Presentation Details
| Optimizing sample preparation of CdSeTe/CdSe photovoltaic absorbers for cathodoluminescence study using FIB, SEM and TEM Zhaoxia Zhou, Stuart Robertson, Sam Machin, Kieran Curson, Luksa Kujovic, Jacques Kenyon, Xiaolei Liu, Rob Ellis, Mike Walls. Loughborough University, Loughborough, United Kingdom |
Abstract
CdTe is the leading second-generation solar technology among thin-film solar cells, offering low cost- solar electricity generation [1]. Recently we have applied cathodoluminescence (CL) in CdSeTe and CdSe to investigate their photoactivity and band gap characteristics, correlated them directly with grain orientation, stacking faults, and composition from micro- to nanoscale [2, 3, 4]. These studies were carried out using CL in conjunction to scanning electron microscopy (SEM) and transmission electron microscopy (TEM). CL is defined as the photon emission when electron beam interacts with typically a semiconductor sample. The light emitted has a frequency (i.e. colour) equal to the band gap (Eg) of the material divided by Planck’s constant, E = hv. Thereby CL measures band gap of materials and sub-band gap states induced by defects and it is widely used for GaN LEDs [5]. ​Utilizing the ultra-fine scanning electron beam in S/TEM, hyperspectral CL is performed and provides band gap mapping with nanoscale spatial resolution. This is a new modality of dataset at the same sampling location in S/TEM, complementary to the established techniques such as EBSD, EDS, HAADF, 4D-STEM and EELS. The instruments employed were (i) an FEI xenon Helios G4 plasma FIB attached with Monarc Pro CL (Gatan) and (ii) a TFS Talos F200i STEM attached with Mönch CL (Attolight). The combination of FIB with STEM allows site-specific sections either parallel (in-plane) or perpendicular (edge) to the film surface to be extracted based on CL map for further STEM. A Mel-Build liquid-nitrogen cryo-holder was used to load specimens for all the STEM/CL measurements, enabling testing from room temperature down to -150°C. This work reports the sample preparation methods and experimental workflow required to maximize the combined benefits of CL with EBSD, EDS, and HAADF in S/TEM. The effects of sample thickness, electron-beam parameters, and testing temperature (using a cryogenic stage) are systematically investigated and discussed.
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No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.
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