Regular Article

Silver photodiffusion into amorphous Ge chalcogenides^★

Excitation photon energy dependence of the kinetics probed by neutron reflectivity

¹ Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), 162-1 Shirakata, Tokai, Naka-gun, Ibaraki 319-1106, Japan
² Department of Electrical and Computer Engineering, Boise State University, 1910 University Dr., Boise, ID 83725-2075, USA

^* e-mail: y_sakaguchi@cross.or.jp

Received: 27 December 2019
Received in final form: 18 May 2020
Accepted: 25 May 2020
Published online: 1 July 2020

Abstract

Silver photodiffusion into amorphous chalcogenides involves the movement of ions controlled by a UV-visible light illumination, and has potential application to memory devices. Understanding the kinetics of this phenomenon will expand the range of possible applications. Herein, we report the excitation photon energy dependence of the silver photodiffusion kinetics in Ag/amorphous Ge₂₀S₈₀/Si substrate stacks, probed by neutron reflectivity using four light-emitting diodes with different peak wavelengths. Time-dependent changes were clearly observed in all three of the Ag/Ag-doped reaction/chalcogenide host layers, in terms of layer thickness, scattering length density, and roughness. Silver photodiffusion effectively occurred when the excitation photon energy was greater than the optical gap of the chalcogenide host material. Excitation of lone-pair electrons to anti-bonding states at the chalcogenide layer therefore appears to play a crucial role in triggering silver photodiffusion.