Raman scattering studies of strain effects in (100) and (311)B GaAs1−xBix epitaxial layers

Abstract

We report room-temperature Raman studies of strained (100) and (311)B GaAs1-xBix epitaxial layers for x ≤ 0.039. The Raman spectra exhibit a two-mode behavior, as well as disorder-activated GaAs-like phonons. The experimental results show that the GaAs-like LO(Γ) mode experiences a strong composition-dependent redshift as a result of alloying. The peak frequency decreases linearly from the value for pure GaAs (∼293 cm-1) with the alloyed Bi fraction x and the introduced in-plane lattice strain ε, by Δ ω LO = Δ ω alloy-Δ ω strain. X-ray diffraction measurements are used to determine x and ε allowing Δ ω alloy to be decoupled and is estimated to be-12(±4) cm-1/x for (100) GaAs1-xBix. Δ ω LO is measured to be roughly double for samples grown on (311)B-oriented substrates to that of (100) GaAs. This large difference in redshift is accounted for by examining the Bi induced strain, effects from alloying, and defects formed during high-index (311)B crystal growth. Raman scattering studies of strain effects in (100) and (311) We report room-temperature Raman studies of strained (100) and (311)B GaAs 1Àx Bi x epitaxial layers for x 0.039. The Raman spectra exhibit a two-mode behavior, as well as disorder-activated GaAs-like phonons. The experimental results show that the GaAs-like LO(C) mode experiences a strong composition-dependent redshift as a result of alloying. The peak frequency decreases linearly from the value for pure GaAs ($293 cm À1) with the alloyed Bi fraction x and the introduced in-plane lattice strain e k , by Dx LO ¼ Dx alloy À Dx strain . X-ray diffraction measurements are used to determine x and e k allowing Dx alloy to be decoupled and is estimated to be À12(64) cm À1

Raman scattering reveals strong LO-phonon-hole-plasmon coupling in nominally undoped GaAsBi: optical determination of carrier concentration

“…where the measured redshift value for the TO band is Δω TO = −27(±4) cm −1 and the value for the LO phonon redshift agrees well with our previous study [18] at Δω LO = −71(±3) cm −1 . Figure 1 indicates that for low hole doping the LOPC mode is slightly blueshifted relative to ω LO before redshifting towards ω TO (crossing at p ∼ 5 × 10 18 cm −3 ) with increasing hole concentrations and reaching ω TO at higher concentrations (p ≥5×10 20 cm −3 ).…”

“…Figure 2(a) shows a typical depolarized RS of (100) GaAs 1−x Bi x , for x = 0.043, showing a two-mode behavior (GaBi-, GaAs-like optical modes) with small disorder-activated GaAslike signatures weakly contributing to the background [18]. confirming the p-type nature of the free carrier present in GaAsBi.…”

“…Two sets of samples were grown, denoted A and B, having nominal epilayer thicknesses 1 μm and 0.3 μm, respectively. Bi content was found by combining X-ray diffraction [18], energy-dispersive X-ray spectroscopy, and photoluminescence [19]. More details of the samples are given elsewhere [20].…”

Photoreflectance and photoluminescence study of localization effects in GaAsBi alloys

“…The average phonon energy of GaAsBi is estimated as $140 cm À1 . This mode is recently observed in GaAsBi Raman studies by Steele et al [47] and also reported by Verma et al [45]. This suggests that the interaction between electrons localized at Bi atoms interact preferentially with the localized GaBi vibration mode.…”

Surface effects of vapour-liquid-solid driven Bi surface droplets formed during molecular-beam-epitaxy of GaAsBi

“…The weak appearance of the GaAs-like TO mode here indicates the presence of Bi-induced structural disorder and matrix deformation, and a subsequent relaxation of the selection rules. Further, there also exists in the spectrum broadband lifting of disorder-activated transverse (DATA) and longitudinal acoustic (DALA) signatures72. The spectrum recorded from the structure at 2 has a very strong TO mode contribution, which is surprisingly large compared to the LO mode, for backscattering from a nominally (001)-oriented growth surface71.…”