Large area plan-view transmission electron microscopy sample preparation for multijunction metamorphic solar cell devices

A focused ion beam (FIB) sample preparation technique is developed to produce very large areas of electron transparent material for plan-view transmission electron microscopy measurements from specific layers in a multi-layer device structure. An initial cross section FIB cut allows plan-view sample creation from any layer of interest, and therefore rapid characterization of the defect density as a function of depth is achievable for structures containing multiple layers, such as multi-junction metamorphic layer structures for high efficiency III-V solar cells. Uniform electron transparent plan-view areas of greater than 100 μm² are extracted from a cross-section to facilitate observation of defect densities as low as ~10⁶ cm^-2. To demonstrate the technique, the active cell layers of two inverted metamorphic III-V solar cell structures have been imaged to reveal defect densities as high as 10⁹ cm^-2 and as low as 10⁶ cm^-2.