Barrier inhomogeneities in titanium Schottky contacts formed on argon plasma etched p-type Si_0.95Ge_0.05

Electrical properties of Ti Schottky barrier diode fabricated on argon plasma etched p-type Si_0.95Ge_0.05 were studied using current–voltage (I–V) over a wide temperature range (100–300 K). The transport properties of the junction were analyzed by investigating the temperature dependence of both the effective Schottky barrier height (Φ _0bp) and the ideality factor (n). It is shown that the ideality factor increases and the Schottky barrier height (SBH) decreases with decreasing temperature. This abnormal temperature dependence of the Φ _0bp and n is explained on the basis of a thermionic emission conduction mechanism with Gaussian distributed barrier heights due to the barrier height inhomogeneities at the metal-p-Si_0.95Ge_0.05 interface. From the linear plot of the experimental SBH versus 1/T, a homogeneous SBH (\(\overline{\varPhi }_{0bp}\)) and a zero-bias standard deviation (σ_0s) values of approximately 0.55 eV and 67 mV, respectively were computed. Furthermore the modified Richardson plot according to the Gaussian distribution model resulted in a homogeneous SBH (\(\overline{\varPhi }_{0bp}\)) and a Richardson constant (A*) of 0.55 eV and 35 A/cm² K², respectively. The A* value obtained from this plot is in very close agreement with the theoretical value of 32 A/cm² K² for p-type Si_0.95Ge_0.05. Furthermore, the SBH is found to decrease linearly as the interface states density (N _ss) increases. It is proposed that the lateral inhomogeneities of the SBH are actually attributed to the distribution of the interface states which are in turns resulting from the plasma etching induced defects beneath the Si_0.95Ge_0.05 surface.