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

Abstract

The concept of ''x-ray-induced displacement currents'' is introduced for x-ray absorption spectroscopy ͑XAS͒ in the local structure analysis of electron traps. Since such a displacement current ͑orthogonal to the conduction current, i.e., the conventional photocurrent͒ 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 XAFS͒ 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 sitespecific spectra independent of the conduction current.

In operando x-ray imaging of nanoscale devices: Composition, valence, and internal electrical fields

“…These features would be related to the density of states, as in x-ray photoelectron spectroscopy (XPS). In large-beam experiments, similar ideas have been published (30)(31)(32); however, they are heavily contested (16). The convincing counterargument is that the large multiplication factor together with the multitude of de-excitation paths for each absorbed x-ray photon statistically negates the difference in the mean number of excited charge carriers between two impinging x-ray photons of differing energy, except for a linear relation to the impinging photon energy.…”

Analysis of Iodide Transport on Methyl Ammonium Lead Iodide Perovskite Solar Cell Structure Through Operando Hard X-ray Photoelectron Spectroscopy

“…First, we underline that the difference in work function between the Ag and the AZO wide band gap semiconductor will likely generate a depletion layer at the Ag/AZO Schottky barrier. − This depletion zone will be sensitive to the level of defect localized in this junction. Furthermore, the V OC drop followed by a slow relaxation of SP_1 in Figure b can be explained by a dynamic process of trap charging and discharging of optically active midgap states. , Indeed, due to contact between the Ag and AZO layer, ultrathin Ag–O–Zn chemical bonds can form upon the interaction between Ag and O. This interfacial bond will also lead to the generation of oxygen vacancies around the first few nanometers of AZO .…”

“…Furthermore, the V OC drop followed by a slow relaxation of SP_1 in Figure 2b can be explained by a dynamic process of trap charging and discharging of optically active midgap states. 87,88 Indeed, due to contact between the Ag and AZO layer, ultrathin Ag−O−Zn chemical bonds can form upon the interaction between Ag and O. This interfacial bond will also lead to the generation of oxygen vacancies around the first few nanometers of AZO.…”

Scanning Tunneling Microscopy Combined with Hard X-ray Microbeam of High Brilliance from Synchrotron Radiation Source

“…7) Although these approaches are successful and valuable examples, they are limited in generality or spatial resolution. Other experiments on inelastic tunneling spectroscopy 8) or capacitance analysis 9) are appropriate for analyzing chemical states, but not for the direct elemental identification. These difficulties often make the interpretation of STM images ambiguous.…”