Raman studies of nitrogen incorporation in GaAs1−xNx

Abstract

We report direct-backscattering Raman studies of GaAs1−xNx alloys, for x⩽0.03, grown on (001) GaAs. The Raman spectra exhibit a two-mode behavior. The allowed GaAs-like longitudinal-optic phonon near 292 cm−1 is found to red shift at a rate of −136±10 cm−1/x. This is well described by the combined effects of strain and alloying. The GaN-like phonon near 470 cm−1 is observed to increase in intensity in direct proportion to x, and to systematically blue shift at a rate of 197±10 cm−1/x. This blue shift is likewise attributed to strain and alloying. The GaAs-like second-order features are also seen to broaden slightly and diminish in intensity with increasing nitrogen concentration. These results are attributed to a weak breakdown in the zincblende-crystal long-range order, possibly related to the presence of ordered domains within the random alloy.

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

“…5 Second-order features appear in the 300-400 and 480-600 cm −1 ranges. 1 As in the case of the strained Ga͑As,N͒, we observe the GaN-like LO mode at ϳ470 cm −1 . 1,5 Next, we carry out a detailed analysis of the frequency behavior of the different first-order optical modes of strainfree, dilute Ga͑As,N͒.…”

“…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.…”

“…The GaN-like LO phonon of Ga͑As,N͒ appears at ϳ470 cm −1 and shifts to higher frequencies with increasing y. 1,4-6 Prokofyeva et al 1 studied a series of strained Ga͑As,N͒ epilayers grown pseudomorphically on GaAs and showed that the downward frequency shifts of the GaAs-like LO mode arise from two different causes: ͑i͒ biaxial strain and ͑ii͒ alloying effects. The interest of studying relaxed Ga͑As,N͒ layers to confirm that alloying redshifts this mode was recognized in that work.…”

“…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.…”

“…The interest of studying relaxed Ga͑As,N͒ layers to confirm that alloying redshifts this mode was recognized in that work. 1 Such type of study on strain-free samples is of particular importance in dilute Ga͑As,N͒ because the elastic constants of this compound might exhibit some deviation from Vegard's law, 8 and this would affect the analysis of the strain-induced phonon frequency shifts in the strained epilayers. Likewise, the frequency shifts observed for the GaN-like LO mode in previous works are likely influenced by biaxial-strain effects.…”