DX-center transformation of Te donors in GaSb under hydrostatic pressure

We have observed the transformation of Te shallow donors in GaSb into DX centers at hydrostatic pressures of 27.8±2.6kbar. The position of the Te DX energy level at zero pressure is calculated to lie 300±70meV above the conduction band at atmospheric pressure, consistent with the theory that in the III-V compounds the DX centers line up in energy with respect to the vacuum level within experimental error. This binding energy at zero pressure of the Te DX compares well with the value of 210 meV calculated from the cation-cation bonded DX-center model recently proposed by Park and Chadi. At pressures where the Te shallow donor into DX-center transformation has taken place we observe evidence of the existence of a bound phonon associated with the Te DX center. From its observed pressure dependence the LO optical phonon Gr\"uneisen parameter is calculated to be γLO=0.93±0.09.