In situ TEM electrical biasing studies on defect based crystal‐amorphous transformation in GeTe nanowire devices
Year: 2016
Type: other
Abstract: Germanium telluride (GeTe), a phase‐change material, switches rapidly and reversibly between crystalline and amorphous phase. The crystalline to amorphous transformation pathway is based on melting the crystalline phase and quenching it to amorphize in nanoseconds timescale. However, this is inefficient and energy consuming, and it is necessary to look for alternate pathways to carry out this transformation. Using in situ TEM electrical biasing experiments on GeTe nanowires, we discovered a defect‐assited low energy pathway for crystal‐amorphous transformation. GeTe is both ferroelectric (FE) and inherently defective (Ge vacancies) metallic material, an unusual combination of properties in any material system. We show through dark‐field TEM movies that interaction between extended defects of different origins (ferroelectric and metallic) can result in a pathway towards amorphization. In the “forming stage”, voltage pulses applied on metallic GeTe act as heat shocks creating anti‐phase boundaries (APB) by coalescing and quenching Ge vacancies in a Ge plane. These APBs interact with the pre‐existing 71° ferroelectric domain boundaries converting them into 109 o boundaries. The partial dislocations surrounding the APBs migrate in the direction of the electrical wind‐force, only to be impeded by the 109° boundaries. Eventually, the mobility of the partial dislocations becomes zero, analogous to a scenario of traffic jam on a highway. Accumulating more extended defects at the jam, eventually collapses the crystallinity ‘nucleating’ an amorphous phase with medium range order, in a very local region that cuts across the cross‐section of the nanowire. The amorphous mark can be recrystallized via another electrical pulse which heat it beyond the crystallization temperature.
Authors: Pavan Nukala, Ritesh Agarwal
Institutions: Supélec, University of Pennsylvania
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W4244013652