Investigation on Degenerate Subbands Induced by Stress and Quantum Confinement in n-Type Silicon Junctionless Nanowire Transistor at Low Temperatures

Abstract

Experimental evidence of one-dimensional multi-subband occupation was observed at low temperature of 6 K in single n-channel junctionless nanowire transistor, resulting in distinct current steps in transfer characteristics. Notably, the height of the first and fourth steps is half of that of the second and third steps, attributed to the formation of two sets of energy subbands with differing degeneracies in the confined channel. To further investigate, we constructed a three-dimensional fabrication process simulation model. Due to the volume expansion of silicon dioxide during oxidation, a stress distribution formed in the channel region. The compressive stresses along the vertical and longitudinal directions were relatively high, reaching 120 MPa and 71 MPa, respectively. We quantified the subbands structure by considering both stress-induced degeneracy splitting and confinement-induced subbands splitting. Under the dual influence of stress and quantum confinement, two-fold and four-fold degenerate subbands are formed within the nanowire channel. The energy level spacings of each subband exhibited good agreement with experimental data. Additionally, the conductance steps disappear at 30 K, where the corresponding phonon energy matches the theoretically calculated subbands energy spacing.