Bertram Frank, Schmidt Gordon, Kernchen Julie, Veit Peter, Schürmann Hannes, Ćutuk Ana, Jetter Michael, Michler Peter, Christen Jürgen
Institute of Physics, Otto-von-Guericke-University Magdeburg, Magdeburg, 39106, Germany.
Institut für Halbleiteroptik und Funktionelle Grenzflächen, Center for Integrated Quantum Science and Technology (IQST) and SCoPE, University of Stuttgart, Stuttgart, 70569, Germany.
ACS Nano. 2022 Mar 22;16(3):4619-4628. doi: 10.1021/acsnano.1c11260. Epub 2022 Mar 8.
We report on nanoscopic exploration of the luminescence from individual InP quantum dots (QDs) by means of highly spatially resolved cathodoluminescence (CL) spectroscopy directly performed in a scanning transmission electron microscope (STEM). A 7-fold layer stack with high-density InP quantum dots is embedded as an active medium membrane in an external-cavity surface-emitting laser. We characterize the vertical transfer of carriers within the periodic separate confinement heterostructure and determine the capture efficiency of carriers from the cladding layer into the quantum dot layers. Benefiting from the nanoscale resolution of our STEM-CL, we perform single-dot spectroscopy on single isolated QDs in the STEM lamella resolving the details of the excitonic structure of individual quantum dots. Executing highly spatially resolved spectrum line scans within the QD layers, we directly visualize the lateral transport, .., the efficient lateral capture of carriers into an individual QD. We observe a characteristic change of the spectral fingerprint during this line scan, while the electron beam is approaching and subsequently receding from the quantum dot position. This directly correlates to the increase and decrease of the numbers of excess carriers reaching the dot, , altering the quantum dot population. The characteristic shift of emission energies visualize the renormalization of the ground-state energy of the single dot, and the intensity ratio of the excitonic recombinations verifies this change of the occupation and the state-filling.
我们报告了通过在扫描透射电子显微镜（STEM）中直接进行的高空间分辨率阴极发光（CL）光谱，对单个磷化铟量子点（QD）的发光进行的纳米级探测。一个具有高密度磷化铟量子点的7层堆叠结构作为有源介质膜嵌入到外腔表面发射激光器中。我们表征了周期性分离限制异质结构内载流子的垂直转移，并确定了从包层到量子点层的载流子捕获效率。受益于我们STEM-CL的纳米级分辨率，我们在STEM薄片中的单个孤立量子点上进行单点光谱分析，解析单个量子点的激子结构细节。在量子点层内执行高空间分辨率的谱线扫描，我们直接可视化了横向传输，即载流子向单个量子点的有效横向捕获。在该线扫描过程中，当电子束接近并随后远离量子点位置时，我们观察到光谱指纹的特征变化。这直接与到达量子点的过量载流子数量的增加和减少相关，从而改变了量子点的占据情况。发射能量的特征性偏移可视化了单个量子点基态能量的重整化，激子复合的强度比验证了占据情况和态填充的这种变化。
