Diffusion of zinc in indium phosphide at 700°C

Abstract

The diffusion of zinc into n-type InP at 700°C is described for a variety of experimental conditions. Radioactive zinc was used and radio-tracer profiles were plotted. Observations were made of the semiconductor surfaces after each diffusion. The p- n junction depths were also measured and some electrical measurements were taken. For some experimental conditions, very high values of zinc surface concentration were found. The samples showing high surface concentrations also exhibited surface features after diffusion, and these were studied using optical microscopy and an X-ray probe microanalyser. In some cases very small changes in diffusion conditions produced large variations in the measured profile. This is attributed to a boundary being crossed in the In/P/Zn ternary phase diagram. A comparison of the radio-tracer and p- n junction measurements shows that the number of zinc atoms in a sample is much greater than the number of shallow acceptors. For diffusions in which excess phosphorus was used, evidence is presented to suggest that the diffusion coefficient varies with zinc concentrations at low densities of zinc, but saturates to a constant value at zinc concentrations above 10 19 cm −3.