Effects of ge-source impurity concentration on electrical characteristics of Ge/Si hetero-junction tunneling FETs

Introduction: Development of the optimum materials, the structures and the fabrication process is essential in enhancing the performance of tunneling field-effect transistors (TFET). For the TFET sources, pure Ge sources grown on Si are expected to improve the TFET performance, because of the type-II staggered band alignment between Ge and Si [1-4]. Tensile strain in Si channel is another critical factor to boost tunneling current by smaller effective bandgap [3]. Fig. 1 shows a schematic band diagram of the Ge/strained-Si junctions. Here, the smaller bandgap of the Ge-source and the band-offset of the hetero-junction can increase the tunneling possibility. Furthermore, an increase in tensile strain in Si-channels reduces effective tunneling bandgap (E
_g
.
_eff
) because of the increase in electron affinity of Si, leading to the increase in tunneling probability with maintaining the leakage current [3]. In this TFET structure, the source impurity concentration, which determines the depletion width and the resulting tunneling distance, is a critical factor to enhance the electrical characteristics. However, the source concentration dependence in the Ge/Si TFETs has not been sufficiently studied yet. In this study, we have experimentally examined the effects of the impurity concentration in the Ge sources on the electrical properties of Ge/Si TFETs with and without tensile strain of Si channels.