Depletion region surface effects in electron beam induced current measurements

Area of Science:

• Materials Science
• Semiconductor Physics
• Nanotechnology

Background:

• Electron beam induced current (EBIC) is crucial for high-resolution characterization of polycrystalline solar cells.
• Existing EBIC models assume perfect charge collection efficiency in the p-n junction depletion region.
• Focused ion beam (FIB) milling preparation can introduce surface effects impacting EBIC measurements.

Purpose of the Study:

• To investigate the reduced and nonuniform EBIC lineshape observed for excitations within the depletion region of CdTe and Si solar cells prepared by FIB milling.
• To develop an improved EBIC model that incorporates surface recombination effects.
• To analyze the influence of neutral and charged surfaces on EBIC response.

Main Methods:

• Utilized focused ion beam (FIB) milling for sample preparation of CdTe and Si solar cells.
• Developed a new EBIC model accounting for surface recombination from neutral and charged surfaces.
• Analyzed experimental EBIC lineshape data from FIB-prepared silicon solar cells.

Main Results:

• Observed reduced and nonuniform EBIC lineshapes in the depletion region of FIB-milled CdTe and Si samples.
• Proposed an analytical formula for EBIC response from neutral surfaces.
• Determined that experimental data for Si solar cells aligns best with a charged surface model.

Conclusions:

• Surface recombination significantly affects EBIC measurements in the depletion region, contrary to previous assumptions.
• The presence of charged surfaces, influenced by Fermi level alignment, plays a critical role in EBIC response.
• This refined understanding is vital for accurate EBIC characterization of polycrystalline solar cells and other semiconductor devices.