Differences between differential phase contrast and electron holographic measurements of a GaN p-n junction

Modern semiconductor devices require control of the electrostatic potential landscape at nanometer scale, which is especially important for materials like the Group III-Nitrides, where polarization effects cause additional sheet charges at interfaces. In this work two complementary electron microscopic methods, differential phase contrast (DPC) and electron holography (EH), are used for characterization of a GaN p-n junction in one and the same sample. In comparison, the values obtained for the junction's characteristics, like the built-in potential step, the maximum fields strength, and the width of the space charge region, were significantly larger and also closer to the expected values, when measured by means of EH. A key difference in the measurements is the vastly lower illumination dose rates within the EH experiments. Therefore, the lower generation rate of electron-hole pairs might lead to a lower beam induced bias during the EH measurement. These findings demonstrate that in future experiments the impact of the electron illumination must be considered for accurate nanoscale electrostatic field and potential measurements.