Deep levels in Si-doped In0.49Ga0.51P grown by compound-source molecular beam epitaxy (MBE) have been investigated by deep level transient spectroscopy. In0.49Ga0.51P samples were grown by compound-source MBE with V/III ratios of 4, 10, and 17. Depending upon the V/III ratio three major deep levels with activation energies of 0.26±0.02, 0.36±0.02, and 0.82±0.05 eV were observed. The effect of thermal annealing on the behavior of deep levels was also investigated. The deep levels in InGaP grown by compound-source MBE showed behavior of phosphorus antisites and related complexes unlike those found in solid-source MBE-grown InGaP that showed behavior of phosphorus vacancies and related complexes. Si-doped InGaP layers grown with a V/III ratio of 4 showed trap concentration and capture cross section as low as 1.38×1014 cm-3 and 2.9×10-16 cm2, respectively. The results indicate the potential of InGaP grown by compound-source MBE for use in improved low-frequency noise applications. © 2001 American Institute of Physics.