Fabrication of Vertical Field-Effect Transistor with a Superlattice Source by Using Focused Ion Beam

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The Purpose of this study is to fabricate the field-effect transistor with a superlattice source ; i. E. A new functional devices, by means of the focused ion beam (FIB) implantations. We also fabricated the quantum wire field -effect transistor and studied the low-temperature characteristics of the operation.We succeeded in fabricating the GaAs quantum wires by the FIB implantation using the two methods ; one is the high-resistivity method and the other is the pn-junction method. For the FIB lithography, we studied the optimum conditions of the FIB implantation such as ion species, implantation doses, and implantation energies. The FIB lithography with a minimum resolution of 0.2mum was achieved. The surface morphology of the PMMA resist after the FIB lithography was traced by means of the scanning tunneling microscopy. Although the boundaries look like rough, we observed the periodicity resulting from the spacing of the dots of the ion beam.We studied the mechanism of saturation of the phase breaking time at low-temperature to analyze the characteristics of the operation of the electron wave interference devices. The quantum wire with an Al gate was fabricated by the direct FIB implantation through the Al gate. The dependence of the phase coherence length on the temperature and electric field was studied. We analyzed the operation limit of the quantum interference devices, such as the temperature and input voltage. Furthermore, we improved the system of molecular beam epitaxy to obtain high-mobility layers. We studied the fabrication processes and design principles of the vertical field-effect transistor with a superlattice source.