The goal of Prof. Mendez's lab is the discovery and elucidation of novel properties in semiconductor heterostructures which have potential applications in optoelectronics. We pursue this goal by studying the optical and electro-optical properties of quantum wells and superlattices, which we design and prepare in our laboratory using a modern technique of epitaxial deposition of thin films called molecular beam epitaxy (MBE). The nature of our work is interdisciplinary, covering physics, materials science, and electrical engineering.
Spectacular advances in atomic physics in the last few years have allowed to investigate the interaction of single atoms with the cavity in which they are contained, leading to the creation of a new field called cavity quantum electrodynamics. Recently it has been possible to mimic the atom-cavity interaction using semiconductor heterostructures. A quantum well formed by two different semiconductors is the analog of an atom, whereas a Fabry-Perot resonator, which takes the place of the cavity, can be created with dielectric mirrors made out of alternating semiconductor films of different index of refraction. The beauty of MBE is that it makes possible to build an almost perfect Fabry-Perot resonator with a quantum well in its middle. Our interest is on the study of the influence of the resonator on the emission properties of the quantum well, and on ways of modifying that influence. For instance, it has been predicted that the optical emission from the well could be enhanced or inhibited, depending on its exact position inside the resonator. Such an effect could be used to build semiconductor lasers with stimulated-emission threshold much lower than today's.
The application of an electric field can affect drastically the optical properties (such as emission, absorption, index of refraction) of semiconductor quantum wells and superlattices, since a field modifies energy levels and energy bands, as well as the electronic wavefunctions. In an isolated well, the effect, frequently called "quantum confined Stark effect," is double: the ground state-the most affected-is shifted to lower energies and its wavefunction is polarized toward the well barrier. In superlattices, the field breaks the energy minibands into distinct states (Wannier-Stark ladder) and the electronic wavefunctions are gradually localized in the individual wells that constitute the superlattice (Stark localization). We are applying those effects to produce new heterostructures that can act as optical switches, either by changing the wavelength or the polarization of the emitted radiation.
|
Postdoctoral fellow I. Wei Tao introducing a GaAs substrate in the growth chamber of a molecular beam epitaxy system to prepare a semiconductor heterostructure that later will be used in the study of the electronic properties of two-dimensional electron gases.* |
Faculty: Prof. Emilio E. Mendez (e-mail)
Technical Support: Ralph Ruf
Postdocs: I. Wei Tao, Carlos Pecharroman
Graduate Students: Joong-Kon Son, Jin Hua Li
Continue with the tour, or return to the Stony Brook Optics home page.