SEM and EBIC system

LEO Gemini 1530 SEM from Carl Zeiss AG, Germany.

Scanning electron microscope

A scanning electron microscope (SEM) uses a scanning focused beam of electrons to image a sample. The interaction between the incident electrons and the sample produces several different signals that contain information about the sample, such as secondary electrons, backscattered electrons and X-rays. By recording their signals as the electron beam is scanned across the sample, images can be formed. Since the wavelength of an electron is significantly shorter than that of visible light, an SEM can resolve objects much smaller than an optical microscope can.

Features

  • Acceleration voltage: 0.1 – 30 kV

  • Resolution: 1 nm (at 30 kV)

  • Detectors: SE2, InLens, Backscatter, EDS

 

Electron Beam Induced Current (EBIC)

In a solar cell that is illuminated, photons can be absorbed and create electron-hole pairs which then are separated and swept away by the built-in electric field of the solar cell, thus driving a current. The creation of electron-hole pairs can however also be achieved by electrons. By sending a beam of electrons onto a solar cell, inelastic scattering events produces electron-hole pairs and a current can be delivered to an external circuit. This is known as electron beam induced current (EBIC). By measuring the current as the electron beam is raster scanned across the sample, the current delivered by the solar cell can be mapped. EBIC measurements allow grain boundaries and other defects to be studied since their enhanced recombination activity makes them appear dark in EBIC maps. Different types of dislocations as well as their level of contamination will cause different EBIC contrast.

We are using a Specimen Current-EBIC Amplifier from Deben Ltd., UK, together with the SEM described above.

The current range is 10-5 - 10-11 A. The spatial resolution of the EBIC maps is limited by lateral diffusion of the generated minority carriers, which depends on the absorption depth of the injected electrons and thus by the acceleration voltage and the sample material. 

 

Examples:

SEM image of a solar cell sample

 

EBIC image of the same region of the solar cell sample