Raman Scattering and Structure Properties in InPSb Alloys

We grew a series of InP1-xSbx on (0 0 1) InAs substrate by gas-source molecular beam epitaxy, and reported on the structural properties of ternaries with two Sb composition, x = 0.17 and x = 0.36. Results from high resolution x-ray diffraction (XRD) and reciprocal space mapping (RSM) show that the sample with x = 0.17 suffers from phase separation while the sample with x = 0.36 is of good crystallinity and coherently strained to the substrate. For the latter sample, the InP bond length obtained from extended X-ray absorption fine structure (EXAFS) coincides with the value from valence force field (VFF) calculation, and the mean atomic deviation from the zincblende lattice is zero. We have shown that because of the zero mean, the XRD and RSM are not affected by the internal distortion. For the sample with x =0.17, the InP bond length obtained from EXAFS is much shorter than the value calculated by VFF model, suggesting the loss of long range order, i. e., the mean of atomic deviation is not zero, in other words, the zincblende lattice from which the atoms deviate no longer exists and the long range order is lost. We believe that the bond distortion in this sample has been partially released through defect generation. Raman scattering also supports these findings. The sample with x = 0.17 shows distinct InP-like and InSb-like modes. While the InP-like modes of the sample with x = 0.36 merge to a wide band, which is attributed to a one-bond-multi-mode behavior induced by the internal distortion. Polar plot with the analyzer aligned to [1 0 0] was used to quantify the effect of distortion on the modes. The three modes for the sample with x = 0.36 show different behaviors. The influence of internal distortion decreasing with the decreasing bending distortion. The strong bending distortion hinders the bond to obey the normal vibration. In the sample with x = 0.17, the three modes are all dominated by asymmetry vibration, suggesting that they are activated by defect vibration. Due to the complexity of these modes, we label the high frequency peak as InP-like I while InP-like II accounts for the low frequency end in the final.