Strain-induced Gunn Effect in Silicon Nanowires

Gunn (or Gunn-Hilsum) Effect and its associated negative differential resistivity (NDR) des not exist in bulk silicon. This effect which is due to transfer of electrons between two different energy subbands, is very pronounced in direct bandgap semiconductors like GaAs which makes them favorable for microwave Gunn-diode based oscillators.
In stark contrast to GaAs, bulk silicon has a very high energy spacing (~1 eV) which renders the initiation of transfer-induced NDR unobservable. However using Density Functional Theory (DFT), Tight Binding and Ensemble Monte Carlo (EMC) methods we show for the first time that: (1) Gunn Effect can be induced in silicon nanowires (SiNW) under 3% tensile strain and an electric field of 5000 V/cm,
(2) the onset of NDR in I-V characteristic is reversibly adjustable by strain, and (3) strain modulates the resistivity by a factor 2.3 for SiNWs of normal I-V characteristics i.e.those without NDR. Results of this study promise applications of SiNW-based Gunn diodes in microwave oscillators. The observed NDC is different in principle from Esaki-Diode and Resonant Tunneling Diodes (RTD) in which NDR originates from tunneling effect not electron transfer between subbands of different effective mass.