The influence of the band edge position upon the reduction kinetics and the etching behaviour at the GaP-Fe(CN)3−6 interface

On the Factors Determining the Morphology of Wet‐Etched n‐ and p ‐ GaP Single‐Crystal Surfaces

“…This confirms the explanation given in Ref. (2) and (3) for the morphology of the GaP surface when etched in alkaline Fe(CN)~-or in acid Br 2 solutions.…”

“…At moderate surface concentrations of h +, the intrinsic rate of the electrochemical steps is lowered and the chemical steps involving OH-are believed to proceed intrinsically faster than the electrochemical ones. The first step, in which a GaP surface bond captures a hole, leading to the formation of a first intermediate X~ with one electron-deficient bond, is assumed to be the intrinsically slowest and hence the rate-determining step GaP+h + k) X~ [2] The rate at which reaction [2] proceeds may then be controlled either by the kinetics of the reaction itself (p-GaP at moderate anodic polarization; the etch rate increases with anodic polarization) or by the supply of holes (n-GaP at moderate light intensities; the etch rate increases with the light intensity). Local variations in the etch rate may then be ascribed to variations either in 'the rate constant k or in the hole concentration at the surface Ps or in both.…”

“…The maximum light intensity incident on the crystal surface amounted to about 80 mW 9 cm -2. For investigating the current-potential behavior of the p-GaP electrodes, a conventional rotating-disk setup was used since, as already mentioned in previous papers (2)(3)(4), the flow cell is not very suitable for investigating electrode kinetics. A saturated calomel electrode (SCE) was used as the reference electrode in all cases.…”

“…Wet etching of GaP single crystals in alkaline Fe(CN)~as well as in acid Br2 solutions leads to a homogeneously etched (lid face, whereas etch pits are formed on the (111) face (2,3). In Ref.…”

“…In Ref. (2) and (3), it was shown that, in the above-cited solutions, the etch rate at the (111) face is determined by the diffusion rate of the reactants toward the GaP surface, whereas at the (111) face it is controlled by the surface reaction itself. From these observations, it was suggested that the morphology of the semiconductor surface after etching depends on the rate-determining step of the etch process.…”