Intrinsic carrier effects in HfO2-Ge metal-insulator-semiconductor capacitors -: art. no. 223507

Germanium metal-insulator-semiconductor capacitors with HfO2 or other high-kappa gate dielectrics show unusual low frequency behavior of the high frequency (1 kHz or higher) capacitance-voltage characteristics when biased in inversion. Here, we provide evidence that this effect is partly due to the high intrinsic carrier concentration n(i) in Ge. We show in particular that the ac conductance in inversion is thermally activated and it is governed either by generation-recombination processes in depletion, varying proportional to n(i) or by diffusion-limited processes varying as n(i)(2), depending on whether the temperature is below or above 45 degrees C, respectively. From these measurements, we also show that the minority carrier response time in Ge is very short, in the microsecond range (much shorter than in Si), depending inversely proportional to n(i) at room temperature. This means that due to high n(i), the inversion charge is built fast in response to high frequency signals at the gate, inducing the observed low frequency behavior. (c) 2005 American Institute of Physics.