Thermal activation of valley-orbit states of neutral magnesium in silicon

Interstitial magnesium acts as a moderately deep double donor in silicon, and is relatively easily introduced by diffusion. Unlike the case of the chalcogen double donors, parameters of the even-parity valley-orbit excited states 1s$(T_2)$ and 1s$(E)$ have remained elusive. Here we report on further study of these states in neutral magnesium through temperature dependence absorption measurements. The results demonstrate thermal activation from the ground state 1s$(A_1)$ to the valley-orbit states, as observed by transitions from the thermally populated levels to the odd-parity states 2$p_0$ and 2$p_\pm$. Analysis of the data makes it possible to determine the thermal activation energies of transitions from the donor ground state to 1s$(T_2)$ and 1s$(E)$ levels, as well as the binding energies of an electron with the valley-orbit excited states.