Schottky barrier height measurements of type-A and type-B NiSi2 epilayers on Si

Abstract

Schottky barrier heights of single-crystal type-A and type-B NiSi2 epilayers on nondegenerate n-(111) Si have been measured by photoresponse and forward I–V methods. High-quality molecular beam epitaxy grown NiSi2 layers of thicknesses ranging from 70 to 600 Å on sputter-cleaned, P-doped Si subtrates (~ 1.5 × 1015 cm – 3) were studied. The type-A and type-B orientations consistently yield photoresponse barrier heights which differ by greater than 0.1 eV. We observe the value phi Bn=0.62 ± 0.01 eV for all type-A structures from both photoresponse and I–V measurements. However, we obtain a discrepancy between barrier heights measured by I–V (phi Bn=0.69 ± 0.01 eV) and photoresponse (phi Bn=0.77 ± 0.05 eV) methods, and in addition consistently observe an unusual bowing of the type-B photoresponse curves at low photon energies. We show that both the detailed shape of the type-B photoresponse curves and the discrepancy between I–V and photoresponse-measured barrier heights can be accounted for by modeling the type-B barrier as a mixture of high and low barrier regions. Quantitative agreement with experiment is obtained for the values phi hi =0.81 ± 0.01 eV and phi lo 0.64 ± 0.01 eV, with effective fractional area coverages of 91% and 9% for high- and low-barrier regions, respectively.