| Hot Electron Transport and Current Sensing (2006) | |||||||||||
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| Hot Electron Transport and Current Sensing thesis presented Mathew Cheeran Abraham The Department Physics partial fulfillment the requirements for the degree Doctor Philosophy the subject Physics Harvard University Cambridge Massachusetts August Mathew Cheeran Abraham All rights reserved Author Mathew Cheeran Abraham Thesis advisors Rajeev Ram Massachusetts Institute Technology Robert Westervelt Harvard University Hot Electron Transport and Current Sensing Abstract The effect hot electrons momentum scattering rates two dimensional electron gas critically examined shown that with hot electrons possible explore the temperature dependence individual scattering mechanisms not easily probed under equilibrium conditions both the Bloch neisen phonon scatu tering phenomena and the reduction impurity scattering are clearly observed The theoretical calculations are consistent with the results obtained from hot electrons experiments function bias current resistance peak formed DEG the low temperature impurity limited mobilities comparable TBG the phonon limited mobility the critical temperature this case the bias current increased the electron temperature rises due Joule heating and the rapid increase phonon scattering can detected before the effect the reduction impurity scattering sets TBG there peak resistance because the impurity scattering dominates sufficiently and its reduction has much Abstract stronger effect the total resistance than the rise phonon scattering Furthermore know. The effect of hot electrons on momentum scattering rates in a two-dimensional electron gas is critically examined. It is shown that with hot electrons it is possible to explore the temperature dependence of individual scattering mechanisms not easily probed under equilibrium conditions; both the Bloch-Gr¨uneisen (BG) phonon scattering phenomena and the reduction in impurity scattering are clearly observed. The theoretical calculations are consistent with the results obtained from hot electrons experiments. As a function of bias current, a resistance peak is formed in a 2DEG if the low temperature impurity limited mobilities ¹I(T = 0) is comparable to ¹ph(TBG) the phonon limited mobility at the critical BG temperature. In this case, as the bias current is increased, the electron temperature Te rises due to Joule heating and the rapid increase in phonon scattering can be detected before the effect of the reduction in impurity scattering sets in. If ¹I(T = 0) ≪ ¹ph(TBG), there is no peak in resistance because the impurity scattering dominates sufficiently and its reduction has a much Abstract iv stronger effect on the total resistance than the rise in phonon scattering. Furthermore, knowing the momentum relaxation rates allows us to analyze the possible interplay between electron-electron and electron-boundary scattering. The prediction that a Knudsen to Poiseuille (KP) transition similar to that of a classical gas can occur in electron flow [26] is examined for the case of a wire defined in a 2DEG. Concurrently, an appropriate current imaging technique to detect this transition is sought. A rigorous evaluation of magnetic force microscopy (MFM) as a possible candidate to detect Poiseuille electronic flow was conducted, and a method that exploits the mechanical resonance of the MFM cantilever was implemented to significantly improve its current sensitivity.. All the research was funded by the National Science Foundation(NSF). | |||||||||||
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