Schottky barrier heights of Pt and Ir silicides formed on Si/SiGe measured by internal photoemission

Lowered-barrier-height silicide Schottky diodes are desirable for obtaining longer cutoff-wave- length Si-based infrared detectors. Silicide Schottky diodes have been fabricated by the reaction of evaporated Pt and Ir films on p-Si_1-xGe_x alloys with a thin Si capping layer. The onset of metal-SiGe reactions was controlled by the deposited metal thickness. Internal photoemission measurements were made and the barrier heights were obtained from these. Pt-SiGe and Ir-SiGe reacted diodes have barrier heights of ∼0.27 and ∼0.31 eV, respectively, higher than typical values of 0.22 and 0.12 eV for the corresponding silicide/p-Si diodes. Their emission constants are also lower and more voltage dependent than silicide/Si diodes. PtSi/Si/SiGe diodes, on the other hand, have lower barrier heights (∼0.15 eV) than the PtSi/Si barrier height. The barrier height shifts in such silicide/Si/SiGe diodes are interpreted by accounting for tunneling through the unconsumed Si layer. This is done analytically using a simple model based on the Cohen, Vilms, and Archer (unpublished) modification to the Fowler equation, and leads to an extracted barrier height, that is, the Si barrier height reduced by the Si/SiGe band offset.