The mid- and far infrared are tantalizing regions of the electromagnetic spectrum, containing great information about thermal and chemical properties of objects and materials; however, semiconductor devices that emit, detect, and manipulate light in this range are often extremely difficult to use, especially at room temperature. Semiconductor devices have high sensitivity but require cryogenic temperatures and are limited by a fixed bandgap. Thermal detectors and emitters are often the best choices for high temperature operation but they have limitations when spectral selectivity is needed.
This presentation discusses both photon and electron states in the infrared. Photons can be manipulated by optical cavities even when the materials they interact with are spectrally uniform. Electron quantum states can be altered in real time using cavity effects of heterostructures on electron waves. Infrared cavities have dramatically different properties depending on their mode volume. The ultimate performance of a detector has been known for decades for large cavities, but as an infrared cavity becomes extremely small, the background noise behaves differently, leading to modified sensitivity. Quantum optical conditions such as the Purcell effect, can also become important. Just as interesting, the thermal phonon properties of devices are altered as we approach the nanoscale as well, affecting even the fundamental definition of what temperature means to such as device.
While resonant energies for photons are very frequently considered as “tunable” in real time, the same is seldom, if ever, said of electron states. However, the same principles that define discrete resonances for light in a cavity also define quantized energies for electrons in quantum wells. Therefore mechanical manipulation of a quantum well barrier should change the energy states of an electron in a way analogous to the resonant frequencies of an optical cavity. The end of the talk describes how heterostructures coupled across a position-dependent gap can tune electron states in much the same manner that optical cavities couple to control photon states. This technique has dramatic implication in the infrared, where both the gain and absorption of materials can be controlled over a wide range, limited only by thermal broadening and band offsets.