Investigation of barrier inhomogeneities in Mo/4H-SiC Schottky diodes

Using current-voltage measurements, we have investigated the electrical behavior of molybdenum on 4H-SiC Schottky diodes of various areas and having different edge terminations consisting of high resistivity guard rings manufactured by carbon ion-implantation. Both forward and reverse electrical characteristics of Schottky contacts indicated a presence of inhomogeneities. The forward I-V characteristics have been primarily analyzed within the framework of a standard thermionic emission theory. Schottky-barrier heights and ideality factors are found to appreciably vary from diode to diode. A more general model which takes into account the inhomogeneity of the Schottky barrier has been then used to extract the parameters pertinent to the barrier height distribution. The description of the experimental results using Tung's model allowed us to determine the value of the average laterally homogeneous SBH barrier height between 1.2 and 1.39 eV for Mo/4H-SiC Schottky diodes. The patch's properties (the number of patches, the patch strength and the local series resistance) were also obtained from the fit to the experimental I-V characteristics of the current through "patchy" diodes. The obtained results are best described with this extended "pinch off" model. With respect to the reverse characteristics, the remarked absence of a non-saturating behavior as a function of bias in the experimental reverse-bias branch may well be attributed to the presence of defects and/or inhomogeneous Schottky barrier heights, associated with the non-ideal contacts.