## 3 Results and Discussion
The bonds in the kink sites are occupied with In cations, and therefore, Ga atoms tend to incorporate at the flat terrace [29]. If this occurs, a severe compositional nonuniformity can arise owing to a \"step-induced\" clustering of In atoms, which can lead to nonuniform components and the formation of local energy level states, and partial strain relaxation occurs with the formation of in clusters. This modulation, or clustering, did not occur in the 0\({}^{\circ}\) substrate due to the absence of a high density of step edges. As for 15\({}^{\circ}\) sample the formation of randomly positioned growth nuclei and the subsequent local strain relaxation at the nuclear locations could occur owing to the large degree of misorientation, resulting in high strain relaxation and the formation of island. To study the optical characteristics of the InGaAs/GaAsP QWs on different substrate orientations, temperature-dependent photoluminescence analysis was performed. Figure 6 shows the temperature-dependent PL spectra of three samples. For the 0\({}^{\circ}\) and 15\({}^{\circ}\) samples, it can be seen that the PL intensity decreased and the PL peak wavelength had a red-shift with increasing temperature. But the peak position of the 15\({}^{\circ}\) sample reached 1206 nm at room temperature and its extremely high FWHM and relatively low intensity indicate the PL characteristics of self-assembled quantum dots. The results are consistent with the AFM results shown in Figure 4c. However, the 2\({}^{\circ}\) sample exhibited an anomalous blue shift tendency of PL peak wavelength in the temperature range from 40 K to 85 K; the reason is discussed in detail below. Figure 5: Schematic illustration of the growth process. Figure 6: Temperature-dependent of PL spectra for InGaAs/GaAsP QWs on (a) 0\({}^{\circ}\), (b) 2\({}^{\circ}\), and (c) 15\({}^{\circ}\) misoriented substrates. Figure 7 shows the temperature dependence of the PL peak energy of the three samples. The PL peak position of the 0\({}^{\circ}\) sample shifted toward lower energies as the temperature increased over the entire range; this typical behavior can be well fitted using the [PERSON] empirical formula [30]:  
\[E_{g}(T)=E_{g}(0)-\alpha T^{2}/(\beta+T), \tag{5}\]  
where \(E_{g}(0)\) is the energy gap between nominal subband edges at 0 K, and \(\alpha\) and \(\beta\) are the Varshni equation parameters. The optimizing parameters, \(\alpha\) and \(\beta\), obtained from optimal fits of the QW data are listed in Table 1.  
The peak energies of systems with the 0\({}^{\circ}\) and 15\({}^{\circ}\) substrates can be well fitted using Equation (5); however, the data corresponding to the 2\({}^{\circ}\) sample cannot be fitted using the Varshni empirical formula in the low-temperature range (T \(<\) 60 K). An anomalous band gap evolution in the form of an S-shaped (redshift-blueshift-redshift) PL peak energy was observed at low temperatures. This abnormal behavior may be attributed to the localization effect caused by composition fluctuation [31; 32; 33; 34; 35]. [PERSON] et al. amended the Varshni empirical equation using band-tail states to fit this type of experimental data as follows [36]:  
\[E_{g}(T)=E_{g}(0)-\alpha T^{2}/(\beta+T)-\sigma^{2}/k_{B}T, \tag{6}\]  
where \(k_{B}\) is the Boltzmann constant and \(\sigma\) represents the degree of the localization effect. The fitting parameters are listed in Table 1.  
Figure 7b indicates that the data representing the 2\({}^{\circ}\) substrate can be adequately fitted in the 60-300 K temperature region. However, the aforementioned empirical models cannot accurately describe the temperature dependence of the peak energy in the InGaAs/GaAsP QW with a 2\({}^{\circ}\) substrate at temperatures below 60 K; the PL peak of the 2\({}^{\circ}\) substrate exhibited a redshift as the temperature increased from 15 to 40 K. The S-shaped variation over the entire temperature range occurred because of the existence of different localization potentials [37; 38].