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 <i>G</i>_sub and high-low transition frequency <i>f</i>_tran, to explore the differences in the minority-carrier response. The Arrhenius-dependent <i>G</i>_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 <i>f</i>_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 <i>C</i>- <i>V</i> 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 <i>G</i>_sub and <i>f</i>_tran obtained from MEDICI predictions and theoretical calculations. In addition, upon increasing the inversion biases, we observed shifts in the <i>G</i>_sub/<i>f</i> 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) &times;10¹⁵ cm^-3 exist in present-day low-doped Ge wafers.