Photoluminescence and Infrared Lifetime Imaging Tool in the Integrated Measurements and Characterization Cluster Tool
This page provides details on photoluminescence and infrared lifetime imaging in the Integrated Measurements and Characterization cluster tool. These capabilities are planned to be operational in 2009.
The photoluminescence and infrared lifetime imaging tool is designed to have two camera imaging systems integrated in a vacuum chamber. One system uses a silicon charge-coupled device (CCD) camera to collect photoluminescence. The other system uses an indium antimonide (InSb) infrared camera.
- A silicon CCD camera is used to characterize solar cells and semiconductor materials at various stages during the solar cell manufacturing process using photoluminescence.
- Photoluminescence (PL) is the light emitted from the semiconductor due to radiative recombination. Light absorbed in a sample generates excess carriers, and the concentration of these carriers builds up to a population that depends on defects, impurities, and other recombination mechanisms in that region.
- Photoluminescence intensity is proportional to carrier concentration. So, in general, bright areas show higher minority-carrier lifetime regions, whereas dark areas show regions of higher defect concentration.
- PL imaging is a contactless technique, which allows it to be applied between processing steps during solar cell manufacturing.
- An infrared (IR) InSb camera can characterize solar cells and semiconductor materials using two contactless lock-in thermography techniques: illuminated lock-in thermography and carrier density imaging.
- Lock-in thermography (LIT)—uses modulated excitation to periodically excite excess carriers. The IR camera's sensitivity is considerably improved when triggered to the excitation frequency. Such sensitivity allows detection of very small changes in the IR radiation or transmission of a sample. Illuminated lock-in thermography (ILIT) uses light to induce a photo-generated voltage and drive a forward-bias current through the shunts. At shunts, localized current generates heat, which is detected by the IR camera. Other techniques sense heat where currents are affected by nonuniform series resistance.
- Carrier density imaging is used to image minority-carrier lifetime and carrier trapping when excess carriers are generated by absorption of light.
- When the background is warmer than the sample, the infrared camera images heat being transmitted through the sample. Excess carriers increase absorption in regions where their concentration is high, which corresponds to where their lifetimes are long, or their lifetimes are prolonged by trapping.
- When the sample is warmer than the background, infrared emission of the excess carriers is imaged. Carrier concentration, such as emitter doping, can also be monitored with such infrared detection.
- Can go back and forth between the vacuum chamber and a table-top enclosure.
Contact Steve Johnston for more details on these capabilities.