The effects of etch time on the damage induced during dry etching have been studied. GaAs- and InP-based materials were etched for different times in an electron cyclotron resonance source and the electrical and optical characteristics were measured, Variations in Schottky diode ideality factor (n) and barrier height (phi(b)) were used to measure dry-etch-induced electrical damage at the surface of GaAs after different etch times. The contact resistance of In0.53Ga0.47As, extracted from transmission line measurements, was also investigated for different etch times and compared to the etch time dependence of GaAs. Capacitance-voltage (C-V) measurements from Schottky diodes and photoluminescence (PL) intensity from GaAs/Al0.30Ga0.70As multiple quantum well (MQW) structures were used to investigate the time dependence of the etch damage farther below the surface. The damage in GaAs as shown by n and phi(b) shows marked deterioration after 10 s of etching but improves after longer etching. The contact resistance of In0.53Ga0.47As was found to increase fastest in the first 10 s, but the electrical characteristics did not improve with etch time as the GaAs did. There was no etch time dependence in the C-V measurements from the diodes or the PL spectra from the MQWs, indicating that variations in dry-etch-induced damage with etch time are mostly confined to the surface. Using wet chemical etching, the damage profile was investigated and the most damage was found within similar to 15 nm from the surface for GaAs while In0.53Ga0.47As did not return to the original value after removing 20 nm of the surface. This indicates that the damage generation, removal, diffusion, and channeling mechanisms or rates may be different for the two materials. By changing the temperature of the stage during etching from -130 to 350 degrees C, the etch time dependence of the n and phi(b) of GaAs was affected, indicating that diffusion of defects may be mainly responsible for the variations in electrical characteristics with etch time.