Joel T. Asubar

Three Dimensional Local Structure Analysis of ZnSnAs2:Mn by X-ray Fluorescence Holography

X-ray fluorescence holographic study on a room-temperature ferromagnetic semiconductor film of ZnSnAs2:Mn was performed using a strong X-ray beam of third generation synchrotron radiation of SPring-8. The real space reconstructions of the environments around Mn atoms were successfully visualized from the observed holograms despite the very small amount of Mn atoms. The reconstructions revealed that the Mn atoms occupy the cation (Zn or Sn) site.

Dependence of MBE-grown ZnSnAs2:Mn epitaxial film properties on Mn doping level

We have prepared Mn-doped ZnSnAs2 thin films with varying Mn doping content (2.1%, 2.7%, and 5.0%) using molecular beam epitaxy, by changing the Mn-to-Sn beam equivalent pressure ratio during growth. All the samples were grown on InP(001) substrates using the optimum substrate temperature Ts=300°C previously reported. As a reference, an un-doped ZnSnAs2 epitaxial film was also prepared. In-situ reflection high-energy electron diffraction observations revealed the transformation from streaky to spotty suggesting increasing surface roughening with increasing Mn-content. From high-resolution X-ray diffraction studies, the lattice constant was found to increase with increasing Mn-doping level. The 5% Mn-doped ZnSnAs2 epitaxial film exhibited a Curie temperature of ~314 K, as revealed from measurement of the zero-field cooled temperature dependence of the remanent magnetization using a magnetic property measurement system superconducting quantum interference device magnetometer. A hysteretic M-H curve was also obtained even at 300 K. From the M-H curve measured at 5K, the magnetic moment was computed to be 1.1μB per Mn atom.

Evidence of Pseudomorphic Growth of ZnSnAs2 Epitaxial Layers on Nearly Lattice Matched InP Substrates

ZnSnAs2 epitaxial films of various thicknesses have been grown on InP(001) substrates by molecular beam epitaxy using different growth times. No manifestations of epitaxial layer lattice relaxation such as broadening of the full width at half maximum of high-resolution x-ray diffraction rocking curves, reduction of the ratio of the diffraction peak intensities of the epitaxial layer and the substrate, and extinction of the Pendellos?ng fringes were observed with increasing sample thickness. This implies that the epitaxial films remain pseudomorphic with the InP substrate to a thickness of at least 285 nm. Micro-Raman spectroscopy measurements revealed that all the samples exhibited A1 vibrational modes that were similar to those observed in chalcopyrite semiconductors

Magnetic Properties and Surface Morphology of MnAs Thin Films Grown by MBE on GaAs(111) Substrates

We formed a ~23-nm-thick MnAs thin film on an epi-ready semi-insulating GaAs(1 11) substrate by molecular beam epitaxy at a growth temperature Ts of 250?C. Streaky in-situ reflection high-energy electron diffraction patterns were obtained during the entire growth process indicating layer-by-layer growth. High-resolution X-ray diffraction revealed two growth orientations, (0001) and (10-11). Magneto metry measurements performed using a superconducting quantum interference device magnetometer revealed a Curie temperature Tc of ~355?C and a large difference in the in-plane and out-of-plane M-H characteristics, even at room temperature. Atomic force microscopy images contained hexagonal patterns or portions, suggesting that the main growth direction is (0001).

Fabrication and structural characterization of nearly lattice-matched p-ZnSnAs2/n-InP heterojunctions

Rectifying p-ZnSnAs2/n-InP heterojunctions have been successfully fabricated by growing p-type ZnSnAs2 epitaxial layers of different thicknesses on n-type InP(001) substrates using molecular beam epitaxy (MBE). The growths were monitored by in-situ reflection high-energy electron diffraction (RHEED). Electron Probe MicroAnalysis (EPMA) investigations have revealed that all the samples are nominally stoichiometric. Reciprocal space mapping of the ∼120-nm-thick sample suggests pseudomorphic growth with respect to the InP substrate. High-resolution x-ray diffraction (HR-XRD), Atomic Force Microscopy (AFM), and Transmission Electron Microscopy (TEM) studies suggest high structural qualities of the epitaxial films.