Raman scattering studies of strain effects in (100) and (311)B GaAs_(1-x)Bi_x epitaxial layers

摘要

We report room-temperature Raman studies of strained (100) and (311)B GaAs_(1-x)Bi_x epitaxial layers for x is contained in 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 (~293cm~(-1)) with the alloyed Bi fraction x and the introduced in-plane lattice strain ε‖, by Δε_(LO) = Δε_(alloy) - Δε_(strain)· X-ray diffraction measurements are used to determine x and ε‖ allowing Δε_(alloy) to be decoupled and is estimated to be -12(±4) cm~(-1)/x for (100) GaAs_(1-x)Bi_x·Δε_(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.