Unveiling competitions between carrier recombination pathways in semiconductors via mechanical damping

TL;DR

This paper introduces LIMAS, a novel spectroscopy technique revealing that carrier recombination pathways in semiconductors compete multiplicatively rather than additively, with pathway dominance influenced by the generation mechanism and dynamic state changes.

Contribution

The study challenges the conventional additive model of recombination rates by demonstrating a multiplicative weighting model using LIMAS, providing new insights into carrier dynamics in semiconductors.

Findings

Recombination rate follows a multiplicative model in ZnS.

Pathway dominance depends on the carrier generation mechanism.

Localized state changes alter pathway competition after light switch-off.

Abstract

The total rate of carrier recombination in semiconductors has conventionally been expressed using an additive model, r_total = \Sigma r_i , which rules out the interactions between carrier recombination pathways. Here we challenge this paradigm by demonstrating pathway competitions using our newly developed light-induced mechanical absorption spectroscopy (LIMAS), which allows us to probe genuine recombination dynamics in semiconductors via mechanical damping. We show that the total recombination rate in zinc sulfide (ZnS), a model semiconductor material, follows a multiplicative weighting model, r_total \propto \Pi r_i ^(w_i) with \Sigma w_i=1. Under both steady-state and switch-on illuminations, the weighting factors w_i for each recombination pathway-direct, trap-assisted, and sublinear-are dictated by the carrier generation mechanism: (i) interband transition favors direct recombination; (ii) single-defect level-mediated generation promotes trap-assisted recombination; (iii) generation involving multiple saturated defect levels gives rise to sublinear recombination. Upon light switch-off, localized state changes drive a dynamic evolution of w_i, altering pathway competitions. These findings reshape our fundamental understanding of carrier dynamics and provide a new strategy to optimize next-generation optoelectronic devices.