Electrical and optical characteristics of Ni/Si junctions

Metal-semiconductor junctions base on microelectronic devices. Hence, variousinvestigations were made about characteristics of these junctions. In these investigations,properties of electrical conductivity and high resistivity against to oxidation of silicidesprepared by transition metals attracted. But , properties of transition metal/Si and silicide/Sijunctions have rarely examined.In this study, Ni/Si junctions were obtained by Ni evoperation on crystal silicon and annealingeffect on characteristics of these junctions was investigated. Photosensivity, barrier height andideality factor calculated from measured current-voltage characteristics after and beforeannealing processes, it has seen occurring of NiSi2 and NiSi phases from XRD analysis andgrain sizes of polycrystallic nickel silicide phase calculated. XRF measurement made addcalculated Ni concentration distrubition in silicon. We obtained the results as follows:Prepared Ni/pSi and Ni/nSi junctions shows properties of Schottky diodes. Properties ofrectification and photosensivity of these junctions decrease by annealing at 500oC. Change ofjunction characteristics by annealing attributed to form new phases at Ni-Si boundary zone.We have seen composition of NiSi and NiSi2 polycrystallic phases by annealing of Ni/Sistructures in vacuum and peak intensities of these phases have increased with increasingannealing times (from 1.5 to 15 hours) in XRD spectrums. Grain sizes calculated from a halfintensity of composed peaks and after 90 minutes annealing, grain sizes for NiSi2 and NiSihave found d(NiSi2) = 465 Å, d(NiSi) = 971 Å, respectively. After 15 hours annealing, grainsize for NiSi decreased to d(NiSi) = 796 Å. On the contrary, grain size for NiSi2 increased tod(NiSi2) = 580 Å.Ni/pSi structures annealed in vacuum (at 500oC for 15 hours ) and then made XRFmeasurements. Two diffusion coefficients calculated from XRF for concentration distrubitionof nickel silicon. It is found Dy ≈ 5.10-14 cm2/sn and Di ≈ 10-8cm2/sn for near to surface andinterior zone, respectively.Slower diffusion on near the surface attributed to composition of NiSi phases on there. Fastactivity of nickel in interior zone concerned on diffusion with interstitial positions. Ni filmswere deposited by evaporation on silicon substrates and thus composed Ni/Si junctions showSchottky diode properties. It is also shown that diode parameters of Ni/pSi junctions arehigher than of Ni/nSi junctions. After annealing at 500oC, diyote properties of Ni/Si junctionsare decomposed due to composition of new Ni/Si and NiSi2 phases on boundary zone.Keywords: Ni/Si junctions, Ni2Si, NiSi, NiSi2, Diffusion.