Electron Transport in Kinetic Heterostructures

Research project P 14604 Electron Transport in Kinetic Heterostructures Jürgen SMOLINER 27.11.2000 In this project, the electronic transport properties of "kinetic" heterostructures shall be studied. Truly kinetic heterostructures consist of materials, where the band offset exists exclusively in the valence band while the conduction band is flat. Due to the differences in electron mass of the involved materials, the transversal and longitudinal components of electron velocity are coupled and electrons show a similar behavior like photons travelling through materials of different refractive index. Thus, electron refraction, reflection and interference effects will occur. A second interesting application of kinetic heterostructures are effective mass superlattices. Such superlattices also have minibands, but in contrast to conventional superlattices, the bottom of the lowest miniband is always at the bottom of the conduction band. This can be exploited for the construction of devices having negative differential resistance but no tunneling barriers. Because the RC constants will be small, they are promising for all high frequency applications. An excellent tool to study such kinetic junctions is ballistic electron spectroscopy, because in analogy to optics, layers of different effective mass can be treated like layers of different refractive index. In this project, low temperature Ballistic Electron Emission Microscopy / Spectroscopy (BEEM/S) will be employed. BEEMIS combines high spectral with high spatial resolution and is a three terminal extension of scanning tunneling microscopy, where ballistic electrons are injected from a STM tip into a semiconductor via a thin metal base layer. BEEM spectra reflect all physical sample properties up to the depth of the electron coherence length and thus, especially the "optical" aspects of ballistic transport can be investigated conveniently. As samples GaAs-AlGaAs and InAs-AlSb based heterostructures will be employed. Especially InAs-AlSb heterostructures are ideal kinetic junctions because the mass difference between those materials is large. Using AlxIn1-xAS1-ySby-GaSb heterostructures of proper composition, truly kinetic heterojunctions and effective mass superlattices were recently demonstrated. Our expertise in growth of GaAs-AlGaAs heterostructures is demonstrated by the continuously increasing number of refereed publications, the required growth techniques for AlxInl-xAS1-ySby-GaSb heterostructures shall be developed in this project.