Determining the defect density of states by temperature derivative admittance spectroscopy

We demonstrate that the temperature derivative admittance spectroscopy method can be used to directly determine the defect density of states. The density of defect states is proportional to the temperature derivative of the capacitance. This method is equivalent to the existing frequency derivative method in principle but possesses certain key advantages for detection of deep levels. To illustrate these advantages, we define the activation energy of a fictitious defect the Arrhenius plot of which extends diagonally across the measurable temperature-frequency range. Below this level (that is, shallower defects), the frequency derivative method is advantageous, and above this level (that is, deeper defects), the temperature derivative method is advantageous. The temperature derivative method allows a wider observation window of defect energy that avoids possible detection failure and facilitates simultaneous observation of multiple defects. For deep defects, it also yields more Arrhenius plot data points and therefore enables more accurate extraction of defect energy and capture cross-sections. In general, the temperature derivative method can avoid system noise at low frequency and is relatively immune to baseline effects due to parasitic circuit effects. (C) 2011 American Institute of Physics. [doi:10.1063/1.3573538]