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(C) mode experiences a strong composition-dependent redshift as a result of alloying. The peak frequency decreases linearly from the value for pure GaAs (similar to 293 cm(-1)) with the alloyed Bi fraction x and the introduced in-plane lattice strain epsilon(parallel to), by Delta omega(LO) = Delta omega(alloy) - Delta omega(strain). X-ray diffraction measurements are used to determine x and epsilon(parallel to) allowing Delta omega(alloy) to be decoupled and is estimated to be -12(+/- 4) cm(-1)/x for (100) GaAs1-xBix. Delta omega(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. (C) 2013 AIP Publishing LLC.