Aluminum Schottky contacts to n-type 4H-SiC

Aluminum Schottky contacts to n-type 4H-SiC were fabricated, and the results of electrical measurements on the devices are presented along with the Schottky barrier height and ideality factor. Furthermore, two different samples having different surface treatments were investigated. The barrier heights obtained from current-voltage (I-V) measurements on both samples are essentially identical, with an average value of 0.64 eV. The ideality factor of Sample 2, which had an HF-dip surface treatment, had an average value of 1.66. The ideality factor of Sample 1, which had a surface treatment similar to the other sample but with the addition of an RCA-like clean, had an average value of 2.60. Measurements on some control devices with Au contacts showed that no significant Fermi-level pinning occurred, and the barrier-height results for all devices approached the Schottky-Mott limit. Capacitance-voltage (C-V) measurements on the Al devices from Sample 1 yielded barrier heights that were much smaller than those obtained from the I-V curves; however, for Sample 2, the barrier heights obtained from both C-V and I-V methods were comparable. Based on these results, we propose a model that accounts for the measured results in terms of a thin interfacial layer produced in Sample 1, which screens the depletion region from the applied electric field. This model yields a possible explanation of how the two surface treatments result in devices with the same barrier height but different ideality factors. The results in this paper represent some of the first experimental data on Al/4H-SiC Schottky contacts.