Strain mapping of LED devices by dark-field inline electron holography: Comparison between deterministic and iterative phase retrieval approaches

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• 作者：Kyung Song^a ; Ga-Young Shin^a ; Jong Kyu Kim^a ; Sang Ho Oh^a ; ^{shoh@postech.ac.kr} ; Christoph T. Koch^b
• 关键词：Dark-field inline holography ; Transport of intensity equation ; Lattice strain ; Light emitting diode ; Multi-quantum well
• 刊名：Ultramicroscopy
• 出版年：2013
• 出版时间：April, 2013
• 年：2013
• 卷：127
• 期：Complete
• 页码：119-125
• 全文大小：1295 K

文摘

Dark-field inline electron holography has recently been established as a convenient method to map strain in semiconductor devices, combining high precision, low noise, sub-nm spatial resolution and fields-of-view larger than 1 ¦Ìm. Here we compare two approaches to reconstruct the geometric phase from a transmission electron microscopy dark-field focal series and their effects on the strain measurement: the transport-of-intensity-equation (TIE) and a flux-preserving iterative approach. For this task, we used a GaN-based light emitting diode with a highly complex heterostructure as a model system. While the TIE relies on 3 images only but requires the optimization of two free parameters (defocus step and low-limit cut-off frequency), the iterative reconstruction algorithm involves no adjustable parameters and uses images recorded at 9 different planes of focus with quadratically increasing defocus values. Optimum parameters for the TIE-reconstruction could be identified. However, the iterative phase retrieval approach yields the strain values that agree best with the expected strain levels and provides also higher spatial resolution.