High-Field Diffusivity of Electrons in Silicon

The diffusivity of electrons in silicon transverse to a high electric field has been measured with precision by a beam-spreading technique. The measurements were carried out on 306-μm-thick double-Schottky-barrier structures fabricated from nearly intrinsic Si in which the applied field depleted the Si and was uniform to within ± 250 V/cm. It was found that the transverse diffusion coefficient D⊥ decreases monotonically from the known zero-field value of 35 cm2/sec for E 1 kV/cm to 22 cm2/sec at 11.5 V/cm, the upper field limit of the measurements. Monte Carlo calculations of the diffusivity tensor were carried out for a simplified band model and yielded D⊥ values in good agreement with the experimental results, thereby lending credence to the calculated values of the longitudinal diffusion coefficient.