A refined step-recovery technique for measuring minority carrier lifetimes and related parameters in asymmetric p-n junction diodes

Minority-carrier lifetime in a forward-biased asymmetrical p-n junction diode can be measured by observing the time response of the diode to a sudden reversing step voltage. An approximate but general theory for p-n junctions with almost arbitrary impurity gradients is developed, and its results are within about 25 percent of those previously obtained for the special cases of ideal step and exponentially graded junctions. A relatively simple experimental technique is described which is suitable for measuring lifetimes down to less than 1 ns. Measurements at extreme ambients are facilitated by the fact that the test diode is mounted at the end of a single coaxial line which can be arbitrarily long. The raw data from the experiment are in the form of an oscilloscope trace, which provides an immediate qualitative and semiquantitative indication of the minority-carrier lifetime and the penetration length for the injected carriers. A graphical presentation of the theoretical results leads quickly to a more precise quantitative evaluation of these parameters. In addition, the technique can be used to measure an average junction depletion capacitance and the device series resistance.