Experimental and theoretical studies of phonons in hexagonal InN

Abstract

The first- and second-order Raman scattering and IR reflection have been studied for hexagonal InN layers grown on (0001) and (11̄02) sapphire substrates. All six Raman-active optical phonons were observed and assigned: E2(low) at 87 cm−1, E2(high) at 488 cm−1, A1(TO) at 447 cm−1, E1(TO) at 476 cm−1, A1(LO) at 586 cm−1, and E1(LO) at 593 cm−1. The ratio between the InN static dielectric constants for the ordinary and extraordinary directions was found to be ε⊥0/ε∥0=0.91. The phonon dispersion curves, phonon density-of-state function, and lattice specific heat were calculated. The Debye temperature at 0 K for hexagonal InN was estimated to be 370 K.

InN Thin Film Lattice Dynamics by Grazing Incidence Inelastic X-Ray Scattering

“…There is excellent agreement between experimental and calculated data. Raman data for the lower energy E 2 mode, 87 cm À1 , reported by Davydov and co-workers [6] are also in agreement with the extrapolation of IXS data at low momentum transfers, 90ð1Þ cm À1 . In conclusion, this work demonstrates the feasibility of grazing incidence IXS to provide valuable information on the lattice dynamics of thin films, with an interest in many fields of material science, such as novel advanced materials, semiconductors, and superconductors.…”

“…Most of the data (purple or light gray solid circles) were taken using an in-plane scattering geometry with mixed longitudinal and transverse character, taking full advantage of the multianalyzer spectrometer of ID28. The (red) squares display data mode from Ref [6]. Momentum transfers are given in reciprocal lattice units.…”

“…Usually grown by molecular beam epitaxy (MBE), state-of-the-art high quality InN films rarely exceed 10 m thickness, thus preventing the use of standard bulk techniques to measure phonon dispersion relations. The available InN experimental data stem therefore mainly from Raman and infrared spectroscopy [5,6], and new technical developments are required to complete this information over the entire Brillouin zone (BZ).…”

Electron–phonon energy transfer in hot-carrier solar cells

“…It has been suggested [9,10] that, since thermal coupling is produced with optical phonons, some materials like InN with large phononic band gap [7,8] might have a poor thermal coupling between optical and acoustic phonons. This behaviour has been also related to the phonon bottleneck in low-dimensional structures.…”

“…gap [7,8]. No HC solar cell has been fabricated so far but an elegant concept has been suggested [9,10] for the thermal isolation of the electrons consisting of avoiding the thermal contact between acoustic and optical phonons while the latter are kept at the electrón temperature.…”