Properties of magnetic layers fabricated by Metal Vapor Vacuum Arc (MEVVA) ion implantation into germanium.

摘要

Ge surfaces were implanted with Fe ions with an acceleration voltage of 30–60 kV using a Metal Vapor Vacuum Arc (MEVVA) implanter at various doses from 2 × 1015 to 5 × 1017 ions/cm2. The implanted Fe profile in Ge and the crystallinity of Ge is studied with Rutherford Backscattering spectrometry (RBS) and ion channeling. The surface morphology is observed with Atomic Force Microscopy (AFM). The implanted Fe profile in Ge is studied with Auger electron spectroscopy (AES). The size of the nanoparticles in the implanted layer is studied with Transmission Electron Microscopy (TEM). The nature of chemical bonding between Fe and Ge is studied by X-ray Photoelectron Spectroscopy (XPS). The magnetic properties of the Fe implanted Ge layer is studied with superconducting quantum interference device (SQUID) magnetometer. Magnetoresistance of the implanted layer is measured using the four-point probe method in a Helium closed cycle refrigerator.; AFM results show that the morphological characteristics of the Fe implanted Ge changes drastically depending on the ion implantation conditions. A low level of roughness is observed up to intermediate dose ∼1016 ions/cm2. The roughness increases dramatically at a dose of 5 × 1016 ions/cm2. The common structural features observed are that all surfaces are composed of grains of sub-micron size. The grains are nearly regular in shape, appearing almost spherical in the low dose range. As dose increases, trapezoidal shaped facetted columnar grains start to appear on the surface. We have found the formation of Fe-rich precipitates in Ge by the elemental mapping using scanning Auger microscopy. The evolution and growth of Fe-rich precipitates is observed with increase in dose. These precipitates are distributed homogeneously on the implanted surface. RBS random/channelling and TEM results show that Fe implanted Ge samples implanted with various doses and accelerating voltages are a mixture of a metastable crystalline phase and an amorphous phase.; The magnetic properties of Fe clusters in Ge were investigated by SQUID magnetometer for temperatures in the range of 4.2 to 300 K. The magnetization vs magnetic field measurements were taken on the samples implanted with dose 2 × 1017 ions/cm2. At low temperatures, the ferromagnetic-like behaviour of the clusters is observed. But, at room temperature, the magnetization curve shows that Fe clusters are superparamagnetic. The size of the Fe clusters (∼3.9 to 4.0 nm) is obtained by fitting the magnetization curve at 300 K. Field-cooled (FC) and zero-field-cooled (ZFC) measurements were performed on various samples to identify the superparamagnetic relaxation of the Fe clusters. The size distribution of the clusters and interaction among the clusters are evident from the behaviour of ZFC and FC curves with temperature. We have obtained a large negative magnetoresistance (GMR) at higher temperatures (up to 8.6% at 300 K for transverse geometry) Ge implanted with dose 5 × 1016 to 5 × 1017 Fe ions/cm2 (accelerating voltage 60 kV). We have obtained large positive MR for perpendicular geometry (up to 8.55% at 300 K).