High frequency capacitance behavior of metal-oxide-semiconductor tunnel structures

• Published in: Journal of applied physics 1994-06, Vol.75 (12), p.7922-7930
• Main Author: Bredimas, Vassiliki
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.356579

We use a simple model based on the steady-state balance of current flowing by tunneling across a Si-SiO2-metal structure. The recombination current is not taken into account. This model yields analytical expressions for the positions of the quasi-Fermi levels at the Si-SiO2 interface which govern the shape of current-voltage and capacitance-voltage characteristics. In particular, the knee which appears in the capacitance-voltage curves of inverse-biased structures and the corresponding plateau or the break in the slope of the 1/C2 versus applied voltage curve is correctly described. Measuring the slopes before and after the plateau or breaking, which marks the boundary of the tunneling domain, could provide information on the surface states when the surface parameters are known or vice versa. The main feature in the interpretation of the curves obtained is the degree of communication between metal and semiconductor, which is dominated by the tunnel transmission coefficient. The main parameters are therefore the oxide thickness and the minority barrier height for reverse polarization and the majority barrier height for forward bias polarization. It turns out that actual structures never have the predicted values for these barriers but notably lower ones when one assumes a perfect oxide layer. This fact may be due to defects in the oxide layer.