# III-Nitride Multi-Quantum-Well Light Emitting Structures with Selective Carrier Injection
## 3 Results
The extra height of the valence band profile around the n-side QW facilitates hole accumulation and ensures better hole supply for capture and subsequent intra-QW recombination. In plain-barrier active region LEDs, the n-side QWs are normally deprived of adequate hole injection, and, as a result, the p-side QW dominates the LED emission. Such injection misbalance is stronger in longer-wavelength emitting LEDs with deeper quantum wells. Figure 2 illustrates this trend by comparing the distributions of carrier recombination rates across the active regions of blue and green-emitting LEDs, with much higher injection and emission non-uniformity in the latter structure. Figure 3 shows the results of IBL active region design optimization in which the IBL parameters have been chosen to alleviate the uneven MQW injection and uniformly populate the active QWs at a specific LED operational point. Figure 3 compares relative distributions of optical emission power among the active QWs (\(P_{i}/\sum P_{i}\)) for blue-emitting and green-emitting designs of three-QW LEDs. Dashed lines present simulation results for plain-barrier LEDs without IBLs, while solid lines show corresponding distributions for LEDs with IBLs optimized for uniform injection at the usual LED operational current, around 50 A/cm\({}^{2}\). For optimal operation, the injection range should include the point of maximum LED external quantum efficiency (EQE). Simulated IBL-LEDs revealed a relatively uniform emission distribution in quite a wide injection range of practically important currents, 10-100 A/cm\({}^{2}\). At the same time, plain-barrier LEDs demonstrated the expected strong dominance of the marginal p-side QW, especially in the green-emitting LED structure. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**QWs (Blue/Green/Red)** & & **Bulk Material** & \\ \hline Capture time, ps & 5/10/20 & Mobility (electrons/holes), cm\({}^{2}\)/V\(\cdot\)s & 200/10 \\ SRH lifetime, ns & 20/40/60 & SRH lifetime, ns & 1.0 \\ Auger coefficient, 10\({}^{-16}\) cm\({}^{4}\)/s & 1.0/1.0/1.0 & Auger coefficient, 10\({}^{-30}\) cm\({}^{6}\)/s & 1.0 \\ Radiative constant \({}^{1}\), 10\({}^{-5}\) cm\({}^{2}\)/s & 3.0/1.5/1.0 & Radiative constant, 10\({}^{-10}\) cm\({}^{3}\)/s & 1.0 \\ QW emission, nm & 440/530/650 & Energy relaxation time, ps & 1.0 \\ \hline \hline \end{tabular} \({}^{1}\) For the nominal population 10\({}^{13}\) cm\({}^{-2}\).  
\end{table} 
Table 1: QW and bulk material parameters. Figure 4 presents the injection dependence of MQW emission and injection uniformity for IBL LEDs. Uniformity characteristics are defined here as the ratios of optical emission powers \(P_{i}\), and correspondingly, intra-QW radiative recombination currents \(J_{i}\) for QWs with the lowest and highest levels of the relevant characteristics; e.g., minimum (\(P_{i}\))/maximum (\(P_{i}\)). The optimization of LED operational conditions has not been specially considered in this work, though the peaks of calculated uniformity characteristics correlate quite well with the position of peak EQE for blue-emitting LED. Table 2 compares the emission uniformity characteristics of plain-barrier LEDs and IBL-LEDs at a nominal injection current of 50 A/cm\({}^{2}\) and shows optimized IBL aluminum compositions and acceptor (Mg) p-doping levels. Figure 4: Injection dependence of MQW active region emission and injection uniformity characteristics in (**a**) blue-emitting and (**b**) green-emitting LEDs with plain-barrier (dashed lines) and optimized IBL (solid lines) active region design. Arrows indicate the LED injection levels corresponding to maximum external quantum efficiency (EQE). Figure 3: Injection dependence of multiple-quantum-well (MQW) relative optical emission in (**a**) blue-emitting (**b**) and green-emitting LEDs with plain-barrier (dashed lines) and optimized IBL (solid lines) active region designs. Quantum wells are counted from n-side of the active region. The area of the uniform MQW injection is encircled.