Charge-Transfer-Controlled Vaporization of Cadmium Sulfide Single Crystals. I. Effect of Light on the Evaporation Rate of the (0001) Face

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Abstract
Light of greater‐than‐band‐gap energy was found to change markedly the vacuum evaporation rate of the (0001) face of cadmium sulfide single crystals. Evaporation temperatures of 680°—740°C and light intensities of 5.0×103−2.0×105 μW/cm2 were used. The results were interpreted assuming that charge transfer is the rate‐determining step in the sequence of vaporization surface reactions. An evaporation mechanism in terms of charge transfer has been proposed. Light (1) changes the free‐carrier concentrations at the vaporizing surface, and (2) under proper conditions, changes the composition of the crystals. High‐resistivity crystals showed a fivefold increase of their evaporation rate under illumination due to the increase by light of both electron and hole concentrations. In low‐resistivity crystals, in which illumination can only significantly increase the minority free‐carrier concentration above the dark equilibrium value, effects, which are due to the change of the crystal composition, dominated.