CURRENT TRANSPORT MECHANISMS STUDIED BY I-V-T AND IR PHOTOEMISSION MEASUREMENTS ON A P-DOPED PTSI SCHOTTKY DIODE

The forward bias current of a moderately p-doped PtSi Schottky diode has been studied in detail over a temperature range of about 80-160 K. These investigations are complemented with photoemission measurements using the same device. In the temperature range of 80 to around 110 K, the forward bias current mechanism is found to be thermionic emission over the barrier, with an ideality factor n of around unity and a zero bias barrier height of 0.253 eV, in a good agreement with the photoemission results. Above 110 K, the ideality factor increases rapidly, to about 2.3 at 150 K. The apparent zero bias barrier height is about 0.253 eV between 80-110 K, but falls rapidly at higher temperatures to about 0.24 eV at 150 K. These results suggest that other mechanisms contribute significantly to the current transport of the p-doped PtSi Schottky diode at higher temperatures, and diffusion is found to be responsible. A numerical routine is then used to fit the higher temperature experimental data to a combined thermionic-diffusion theory. The zero-bias barrier height, acceptor density and series resistance obtained from this numerical modelling are in good agreement with the results obtained in the lower temperature region and by internal photoemission measurements. The current mechanisms of a moderately p-doped PtSi Schottky diode over the large temperature range, including that of lower temperature (T < 80 K) are then discussed in detail. The region where diffusion is important is defined according to a boundary condition of 0.67nu > muE, where nu, mu and E are the average velocity of the charge carrier, hole mobility and electric field respectively.