon energy. The first mid-infrared (mid-IR) intersubband (ISB) emission in III-nitride QC structures is demonstrated, as well as the first III-nitride QC detector grown by metal organic chemical vapor deposition. These results are important milestones in implementing QC structures in the III-nitride material system, which is highly expected to extend the wavelength range, improve the temperature performance and increase the response speed of ISB semiconductor devices.
Since it is very challenging to achieve ultra-short pulsed laser operation in ISB devices due to fast ISB scattering lifetime (sub-ps), an alternative route is explored. We study light emission from a Fe2+:ZnSe polycrystal with QC laser pumping. Photoluminescence is achieved, which effectively transfers energy stored in the upper state of the QC laser to the upper manifold of Fe2+:ZnSe with a 106 - 108 times longer lifetime.
To sum up, in this dissertation novel phenomena and devices related to thin layered semiconductor structures are studied from both the theoretical and the experimental perspectives. And the results pave the way for new realms of operation in ISB based detectors and lasers.