Assessing metal–semiconductor contact properties using in situ -biasing off-axis electron holography

Characterizing metal–semiconductor contacts, particularly detecting Schottky barriers and distinguishing between ohmic and Schottky contacts, is essential for developing efficient semiconductor devices. Off-axis electron holography enables direct visualization of electrostatic potentials in a transmission electron microscope and has previously been used to study semiconductor p–n junctions under applied bias. Here, it is demonstrated that in situ biasing off-axis electron holography enables the direct characterization of the electrical properties of Schottky and ohmic metal–semiconductor contacts, including the visualization and quantification of Schottky depletion widths while simultaneously probing the behavior of the semiconductor p–n junction under operating conditions. To demonstrate this, Pt and W contacts with intentionally low and high contact resistance were deposited on GaAs p–n diodes using Ga-focused ion beam-induced deposition. The electrostatic potential across the metal–GaAs interface and p–n junction was mapped using electron holography under applied reverse bias. Electron holography successfully detected and quantified the Schottky depletion width in situ at the interface between W and p-GaAs and confirmed the ohmic behavior of the Pt contact to p-GaAs, demonstrating that electron holography can directly distinguish and characterize Schottky and ohmic contacts while simultaneously probing the behavior of the p–n junction. Thus, the results demonstrate its effectiveness for measuring nanoscale contacts in operating devices.