Resonant Interaction between Hydrogen Vibrational Modes in AlSb:Se

Vibrational modes and their interactions affect numerous physical processes in condensed-matter systems. In the present work, hydrogen vibrations in Se-doped AlSb were investigated with first-principles calculations. Vibrational frequencies were calculated for the longitudinal, transverse, wag (bending), and stretch modes of the Al-H complex. The Al-H stretch mode interacts with a combination mode involving a wag overtone and transverse fundamental. This resonant interaction yields vibrational states that are linear superpositions of the stretch mode and the combination mode. The spatial extent of such excitations is significantly larger than that of a local vibrational mode.

Figure 1

Experimental IR spectrum of AlSb:Se,H [8], showing a resonant interaction between the stretch mode and a combination mode.

Figure 2

Total energy of the AlSb:Se,H complex, calculated for displacements of the Al and H atoms along the stretch- and wag-mode coordinates. Solid lines are fits to anharmonic potentials.

Figure 3

Vibrational density of states versus frequency, calculated using a spring-and-mass model. The height of each bar is proportional to the number of modes. The longitudinal and transverse modes are indicated; the wag and stretch modes are not shown. The black plot is from ab initio calculations [30].

Figure 4

Atomic displacement magnitude versus distance from the H atom in AlSb:Se,H, for the transverse, wag, and stretch modes. The transverse mode lies in the forbidden gap and is therefore much less localized than the wag and stretch modes.