Effects of growth pressure on the structural and optical properties of multi quantum wells (MQWs) in blue LED

The effects of growth pressure in metal-organic chemical vapor deposition (MOCVD) on the structural and optical properties of InGaN/GaN multiple-quantum-wells (MQWs) grown on c-plane sapphire substrate were investigated by scanning transmission electron microscopy (STEM), atom probe tomography (APT), Raman spectroscopy and electroluminescence (EL) spectroscopy. As the growth pressure decreased, the growth rate of the InGaN layer increased, leading to a decrease in the frequency of the GaN A1(LO) mode peak and broadening of its full width half maximum (FWHM). The intensity of the EL spectra peaked at a growth pressure of 250 Torr with a narrow FWHM at high forward current. These optical properties are explained by either a high degree of compositional fluctuation of indium in the MQW and/or the high crystallinity of the InGaN layer due to the low growth rate under high pressure.