Nanometer-scale test of the Tung model of Schottky-barrier height inhomogeneity - art. no. 075310

Tung has shown [Phys. Rev. B 45, 13 509 (1992)] that a range of "nonideal" behaviors observed in metal/semiconductor (MS) Schottky diodes could be qua ntitatively explained by assuming that specific microscopic distributions o f nanometer-sized "patches" of reduced barrier height exist at the MS inter face. Here we report a simultaneous microscopic and macroscopic test of thi s model as applied to metal/6H-SiC Schottky diodes, by (1) measuring the nm -scale barrier-height distribution (BHD) of particular Schottky diodes usin g ultrahigh vacuum (UHV) ballistic electron emission microscopy (BEEM), (2) extending the Tung model to calculate the expected nm-scale BHD for partic ular parameter values, and (3) quantitatively relating the measured nm-scal e BHD of a particular Schottky diode to its macroscopic I-V characteristic. Our studies indicate that (1) for relatively ideal diodes, both the micros copic and macroscopic behaviors are explained well by the Tung model with a large coverage (>5%) of shallow patches, (2) the measured BHDs are nearly identical for relatively ideal and highly nonideal diodes, and (3) a simple Tung model can account for highly nonideal behavior only by assuming an un physical patch distribution in which the excess current is dominated by a f ew patches in the extreme tail of the patch distribution. Our measurements instead suggest that all the diodes contain a broad "intrinsic" distributio n of shallow patches, while the large excess current in highly nonideal dio des is due to a few large defects of extrinsic origin. This last conclusion is consistent with a recent study by Skromme and co-workers [J. Electron. Mater. 29, 376 (2000)].