The assessment of emission mechanism in GaN-based nano-structures by scanning near-field optical microscopy

本项目的目的是利用扫描近场光学显微镜（SNOM）的光致发光（PL）映射来评估和/或控制InGaN/ gan基量子阱中的辐射复合过程，通过该方法可以在发光二极管（led），激光二极管（ld）和新型荧光粉等发射器中实现发射效率的显着提高以及可操作波长的延长。我们的方法是制造用于多波长照明的微/纳米结构，阐明基本的光学性质，并对未来的器件结构做出积极的反馈。主要结果总结如下。(1)我们将SNOM-PL与原子力显微镜（AFM）相结合，开发了实验技术，其中位错与弱发射区之间的相关性被清楚地揭示出来。此外，用这种方法进行的时间分辨PL测量显示了光产生的载流子和/或激子在电位波动中的动力学行为。研究发现，位错周围的成分调制有效地阻碍了通往非辐射复合中心的路径，使得载流子扩散在空间上是一个各向同性的过程。(2)我们提出了再生技术，其中成熟的c取向氮化镓用作种子。研究表明，在沿[11^^-00]方向呈条纹图案的c取向GaN上生长形成（0001）、<112^^-2>和<112^^-0>面，并且与传统的c取向InGaN/GaN QW相比，<112^^-2>面上的QW涉及更弱的电场，具有更高的PL效率。此外，在<112^^-2>面的InGaN/GaN qw上，以几微米的宽度实现了覆盖整个可见范围的彩虹色PL。

The purpose of this project is to assess and/or control the radiative recombination processes in InGaN/GaN-based quantum wells by employing photoluminescence (PL) mapping with scanning near field optical microscopy (SNOM), by which dramatic improvement of emission efficiency as well as the extension of operatable wavelength can be achieved in emitters such as light emitting diodes (LEDs), laser diodes (LDs) and new phosphors. Our approach is to fabricate micro/nano structures for multi-wavelength lighting, to elucidate fundamental optical properties, and to make a positive feedback to future device structures. Main results are summarized as shown below.(1)We have developed the experimental technique by combining the SNOM-PL with atomic force microscopy (AFM), where the correlation was clearly revealed between dislocations and weak emission regions. Moreover, time-resolved PL measurements with this method showed the dynamical behavior of photo-generated carriers and/or excitons in potential fluctuations. It was found that the pathway to nonradiative recombination centers is effectively hindered by the compositional modulation around the dislocations, so that the carrier diffusion is spatially unisotropic process.(2)We have proposed the re-growth technique, where well-established c-oriented GaN is used as a seed. It has been demonstrated that the growth on c-oriented GaN patterned with a stripe along the [11^^-00] direction forms (0001), <112^^-2>, and <112^^-0> facets and that the QW on the <112^^-2> facet involves weaker electric fields and has a higher PL efficiency, compared with conventional c-oriented InGaN/GaN QWs. Moreover, rainbow color PL covering the entire visible range has been achieved from InGaN/GaN QWs on the <112^^-2> facets with a few micron-width.