Epitaxy Development

Aixtron 2800G4R MOVPE reactor
© Fraunhofer ISE
Aixtron 2800G4R MOVPE reactor in the MOVPE laboratory of Fraunhofer ISE
© Fraunhofer ISE
CRIUS Close Coupled Showerhead reactor in the MOVPE laboratory of Fraunhofer ISE.

In order to achieve highest opto-electric conversion efficiencies, it is necessary to have material of the highest quality. Here we apply our expertise in the field of epitaxy development for record efficiency solar cells to monochromatic light applications. For epitaxial growth of photovoltaic cell structures, we have two modern, industry-level MOVPE reactors in our laboratories: AIX2800 G4-TM reactor with 8x6-inch configuration and a CRIUS Showerhead reactor for 7x4 inch or 1x300 mm substrates.

Decisive for an efficient laser power converter is a suitable match between the semiconductor material (or more specifically the semiconductor bandgap) and the laser wavelength. With a good match, the thermalization losses, one of the main loss mechanisms in solar cells, can be reduced to nearly zero. III-V compound semiconductors in different compositions cover a wide range of laser wavelengths. Examples of materials used are: Ga0.51In0.49P (660 nm), GaAs (870 nm), Ga0.83In0.17As (1050 nm), Ga0.16In0.84 P0.69As0.31 (1100 nm), Ga0.47In0.53As (1680 nm) and GaSb (1700 nm) , where the cutoff wavelength is given in parentheses.

For the application-dependent development of materials, we have a broad range of characterization and analysis methods available: electrochemical capacitance-voltage (ECV) profiling techniques, spectrally and spatially resolved photoluminescence (PL) and electroluminescence (EL) measurements, X-ray diffraction (XRD), Nomarski differential interference contrast (DIC) microscopy, electron beam induced current (EBIC) measurements, atomic force microscopy (AFM), or Hall-Van der Pauw measurements.