Differential phase contrast (DPC) mapping electric fields: Optimising experimental conditions.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Electron Microscopy

Background:

• Differential Phase Contrast (DPC) is a powerful technique for visualizing electric fields within semiconductor materials using Scanning Transmission Electron Microscopy (STEM).
• Optimizing experimental parameters is crucial for accurate electric field mapping but remains a significant challenge.

Purpose of the Study:

• To systematically evaluate and compare critical experimental parameters influencing DPC measurements in STEM.
• To determine the detection limits and practical applicability of DPC for electric field mapping in semiconductors.

Main Methods:

• Investigated DPC performance by varying convergence angle, camera length, acceleration voltage, sample configuration, and orientation.
• Utilized a four-quadrant segmented detector and a silicon specimen with varying Arsenic (As) concentrations.
• Correlated DPC measurements with estimated electric fields across different sample thicknesses.

Main Results:

• DPC measurements demonstrated a near-linear relationship with electric fields down to approximately 0.5 mV/nm for a 145 nm thick sample.
• The signal-to-noise ratio of DPC can be enhanced by increasing specimen thickness for planar junctions.
• DPC's reliability decreases for electric fields below 0.5 mV/nm or in the presence of curved junctions.

Conclusions:

• DPC with a segmented detector is a practical method for mapping electric fields above 0.5 mV/nm at planar junctions in semiconductors.
• For weaker electric fields or curved junctions, alternative high-sensitivity techniques like 4D STEM with pixelated detectors are necessary.
• This study provides essential guidance for selecting appropriate techniques for electric field characterization in diverse semiconductor devices.