Investigation of trapping properties in SIMOX films by photo-induced transient current spectroscopy

Minority carrier trapping in unprocessed SOI materials has been studied by photoinduced transient current spectroscopy (PTCS). The method consists of filling interface states and bulk traps by means of pulsed photoexcitation and then monitoring the transient current that corresponds to the carrier emission process. The experiment was carried out in SIMOX (separation by implanted oxygen) material synthesized by deep oxygen implantation and high-temperature annealing. The illumination was provided by a light-emitting diode array. The sample was biased at 0.2 V, and the current was monitored using a measured system composed of a current-to-voltage converter and a lock-in amplifier. The output voltage is related to the density of traps while the frequency gives their emission rate and energy position in the gap. A typical energy profile is shown, which demonstrates a clear increase of the trap density near the valence band edge. The density of 10¹² traps/cm² is a reasonable value as far as the proximity of the buried interface is concerned and should not significantly affect the performance of integrated circuits. PTCS experiments have been conducted in parallel with conventional static photoconductivity and photo Hall effect. A donorlike process-induced contamination was found to occur due to the oxygen activation of annealing conditions. The region situated near the buried interface is shown to be responsible for the transition to hopping conduction mechanism below 60 K. A two-band model accounts for the minimum observed in the carrier concentration curve