Christopher McKitterick

This dissertation investigates a new scheme for the detection of terahertz (THz) photons. The vast majority of photons visible to outer space observatories occur in the far-infrared, but there do not yet exist detectors sensitive enough to accurately measure the faintest signals. I propose to use graphene, a single atomic layer of graphite, as the detecting element to observe these weak sources. As a result of its nano-scale dimensions, there are few charge carriers in graphene systems per unit area. Thus it is envisioned that the few charge carriers will be significantly heated by photon absorption. By measuring the increase of emitted blackbody radiation (Johnson noise) as a result of the heated charge carriers, ideally one would be able to measure even very weak THz signals.

After outlining the detection requirements that motivate the research, I describe the mechanisms which affect the sensitivity of graphene-based photodetectors. Then I describe measurements which probe the physical parameters of graphene to allow for accurate predictions of device performance. Chiefly, the studies focus on the electron-phonon cooling pathway, which has a substantial role in determining device sensitivity. I find that my results are consistent with theories for electron-phonon cooling in two separate regimes: cooling in the absence of disorder (i.e., infinite mean free path) and disorder-assisted scattering at low temperatures.

From the results of my studies on electron-phonon scattering, I make preliminary estimates of the performance of a prospective graphene photodetector using Johnson noise emission as its detection mechanism. I find that the outlook for using graphene as a single photon detector for THz photons is not promising. However, larger areas of graphene could be used to perform power measurements by averaging over the detection of thousands of arriving photons. The performance of the device is competitive with current state-of-the art detectors.