Acoustic Properties of n-Type Ge with Donor Pairs
In a semiconductor lightly doped with shallow donor impurities, donors are isolated and the system is simply a collection of noninteracting donor states which are described by the effective-mass theory. In the case of group V donors in Ge, the donor states consist of the singlet ground state and the triplet excited states which are energetically separated by the valley-orbit splitting 4Δ. The magnitude of 4Δ is sensitive to the species of impurities, i.e., 4Δ/kB=49 K (As), 33 K (P), and 3.7 K (Sb)/1/. Because of the donor states mentioned above, donors strongly interact with the low-frequency phonons.
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