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Abstract: The Raman spectra of N-doped 4H–SiC single crystal films is investigated between 100 and 600K. The temperature dependence of the three optical modes is obtained. These measurements reveal that all Raman peaks shift to lower frequencies with increasing temperature, except A1(LO). The temperature dependence of A1(LO) phonon modes in the round pit also manifests different features with temperature increasing, but the demarcation temperature point of the blueshift and the redshift in the round pit is higher than that in the outer area. At high temperature, all active phonon modes clearly become broader, but the linewidth of the E1(TO) phonon mode from round pit increases with temperature more rapidly than that from the outer area, this indicates that the lifetime of the E1(TO) phonon in round pit is more sensitive than that in the outer area. [Copyright &y& Elsevier]

Deep level luminescence in In0.07Ga0.93N:Mg was examined. A strong photoluminescence (PL) band at 2.45 eV was observed with a well-resolved fine structure that was attributed to phonon-assisted donor-acceptor pair (DAP) recombination. Analysis of the fine structure reveals a large Huang--Rhys parameter of 6.5 for this DAP band, indicating strong localization of carriers at DAP centers. From the phonon replicas, the longitudinal-optical (LO) phonon energy was determined to be 105 meV. The large, measured phonon energy was attributed to the large compressive strain caused by compositional fluctuations in the films. [ABSTRACT FROM AUTHOR]

Noncontact temperature measurements based on Raman scattering were performed on 4H-SiC with hexagonal defects. These measurements show that the four-phonon process makes a greater contribution to the E2(TO) mode than to the E1(TO) mode. The longer lifetimes of E2(TO) and E1(TO) phonons in hexagonal defects demonstrate that there are fewer possible decay channels than in the defect free zone. The absence of electronic Raman peaks in the hexagonal defects suggests that hexagonal defects seriously limit the uniformity of the nitrogen distribution. The intensity of electronic Raman spectra is related to the density of neutral nitrogen atoms. [ABSTRACT FROM AUTHOR]

The optical properties of Mn-Mg-codoped epitaxial GaN were studied. Addition of Mg acceptors quenches the weak manganese-related photoluminescence (Pl) band at 1.3 eV in GaN:Mn and a series of sharp PL peaks are observed at 1 eV in codoped epilayers. The change in PL spectra indicates that the Mg addition stabilizes the Mn4+ charge state by decreasing the Fermi level. The 1 eV PL peaks are tentatively attributed to intracenter transitions involving Mn4+ ions. Spin-allowed 3d-shell 4T2-4T1 transitions and their phonon replicas are involved. The relative intensities of the sharp peaks are strongly dependent on the excitation wavelength, indicating that the optically active Mn4+ centers involved in the separate peaks are different. The temperature dependence of the PL spectrum suggests the presence of at least three distinct Mn4+ complex centers. [ABSTRACT FROM AUTHOR]