Spin-valley splitting

Fig. 6.5. Absorption spectrum from the Is excited states of Sb donors in silicon, showing the spin-valley splitting of the ls(T2) state, observed by raising the temperature of the sample to 30K. The lowest energy line of the Is (Ai) spectrum is at 31.24meV (251.9cm-1). The spectral range is 145.2-243.6cm-1. [Sb] is 2.6 x l()lr crri 3 [163]. Copyright 1993 by the American Physical Society...

Some lines associated with the deepest donor excited states of the S2+ and Se2+ pairs and of ScXi+ and SecXi+ have also been observed and their positions are given in Table6.19. By analogy with the ls(T2) state of the Ch+ donors, the 1 s (E-) state of the Ch.j donors with />j(j symmetry can be assumed to be split by spin-valley interaction into 1 sly and 1 sTg, where IV, and T are single-valued IRs of the double group of Dm. In Table 6.19, the two first low-energy lines of S2"1" and Se2+ are labelled accordingly. 

The Ch-related donor spectra differ on that point as several parity-forbidden transitions are observed. They start with symmetry-allowed transitions from the Is ground state to the valley-orbit split Is excited states, and are supplemented with 2s (T2) and 3s (T2) lines and Fano resonances within the photoionization spectrum. This is shown in Fig. 6.13 for Se°. Compared to group-V donors, this extends the energy span of the Ch°-related spectra to the ionization energy of the Is (T2) level (35-40 meV in isolated chalcogens) and it can even increase to 40-48 meV when singlet-triplet spin-forbidden transitions are observed. 

---