Strain-voltage and current-voltage Scanning Probe Microscopy (SPM) response of ionic semiconductor thin films: probing of deformation potential

TL;DR

This paper analytically investigates the strain-voltage and current-voltage responses of ionic semiconductor thin films using SPM, revealing new contributions from charge state changes and electron-phonon interactions, with implications for local property probing.

Contribution

It introduces the first analytical calculation of the recharging contribution to strain-voltage SPM and predicts the significance of electron-phonon coupling effects in ionic semiconductors.

Findings

Recharging contribution to strain-voltage SPM was previously uncalculated.

Electron-phonon coupling effects are comparable to ion concentration effects.

Predicted nonlinear hysteresis loops in current-voltage and strain-voltage responses.

Abstract

We performed analytical calculations of the current-voltage and strain-voltage response of the heterostructure like "charged SPM tip electrode / gap / ionic-semiconductor film" caused by the local changes of (a) ions concentration (stoichiometry contribution); (b) acceptors (donors) charge state (recharging contribution via ionic radius variation); (c) free electrons (holes) concentration (electron-phonon coupling via the deformation potential). The contribution (b) into the strain-voltage SPM was not calculated previously, while the contribution (c) was not even predicted before, while our estimations performed for correlated oxides show that strength of (c) appeared comparable with (a,b). For the case of ion-blocking tip and substrate electrode mainly the changes in holes (electrons) concentration contribute into the voltage-dependent mechanical displacement of the film surface, directly registered by strain SPM. Thus, we predict that the SPM measurements of the ionic semiconductor surface displacement could provide important information about the local changes of the acceptors (donors) charge state and electron (hole)-phonon correlations via the deformation potential. We obtained the great variety of the nonlinear static and dynamic current-voltage and strain-voltage hysteresis loops in the ionic semiconductor thin film with mobile acceptors (donors) and holes (electrons). Some types of the current-voltage hysteresis with pronounced memory window and double loops are observed experimentally in the correlated oxides and resistive switching materials like p-La1-xSrxMnO3-d and La1-xSrxCoO3-d, while predicted strain-voltage hysteresis of piezoelectric-like and butterfly-like shape requires experimental justification by SPM.