INTERIMPURITY RECOMBINATIONS INVOLVING ISOELECTRONIC TRAP BISMUTH IN GALLIUM PHOSPHIDE

A new type of pair spectrum involving the radiative recombination of holes bound to Bi isoelectronic traps with electrons bound to remote shallow group-VI donors has been observed in GaP. The existence of these spectra proves that an isoelectronic impurity forms a stable trapping state for a single electronic particle. The binding energy of this state can be calculated from the positions of the pair spectra, and is 401 meV for the Bi hole trap in GaP. The prominent phonon sidebands in the Bi-donor pair spectra and in the luminescence spectrum due to recombination from the J=1 Bi bound exciton state are similar, although the latter contains more detailed structure. The relatively large increase in the transition energy with decreasing pair separation r, characteristic of donor-acceptor pair spectra, is not observed in the Bi-donor pair spectra, where the first-order Coulomb interaction is zero because the Bi trap is neutral before the hole is captured. Instead, the Bi-donor pair transition energy decreases slightly with decreasing r as a result of the electrostatic polarization interaction between the charged Bi trap and the neutral donor. The low-temperature time decay of both the Bi-donor and donor-acceptor pair spectra in GaP are slow and nonexponential, confirming that remote Bi-donor pairs of widely variable separation are involved. The decay time of the total luminescence is dramatically reduced, and the slow-decaying Bi-donor pair luminescence is quenched relative to the fast Bi-exciton luminescence, when the temperature is increased above 15°K. These changes are attributed to the phonon-assisted tunneling of electrons from the donors to Bi traps already filled by holes. © 1969 The American Physical Society.