# III-Nitride Multi-Quantum-Well Light Emitting Structures with Selective Carrier Injection
## 3 Results
By combining both compositional and doping degrees of freedom, the IBL concept represents a versatile design element. Most natural IBL design applications, however, include structures which essentially require the injection distribution control over MQW active regions with only few QWs, such as monolithic tunable multi-color LEDs. Color control ability of IBL the active region has been demonstrated in the full red-green-blue (RGB) spectrum [11] and recently also used in a white-color LED with a tunable color temperature [13]. Figure 5 presents an example of chromaticity characteristics' control in the three-color IBL LED of the current design. Single-color quantum wells have been replaced here with blue, green, and red-emitting QWs, and IBLs have been re-optimized to provide white color emission at a nominal injection of 50 A/cm\({}^{2}\); see Table 2. Figure 5a shows the chromaticity diagram of the white-color LED with a solid black locus line spanning the LED injection range, from 0.1 A/cm\({}^{2}\) to 5 kA/cm\({}^{2}\). Figure 5b illustrates the evolution of the representative point on the diagram locus line; i.e., the injection dependence of the corresponding locus point chromaticity coordinates x, y, and z = 1 - x - y. The circles in both subplots indicate the regions of white light LED emission. To illustrate the simulation sensitivity to IBL doping and composition, Figure 5a has been completed with two additional locus lines for LEDs with (_i_) the plain-barrier active region of the same doping profile (dashed locus line) and (_ii_) the active region with undoped IBLs of the same Al content (dash-dotted locus line). Both examples clearly indicate the loss of white emission if either part of optimization is skipped. Thin dashed lines in Figure 5b show the injection dependence of chromaticity coordinates for an LED with an undoped plain-barrier active region. It is worth mentioning that both our case studies employ the physics-based model simulations, with only typical material parameters, which renders the simulation results qualitative by nature. \begin{table}
\begin{tabular}{c c c c} \hline
**LED** & **Aluminum, \%** & **Acceptors, 10\({}^{17}\) cm\({}^{-3}\)** & **P\({}_{\text{min}}\)/P\({}_{\text{max}}\)** \\ \hline Blue, plain-barrier & - & - & 0.114 \\ Blue, IBL1/IBL2 & 23/12 & 3/61 & 0.910 \\ Green, plain-barrier & - & - & 0.008 \\ Green, IBL1/IBL2 & 20/20 & 26/38 & 0.867 \\ White, IBL1/IBL2 & 10/6 & 10/8 & - \\ \hline \end{tabular}
\end{table} 
Table 2: IBL characteristics in simulated structures. Figure 5: Injection dependence of white-color LED chromaticity characteristics. (**a**) chromaticity diagram of LED emission. Large cross markers indicate white light (black cross) and RGB main colors; small colored cross markers show nominal QW emission locus points. (**b**) Injection dependence of the chromaticity coordinates of representative points on the LED chromaticity locus line. This raises the question about the critical parameters which can affect the presented values of optimized IBL characteristics. The question cannot be unambiguously answered at this point. Since IBL design combines the composition and doping variation, the deviations in band offsets, polarization charges and layer widths would naturally affect the results. We emphasize, however, that QW parameters should enter that list on equal footing. The IBL effect on QW injection can be different for all active QWs, depending on the balance between the carrier capture and intra-QW recombination rates, with capture rates for each type of carrier strongly affected by the adjacent IBLs. These considerations, however, require more extensive study and are beyond the means of this Communication which is intended only to illustrate the versatility of the IBL concept, and does not provide an ultimate design or final solution to the problem of MQW injection.