Growth study of GeTe phase change material using pulsed electron-beam deposition

Abstract

Thin film growth of chalcogenides composition is an exciting field, owing to the interesting optical and electrical properties of them. In this work, a novel, physical vapor deposition (PVD) method called pulse electron-beam deposition (PED) experimentally studied to investigate the requirements for ablation of phase change materials (PCM). To evaluate the qualifications of the PED method, thin films of Germanium Telluride (GeTe) are grown and investigated by contemplating the surface morphology and the material composition. High-quality GeTe thin films with thicknesses from 30 to 200 nm, were successfully grown on top of silicon wafers at room temperature to demonstrate the ability of PED. To optimize the growth procedure, several growth parameters were thoroughly investigated, including background pressure, pulse energy, and growth temperature. A series of material characterization methods were adopted to study the GeTe material quality after the growth. These methods include field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and thickness profilometer. It was found that higher material growth rate can be obtained in lower background pressure (∼ 2.6 mTorr), lower temperature (room temperature) but higher pulse energy (e.g., 15 kV). Besides, by increasing the target-to-substrate distance, the surface quality (e.g., smoothness) was improved substantially, but the growth rate decreased linearly. Finally, after the growth optimization, FESEM images revealed that the as-grown GeTe films were of high smoothness and uniformity. EDX analysis indicated that the compositions of the GeTe films were pressure dependent. Through the XRD spectrum, it is found that the as-grown GeTe films were amorphous. In order to convert them into crystalline formation, further post-treatment approaches (e.g., annealing) will be required.