Microwave Detected Photo Induced Current Transient Spectroscopy (MD-PICTS)

In order to investigate defects in semiconductors it is widely spread to use temperature dependent methods as deep level transient spectroscopy (DLTS). Usually for these methods it is necessary to form contacts on the samples, which means the sample itself is often altered due to annealing steps. Furthermore for lot of semiconductors some effort is needed to create ohmic contacts at all. MD-PICTS is a non-destructive, contactless method with which the activation energies and capture cross sections of defects can be determined with a high accuracy.

For MD-PICTS measurements the photoconductivity of a sample after the irradiation with light is measured with a resonant microwave cavity. For the determination of the activation energy the temperature dependent change of the photoconductivity transient is determined via a window analysis, which is also used for DLTS measurements (fig. 1).

Fig.2 shows a so called MD-PICTS spectrum which results from the window analysis. Every peak in this spectrum is a certain defect in the sample.

The temperature shift of the maximum of this peak is plotted in an Arrhenius plot according to this formula of the emission rate:

From the slope of the Arrhenius plot (Fig. 3) the activation energy can be determined.

With the novel commercially available MD-PICTS equipment it is possible to measure the temperature dependence of the photoconductivity transient in a range from 20…500 K. In the past Si, GaAs, InP, SiC and many more semiconductors have already been successfully investigated with this method.