Site-specific x-ray absorption spectroscopy of electron traps by x-ray-induced displacement current measurement

The concept of 'x-ray-induced displacement currents' is introduced for x-ray absorption spectroscopy (XAS) in the local structure analysis of electron traps. Since such a displacement current (orthogonal to the conduction current, i.e., the conventional photocurrent) is responsive to localized electrons, it allows XAS to provide site-specific x-ray absorption of electron traps. Capacitance x-ray absorption fine structure (Capacitance XAFS) measurement based on this idea is adopted for defect observation in a compound semiconductor, and the result is a nonlinear dependence of the XAFS signal intensity on the bias voltage applied to the sample. This nonlinearity is formulated by the theory of the Schottky barrier diode, which is used for the capacitor formation; the x-ray-induced photoionization of the defect reduces the trapping charge at interface between depletion layer and semiconductor, resulting in capacitance increase. The temperature dependence of capacitance XAFS spectra indicates that the conduction current has no site specificity owing to the mixing of the photocarrier from the defect and crystal sites, while the x-ray-induced displacement current provides site-specific spectra independent of the conduction current