[Optical characteristics of InGaN/GaN light emitting diodes on patterned sapphire substrate]

In the present paper, optical characteristics of InGaN/GaN multiple quantum wells light emitting diodes fabricated on the conventional (C-LEDs) and patterned sapphire substrates (PSSLEDs) were investigated by electroluminescence (EL) and photoluminescence (PL). PSSLEDs show higher light output power and smaller full width at half maximum (FWHM) of EL than those of C-LEDs for their better crystalline quality. The FWHM of EL for PSSLEDs exhibits faster broadening as current increases than C-LEDs, while the same broadening of FWHM of PL as excitation power increases is shown in PSSLEDs and C-LEDs, which indicate that there is stronger band filling effect in PSSLEDs caused by relatively higher carrier density in their QWs at the same current injection level. Besides, smaller blue-shift of peak wavelength of EL as injection current increases in PSSLEDs suggests that piezoelectric field in PSSLEDs is weaker than that in C-LEDs. Therefore, comparing the changes in external quantum efficiency as current increases for PSSLEDs and C-LEDs, more serious efficiency droop for PSSLEDs could not be mainly caused by piezoelectric field in QWs.