The Effect of Air-Exposed Layer on Electrical Properties of Cu/n-Si/Al Schottky Diodes

In this work, we studied the effect of air-exposed layer on the current-voltage (I-V) capacitance versus voltage (C-V) and capacitance versus frequency (C-f) characteristics of Cu/n-Si/Al Schottky diodes. We fabricated with and without thin oxide layer Cu/n-Si/Al diodes. Firstly, n-Si wafer having (100) oriented and 15 Ω.cm resistivity was cut into eight pieces labeled Diode 1 (D1) to Diode 8 (D8). We formed the referents Cu/n-Si/Al Schottky diode (D1) which has not exposed to air. Rest of the samples, before formation of Schottky contact, was exposed to clean air at the room temperature for 2, 4, 8, 16, 32, 48 and 64 days. Therefore, Schottky contact with native oxide layer on the polished n-Si surface was obtained. From ln(I)-V plot of the Cu/n-Si/Al diodes, ideality factor (n), barrier height (eb), the interface state density of the Schottky junctions (Ns), saturation current (I0) and serial resistor (RS) were calculated. In addition, same parameters were verified using both Cheung functions and C-2-V characteristics. Moreover, the interface state densities of the Schottky junctions versus energy Ns-(Ec-Es) also was calculated and plotted. What causes to excess capacity of the space charge have also been investigated. While the value of ideality factor and series resistance increased with increasing exposure time to air, the barrier height Φb value of the Schottky diode with oxide layer is smaller than those without oxide layer. This is attributed to formation oxide layer occurring between interfaces of metal and semiconductor surface