The dielectric functions of GaN for the temperature and frequency ranges of 10–300 K and 0.3–1 THz are obtained using terahertz time-domain spectroscopy.It is found that there are oscillations of the dielectric functions at various temperatures.Physically,the oscillation behavior is attributed to the resonance states of the point defects in the material.Furthermore,the dielectric functions are well fitted by the combination of the simple Drude model together with the classical damped oscillator model.According to the values of the fitting parameters,the concentration and electron lifetime of the point defects for various temperatures are determined,and the temperature dependences of them are in accordance with the previously reported result.Therefore,terahertz time-domain spectroscopy can be considered as a promising technique for investigating the relevant characteristics of the point defects in semiconductor materials.
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.
