Radiative efficiency and spontaneous recombination rate of staggered InGaN quantum wells LED at 420-510 nm

Staggered InGaN quantum wells (QW) grown by metalorganic chemical vapor deposition was demonstrated as improved active region for visible light emitters. Fermi's Golden Rule indicates that InGaN QW with step-function like In distribution leads to significantly improved radiative recombination rate and optical gain due to increased electron-hole wavefunction overlap, in comparison to that of conventional InGaN QW. Spontaneous emission spectra of both conventional and staggered InGaN QW were calculated based on energy dispersion and transition matrix element obtained by 6-band k.p formalism for wurtzite semiconductor, taking into account valence-band-states mixing, strain effects, and polarization-induced electric fields. The calculated spectra for the staggered InGaN QW showed enhancement of radiative recombination rate, which is in good agreement with photoluminescence and cathodoluminescence measurements at emission wavelength regime of 425-nm and 500-nm. Experimental results of light emitting diode (LED) structures at 450-nm utilizing staggered InGaN QW show improvement in output power much higher than what is predicted theoretically. Reduction in non-radiative recombination rate due to improved materials quality, in addition to the enhancement in radiative recombination rate in the staggered InGaN QW could presumably be the reason behind this significant output power improvement.