Hiroto Oomae

Anomalous Hall Effect and Magnetoresistance in Mn-Doped ZnSnAs2 Epitaxial Film on InP Substrates

We present for the first time the temperature dependence of resistivity, anomalous Hall effect, and extraordinary magnetoresistance (MR) in 6.5% Mn-doped ZnSnAs2 epitaxial film prepared by molecular beam epitaxy (MBE) on InP(001) substrates. The magnetic field dependence of magnetization (M–H curve) show clear hysteresis loops at 300 K for magnetic fields applied both perpendicular and parallel to the sample surface. The Curie temperature was evaluated to be 350 K. Near-zero-field hysteresis loops in the anomalous Hall resistance were also observed at various temperatures corresponding to the hysteretic out-of-plane magnetization of the sample. Negative and positive values of MR were observed in the low-field region. The behavior of the MR can be properly described by the Khosla–Fischer semi-empirical model for spin scattering of carriers in an impurity band. These characteristics strongly indicate a carrier-spin interaction in Mn-doped ZnSnAs2.

Room-Temperature Ferromagnetism in (Zn,Mn,Sn)As2 Thin Films Applicable to InP-Based Spintronic Devices

We investigated the growth and magnetic properties of ternary ZnSnAs2 thin films doped with a various degrees of Mn content. It was confirmed that Mn-doped ZnSnAs2 thin films are pseudomorphically grown on nearly lattice-matched InP(001) substrates. Magnetization measurements on Mn-doped ZnSnAs2 thin films revealed a ferromagnetic transition temperature of around 330 K, and clearly showed hysteresis loops even at room temperature. No evidence of magnetic secondary-phase MnAs formation in the host ZnSnAs2 thin films was observed within the limit of our measurement system. We also prepared a trilayer structure consisting of Mn-doped ZnSnAs2 layers and an undoped ZnSnAs2 intermediary layer as a preliminary structure for a tunneling magnetic junction. This structure was confirmed to demonstrate ferromagnetism at room temperature. The present results suggest that diluted ferromagnetic (Zn,Mn,Sn)As2 thin films are one of the most promising building blocks for InP-based spintronic devices.

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.

Influence of Carbon in In-situ Carbon-Doped SiGe Films on Si(001) Substrates on Epitaxial Growth Characteristics

Carbon doped SiGe (SiGe:C)/Si(001) heterostructure were grown by reduced pressure chemical vapor deposition using silane, germane and methylsilane as a source of Si, Ge, and C, respectively. We performed a systematic experiment of growth of SiGe:C and carried out measurements to determine the surface roughness and occupation sites of carbon atoms as functions of C source flow, Ge concentration, growth temperature and growth rate. Ge concentration range was from 0 to 23.0%. Growth temperature was 575 to 625 °C. The range of Growth rate was between 1.5 and 4.3 A/s. These SiGe:C analyzed by atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), high-resolution X-ray diffraction (HR-XRD) and cross-sectional transmission electron microscopy (TEM). Total C compositions did not depend on growth temperature with the constant Ge concentration and with SiH3CH3 flow ratio. Surface roughness of SiGe:C with high Ge concentration increased with the increase of C source gas flow. Interstitial C concentration in SiGe:C films with rough surface increased with the increase of C source gas flow. The roughness of SiGe:C layer grown constant C gas source flow ratio decreased for low growth temperature and/or faster growth rate. From these results, we revealed that the mechanism of defect formation with localized C as the cause of rough. The excess migration can suppress surface roughness.

Experimental evidence for site preference of Mn substitution in ferromagnetic (Zn,Mn,Sn)As2 films

We investigated the site preference for Mn atoms in ferromagnetic (Zn,Mn,Sn)As2 thin films grown by molecular beam epitaxy. All the (Zn,Mn,Sn)As2 samples used exhibited ferromagnetism with Curie temperatures above room temperature. The chemical compositions of the (Zn,Mn,Sn)As2 thin films were measured by electron probe microanalysis. Under the present growth conditions, increasing the Mn concentration in (Zn,Mn,Sn)As2 reduced the Sn content almost three times more than the Zn content. This result reveals for the first time that Mn substitution in (Zn,Mn,Sn)As2 thin films prefers Sn sites over Zn sites. To explain the carrier-mediated ferromagnetism of (Zn,Mn,Sn)As2 with p- or n-type conductivities, we discuss the possibility that Mn3+ substitution occurs at both Zn and Sn sites in addition to Mn2+ and Mn4+ substitutions.

Influence of Carbon in in-situ Carbon Doped SiGe (SiGe:C) Films on Si (001) Substrates on Epitaxial Growth Characteristics

�C. The range of Growth rate was between 1.5 and 4.3 A ˚ /s. These SiGe:C analyzed by atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), high-resolution X-ray diffraction (HR-XRD) and cross-sectional transmission electron microscopy (TEM). Total C compositions did not depend on growth temperature with the constant Ge concentration and with SiH3CH3 flow ratio. Surface roughness of SiGe:C with high Ge concentration increased with the increase of C source gas flow. Interstitial C concentration in SiGe:C films with rough surface increased with the increase of C source gas flow. The roughness of SiGe:C layer grown constant C gas source flow ratio decreased for low growth temperature and/or faster growth rate. From these results, we revealed that the mechanism of defect formation with localized C as the cause of rough. The excess migration can suppress surface roughness. # 2010 The Japan Society of Applied Physics