title: Interface phonon modes in the [AlN/GaN]20and [Al0.35Ga0.65N/Al0.55Ga0.45N]202D multi-quantum well structures.
abstract: The observation of interface (IF) phonon modes in the recorded Raman spectra of c-plane oriented [AlN/GaN]20and [Al0.35Ga0.65N/Al0.55Ga0.45N]20multi-quantum well (MQW) structures grown via plasma assisted molecular beam epitaxy is reported. The nominal shift in the IF phonon mode of E1symmetry for [Al0.35Ga0.65N/Al0.55Ga0.45N]20compared to that of the [AlN/GaN]20MQW structure is understood on the basis of change in dielectric constants (εm) of the surrounding medium. The presence of buffer layers in [Al0.35Ga0.65N/Al0.55Ga0.45N]20MQW over a sapphire substrate is also understood by characterizing the IF phonon mode of A1symmetry. The observed IF phonon modes in the spectra are attributed to the relaxation of Raman selection rules away from the Brillouin zone centre because of the breakdown of the translational symmetry of surface potential due to the presence of the periodic interfaces and surface modulations in the superlattice structures of MQWs. The corresponding required edge lengths (L) of 2D plates, for the observation of the breakdown of the surface potential, are computed from the simulated dispersion relation curve of IF modes. The integral multiples of uniformly distributed platelets, originated due to the horizontal uneven irregularities on the surface of superlattices, are matched with the calculated L values.
authors.affiliation: Nanomaterials and Sensors Section, Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Homi Bhabha National Institute, Kalpakkam-603102, India. sivankondazhy@gmail.com dhara@igcar.gov.in.
authors.forename: A K
authors.initials: AK
authors.lastname: Sivadasan
authors.affiliation: Centre for Research in Nanoscience and Nanotechnology, University of Calcutta, JD2, Sector-III, Saltlake City, Kolkata-700106, West Bengal, India.
authors.forename: Chirantan
authors.initials: C
authors.lastname: Singha
authors.affiliation: Institute of Radio Physics and Electronics, University of Calcutta, 92, A.P.C. Road, Kolkata-700009, West Bengal, India.
authors.forename: A
authors.initials: A
authors.lastname: Bhattacharyya
authors.affiliation: Nanomaterials and Sensors Section, Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Homi Bhabha National Institute, Kalpakkam-603102, India. sivankondazhy@gmail.com dhara@igcar.gov.in.
authors.forename: Sandip
authors.initials: S
authors.lastname: Dhara