Optimization of InGaN/GaN quantum wells for violet GaN/InGaN/AlGaN LEDs

We report on the optimization of InGaN/GaN quantum wells (QWs) for use as the active region in violet GaN/InGaN/AlGaN LEDs. Strained In(0.13)Ga(0.87)N/GaN QWs were grown by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. Photoluminescence (PL) measurements revealed the presence of a sizable piezoelectric field, which strongly influences the luminescence properties for InGaN QW widths in the 3 to 12 nm range. The fundamental band gap resonance in the InGaN dielectric function spectrum was found to broaden for an InGaN layer width of 12 nm, as compared to bulk-like InGaN layers, due to piezoelectric field effects. Reducing the QW width to 1.7 nm, however, was found to result in a much sharper band gap resonance, shifted to higher energies and with an increased oscillator strength due to quantum confinement effects. Accordingly, also the highest PL efficiency was observed for that well width, with only very little shift in PL peak position upon variation of the excitation power density. Finally, LEDs were fabricated employing a 2 nm wide GaN/InGaN/AlGaN QW as the active region. These LEDs showed intense electroluminescence with a peak wavelength of 418 nm and a narrow spectral width of 17.4 nm