Control of biexciton localization and optical functionality in nitride-based ultraviolet alloy semiconductors

研究了合金无序局域化对富Ga Al_x，Ga_t；1-x&Gt；N三元合金外延层中双激子的影响。我们测量了从x=0.019到0.092的五个不同铝组分的样品的双激子激发光谱。在双激子双光子吸收的基础上，得到了双激子结合能随铝组分的变化关系。随着铝组分的增加，双激子结合能显著增强。Al&lt；0.002&gt；Ga&lt；0.908&gt；N三元合金外延层的双激子结合能为16.6 meV，是GaN中双激子结合能(5.6 meV)的三倍。此外，为了定量评价双激子的局域化程度，我们定义了双激子的斯托克斯位移。我们观察到双激子的强烈局域化。双激子斯托克斯漂移与激子斯托克斯漂移之比估计为0.8…更多。双激子的强烈局域化导致了双激子结合能的显著增强。我们还用时间分辨发光光谱的方法研究了Al_xGa_&lt；1-x&gt；N三元合金中局域双激子的动力学行为。我们用表示双激子和单激子布居动力学的速率方程分析了观测到的含时发光。通过分别考虑双激子和单激子的局域化时间，考虑了合金无序引起的局域化效应，对分析进行了修正。分析表明，激子和双激子的局域化时间都随着铝成分的增加而增加，这是由于合金无序导致局域化程度增加所致。分析还发现，双激子的形成时间在目前的组成范围内(x&lt；0.1)保持不变，这表明双激子的形成速度与单激子的局域化深度无关。较少

We have studied the effect of localization due to alloy disorder on biexcitons in Ga-rich Al_x,Ga_<1-x>N ternary alloy epitaxial layers. We measured photoluminescence excitation spectra of biexcitons for five samples with different aluminum compositions from x=0.019 to 0.092. On the basis of the two-photon absorption of biexcitons, the binding energy of biexcitons was obtained as a function of aluminum composition. The strong enhancement of the biexciton binding energy was observed with an increase in aluminum composition. The biexciton binding energy in the Al_<0.002>Ga_<0.908>N ternary alloy epitaxial layer was estimated to be 16.6 meV, which was three times as large as the biexciton binding energy in GaN (5.6 meV). In addition, we defined the Stokes shift of biexcitons in order to evaluate the degree of biexciton localization quantitatively. We observed the strong localization of biexcitons. The ratio of biexciton Stokes shift relative to exciton Stokes shift was estimated to be 0.8 … More . The strong localization of biexcitons resulted in the strong enhancement of the biexciton binding energy. We have also studied the dynamical behavior of localized biexcitons in Al_xGa_<1-x>N ternary alloys by means of time-resolved luminescence spectroscopy. We analyzed the observed time-dependent luminescence using rate equations which expressed population dynamics of biexcitons and single excitons. The analysis was modified by considering the localization time of both biexcitons and single excitons individually in order to take account of the effect of localization due to alloy disorder. The analysis revealed the increase in the localization time of both excitons and biexcitons with increasing aluminum composition, which resulted from the increase in the degree of localization due to alloy disorder. The analysis also revealed the unchanged formation time of biexcitons in the present compositional range (x<0.1), which indicated the independence of the formation rate of biexcitons from the localization depth of single excitons. Less