AFM images of surfaces (a) E856 and (b) E867. The root-mean-square surface roughness values are 0.7 and 0.5 nm for E856 and E867, respectively.
IRR spectra (a) E856 on a GaN layer on an (0001) substrate and (b) E867 on a bulk GaN substrate. The bandgap and the absorption edge energies are indicated. The open circles are the experimental plots and the solid curves are the best-fit functions.
Williamson–Hall plots of the FWHM values of the XRC peaks. The symbols are the experimental results and the solid curves are the best-fit functions.
Dependence of PL spectra of E867 on temperature. The peak intensity is normalized.
Dependence of PL peak energy and emission efficiency of E856 on excitation power . The open circles represent the PL peak energy and the closed circles represent . and .
Dependence of on (a) and (b) for samples with various electron densities and twist angles. The measurement temperature and excitation power are 294 K and 1 mW, respectively. Two points on E856 and E867 are labeled with the sample numbers in each figure.
PLE spectra for several and values. Absorption spectrum (solid curve) is plotted as a reference. PL is observed at the energy level indicated by the arrow. The values of and are denoted in the figure.
Dependence of the normalized PL intensity on (a) and (b) .
Dependence of the normalized PL intensity on temperature. [(a) and (b)] and [(c) and (d)] are plotted as a function of or . These parameters of and are independent of the XRC peak widths.
InN layer parameters obtained by IRR spectrum fitting for E856 and E867. The sheet electron density of near the GaN interface is for E856 grown on an substrate and for E867 grown on a bulk GaN substrate. Plasmon broadening factor is for these layers. The electron density and plasmon broadening of the bulk GaN substrate are and , respectively.
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