## 3 Results and Discussion
### Recombination Coefficients
The comparison demonstrates good quantitative agreement between the theory  
Figure 3: RRC (**a**) and ARC (**b**) of [0001]-polar and nonpolar SQW LED structures as a function of emission wavelength. Symbols are data from [20; 21]; dashed, dash-dotted, and solid lines correspond to calculations with mean electron energies of 26, 80, and 40 meV, respectively. Dotted lines show the recombination coefficients reported in [48]. The red, orange, and purple lines are mentioned in the capture as “solid”, “dashed”, and “dash-dotted” lines, respectively. and experiment achieved simultaneously for both RCs. RRC is found to depend weakly on \(E_{e}\), whereas ARC is proportional to the mean electron energy. RCs calculated for nonpolar LED structure (grey solid lines in Figure 2), appear to be much higher than those corresponding to the polar structure, which is the consequence of the difference in the \(\left\langle\psi^{2}\right\rangle/w_{e}\) seen in Figure 2a. Since the theoretical \(B/C\) ratio does not depend on \(\left\langle\psi^{2}\right\rangle/w_{e}\), according to Equations (3) and (4), the ratios plotted in Figure 2b by lines actually correspond to both polar and nonpolar LED structures. Dotted lines in Figure 3 show the results of ab initio simulations of the recombination coefficients reported in [48] for 3 nm InGaN/GaN QWs. In the case of polar QW, the simulation predicts a decrease in both RRC and ARC with the emission wavelength, which is in qualitative agreement with observations [20; 21]. However, the theoretical values of RRC and ARC are one and two-three orders of magnitude lower than the experimental ones. In the case of nonpolar QW, the simulations [48] predict that both RRC and ARC will increase with wavelength, which is the trend opposite to that predicted by the semi-empirical model. Though data on the spectral dependence of RCs in nonpolar InGaN QWs are not available to date, the above trend seems to be erroneous. Indeed, using the RRC and ARC obtained in [48] and the experimental SRH recombination coefficient \(A\) (see Figure 1), one can calculate the dimensionless factor \(Q=B/(AC)^{1/2}\) and then the maximum IQE value \(IQE_{max}=Q/(Q+2)\) as a function of wavelength. They are predicted in such a way that \(IQE_{max}\) would grow with the wavelength, which contradicts the observed efficiency decline of the nonpolar LEDs in the \"green gap\" [15]. In contrast, the semi-empirical model presented in this paper implies that both RRC and ARC in a nonpolar InGaN QW decrease with its emission wavelength (see Figure 3). Estimation of \(IQE_{max}\) via \(Q\)-factor shows the emission efficiency to decline when the hole localization becomes stronger, i.e., when the localization radius decreases. The prediction of the model is in line with the data reported in [49], where the efficiency droop in nonpolar InGaN QWs was observed at lower optical excitation powers, and if the InGaN material exhibited a stronger disorder, this resulted in a deeper carrier localization. One more alternative model of the Auger recombination in InGaN QWs mediated by interface roughness has been suggested in [50]. Authors of the paper have considered enhancement of Auger recombination caused by violation of the momentum selection rule and originating from fluctuations of the QW width. Unfortunately, an accompanying effect, i.e., suppression of the recombination rate due to decreasing overlap of the electron and hole wave functions due to lateral carrier localization, was not accounted for in the model, making its quantitative predictions doubtful. Besides, the model does not regard any correlations between the width fluctuations, InGaN composition, and conditions of QW growth. Until such a correlation is established, the model of [50] seems to be ineffective for predicting trends in the LED efficiency variation inside the \"green gap\".