4.3 Analysis of minority carrier traps using photo-assisted CV

In a wide band gap semiconductor like SiC, the impact of minority carriers is not visible in the CV curve due to the extremely small intrinsic carrier density. Therefore, the interface charge density was extracted using photo-assisted capacitance voltage measurements as described in Section 1.3.5.

Fig. 4.6 shows a photo-assisted CV measurement after processing step . Starting in accumulation at 15 V, the gate voltage is swept to deep-depletion in the dark (cyan). While the bias is held in deep-depletion, the sample is illuminated with 350 nm light to populate the inversion layer, which results in an increase of the capacitance. Minority carriers are generated and move to the interface, where they are trapped in available interface states. Afterwards, the light is turned off and the gate voltage is swept back to accumulation in the dark, which results in the red curve. As can be seen, a voltage shift occurs in the CV curve due to the trapped minority carriers. The dashed lines represent the simulated CV-curves of the MOS system [131]. For the simulation of the illuminated curve (red), remains at the value of the dark-curve and the interface trap density is increased until the simulated and the measured CV curves match. The photo-assisted CV measurements for all high temperature processing steps are shown in Fig. 4.7. For , the photo-assisted data is missing because such a measurement was not possible in combination with the mercury probe. The number of oxide traps and the density of interface states extracted from all measurements is given in Fig. 4.8.