Temperature Dependence of I-V Characteristics of Au/n-Si Schottky Barrier Diode

The current-voltage characteristics of Au/n-Si Schottky barrier diodes were measured in a wide temperature range of 70-310 K. The forward current-voltage characteristics have been analyzed on the basis of standard thermionic emission (TE) theory and assuming Gaussian distribution (single) of barrier height. Findings are investigated to explore TFE-mechanism with high value of characteristic energy. The high values of ideality factor are analysed for interfacial layer and density of interface state. The temperature dependence of ideality factor was found to obey the “To-effect” and the true barrier height (φbη) obtained is almost independent of temperature. 1.0 Introduction For an ideal Schottky diode, the current flow is only due to thermionic emission mechanism and the ideality factor should be equal to unity (η=1). However, due to various factors such as device temperature, dopant concentration, device area, density of interface states, structural properties of interface etc., the current-voltage characteristics of Schottky contact exhibit deviations from TE-mechanism with temperature dependent ideality factor [13,9]. Generally, the ideality factor increases with decrease in temperature, the phenomena is commonly referred as “To-effect” and was first proposed by Padovani and Sumner [10]. Whereas, the barrier height for these diodes is found to be decreases with fall in operating temperature. It is shown for the To-effect that the error may be connected either with the lateral inhomogeneity of barrier height [11, 12], or with the role of recombination and tunneling current components [12], or with the anomalous high level of thermionic field emission dominating the current [13]. In the present work, an attempt has been made to study the anomalies observed in the temperature dependent I-V characteristics of Au/n-Si Schottky contact on the basis of well established models mentioned above. 2.0 Experimental The Schottky diodes used in this study were fabricated on n-type Si wafer of (100) orientation and n/n configuration. The nregion comprising of 8.2 μm thick epitaxial nlayer (ND=1.35×10cm) of resistivity 2.6 Ω cm over the heavily doped n silicon substrate. Prior to fabrication, sample was first degreased with soap solution and then thoroughly cleaned with organic solvents. Finally, the sample was etched using dilute HF (HF:H2O≈1:10) followed by washing in deionized water. Ohmic contact was made by depositing 200 nm thick Al layer and than annealed in vacuum (10 mbar) at 450 C for 30 minutes. Sample was again cleaned from the epitaxial n-layer (i.e. front) side by using the cleaning processes as mentioned above. Finally, a gold (Au) film of thickness 80 nm was deposited on epitaxial n-layer. All depositions were carried out in a HHV coating unit using thermal evaporation source under vacuum 5×10 mbar. For I-V measurements, diodes were mounted and bounded on To-39 header. The forward I-V characteristics from 70-310K Journal of Electron Devices, Vol. 8, 2010, pp. 286-292 © JED [ISSN: 1682 -3427 ] Journal of Electron Devices www.jeldev.org Received 30 September 2010, accepted 18 October 2010