RESONANT INTERACTION BETWEEN LOCAL VIBRATIONAL MODES AND EXTENDED LATTICE PHONONS IN AlSb

Using infrared spectroscopy we have observed Se-H stretch and wag local vibrational modes (LVM’s) in AlSb. The frequencies of the wag mode harmonics are explained by perturbation theory. In addition, there is evidence of a resonant interaction between LVM’s and multi-phonon modes. This interaction leads to a splitting of the SeH stretch mode into three peaks at 1606.3, 1608.6, and 1615.7 cm at liquid-helium temperatures. As the temperature or pressure is increased, the stretch mode and multiphonon modes show anti-crossing behavior. Introduction. In this paper, we report evidence of a resonant interaction between LVM’s and extended lattice phonons that gives rise to a new collective excitation called a “localon.” This resonance is similar to the Fermi resonance between wag and stretch local vibrational modes (LVM’s) in donor-hydrogen complexes in silicon [1]. By varying the temperature and pressure to change the phonon energies, we have studied the evolution of the localon spectra in AlSb. As we have noted previously [2], at liquid-helium temperatures, hydrogenated AlSb:Se has stretch mode peaks at 1608.6 and 1615.7 cm, whereas the Se-D mode has only one stretch mode peak at 1173.4 cm. In addition, there is a small Se-H peak at 1606.3 cm. Hydrogenated and deuterated AlSb:Te have only one stretch mode peak each, at 1599.0 and 1164.4 cm respectively. The ratio of the three Se-H peak areas is constant from sample to sample, which suggests that they are not due to additional impurity complexes. The details of the crystal growth, sample preparation, and hydrogenation techniques are given in Ref. 2. Experimental details. Variable temperature spectra were obtained with a Bomem DA8 spectrometer with a KBr beamsplitter and a mercury cadmium telluride (MCT) detector. Variable pressure spectra were obtained with a Digilab 80-E spectrometer with a KBr beamsplitter and an instrumental resolution of 1 cm. To generate hydrostatic pressures up to 15 kbar, we used a modified Merrill-Basset diamond-anvil cell [3,4]. The liquid immersion-technique [5] was used to load the cell with liquid nitrogen. A light-concentrating cone focused the light through the diamonds and sample and into a Ge:Cu photoconductor mounted directly behind the sample. We used the pressure dependence of the AlSb:CSb LVM as a precise in situ calibration of the sample pressure [6]. Materials Science Forum Vols. 258-263 (1997) pp. 1247-1252