Redetermination of the valley-orbit (chemical) splitting of the 1sground state of group-V donors in silicon

The sixfold degeneracy of the 1s(${\mathit{A}}_1$+E+${\mathit{T}}_2$) ground state of substitutional group-V donors in Si, originating from the six Δ conduction-band minima, is lifted by the valley-orbit (chemical) splitting, with 1s(E) and 1s(${\mathit{T}}_2$) remaining close to the effective-mass position and 1s(${\mathit{A}}_1$) depressed significantly. The binding energies of 1s(${\mathit{A}}_1$), 1s(E), and 1s(${\mathit{T}}_2$) are accessible to an experimental determination through the observation of the 1s(${\mathit{A}}_1$),1s(E),1s(${\mathit{T}}_2$)→${\mathit{np}}_0$,${\mathit{np}}_{\pm }$ transitions in the Lyman spectrum of the neutral donors, where the ${\mathit{p}}_0$ and ${\mathit{p}}_{\pm }$ levels are accurately described in the effective-mass theory. We have remeasured the excitation spectrum of Si(P, As, Sb, or Bi) in the temperature range 1.8–100 K under high resolution and signal-to-noise ratio; while only the 1s(${\mathit{A}}_1$)→${\mathit{np}}_0$, ${\mathit{np}}_{\pm }$ transitions are observed at the lowest temperature, the 1s(E),1s(${\mathit{T}}_2$)→${\mathit{np}}_0$,${\mathit{np}}_{\pm }$ transitions appear on thermally populating 1s(E) and 1s(${\mathit{T}}_2$).