Quantum electrodynamics (QED) effects in intense laser-plasma interaction were investigated using particle-in-cell (PIC) simulations, specifically the generation of electron-positron pairs. Linearly polarized intense laser pulses were used to irradiate a thin foil (1-\mu \text{m} ) with an intensity of 4\times 10^{23} W cm-2. A scan of targets with varying Z (Al, Cu, and Au) is investigated to determine the effect of target Z /density on electron-positron pair production. The total number of pairs created for Al and Cu targets is 1014 and 1013, respectively. In the case of Au, we did not observe any pair production to occur. We have also calculated the variation in electron energy in these targets. The results indicate that target Z plays a very important role with the laser interaction in the pair production process, which will be explained in this article. © 1973-2012 IEEE.