Coupling of LO and TA Phonons to the 1.39-eV Broad-Band Luminescent Center in GaAs:Zn

The phonon structure accompanying the broad-band luminescence spectrum centered at 1.39 eV in GaAs:Zn at 4.2^∘{}K has been analyzed to obtain the low-temperature coupling strengths S of both LO and TA, phonons to the center. Values of S(LO)=0.439 and S(TA)=0.818 are obtained. The value of S(LO) is then used in a procedure developed by Hopfield to limit the geometrical extent of the exciton responsible for the luminescence. In the Appendix, Hopfield's procedure is used to obtain formulas for the coupling strength S(LO) for charge densities composed of electron-hole pairs. The results of this calculation are pertinent not only to phonon coupling to exciton charge distributions, but also to coupling to donor-acceptor-pair charge distributions.