Phonon spectra of ultrathin GaAs/AlAs superlattices: An ab initio calculation

Phonon spectra of ultrathin (GaAs)n(AlAs)n (001) superlattices are studied theoretically using linear-response density-functional techniques. Results are presented for n=1,2,3 superlattices, along with prototype supercell calculations aimed at simulating a completely disordered (alloy) as well as some partially disordered superlattices. Besides interfacial disorder, which modifies the effective confinement length of low-order longitudinal-optic phonons, we find that—in the ultrathin regime—some degree of cationic mixing must also affect inner planes in order to explain experimental findings.