Longitudinal Optical Phonons in Thin Films of CdS, CdSe, and Their Mixtures

LO phonon energies have been determined by means of electron tunneling in Sn-SnO-semiconductor-Sn junctions. For mixtures of CdS and CdSe, we find two distinct structures in the tunneling data which occur at lower energies than the LO phonons for pure CdS and CdSe. These results agree with infrared spectroscopic data on bulk crystals. This agreement provides strong evidence that only short-range forces are important in determining the optical-phonon spectra.