Pulsed chemical vapour deposition of conformal GeSe for application as OTS selector

Ovonic threshold switch (OTS) selector based on the voltage snapback of amorphous chalcogenides has received tremendous attention as it provides several desirable characteristics such as bidirectional switching, a controllable threshold...

Silver photodiffusion into amorphous Ge chalcogenides

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.

Kinetics of silver photodiffusion into amorphous S-rich germanium sulphide – neutron and optical reflectivity

Silver photodiffusion is one of the attractive photo-induced changes observed in amorphous chalcogenides. In this research, we focus on amorphous S-rich germanium sulphide and study the kinetics of the silver photodiffusion by neutron reflectivity, as well as optical reflectivity. It was found from the neutron reflectivity profiles with 30 s time resolution that silver dissolved into the germanium sulphide layer, forming a metastable reaction layer between the Ag and the germanium sulphide layers, within 2 min of light exposure. Subsequently, silver slowly diffused from the metastable reaction layer to the germanium sulphide host layer until the Ag concentration in both layers became identical, effectively forming one uniform layer; this took approximately 20 min. Optical reflectivity reveals the electronic band structure of the sample, complementary to neutron reflectivity. It was found from the optical reflectivity measurement that the metastable reaction layer was a metallic product. The product could be Ag8GeS6-like form, which is regarded as the combination of GeS2 and Ag2S, and whose backbone is composed of the GeS4 tetrahedral units and the S atoms. We attribute the first quick diffusion to the capture of Ag ions by the latter S atoms, which is realised by the S–S bond in amorphous S-rich germanium sulphide, while we attribute the second slow diffusion to the formation of the Ag–Ge–S network, in which Ag ions are captured by the former GeS4 tetrahedral units.