Dielectric Anomaly in ZnS Films

Abstract

The dielectric constant of vacuum‐deposited ZnS films was measured as a function of thickness in the range of 350 Å to 4 μ. For room temperature deposition, a sharp anomaly was found in the dielectric constant vs thickness curve. The highest measured constant was 34.7 at a thickness of 900 Å. As the thickness increased, the dielectric constant dropped sharply and a shallow minimum less than bulk value (8.3) was observed. This minimum was 5.3 at about 1 μ. At thickness greater than 2 μ the dielectric constant was about 10. For increasing substrate deposition temperatures, 150° and 250°C, the dielectric constant approached bulk values, the anomalous peak broadened, and the maximum occurred at greater film thicknesses. The dielectric loss curves showed minima at film thicknesses corresponding to the region on the thicker side of the anomalous peaks where the dielectric constant first became or approached bulk value. It is postulated that the departure of dielectric constant from bulk values is related to the stresses generated in the film during deposition, and that the effect is enhanced because of the piezoelectric nature of ZnS.