Molecular Tuning of Electrical Properties of Mercury-Insulator-Silicon Diodes

The influence of silicon surface modification via Si-C_nH_2n+1 (n=10,12,16,22) devices on p-type (100) silicon is studied by forming MIS (metal-insulatorsemiconductor) diodes via a mercury probe. With the use of current density - voltage (J-V) and capacitance - voltage (C-V) measurements the relevant parameters describing the electrical behavior of these diodes are derived and compared with samples with a native oxide insulator. The insulating properties of these MIS diodes can be precisely tuned by varying the monolayer thickness. Insulating layers with n ≥ 12 show better insulating behavior than native oxide. Despite a comparable thickness of the C₁₆ monolayer as compared to the native oxide layer, the former showed even a tenfold decrease in leakage current. Evaluation of the average tunneling constant (β) of these monolayers reveals 0.45 Å^-1. Evaluation of the dielectric constants (εr) gave values of 1.7 ± 0.3 and 2.2 ± 0.4 for n = 16 and 22, respectively, whereas for the fixed charge (Nf) low values of 5.4.10¹¹ and 5.9.10¹¹ cm^-2 were found for n = 16 and 22, respectively. The results suggest that Si-C linked monolayers on flat silicon may be a viable, alternative insulator for future electronic devices.