A New Look on InN2474. Optical Characterizations Although 1.9 eV was taken to be the energy gap of InN, light emission at 1.9 eV has never been reported before 2002 while other optical measurements, like absorption and Raman, can be seen in literatures with quite a quantity. In 2002, Davydov et al. reported the first InN PL at 0.8 ~ 0.85 eV for samples with n - 9 - 12xl018 cm"3. This near IR light emitted from InN creates great momentum towards achieving more solid facts around this new finding. A typical PL spectrum measured at room temperature is shown in Fig. 7. Proper selection of the detectors and gratings in the visible and the IR range has to be done to ensure the optimization of the signal. Usually, a photomultiplier tube (PMT) is used in the visible range and either an IR-enhanced InGaAs or a PbS detector is used in the IR range. All the samples in Fig. 2, poly- or single-crystals, displayed a unique peak in the IR and no 1.9 eV was observed. PL dependence on temperature110 and laser power66 was performed. It is worth a note that reports from samples grown by the technique of electron cyclotron resonance MBE (ECR-MBE) yield a luminescence around 1.9 eV which may result from possible system-related oxygen inclusion.25'67c3nii'i'i.Q8lnNonSi(111)3, 6�4J:B 2i �I i I i Lca! 0.51.01.52.02.5Energy (eV)Fig. 7. Room-temperature PL results of InN epifilm on Si. No prominent peak can be detected in the range of 1.0 - 2.3 eV.
