A-Crater-within-a-Crater Approach for Secondary Ion Mass Spectrometry Evaluation of the Quality of Interfaces of Multilayer Devices

Further development and optimization of modern optoelectronic devices requires fast and reliable procedures that may evaluate the quality of interfaces. For thick multilayer devices, mixing effect may significantly prevent proper interpretation of secondary ion mass spectrometry depth profiles especially if a region of interest is located far from the sample surface. In this work, we present how to overcome this problem with a so-called a-crater-within-a-crater approach. In this notion, a high energetic primary ion beam is used to rapidly remove most of the material forming a large crater. Then, the energy is significantly reduced and a new smaller crater is formed at the bottom of the previous one. Close to the region of interest, the impact energy is decreased to 150 eV and thus an interface can be analyzed with minimal mixing effect and thus its quality can be adequately assessed. Usefulness of this approach is tested on an epitaxial structure of a triple-junction solar cell and reliable information about the structure imperfection has been obtained: p and n dopants in the tunnel junction overlapped, deteriorating the operation of the device.