ESR study of heavily doped GaAs:Er grown by organometallic vapor phase epitaxy

X-band ESR measurements of heavily doped GaAs:Er, whose Er concentration was 1.7x10(20) Cm 3 grown without additional 0, flow by organometallic vapor phase epitaxy (sample II), have been performed at 3.5K. Although we observed an isotropic ESR signal around g=6 in the GaAs:Er sample whose Er concentration was 3.6x10(18) cm(-3) gown with additional O-2, flow by OMVPE (sample I), we did not observe an isotropic ESR signal around g=6 in sample II. It suggests that Er centers at the tetrahedral sites decreased in sample II Several ESR signals with anisotropic g-values, which are different from those in sample I, were also observed in sample II, suggesting the formation of new Er centers with oxygen in sample II The origin of these ESR signals will be discussed in connection with PL results.