Generation-recombination measurements in silicon M.O.S. capacitors

Abstract

This thesis is concerned with the change in charge on a silicon MOS capacitor (MOS-C) subjected to a voltage step. The transient charge (Q-t) is controlled by the generation and recombination processes in the silicon. A review of these processes in the MOS-C, and of Q-t and other methods of measuring generation lifetime (T(_g)) is given. A thorough experimental investigation of Q-t transients is given including the effects of the guard ring voltage, applied bias, voltage step magnitude, and voltage step polarity. The measurements were performed with an automated apparatus, using a micro computer controlled measuring system developed for the purpose. An improved theory for the Q-t transient has been developed for determining the lifetime. This is midway between the simple theory of Hofstein and the more elaborate computer method of Collins and Churchill. Both the generation and recombination cases of the Q-t transient are covered for the first time and the theoretical results compare well with the experiments. The present Q-t method of determining lifetime is also compared to other Q-t analyses and with the C-t, C-V, and fast ramp methods. Good agreement is obtained with other Q-t and C-t methods, but not with the C-V and fast ramp methods. More than one hundred samples were used in this work but detailed results are presented for typical ones only. This investigation gives confidence in the use of the Q-t method for measuring the minority carrier lifetime easily and accurately.