Browsing by Author "Laakso, Sampo"

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Coupled electron-hole transport phenomena in double-gate silicon
(2010) Laakso, Sampo
School of Electrical Engineering | Master's thesis
In this Thesis, coupled transport phenomena between two-dimensional electron and hole gases in double-gate silicon field-effect transistor devices are studied. These studies are enabled by an electron-hole bilayer that is induced into 22 nm thick silicon channel by strong push-pull double-gate voltage. We focus on two phenomena in this electron-hole bilayer system. The first explored phenomenon is electron-hole drag effect, where momentum transfer between the electron and hole gases leads to a finite interlayer transresistance. This so-called drag resistance is measured as a function of temperature and charge carrier density, mainly at cryogenic temperatures and from low to moderate carrier densities. A numerical model is then applied in attempt to identify the underlying physical processes. The results support the view that the phenomenon is caused mainly by interlayer Coulomb interactions between electrons and holes. This is known as the Coulomb drag phenomenon. In addition, the disorder inherent to the system is found to significantly affect the results. The second investigated phenomenon is bistable electron-hole gating, where the hole layer acts as a gate controlling the drive current of the electron layer. Under certain conditions, a positive feedback effect between electrons and holes occurs, and as a result we observe two stable electron layer current states corresponding to the same hole layer gating voltage, i.e., the system is bistable. The bistahle electron-hole gating effect is further explored by varying the electron layer drive bias and also temperature. We find that the bistabi1ity can be observed only at relatively high drive bias and at cryogenic temperatures. Furthermore, it exhibits thermally activated behaviour. Most important observation is that the bistability occurs always at the threshold of the hole layer depletion. This suggests that the hole layer operates as a low-dimensional gate, the state of which is strongly affected by the carrier density and drive current of the electron layer.