Intrinsic carrier effects in HfO2–Ge metal–insulator–semiconductor capacitors

• Published in: Applied physics letters 2005-05, Vol.86 (22)
• Main Authors: Dimoulas, A., Vellianitis, G., Mavrou, G., Evangelou, E. K., Sotiropoulos, A.
• Format: Article
• Language: English
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.1944227

Germanium metal–insulator–semiconductor capacitors with HfO2 or other high-κ 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 ni 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 ni or by diffusion-limited processes varying as ni2, depending on whether the temperature is below or above 45 °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 ni at room temperature. This means that due to high ni, the inversion charge is built fast in response to high frequency signals at the gate, inducing the observed low frequency behavior.