Hot electron interactions in nanostructures

Abstract

Modern semiconductor growth and processing techiques have provided the capability of fabricating a huge variety of devices which have atomically precise layered structures and lateral patterns with nanometer sizes. This not only provided novel device possibilités but also opened a new field in condensed matter physics, so called mesoscopics. It does not seem likely that the mesoscopic electronic devices will be available in the near future. Two main obstacles for mesoscopic electronics are the low temperature requirements and the breakdown of the phase coherence of the carriers as their energies exceed the Fermi level. This strongly suggests the investigation of the excited carriers with energies well in excess of their thermal equilibrium energy as the dimensions shrink. In this thesis, the interactions of hot electrons in semiconductor and metal structures with deep submicron characteristic dimensions have been studied. Tunneling Hot Electron Transfer Amplifier (THETA) constructed by abrupt semiconductur heterojunctions is a perfect system to analyze the interaction of hot electrons with cold electrons and the other possible excitations in solids. Recently, it has been discovered that an electron multiplication effect took place in such devices under certain conditions and resulted in a transfer ratio of greater than unity. In this work a novel fabrication technique has been developed. It would make it possible to utilize this effect for fabrication of a high frequency oscillator in the THz regime, in a future work. In addition, a kind of lateral THETA device has been constructed using a Two Dimensional Electron Gas structure. Electron multiplication effect for the first time has been observed in 2DEG structures. Moreover, the dependence of the effect on parameters such as injection energy, emitter and collector barrier heights and electron transit length has been investigated. The other direction of the work has been the investigation of metal wires under extremely high current densities. A strong nonlinearity in conductivity is introduced when a free standing submicrometer wire is biased to heat upto very high temperatures. The geometry of two crossing wires has been investigated under this condition.