Material-Device Simulations of High-Frequency Performances of n-type MOSFET with GeSn Channel

Abstract

Recently, GeSn has been identified as a promising candidate for group-IV-driven electronic and photonic devices owing to its high carrier mobility and indirect-to-direct bandgap transition property. In this work, a comprehensive study of primary material characteristics, including electron affinity, bandgap energies at local minimum valleys, and effective density of states (DOS) of the GeSn alloy, has been conducted as a function of Sn fraction and in-volume stress. As the Sn fraction increases, leading to the transition from an indirect-to-direct bandgap, the electron affinity rises sharply, while the energy bandgap and the effective DOS decrease. Based on these material parameters, an n-type metal-oxide-semiconductor field-effect transistor has been designed and optimized in terms of DC parameters and high-frequency performance as a function of Sn fraction and the corresponding in-volume biaxial stress in the channel region. As tensile stress or Sn fraction increases, both the on-state (I-on) and off-state currents (I-off) rise due to a narrowed bandgap energy, while the subthreshold swing (S) value also degrades. In contrast, compressive strain reduces Ioff. Finally, the incorporation of GeSn channel is reported to be advantageous for high-speed operation.