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9 February 2012 The impact of active layer design on quantum efficiency of InGaN light emitting diodes
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The effect of active layer design on the efficiency of InGaN light emitting diodes (LEDs) with the light emission in blue (~420 nm) has been studied. Correlation between the internal quantum efficiency (IQE) and relative external quantum efficiency (EQE) and salient features of structures on c-plane InGaN LEDs which contain multiple quantum wells (MQWs) of different barrier height (either In0.01Ga0.99N or In0.06Ga0.94N barriers) and thickness (3 nm and 12 nm) as well as different double heterostructure (DH) designs (3 nm, dual 3 nm, 6 nm, dual 6 nm, 9 nm and 11 nm) with inserted 3 nm In0.06Ga0.94N barrier. Pulsed electroluminescence (EL) and optical excitation power-dependent photoluminescence (PL) measurements indicated that the thinner and lower In0.06Ga0.94N barriers bode well for high EQE and IQE. Furthermore, increase of the effective active region thickness by multiple InGaN DH structures (dual, quad and hex) separated by 3 nm In0.06Ga0.94N barriers is promising at high injection levels. Although increasing the single DH thickness from 3 to 6 nm improves the peak relative EQE by nearly 3.6 times due to increased density of states and increased emitting volume, the IQE suffers a nearly 30% loss. Further increase in the DH thickness to 9 and 11 nm results in a significantly slower rate of increase of EQE with current injection and lower peak EQE values presumably due to degradation of the InGaN layer. Increasing the number of 3 nm DH active regions with 3 nm In0.06Ga0.94N barriers improves EQE, while still maintaining high IQE (above 95% at a carrier concentration of 1018 cm-3) and showing negligible EQE degradation up to 550 A/cm2 due to increased emitting volume and high radiative recombination coefficients and high IQE.
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F. Zhang, X. Li, S. Okur, V. Avrutin, Ü. Özgür, H. Morkoç, S. M. Hong, S. H. Yen, T. S. Hsu, and A. Matulionis "The impact of active layer design on quantum efficiency of InGaN light emitting diodes", Proc. SPIE 8262, Gallium Nitride Materials and Devices VII, 82621G (9 February 2012);

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