Ordering effects in Raman spectra of coherently strainedGaAs1−xNx

Abstract

Raman spectra of coherently strained layers of GaAs 1Ϫx N x grown on ͑001͒ GaAs with xϭ0 -0.05 by metalorganic molecular-beam epitaxy are reported. The optical phonons of the GaAs and GaN types, as well as disorder-activated acoustical phonons, are observed. A strongly confined GaAs optical mode at ϳ255 cm Ϫ1 , indicating the ordering of As and N atoms, is also detected. The GaAs-and GaN-type optical phonons exhibit strong diagonal components, forbidden for the zinc-blende structure. A bond polarizability analysis of the Raman selection rules shows that these components are activated by the trigonal distortion of the alloy lattice. The trigonal distortion arises from the formation of ordered ͕111͖-(GaN) m (GaAs) n clusters with nϭmϭ1.

Structural properties of GaAsN∕GaAs quantum wells studied at the atomic scale by cross-sectional scanning tunneling microscopy

“…Nevertheless, the optical emission of ͑In͒GaAsN / GaAs quantum wells ͑QWs͒ showed typically a strong degradation when the N content is increased. [1][2][3] This has been frequently attributed to different phenomena, such as N being incorporated in interstitial positions, 4,5 compositional fluctuations in the alloy, [6][7][8] or a rough top interface. 8 All these have motivated a strong effort in the last years on the structural characterization of ͑In͒GaAsN alloys, but only very few of these studies were performed using cross-sectional scanning tunneling microscopy ͑X-STM͒.…”

Optical phonon behavior in strain-free dilute Ga(As,N) studied by Raman scattering

“…In contrast, a very small redshift, which could be attributed to biaxial-strain effects, was observed in Ref. 2. With regard to this, we would like to remark that the determination of the frequency of the GaAs-like TO peaks performed in the previous works was hampered by the fact that this mode is forbidden due to the selection rules, giving rise to weak, broad features in the Raman spectra.…”

“…It has been shown that the GaAs-like longitudinal optical ͑LO͒ branch of GaAs 1−y N y ͑y Շ 5%͒ shifts to lower frequencies with increasing y. 1,2,5 In contrast, no appreciable frequency variation with composition of the GaAs-like transverse optical ͑TO͒ phonon mode of Ga͑As,N͒ has been observed. The GaN-like LO phonon of Ga͑As,N͒ appears at ϳ470 cm −1 and shifts to higher frequencies with increasing y.…”

“…Several works have used resonant and nonresonant Raman scattering to investigate dilute GaAs 1−y N y layers. [1][2][3][4][5][6][7] In particular, the resonant Raman studies have provided valuable information about the wave function symmetry of the E − and E + subbands of Ga͑As,N͒ observed by reflectance spectroscopy. [3][4][5] The optical phonons of Ga͑As,N͒ exhibit a two-mode behavior in the dilute regime.…”

Optical Properties of GaNAs Grown by MBE

“…However, we have not observed any specific manifestation of the GaN x As 1-x ternary alloy in the Raman spectra, probably because the vibrational LO mode in GaAs is close to the one in the solid solution with very low nitrogen concentration x = 0.017 (as determined by XRD). A recent Raman scattering study of GaN x As 1-x layers with x = 0 -0.05 [24] demonstrated the presence of diagonal components for both the GaAs-and GaN-type optical phonons.…”