Raman Scattering Study of In_(x)Ga_(1-x)N Alloys with Low Indium Compositions

In_(x)Ga_(1-x)N alloys with low indium composition x in the range 0.13 ≤ x ≤ 0.23 are systematically studied mainly based on a Raman scattering technique.Scanning electron microscopy and x-ray diffraction results show that our samples can be divided into two groups:pseudomorphic (0.13 ≤ x ≤ 0.16) and relaxed (0.18 ≤ x ≤ 0.23).The prominent enhancement of A1 longitudinal-optical (LO) mode is found with 325nm laser excitation.For pseudomorphic samples,the frequencies of A1 (LO) phonons agree well with the theoretical predictions,which verifies that the samples are fully strained.For relaxed In_(x)Ga_(1-x)N samples,a linear dependence of the A1 (LO) mode frequency is obtained:Ωo(x) =(740.8 ± 3.3) - (143.1 ± 16.0)x,which is the evidence of one-mode behavior in In_(x)Ga_(1-x)N ternary alloys.Residual strains in these partially relaxed samples are also evaluated.