Bound Phonons and Bistability of Donors in Ga_l-xA1_xAs: Te

Bound phonons in Te-doped Ga_l-xA1_xAs were first observed in Raman scattering experiments at low temperature. They are assigned to electrons trapped at an effective-mass-like level. At higher temperatures, this level disappears to the benefit of a stable DX-like deep level. These results reveal a shallow-deep bistable characters of donors in Ga_l-xA1_xAs: Te under some conditions.