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 obta ining longer cutoff-wavelength Si-based infrared detectors. Silicide S chottky diodes have been fabricated by the reaction of evaporated Pt a nd Ir films on p-Si1-xGex alloys with a thin Si capping layer. The ons et of metal-SiGe reactions was controlled by the deposited metal thick ness. Internal photoemission measurements were made and the barrier he ights were obtained from these. Pt-SiGe and Ir-SiGe reacted diodes hav e barrier heights of approximately 0.27 and approximately 0.31 eV, res pectively, higher than typical values of 0.22 and 0.12 eV for the corr esponding silicide/p-Si diodes. Their emission constants are also lowe r and more voltage dependent than silicide/Si diodes. PtSi/Si/SiGe dio des, on the other hand, have lower barrier heights (approximately 0.15 eV) than the PtSi/Si barrier height. The barrier height shifts in suc h silicide/Si/SiGe diodes are interpreted by accounting for tunneling through the unconsumed Si layer. This is done analytically using a sim ple model based on the Cohen, Vilms, and Archer (unpublished) modifica tion to the Fowler equation, and leads to an extracted barrier height, that is, the Si barrier height reduced by the Si/SiGe band offset.