Su Chia-Ying, Tsai Meng-Che, Chou Keng-Ping, Chiang Hsin-Chun, Lin Huang-Hui, Su Ming-Yen, Wu Yuh-Renn, Kiang Yean-Woei, Yang C C
Opt Express. 2017 Oct 30;25(22):26365-26377. doi: 10.1364/OE.25.026365.
An AlGaN quantum well (QW) structure of a deep-ultraviolet (UV) light-emitting diode (LED) needs to be well designed for controlling its band structure such that the heavy-hole (HH) band edge becomes lower than the split-off (SO) band edge and hence the transverse-electric (TE) polarization dominates the emission for achieving a higher light extraction efficiency. Here, we report the discovery of un-intentionally formed high-Al AlGaN nano-layers right above and below such a QW and their effects on the QW for changing the relative energy levels of the HH and SO bands. The comparison between the results of simulation study and polarization-resolved photoluminescence measurement confirms that the high-Al layers (HALs) represent the key to the observation of the dominating TE-polarized emission. By applying a stress onto a sample along its c-axis to produce a tensile strain in the c-plane for counteracting the HAL effects in changing the band structure, we can further understand the effectiveness of the HALs. The formation of the HALs is attributed to the hydrogen back-etching of Ga atoms during the temperature transition from quantum barrier growth into QW growth and vice versa. The Al filling in the etched vacancies results in the formation of an HAL. This discovery brings us with a simple method for enhancing the favored TE-polarized emission in an AlGaN deep-UV QW LED.
深紫外发光二极管（LED）的AlGaN量子阱（QW）结构需要精心设计，以控制其能带结构，使重空穴（HH）带边低于分裂-off（SO）带边，从而横向电（TE）极化主导发射，以实现更高的光提取效率。在此，我们报告了在这种量子阱的上方和下方意外形成的高Al含量AlGaN纳米层的发现，以及它们对量子阱改变HH和SO带相对能级的影响。模拟研究结果与偏振分辨光致发光测量结果的比较证实，高Al层（HALs）是观察到主导TE极化发射的关键。通过沿样品的c轴施加应力，在c平面产生拉伸应变，以抵消HALs在改变能带结构方面的影响，我们可以进一步了解HALs的有效性。HALs的形成归因于在从量子势垒生长到量子阱生长以及反之的温度转变过程中Ga原子的氢反蚀刻。蚀刻空位中的Al填充导致了HAL的形成。这一发现为我们带来了一种在AlGaN深紫外量子阱LED中增强有利的TE极化发射的简单方法。
