Carrier and Spin Dynamics in Narrow Gap Parabolic Quantum Well Structures

Heterostructures with parabolic confinement potentials are important systems to study for many reasons. In a perfect Parabolic Quantum Well (PQW), the subbands are equally spaced and electron-electron interactions are virtually non-existent, allowing coupling of long-wavelength radiation only to the center-of-mass coordinate of the electron system. Narrow band PQW systems are well suited for THz devices because by careful design, one can tune the transition frequency, temperature stability, and narrow-band emission. In our studies, the parabolic confinement was created by an effective parabolic Al compositional gradient inside each well. We studied carrier/spin dynamics in an InSb/$Al_{x}In_{1-x}Sb$ multiple- PQW structure using several time resolved differential transmission schemes in the mid-infrared. Our results demonstrate the unique and complex dynamics in InSb heterostructures that can be important for electronic and optoelectronic devices.