OBSERVATION OF IMPURITY MIGRATION IN LASER-DAMAGED JUNCTION DEVICES

Redistribution of phosphorus dopant in 1N2175 phototransistors damaged by a pulsed neodymium laser has been investigated using the electron microprobe technique. Four different effects observed in the concentration profiles were explained by the action of diffusion and segregation, in the presence of temperature and compositional gradients. One specific effect was analyzed using a simplified model consisting of diffusion in the melt followed by the segregation upon refreezing. It was estimated that certain areas of the phototransistor surface remained above the melting point for times of the order of 10** minus **4 sec. Correlation was made between the results of these microprobe measurements and previously observed laser-damage effects in the electrical characteristics. It is suggested that impurity migration may be an important mechanism for damage to junction devices by pulsed lasers in an intermediate energy range.