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 In_0.01Ga_0.99N or In_0.06Ga_0.94N 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 In_0.06Ga_0.94N barrier. Pulsed electroluminescence (EL) and optical excitation power-dependent photoluminescence (PL) measurements indicated that the thinner and lower In_0.06Ga_0.94N 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 In_0.06Ga_0.94N 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 In_0.06Ga_0.94N 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.

Date Published: 9 February 2012
PDF: 8 pages
Proc. SPIE 8262, Gallium Nitride Materials and Devices VII, 82621G (9 February 2012); doi: 10.1117/12.903931

Published in SPIE Proceedings Vol. 8262:
Gallium Nitride Materials and Devices VII
Jen-Inn Chyi; Yasushi Nanishi; Hadis Morkoç; Joachim Piprek; Euijoon Yoon, Editor(s)