Edge-emitting electrically pumped room-temperature spin laser

我们的目标是实现世界上第一个可以在没有外部磁场的情况下工作的电泵室温自旋二极管激光器。通过自旋注入，我们的目标是使圆极化度达到30%以上。为此，我们的概念是基于具有大块有源区的边缘发射二极管激光器。这对于实现偏振不敏感的光学增益是必要的，然后可以通过从剩余物中的铁磁接触中注入自旋来有意地修改光学增益。实际商用量子阱激光器的光学增益依赖于偏振，因此这种设备不适合我们的项目。垂直腔面发射激光器（VCSELs）通常是自旋激光概念的基础，注入载流子的输运路径通常在几µm的范围内，因此远长于自旋弛豫长度，我们发现自旋弛豫长度仅为25nm左右。在边缘发射激光二极管中可以潜在地实现更短的注入长度（载流子从注入接触到有源区域的路径）。因此，为了演示室温下的电自旋注入，本项目选择了这种边缘发射器件几何形状与提供偏振不敏感光学增益的有源区域相结合。参与小组的专业知识对这个项目是完全互补的。子任务如下：Hofmann集团与其他合作伙伴密切合作，详细阐述结构设计（活跃区域架构，注入器）。该小组还进行了部分处理和最终的光学表征。威克集团负责半导体的生长、部分加工和传输特性。Wende组沉积了具有氧化镁隧道势垒的铁磁性n-触点（例如Fe-或fe3si层）。这些磁接触将在同步加速器源上通过x射线吸收光谱和x射线圆二色性进行分析，并在自己的实验室中通过Mössbauer光谱（CEMS）进行分析。在进一步的步骤中，激光器件将在Hofmann和Wieck团队的合作下，通过等离子体蚀刻触点和键合来进行最终表征。在最后的光学表征中，我们的目标是证明注入自旋对光输出偏振的控制，并且我们想分析自旋控制激光器与传统激光器相比可能具有哪些潜在优势。为此，通过自旋注入的极化开关动力学将被表征，重点是不同极化状态和时间开关动力学之间的对比。对这些测量结果的解释将得到自旋注入时光学增益的偏振敏感测量结果的支持。

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.