Abstract
The interaction between thin films of sputter deposited chromium and hydrogenated amorphous silicon has been studied. Following deposition of the chromium films at room temperature the films were annealed over a range of times and temperatures below 350° C. It was found that an amorphous silicide was formed only a few nanometers thick with the square of thickness proportional to the annealing time. The activation energy for the process was 0.55+/-0.05 eV and the silicide growth rate prefactor ≈ 10-12 cm2/s. The formation process of the silicide was very reproducible with the value of density derived from the thickness and Cr surface density being close to the value for crystalline CrSi2 for all films formed at temperatures ≤300° C. The specific resistivity of the amorphous CrSi2 was ≈600 muO.cm and independent of annealing temperature. It was shown that the a-CrSi2 was physically and chemically stable. We have shown that a Schottky barrier is formed between a-CrSi2 and a-Si:H with a barrier height of ≈ 0.9 eV and an ideality factor ≈1.1. The current transport is controlled by diffusion or thermionic emission mechanism at low voltages but it becomes space charge limited at higher voltages. Applying a reverse or forward bias to the Cr/a-Si:H system during annealing does not change the physical and electrical properties of the interface and the behaviour is controlled only by the heat treatment history of the sample. In the Mo/a-Si:H system a very thin and stable amorphous MoSi2 layer is formed after annealing below 300° C and the formation of MoSi2 follows the diffusion law. The activation energy of silicidation is ≈ 0.4 eV and the prefactor is ≈ 10-14cm2/s. The specific resistivity of a-MoSi2 is ≈ 1000 muO.cm. In the Co/a-Si:H the composition of the resulting silicide is close to CoSi below 300° C with a resistivity of ≈ 120 muO.cm. The barrier height of the MoSi2/a-Si:H and CoSi/a-Si:H systems is ≈ 0.9 eV and confirms that the barrier height is controlled by interface states.