Measurement of recombination lifetime profiles in epilayers using a conductivity modulation technique

A new experimental techique is described to accurately measure the recombination lifetime profile in lightly doped epitaxial layers of thickness less than the minority-carrier diffusion length. This technique requires the use of a particular "test" structure composed of a lateral p⁺-n-n⁺diode on the surface of the epilayer and a control electrode on the substrate layer. Using a conductivity modulation technique, the proposed measurement method is independent of recombination effects in the highly doped regions needed for every test structure. Moreover, the evaluation of lifetime profiles along the epilayer is made possible by varying the width of the conductivity modulated region through the control electrode bias. The measurement theory is developed for the high-injection regime, usually applicable to the lightly doped layers of bipolar power devices.