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Mapping Relative Carrier Trap Density via Band Bending from Oxide Surface Layers.
Daniel X Du1,2,3, Ebrahim Najafi4, Anthony W P Fitzpatrick1,2,3
1Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, New York 10027, United States.
JACS Au
|March 27, 2026
Summary
Scanning ultrafast electron microscopy reveals heterogeneous contrast on semiconductor surfaces. This is caused by interlayer defects influencing band-bending, not heterostructures, offering new insights into charge carrier dynamics.
Area of Science:
- Materials Science
- Surface Science
- Electron Microscopy
Background:
- Photoexcitation in scanning ultrafast electron microscopy (SUEM) images charge-carrier transfer on semiconductor surfaces.
- Contrast typically arises from secondary electron emission influenced by excited electrons or band-bending in oxide films.
Purpose of the Study:
- To investigate the origin of heterogeneous ultrafast contrast features in SUEM on semiconductor surfaces without heterostructures.
- To correlate observed contrast variations with material properties like defects and charge carrier concentration.
Main Methods:
- Utilized scanning ultrafast electron microscopy (SUEM) with photoexcitation.
- Performed rigorous controls and randomized time point scans to validate findings.
- Analyzed contrast intensity variations in relation to material properties.
Main Results:
- Observed heterogeneous ultrafast contrast features on semiconductor surfaces lacking heterostructures.
- Attributed contrast heterogeneity to variations in oxide-bulk interlayer defects affecting band-bending.
- Demonstrated a direct correlation between contrast intensity and charge carrier concentration (bare semiconductor) or interlayer trap state concentration (oxide thin film).
Conclusions:
- Interlayer defects, not heterostructures, can induce heterogeneous ultrafast contrast in SUEM.
- Band-bending modulation by defects is the primary mechanism for observed contrast.
- SUEM can quantify charge carrier and trap state concentrations via contrast analysis.
