Effects of Minority-Carrier Response Behavior on Ge MOS Capacitor Characteristics: Experimental Measurements and Theoretical Simulations

In this paper, we present MEDICI simulations of the admittance-voltage properties of Ge and Si MOS devices, including analyses of substrate conductance G_sub and high-low transition frequency f_tran, to explore the differences in the minority-carrier response. The Arrhenius-dependent G_sub characteristics revealed that a larger energy loss-by at least four orders of magnitude-occurs in Ge than in Si, reflecting the fast minority-carrier response rate, i.e., a higher value of f_tran. We confirmed that the higher intrinsic carrier concentration in Ge, through the generation/recombination of midgap trap levels as well as the diffusion mechanism, resulted in the onset of low-frequency C- V curves in the kilohertz regime, accompanying the gate-independent inversion conductance. The experimental data obtained from Al₂O₃/Ge MOS capacitors were consistent with the values of G_sub and f_tran obtained from MEDICI predictions and theoretical calculations. In addition, upon increasing the inversion biases, we observed shifts in the G_sub/f conductance peaks to low frequencies that mainly arose from the transition of minority carriers with bulk traps in the depletion layer. Meanwhile, we estimated that the bulky defects of ca. ( 2-4) ×10¹⁵ cm^-3 exist in present-day low-doped Ge wafers.