AlGaN极化场调控对内量子效率的影响

The internal quantum efficiency(IQE) of AlGaN-based ultraviolet(UV) LED was far below that of blue and green LED. Internal quantum efficiency is the basis for improving the luminous efficiency, mainly depend on the electronic structure of multi-quantum wells(MQW) and crystal quality of the active region. In this application project, the influence of polarization field in AlxGa1-xN/AlyGa1-yN (x < y) quantum well structure on stress, localized states, conduction band and valence band level distribution and the spatial distribution of the electron and hole wave functions as the research object, through the special design of AlGaN quantum well structure to improve the internal quantum efficiency of UV LED: inserting AlGaN step layer between barrier and quantum well (step well), Al fraction grade change well(grade well), pre-flow of TMAl before well (- AlN) and so on, and made these samples in our specially design high temperature MOCVD. By calculating the Schrodinger - Poisson equation, giving the fine structure of quantum well in different polarization fields. Using micro zone deep ultraviolet electroluminescence(EL) spectrum and time-resolution variable temperature photoluminescence(PL) spectrum measurement of polarization field regulation of AlGaN quantum well localized state. Using external bias of deep UV PL spectra combined with pressure spectrum technology, quantitative analysis of the influence of polarization field engineering on the internal stress of MQW.

AlGaN基紫外LED的内量子效率远远低于蓝绿光LED的内量子效率。其中内量子效率提升是改善发光效率的基础，主要与有源区的电子结构以及材料中的高密度缺陷有关。本申请项目以AlGaN量子阱结构中极化场调控对应力、局域化状态、导带和价带能级分布以及电子和空穴波函数的空间分布影响为研究对象，通过特殊设计的AlGaN量子阱提升紫外 LED 的内量子效率：量子阱前插入Al组份界于势垒和势阱的台阶阱、势阱组份呈阶梯变化规律的阶梯阱、阱中预通Al的delta-AlN阱等，并在特有的高温MOCVD上得到实现。通过求解 Schrodinger–Poisson 方程，计算给出量子阱在不同极化场下的能带精细结构。采用微区电致发光谱和时间分辨的深紫外变温PL谱测量极化场调控对AlGaN量子阱局域化状态的影响。采用外置偏压的深紫外PL谱结合压力光谱技术，定量分析极化场调控对量阱内应力的影响。

设计特殊的Step Well、Grade Well、δ-AlN Well等AlxGa1-xN/AlyGa1-yN多量子阱结构，以实现对量子阱内应力、极化场的调控。研究SW、GW、δ-W等特殊多量子阱结构中导带和价带能级分布以及电子和空穴波函数的空间分布，计算电子和空穴波函数空间重叠几率及辐射复合速率分布，为分析辐射复合变化规律提供理论指导，据此设计出能够提升紫外LED内量子效率的样品。根据设计的样品，实验结构发现采用GW的量子阱结构比SW、δ-W及普通的量子阱结构具有更好的内量子效率，内量子效率提升为10%左右。空穴和电子在量子阱内的分布，GW量子阱结构比普通的量子阱结构分布更加均匀。同时该研究成果应用在GaN基HEMT领域能够更好的改善HEMT的材料质量及耐压。