We have studied low temperature grown GaAs by electromodulation reflectance spectroscopy for growth temperatures between 200 and 320 °C. The reflectance spectra can be observed only when the concentration of the arsenic antisite defect is lower than3.4×1019 cm−3.The absence of the signal for a rich defect sample is related to the short carrier lifetime and surface depletion width. The transition energies ofE0andE1are found to increase with the decrease of the growth temperatures. The increase of the transition energies is attributed to lattice mismatch and deviation of the stoichiometry. ©1997 American Institute of Physics.