In Charge Pumping (CP), an electrical characterization technique for carrier traps, the gate of the transistor is pulsed between accumulation and inversion at a certain CP frequency. Through this gate pulse, positive and negative charge carriers are alternatingly flowing through the interface. These charge carriers can be trapped in defects at this interface, and generate a recombination current, the so-called CP current. By varying the CP parameters, such as the voltage, the frequency or amplitude of the gate pulse as well as its shape (rise and fall times), the technique becomes sensitive to various trap characteristics, such as capture and emission cross sections as well as energy level distributions. While the technique is already very interesting on its own, in our lab we can further combine it with electrically-detected magnetic resonance.
Electrically detected magnetic resonance (EDMR) combined with charge pumping is a powerful spectroscopic technique to characterize paramagnetic interface point defects in metal-oxide-semiconductor field-effect transistors (MOSFETs), as it is selective to those defects that are relevant for the device operation. Since the CP current is a recombination current, it is intrinsically spin-dependent and can thus be manipulated by magnetic resonance. For example, the spins of the electron-hole pairs, prior to recombination, form either a singlet or triplet state, where ethe singlet pairs recombine leaving an excess of triplets. Recombination of triplet states can only occur after flipping the spin of one of the two charge carriers by the magnetic resonance process, otherwise they dissociate. As such, in EDMR we can either promote or prevent the recombination of the intermediate pairs and as such obtain information on their exact dynamics.
Finally, the EDMR spectrum is sensitive to the spin density distribution of the charge carriers in the defect, and through hyperfine interactions with neighboring nuclear spins the spectrum can reveal the specific structure of the trap.
References of setup: J. Lettens et al, J. Appl. Phys. 137, 065705 (2025), https://doi.org/10.1063/5.0245349