Imaging p–n Junctions Using Operando Photoemission Electron Microscopy

We propose a method to visualize the modification of the band alignment and depletion layer structure of p-n junctions under device operation. The cross-section of the p-n interface of a GaAs backward tunnel diode was directly observed by operando photoemission electron microscopy (PEEM) under forward and reverse bias operation. In addition to obtaining the external voltage dependent energy band alignment, further spectral signatures were observed in the n-type region, which provided evidence of the tunneling of electrons under reverse bias. Moreover, the PEEM images allowed us to directly visualize the depletion layer and its widening under increasing reverse bias voltages. This method can straightforwardly be applied to any semiconductor material for a thorough understanding of the electronic structure at the interface, leading to improved efficiency and device performance.