Minority carrier lifetime is an important material parameter in PV. Minority carrier lifetime is highly sensitive to impurities and intrinsic defects, both which affect cell efficiency. Hence, minority carrier lifetime measurement is an ideal parameter for characterization of material quality and process control. By accurately and quickly measuring minority carrier lifetimes, materials can be adjusted and manufacturing defects can be caught quickly and cost effectively.
Solar power generating capacity has grown from 83 MW in 2003 to over 7,200 MW in 2012, in the U.S. alone. As the solar industry grows, there is a significant need for quality control and testing methodologies. Both testing and quality control of photovoltaics (PV) and power electronics are essential to innovation and efficient production. Accurately testing new materials and manufacturing techniques in a quick and simple way can lead to unique insights and reduced manufacturing costs and throughput times.
NREL scientists have developed a unique apparatus and process to determine BULK-minority carrier lifetime. This development measures the minority carrier lifetime in a semiconductor wafer or thin film from the frequency dependence of the capacitance of the junction formed by the semiconductor and a liquid conductor.
This is done by contacting the surface of a semiconductor material at a first location with the first conductive liquid probe to form a Schottky junction and contacting the surface of the semiconductor material at a second location with a second contact. A forward bias is applied to the Schottky junction causing minority carrier injection in the semiconductor material. The minority carrier lifetime of the semiconductor material is determined from the inflection frequency of the total capacitance between the contacts as a function of frequency.
This in turn results in BULK lifetime measurement and is less sensitive to surface recombination velocity and treatment. The measurement can be taken without a source of light and takes only seconds to accomplish the measurement. This method could be used for any sort of semiconductor manufacturing processes.
For more information, please contact Erin Beaumont at:
Applications and Industries
- Photovoltaics Manufacturing
- Power Electronics
- No light needed
- Accurate measurement of BULK minority carriers
- Electric test only
- Less expensive