Formation and electrical properties of Hf Si2 grown thermally from evaporated Hf and Si films

Abstract

2 MeV 4He+ backscattering spectrometry and x-ray diffraction have been used to study Hf Si2 formed by thermal annealing of a Hf Si film on evaporated Si (Sie) at temperatures between 575 and 650 °C. A laterally uniform layer of Hf Si2 forms and its thickness is proportional to the square root of time at a fixed temperature. The activation energy of this reaction is found to be 3.5±0.3 eV. This transport-limited process differs from that observed on single crystal Si, where Hf Si2 forms at temperatures above 700 °C by a process believed to be nucleation controlled. Four-point probe measurements of resistivity and Hall coefficient at room temperature on samples with both Hf Si and Hf Si2 were used to determine that both Hf Si and Hf Si2 are electron conductors. For Hf Si2, the electron concentration is 2.9±0.2×1021 cm−3 and the mobility is 36±4 cm2/Vs, giving a resistivity of 60±3 μΩ cm. Schottky barrier diodes formed either by reacting a Hf film deposited directly on 〈111〉 Si or by reacting a Hf film with Sie in a 〈111〉 Si/Hf/Sie/Hf configuration at temperatures above 600 °C were prepared. The Schottky barrier height of Hf Si2 on n-type 〈111〉 Si as evaluated from forward and reverse I–V characteristics is 0.54±0.01 eV in both cases.