A common origin of photoplastic and electroplastic effects in ZnS

TL;DR

This paper reveals that charged dislocations in ZnS respond to optical and electronic stimuli, affecting plasticity, and demonstrates how this understanding can be used to engineer dislocation behavior in semiconductors.

Contribution

It experimentally validates that charged dislocations in ZnS respond to optical and electronic doping, unifying the understanding of photoplastic and electroplastic effects.

Findings

Optical excitation reduces Zn-core dislocation glide in ZnS.

Electron doping decreases Zn-core dislocation density significantly.

S-core dislocations are insensitive to optical and electronic stimuli.

Abstract

Dislocation motion--the atomic-scale mechanism of crystal plasticity--governs the strength and ductility of materials. In functional materials, external stimuli beyond mechanical stress can also affect dislocation glide. In the wide band gap semiconductor ZnS, optical illumination suppresses plasticity, whereas electric fields can enhance dislocation motion. Here, we show that the common underlying mechanism for these phenomena is the charged dislocations that respond to the changes in carrier concentration. Our prior theoretical work showed that locally charged dislocations in ZnS trap excess carriers, triggering core reconstructions that modify their mobility, with the positively charged Zn-rich core dislocations showing the most drastic change. Here, we validate this prediction experimentally by showing that either optical excitation or electronic doping selectively inhibits the glide of Zn-rich dislocations in epitaxially grown ZnS. First, imaging individual interface misfit dislocations under different optical excitation conditions shows that Zn-core glide is strongly reduced as optical power is increased, while the S-core dislocations show negligible sensitivity to light, marking the first, single misfit dislocation imaging of the photoplastic effect. Next, we show that a similar behavior is observed with direct electron (n-type) doping of ZnS epitaxial layers grown beyond the critical thickness. As the n-type dopant density is increased, the resulting Zn-core dislocation density is reduced by more than one order of magnitude, while the S-core density remains essentially unchanged, causing a sign reversal of the strain-anisotropy with n-type doping. These results demonstrate a common origin for the opto-electronic sensitivity of dislocations in ZnS and provide a pathway for the engineering of dislocation content in compound semiconductors.