Study of Two-Electron Transitions of a Donor in CdSe

Two-electron transitions, in which an exciton bound to a neutral donor decays leaving the donor in an excited state, were measured in CdSe. The donor was not identified. The transition energies from the 1s ground state to the $2s$, $2p$, $n=3\mathrm{}$, and $n=4\mathrm{}$ levels were measured. The transitions were identified by their Zeeman splittings. The spectrum was complicated because a number of the transitions originated from excited states of the three-particle bound-exciton complex. There was a one-to-one correspondence between this spectrum and the two-electron spectrum previously observed in CdS. From these measurements, we deduce that $E_D=19.5\mathrm{}\pm 0.3$ meV and $m=(0.13\mathrm{}\pm 0.005)m_e$, where $E_D$ is the donor binding energy, $m$ is the measured electron mass, and $m_e$ is the free-electron mass.