Temperature Dependence of Raman Scattering in 4H-SiC Films under Different Growth Conditions

The microRaman scattering of 4H-SiC films, fabricated by low pressure chemical vapor deposition under different growth conditions, is investigated at temperatures ranging from 80 K to 550 K. The effects of growth conditions on E₂(TO), E₁(TO) and A₁(LO) phonon mode frequencies are negligible. The temperature dependences of phonon linewidth and lifetime of E₂(TO) modes are analyzed in terms of an anharmonic damping effect induced by thermal and growth conditions. The results show that the lifetime of E₂(TO) mode increases when the quality of the sample improves. Unlike other phone modes, Raman shift of A₁ (longitudinal optical plasma coupling (LOPC)) mode does not decrease monotonously when the temperature increases, but tends to blueshift at low temperatures and to redshift at relatively high temperatures. Theoretical analyses are given for the abnormal phenomena of A₁(LOPC) mode in 4H-SiC.