The influence of illumination conditions in the measurement of built-in electric field at p-n junctions by 4D-STEM

TL;DR

This study evaluates how different 4D-STEM imaging modes affect the measurement of built-in electric fields at p-n junctions, demonstrating that low-dose, low-magnification conditions can reliably measure electric fields with high sensitivity.

Contribution

It compares nanobeam and low magnification modes in 4D-STEM, showing low-dose, low-magnification imaging can accurately measure electric fields without beam damage.

Findings

Low magnification improves signal-to-noise ratio by nearly tenfold.

Electric field measurements are unaffected by electron dose variations down to 24 e^-/A^2.

Low-dose 4D-STEM reliably measures built-in electric fields in beam-sensitive materials.

Abstract

Momentum resolved 4D-STEM, also called center of mass (CoM) analysis, has been used to measure the long range built-in electric field of a silicon p-n junction. The effect of different STEM modes and the trade-off between spatial resolution and electric field sensitivity are studied. Two acquisition modes are compared: nanobeam and low magnification (LM) modes. A thermal noise free Medipix3 direct electron detector with high speed acquisition has been used to study the influence of low electron beam current and millisecond dwell times on the measured electric field and standard deviation. It is shown that LM conditions can underestimate the electric field values due to a bigger probe size used but provide an improvement of almost one order of magnitude on the signal-to-noise ratio, leading to a detection limit of 0.011MV/cm. It is observed that the CoM results do not vary with acquisition time or electron dose as low as 24 $e^-/A^2$, showing that the electron beam does not influence the built-in electric field and that this method can be robust for studying beam sensitive materials, where a low dose is needed.