阶梯状InGaN量子阱发光二极管的光学特性

利用有效质量理论,研究了传统量子阱结构(样品A)、In_(0.15)Ga_(0.85)N/In_(0.25)Ga_(0.75)N阶梯状量子阱结构(样品B)和In_(0.25)Ga_(0.75)N/In_(0.15)Ga_(0.85)N阶梯状量子阱结构(样品C)发光二极管的光学性质。数值结果表明,在较大的注入电流密度下,样品B具有最大的内量子效率,并且能有效地抑制效率下降效应。其可归因于二方面:一方面,相比样品A和C,样品B在较高跃迁能级具有更大的光学动量矩阵元和电子-空穴费米分布函数之积,从而导致了更大的总辐射复合率;另一方面,由于样品B在导带中具有更大的内部电场,致使电子在阱层中分布在更窄的区域内,降低了电子-空穴交叠,俄歇复合率也被降低了。值得注意的是,样品C在价带中具有较大的内部电场,导致了空穴在阱层中分布在较窄的区域内。尽管如此,由于电子空穴的有效质量不一样,内部电场对电子空穴分布的影响也不同,反而导致了样品C具有更大的电子-空穴交叠,更高的俄歇复合率。此外,通过降低阶梯状量子阱中第一层InGaN层的厚度,样品B的发光效率能进一步提高。

Optical Properties of Step-Like InGaN Quantum Well Light Emitting Diodes

The optical properties of the conventional quantum well (QW) structure (sample A), the In0.15Ga0.85N/In0.25Ga0.75N (sample B) and In0.25Ga0.75N/In0.15Ga0.85N (sample C) step-like QW structures are investigated by using the effective mass theory. The numerical results reveal that sample B has the largest internal quantum efficiency (IQE) at the larger injection current density and can effectively suppress the efficiency droop effect. The reasons can be attributed to two aspects. On the one hand, as compared with samples A and C, sample B has the larger optical matrix elements and the product of Fermi-Dirac distribution functions of electron and hole at the higher transition energy level, which leads to the larger total radiation recombination rate. On the other hand, the electron distribution for sample B in the well layer is localized in a narrower area due to the larger electric field of conduction band, which will reduce the electron-hole overlap and Auger recombination rate. Note that sample C has a large internal electric filed in the valence band, which will result in the distribution of hole in a narrower region. However, due to the different effective mass of electron and hole, the effect of internal electric field on the distribution of electron and hole is also different. As a result, sample C has the larger electron-hole overlap and higher Auger recombination rate. In addition, the sample B can be further optimized by reducing the thicknesses of the first InGaN layer in the step-like InGaN quantum well.