Poenariu, Sorin Avram:
ISBN 9783899594959

Ballistic transport in nanoscale Si/SiGe wires and cross-junctions. Beiträge zur Nanoelektronik Bd. 5 # Pb., 136 S., 60 Abb., 1 Tab.

SCHLAGWORTE:
ballistic transport
quantum wires
Si/SiGe heterostructures
low-dimensional systems
phonon scattering
bend resistance

The high-mobility two-dimensional electron gas (2DEG) embedded in modulation-doped Si/SiGe heterostructures stands as the starting point for this work. Quantum wires and cross-junctions were fabricated through local depletion of the 2DEG via lateral nanoscale patterning of the heterostructures. The patterning was performed using a mix-and-match process which combines high-resolution electron-beam lithography on calixarene and optical lithography on standard photo resist. The resulting resist pattern was transferred into the heterostructure by a low-damage CF4/O2 plasma process.

In quantum wires the quantisation of the differential conductance in multiple integers of 4e2/h was observed. The maximum value of the energy separations between 1D-subbands was found to be 2.9 meV. Under small current injection into orthogonal leads of a four-terminal cross-junction the nonlocal current-voltage characteristics showed negative bend resistance due to the ballistic motion of electrons. Additionally, in an asymmetric cross junction a polarity-dependent breakdown of the negative bend resistance accompanied by negative differential conductance (NDC) was observed. The NDC arises from phonon emission by hot electrons localized at the high-field domain of the narrow lead of the device. An upper limit for the phonon energy of 19 meV was found.

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