Blue SQW and MQW LED heterostructures
Shown below are simulation results for a simple blue SQW LED structure consisting of n-GaN contact layer (Nd = 3×1018 cm-3), an undoped InGaN SQW active region 3.5 nm thick, a p-type 10%-AlGaN electron blocking layer (Na = 7×1019 cm-3), and a p-GaN contact layer (Na = 7×1019 cm-3).
Figure 1. Schematic view of an SQW heterostructure
Figure 2(a). Variation of the band diagram with the bias
Figure 2(b). Variation of the carrier concentrations with the bias
Figure 2(c). Variation of SQW profile with the bias
Figure 2(d). Variation of emission spectra with the bias
Band diagrams, and distributions of carrier concentrations and recombination rates in the LED structure. It is seen that electrons are uniformly distributed over different QWs. In contrast, holes are injected mainly into the QW adjacent to the p-AlGaN emitter. Computations predict that the hole distribution over the QWs becomes much more uniform if the lightly doped barriers are employed in the LED structure. This is due to a lower carrier recombination rate (a higher diffusion length) in the active region directly controlled by the electron concentration.
Figure 3. Schematic view of the heterostructure, see S.S. Mamakin et al., Semiconductors 37 (2003) 1107
You can find detailed discussion of MQW heterostructure for blue LED in “Modelling study of MQW LED operation” by V.F. Mymrin, K.A. Bulashevich, N.I. Podolskaya, I.A. Zhmakin, S.Yu. Karpov, and Yu.N. Makarov, phys. stat. sol. (c) 2, 2928-2931 (2005)
RIGHT: Figure 4 (d). Dependence of Internal Emission Efficiency predicted numerically and External Efficiency measured experimentally on current density