Phonons in strained In1-xGaxAs/InP epilayers.

Raman spectroscopy has been used to assess the concentration dependence of optical phonons in In[sub 1-x]Ga[sub x]As epilayers grown by chemical beam epitaxy on InP(100). The alloy composition was varied from x=0.325 to x=0.55 to cover the technologically important and physically interesting range where the strain changes sign at x=0.468 from negative to positive. The Raman spectra were curve resolved to reveal the GaAs-like longitudinal optic (LO), disorder induced, InAs-like LO, and InAs-like transverse optic phonons. An examination of the concentration dependence of the phonon frequencies showed that the GaAs-like LO mode varied as ω(cm[sup -1])=252.77+58.643x-50.108x[sup 2] for 0.325≤x≤0.55. A comparison of these results with previous infrared and Raman work on In[sub 1-x]Ga[sub x]As has revealed that the concentration dependence of the optical phonon frequencies in the unstrained system is still not accurately known. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]