Modification of CdSe resistivity by laser annealing

The resistivity of CdSe thin films, vapor deposited on insulating substrates, has been reduced by more than two orders of magnitude by irradiation with a cw argon-ion laser. A threshold power density of about 0.6 W for a beam diameter of 250 μm is necessary to cause a measurable decrease in the resistivity of a 0.4-μm-thick film; above this value, the resistivity decreases rapidly with increasing power to a minimum value. Electron and x-ray diffraction analyses show that there is an increase in film grain size by only a factor of 2 on annealing, but SEM and Auger studies indicate that there are significant changes in the surface topography and composition. Calculations show that the power absorbed by the CdSe film is sufficient to cause melting. The decrease in resistivity can be attributed to the effect of Se vacancies created by preferential loss of Se from the film surface at these elevated temperatures.