GaAs layers with a high tin (Sn) doping concentration and a smooth surface morphology were successfully grown at temperatures as low as 425 degrees C using tetraethyl tin (TESn) by metal organic vapor phase epitaxy (MOVPE). The samples grown at 650 degrees C showed Sn-rich droplets even with a low TESn molar flow rate of 0.06 mu mol/min, indicating that Sn atoms were not incorporated into the GaAs film but segregated and accumulated on the film surface. Droplet formation was suppressed at a low growth temperature of 425 degrees C. This suggests that the segregation process is kinetically-limited, with the segregation mechanism is slow compared to the growth rate at low growth temperatures. Uncorrected Hall effect measurements found an electron concentration of similar to 1 x 10(19) cm(-3), which is close to the maximum reported doping-limit obtainable in GaAs: Sn grown by MOVPE, while avoiding droplet formation and maintaining a smooth surface morphology. The electron mobility is dominated by the ionized impurity scattering. The sample possesses a generally flat Sn profile extending from the substrate to the film surface. Secondary ion mass spectroscopy indicates that the Sn is electrically active but compensated by carbon acceptors to yield the measured carrier concentration.