Valley-orbit splitting

Table 6.6. Valley-orbit splitting ls(Ai) — Is (T2)(rneV(crri 1 in parentheses)) of the isolated single donors in germanium...

A valley-orbit splitting of the Is state of Nc is apparent from this figure as a temperature raise populates the ls(E) state (a normal ordering of the levels is assumed). The transitions from the ls(E) state are clearly broader than those from ls(Ai). Small sharp lines can also be observed in the two spectra of Fig. 6.10, showing no thermalization effect. They are attributed to an unidentified effective-mass donor with no detectable valley-orbit splitting, denoted EMD in the original reference [170]. 

The measured Is (Ai) - ls(E) valley-orbit splitting of the Nc donor is 8.36meV so that the ls(E) level energy is 45.83meV, slightly less than the one-valley EM value, but such a situation is also encountered for the Sb and Bi ls(E) levels in silicon (Table 6.5). For EMD, E10 is close to that calculated in the EMA and no valley-orbit splitting is detected. 

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. 

Table 5.9. Comparison between the experimental values and spacings (meV) of the Is manifold energy levels showing the amplitude of the valley-orbit/chemical splittings of the group-V donors in silicon and germanium and the calculated values of [2], where no chemical effect is included. More accurate experimental values of the E (Is (Ai)) are given in Tables 6.3 and 6.7...

Fig. 6.17. Enlargement of the spectral regions of the 2p i and 3p i lines of Mg+ showing their splitting (236 and 74 peV, respectively) by valley-orbit and central-cell interactions. The split components are indexed l and h in Table 6.18 [249]. Copyright 1994 by the American Physical Society...

All ZPS profiles show respectively a main valley corresponding to the bulk component. The peak above the valley results from polarization (P) of the otherwise valence electrons by the densely entrapped electrons (T) in the bonding and core orbits. The second peak and the second valley at the bottom edge of the bands result from the joint effects of entrapment and polarization. The locally polarized electrons screen and split the crystal potential and hence split the core band into the P and the T components, which has no effect on the bulk component. The valence LDOS of W(320) atoms exhibits apparently the CN-resolved polarization of W atom at the terrace edge, which is the same to the Au clusters in Fig. 13.3. 

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