Infrared capacity mapping of semiconductor junctions by lock-in thermography

We image the reverse-bias-modulated space charges in a heated p-n junction using infrared (IR) lock-in thermography. The modulation of the space charges leads to a change of the free carrier IR emission signal of the sample, which is detected by an IR camera. This way charge carrier densities are measured, which in combination with the voltage applied yield the capacitance of the junction. Experimentally measured capacitance-voltage curves agree with the theoretical model of an abrupt p-n junction. Using lock-in thermography, we deduce the spatially resolved acceptor doping concentration of a crystalline silicon wafer. A sensitivity analysis shows that our system detects a noise equivalent capacitance of 1 nF cm(-2) after a measurement period of 28 min at a lateral resolution of 170 mu m. (c) 2005 American Institute of Physics.