Effects of Thickness and Si₃N₄ Coverage on the Phase Transition Characteristics of GeTe Thin Films

Abstract

GeTe is one of the most widely used phase-change materials for reconfigurable optical and electrical integrated devices. The development of highlevel integration requires scaling down of devices to increase the integration density. However, the influence of thickness and the interfacial effect on the phase-change behavior of GeTe films is still unclear. Here, we study the phasechange properties and thickness reduction of both uncovered and Si 3 N 4 -covered GeTe films. With decreasing film thickness, the resistance and optical band gap of the GeTe film remarkably increase, and the thermal stability properties including crystallization temperature and data retention ability are significantly improved because of a larger surface-area-to-volume ratio and a smaller grain size. The crystallization mechanism presents a nucleation-dominated process during the scaling down of the GeTe film. The coverage of Si 3 N 4 further improves the thermal stability, resistance drift, and optical band gap of GeTe. The production of nitrides inhibits the crystallization process. Various orientations of crystal grains appear with different polarization directions under the application of an electric field. These results are of great significance for the design of high-density storage and low-power nonvolatile tunable devices by scaling down phase-change films.

Evolution of Short‐Range Order of Amorphous GeTe Upon Structural Relaxation Obtained by TEM Diffractometry and RMC Methods

“…While an enhancement of heavily PD‐like/pyramidal motifs has been found in the current study and in former work, [ 22 ] other studies found interesting behavior upon aging as well: An increasing bandgap [ 22 ] and increasing crystallization times [ 69 ] were found concomitant with the resistance increase upon aging. An intriguing coincidence with the behavior of crystalline GeTe films upon reducing the film thickness becomes apparent: The optical bandgap and the resistivity [ 49 ] as well as the crystallization temperature [ 49,70 ] are observed to increase upon decreasing film thickness. Most importantly, those property changes are all accompanied by an increase of the Peierls distortion as a result of the increasing confinement.…”

“…Such solids often show Peierls distortion that raises the bandgap and increases the electron localization. [ 22 , 48 , 49 ] Starting from the perfect octahedral GeTe structure (NaCl), the Peierls distortion is manifested in a shift of one of the (Ge or Te) sublattices in the (1 1 1) direction. That is, instead of each octahedral site having six equally distant nearest neighbors, they divide into three long bonds and three short bonds.…”

Application of Ge2Sb2Te5 phase change films in flexible memory devices

“…The effects of PEEK substrates on Ge 2 Sb 2 Te 5 materials under different conditions, including microscopic changes, surface morphology effects, volume changes, and effects on the electrical switching characteristics of PCM devices, were systematically investigated. 14,15 The results show that Ge 2 Sb 2 Te 5 films based on PEEK substrates have good thermal stability and electrical properties, as well as good resistance to bending, and can be used as flexible memory materials.…”

Space‐Confined Growth of Ultrathin P‐Type GeTe Nanosheets for Broadband Photodetectors

“…[47] Hu et al explained that a reduction in thickness would inhibit crystallization by destroying the long-range ordered crystal structure. [48] To investigate the semiconductor properties of GeTe, most studies have focused on bulk materials or irregular amorphous films. [49][50][51][52] However, the synthesis of ultrathin 2D GeTe nanosheets with excellent p-type semiconductor properties remains a challenge.…”