Mechanism of the suppression of the floating-body effect for SOI MOSFETs with SiGe source structure

SiGe layers were formed in source regions of partially depleted 0.25 /spl mu/m SOI nMOSFETs with the Ge implantation technique and the floating-body effect was investigated for the SiGe source structure. It was confirmed that kinks in the Id-Vd characteristics and the anomalous lowering of the subthreshold swing were suppressed and that the drain breakdown voltage increased for this structure. The mechanism of this suppression effect is presented for the first time. It is found that this suppression originates from the decrease in the current gain for source/channel/drain lateral bipolar transistors with the SiGe source structure. The temperature dependence of the base current indicates that the bandgap narrowing in the source region is the major reason for the decrease in the current gain.