Suppression of the floating-body effect in partially-depleted SOI MOSFETs with SiGe source structure and its mechanism

SiGe layers were formed in source regions of partially-depleted 0.25-μm SOI MOSFETs by Ge implantation, and the floating-body effect was investigated for this SiGe source structure. It is found that the increase of the Ge implantation dosage suppresses kinks in I_d-V_d characteristics and that the kinks disappear for devices with a Ge dose of 3×10¹⁶ cm^-2. The lowering of the drain breakdown voltage and the anomalous decrease of the subthreshold swing are also suppressed with this structure. It is confirmed that this suppression effect originates from the decrease of the current gain for source/channel/drain lateral bipolar transistors (LBJTs) with the SiGe source structure. The temperature dependence of the base current indicates that the decrease of the current gain is ascribed to the bandgap narrowing of the source region