Potential-dependent electron and holegvalues and quenched diamagnetism in GaP. I. Experimental results and properties of the donor states

In this paper we present the results of an investigation of the radiative recombination of excitons bound to neutral S, Se, and Te donors in GaP in external magnetic fields of up to 16.5 T and, in one case, 18 T. The complete set of spectroscopic $g$ values for the initial bound exciton and the final donor state and the different diamagnetic effects are evaluated for all three donors. This is the first report of diamagnetic effects in GaP. A diamagnetic shift and a splitting are observed, both anomalously small. A small tendency for an increase in the diamagnetic coefficients of the principal bound-exciton transition which leaves the donor in its ground state and a more dramatic increase for transitions to donor excited states with increasing quantum number are established. It is suggested that the principal two-electron lines all involve transitions to the $s\left(A_1\right)$ donor excited states. This new identification provides a more plausible position of the series limit $E_{\lim }$ of the donor than hitherto. The electronic $g_e$ value of the donor turns out to be equal to 2.00, independent of the chemical nature of the donor. This value agrees with the value derived from ESR experiments. A recent supposition, that in general there might be a difference between luminescence and ESR $g_e$ values is disproved. The isotropic hole $g$ value is observed to decrease with increasing localization of the hole due to changes in the impurity central cell potential. These effects are given a detailed interpretation in the following paper.