The narrow gap III-V semiconductors, InAs/AlSb/GaSb and InSb, exhibit an array of extreme physical properties, from the lightest effective mass and largest nonparabolicity of III-V semiconductors to heterostructure conduction band offsets ranging from -0.15 to +2.0 eV. In this work, I present three spectroscopic techniques which exploit these unusual properties to provide new insight into the physics of these materials.
First, my measurement of cyclotron resonance in InAs/AlSb and InSb/AlInSb quantum wells was the first spectroscopic application of a new laser, the THz quantum cascade laser. The physical properties mentioned above put these materials into an experimentally accessible range, and InAs's high room temperature mobility and low temperature carrier density enabled us to explore a large temperature range. Previous investigations of other materials in limited temperature ranges had suggested what we confirmed: the cyclotron resonance effective mass increases with temperature, contrary to theoretical expectations.
Second, we applied time resolved cyclotron resonance to InSb quantum wells for the first time. Because of InSb's large effective g-factor and nonparabolicity, time resolved cyclotron resonance enabled us to monitor the carrier relaxation and recombination from each Landau- and Zeeman-quantized state directly in time. This unprecedented level of detail could be extended to longer times to probe spin-flip relaxation, a significant parasitic process in quantum computation.
Finally, I measured intersubband absorption in narrow InAs/AlSb quantum wells with widths from 10.5 to 1.8 nm. I observed the highest energy intersubband resonance in InAs/AlSb quantum wells: 650 meV at 77 K in a 1.8 nm well. I also performed detailed measurements of the temperature dependence of intersubband absorption and confirmed the correlation between the integrated intensity of intersubband absorption and the carrier distribution inferred from Shubnikov-de Haas and Hall measurements. Because of InAs/AlSb intersubband transitions' large accessible energy and temperature robustness, they are ideal candidates for resonant nonlinear optics. In particular, I discuss the potential of InAs/AlSb double quantum wells as a compact, room temperature, and coherent THz source. Such a source could revolutionize chemical sensing by providing convenient access to the strong fundamental vibrational fingerprints which all molecules have in the THz, potentially transforming applications from medicine to the military.