GaN/In_xGa_(1-x)N型最后一个量子势垒对发光二极管内量子效率的影响

GaN/In_xGa_(1-x)N型最后一个量子势垒结构能有效提高发光二极管(LED)器件内量子效率,缓解LED效率随输入电流增大而衰减的问题.本文综述了该结构及其结构变化——In组分梯度递增以及渐变、GaN/In_xGa_(1-x)N界面极化率改变等对改善LED器件性能的影响及优势,归纳总结了不同结构的GaN/In_xGa_(1-x)N型最后一个量子垒的工作机理,阐明极化反转是该结构提高LED性能的根本原因.在综述该结构发展的基础之上,通过APSYS仿真计算,进一步探索和深入分析了该结构中In_xGa_(1-x)N层的In组分及其厚度变化对LED内量子效率的影响.结果表明:In组分的增加有助于在GaN/In_xGa_(1-x)N界面产生更多的极化负电荷,增加GaN以及电子阻挡层处导带势垒高度,减少电子泄漏,从而提高LED的内量子效率;但GaN/In_xGa_(1-x)N型最后一个量子势垒中In_xGa_(1-x)N及GaN层厚度的变化由于会同时引起势垒高度和隧穿效应的改变,因而In_xGa_(1-x)N和GaN层的厚度存在一个最佳比值以实现最大化的减小漏电子,提高内量子效率.

Identifying the influence of GaN/InxGa1-xN type last quantum barrier on internal quantum efficiency for III-nitride based light-emitting diode

GaN/In_xGa_1-xN-type last quantum barrier (LQB) proves to be useful for Ⅲ-nitride based light-emitting diode (LED) in enhancing the internal quantum efficiency (IQE) and suppressing the efficiency droop level that often takes place especially when the injection current is high. In this work, GaN/In_xGa_1-xN-type LQB reported by the scientific community to enhance the IQE is first reviewed and summarized. Then, the influences of indium composition and thickness of the In_xGa_1-xN layer on the performance of LED incorporated with the GaN/In_xGa_1-xN-type LQB are studied. Through analyzing energy band diagrams calculated with APSYS, we find that the0001] oriented LQB features an electron depletion due to the polarization induced negative charges at the GaN/In_xGa_1-xN interface. The electron depletion enhances the electron blocking effect and reduces the electron accumulation at the In_xGa_1-xN/AlGaN interface, leading to an improved IQE for the LED. In addition, increasing the indium composition of the In_xGa_1-xN layer will generate more negative interface charges, which result in further increased conduction band barrier height for the electrons and reduced electron leakage. On the other hand, for the GaN/In_xGa_1-xN-type LQB with a fixed indium composition, there exists an optimum thickness for the In_xGa_1-xN layer in maximizing the improvement of IQE for the LED, mainly because the interaction between two mechanisms co-exists when varying the thickness of the In_xGa_1-xN layer, i.e., the initial increase in the In_xGa_1-xN layer thickness will lead to an increased conduction band barrier height, which prevents electrons from leaking into the In_xGa_1-xN layer. However, further increasing the In_xGa_1-xN layer thickness to a certain value, tunneling effect will kick in as a result of the simultaneously reduced GaN thickness-the electrons will tunnel through the thin GaN layer in the LQB from the quantum wells to the In_xGa_1-xN layer. This will cause electrons to increase in the In_xGa_1-xN layer. Therefore, as a result of the interaction between the above-mentioned two mechanisms, there is an optimum thickness for the In_xGa_1-xN layer such that the electrons in the In_xGa_1-xN layer will reach a minimal value, which in turn will lead to a maximized conduction band barrier height for the AlGaN electron blocking layer and facilitate the performance of LEDs.