Correlation between luminescence and defects in nonpolar and semipolar InGaN/GaN quantum wells on planar and patterned sapphire substrates

The optical and structural properties of nonpolar and semipolar InGaN/GaN quantum wells (QWs) grown on planar sapphire substrates and patterned sapphire substrates (PSSs) were investigated in order to understand the effect of defects on the luminescence. By introducing the PSS technique, surface morphological features were varied in number and size, and the defect density was significantly reduced by the PSS patterns, which resulted in the formation of low-defect regions. The photoluminescence (PL) analyses of nonpolar and semipolar QWs samples revealed that the semipolar (112̅2) QWs, which had better optical performance and higher In incorporation, are more suitable for application to long-wavelength emitters in the green-red spectral range and beyond. Moreover, particularly in the semipolar QWs, we could observe that the optical properties were enhanced by the decrease in defect density. It was also noted that In incorporation was increased in the high-defect regions and in the regions where arrowhead-like features existed.