Blue SQW and MQW LED heterostructures

 

Schematic view of the heterostructure

Figure 1. Schematic view of the heterostructure

Shown below are some results of simulations of 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).

Variation of the band diagram with the bias

Figure 2(a). Variation of the band diagram with the bias

Variation of the carrier concentrations with the bias

Figure 2(b). Variation of the carrier concentrations with the bias

Variation of SQW profile with the bias

Figure 2(c). Variation of SQW profile with the bias

Variation of  emission spectra with the bias

Figure 2(d). Variation of emission spectra with the bias

Schematic view of the blue MQW heterostructure

Figure 3. Schematic view of the heterostructure, see S.S. Mamakin et al., Semiconductors 37 (2003) 1107

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. You can find detailed discussion of MQW heterostructure for blue LED in the article by V.F. Mymrin, K.A. Bulashevich, N.I. Podolskaya, I.A. Zhmakin, S.Yu. Karpov, and Yu.N. Makarov “Modelling study of MQW LED operation”, phys. stat. sol. (c) 2, 2928-2931 (2005)

Band diagram

Figure 4 (a). Band diagram

Recombination rates

Figure 4 (c). Recombination rates

Carrier concentrations

Figure 4 (b). Carrier concentrations

Dependence of Internal Emission Efficiency predicted numerically and External Efficiency measured experimentally on current density

Figure 4 (d). Dependence of Internal Emission Efficiency predicted numerically and External Efficiency measured experimentally on current density