Evidence for Dark States in the Temperature Dependent Recombination Dynamics of InGaN/GaN Quantum Wells

• Published in: Japanese Journal of Applied Physics 2013-08, Vol.52 (8), p.08JL12-08JL12-5
• Main Authors: Badcock, Tom J, Dawson, Phil, Oliver, Rachel A, Kappers, Menno J, Humphreys, Colin J
• Format: Article
• Language: English
• Subjects: Decay; Density; Excitation; Gallium nitrides; Indium gallium nitrides; Monitors; Quantum wells; Reduction; Temperature dependence
• ISSN: 0021-4922; 1347-4065
• DOI: 10.7567/JJAP.52.08JL12

The photoluminescence (PL) transients in two highly efficient blue and cyan emitting InGaN/GaN multiple quantum well structures are studied as a function of recombination energy, temperature and excitation density. Based on the form and spectral dependence of the PL decay, the emission is attributed to the recombination of independently localised electron hole pairs throughout the investigated temperature range (10--300 K). To account for the variation of the decay time across the PL linewidth, the $T = 10$ K detection energies are purposely shifted according to the predicted change in InGaN bandgap with increasing temperature. In this way, we monitor the temperature dependence of the recombination lifetime in separate subsets of localised states. We suggest that the observed reduction in decay rate with increasing temperature above ${\sim}80$ K is caused by the thermally induced occupation of optically inactive "dark" states. The reduced temperature sensitivity of the PL decay time under high levels of excitation is consistent with the nature of the dark states being other, higher energy (more weakly) localised states within the distribution.