Edge-emitting electrically pumped room-temperature spin laser

我们的目标是实现世界上第一台电泵浦室温自旋二极管激光器，它可以在没有外部磁场的情况下工作。通过自旋注入，我们的目标是实现30%以上的圆偏振度。 为此，我们的概念是基于一个边缘发射二极管激光器与散装活性区。这是必要的，以便实现偏振不敏感的光学增益，然后可以通过从剩磁铁磁接触的自旋注入来有意地修改。在实际商业使用的量子阱激光器中的光增益是偏振相关的，因此这样的设备不适合我们的项目。在垂直腔面发射激光器（VCSEL）中，这通常是自旋激光器概念的基础，注入载流子的传输路径通常在几μ m的范围内，因此比我们发现的自旋弛豫长度长得多，只有大约25 nm。在边缘发射激光二极管中可以潜在地实现短得多的注入长度（载流子从注入接触到有源区的路径）。这种边缘发射器件的几何形状与提供偏振不敏感的光学增益的有源区相结合，因此被选择用于该项目，以证明在室温下的电自旋注入。参与小组的专业知识对这个项目是完全互补的。其子任务如下：霍夫曼集团与其他合作伙伴密切合作，详细阐述了结构设计（活性区，注射器的架构）。该小组还进行部分处理和最终的光学表征。威克集团负责半导体生长、部分加工和传输特性。Wende族沉积具有MgO隧道势垒的铁磁n接触（例如Fe层或Fe3Si层）。这些磁性触点将在同步加速器源通过X射线吸收光谱和X射线圆二色性进行分析，并在自己的实验室通过穆斯堡尔光谱（CEMS）进行分析。在进一步的步骤中，激光器件将通过等离子体蚀刻接触和焊接进行处理，以进行最终表征，这是Hofmann和Wieck团队的合作。在这最后的光学特性，我们的目标是证明由注入的自旋的光输出偏振的控制，我们要分析哪些潜在的优势，自旋控制的激光器可能与传统的激光器相比。为此目的，通过自旋注入的极化切换的动力学的特征在于强调不同的极化状态和时间切换动力学之间的对比。这些测量的解释将支持自旋注入后的光学增益的偏振敏感测量。

Our goal is to realise the first electrically pumped room temperature spin diode lasers in the world, which can operate without external magnetic field. By spin injection we aim to achieve a circular polarization degree above 30%. Our concept for that purpose is based on an edge emitting diode laser with bulk active region. This is necessary in order to achieve a polarization insensitive optical gain which then can be intentionally modified by spin injection from ferromagnetic contacts in remanence. The optical gain in the actually commercially used quantum well lasers is polarisation dependent, and therefore such devices are not suited for our project. In vertical cavity surface emitting lasers (VCSELs), which are typically the basis for spin-laser concepts, the transport paths of the injected carriers are typically in the range of several µm and therefore much longer than the spin relaxation length which we found to be only about 25nm. Much shorter injection lengths (path of the carriers from injection contact to active region) can potentially be achieved in edge emitting laser diodes. This edge emitting device geometry in combination with an active region that provides polarization insensitive optical gain, is therefore chosen for this project in order to demonstrate electrical spin injection at room temperature. The expertises of the participating groups are perfectly complementary for this project. The sub-tasks are as follows: Group Hofmann elaborates the structure design (architecture of active region, injector) in close collaboration with the other partners. The group also does part of the processing and the final optical characterisation. Group Wieck does the semiconductor growth, parts of the processing, and the transport characterisation. Group Wende deposits the ferromagnetic n-contacts (e.g. Fe- or Fe3Si-layers) with MgO-tunnel barriers. These magnetic contacts will be analysed at synchrotron sources via x-ray absorption spectroscopy and x-ray circular dichroism, and in the own laboratory via Mössbauer spectroscopy (CEMS). In further steps, the laser devices will be processed for the final characterisation by plasma etching of the contacts and bonding in collaboration of the groups Hofmann and Wieck. Within this final optical characterisation, we aim to prove the control of the optical output polarisation by the injected spins and we want to analyse which potential advantages a spin-controlled laser may have in comparison with a conventional laser. For that purpose, the dynamics of the polarisation switching via spin injection will be characterized with emphasis to the contrast between the different polarization states and the temporal switching dynamics. The interpretation of these measurements will be supported by polarization sensitive measurements of the optical gain upon spin injection.