Moo Seong Kim

Magnetic and Transport Properties of Ferromagnetic Semiconductor GaDyN Thin Film

Magnetic properties and temperature dependence of electrical transport properties of rare-earth-metal Dy-doped GaN thin film are experimentally studied with a superconducting quantum interference device magnetometer and van der Pauw method. It was found that this thin nitride film has both semiconductor properties and ferromagnetism from 10 K to room temperature. The dopant-band (conducting band due to doping) electron conduction dominates the transport properties of this film at low temperatures. These results indicate that Dy-doped GaN is an n-type ferromagnetic semiconductor at room temperature.

Polymorphism in the ferromagnetic GaCrN-diluted magnetic semiconductor: Luminescence and structural investigations

Luminescence properties of the transition-metal chromium-doped gallium nitride (GaCrN) epitaxial layers on sapphire substrates have been extensively studied by varying the doping level, excitation intensity, and temperature of study. Photoluminescence spectra of the doped films were found to be dominated by an excitonic peak around 3.25–3.29 eV in accordance with the doping level, due to the transition of neutral-donor bound excitions of GaCrN cubic modification. It is attributed that Cr, which is an acceptor in GaN matrix, acts as a surfactant and modifies the growth kinetics to induce phase modification from wurtzite to zinc blende of GaN. Moreover, Cr doping induced a blue band centered around 2.9 eV, which is a donor-acceptor pair, and also two bound excitonic lines at 3.36 and 3.31 eV at some locations of the sample: the expected origin of these is due to the transitions of excitons bound at the stacking faults which are formed due to the co-existence of hexagon and cubic modifications of GaN. The Ra...

Nature of Deep-Level Defects in GaCrN Diluted Magnetic Semiconductor

The effects of chromium doping on the luminescence properties of the deep levels in gallium nitride (GaN) have been studied exclusively. Chromium (Cr) doping induced a blue luminescent band (BL) centered in the range of 2.79–2.91 eV with the limited Cr doping concentration varying from 0.5% to 1.5% and also a slight increase in the intensity of the yellow luminescent band (YL). By analyzing the luminescent spectrum obtained with different excitation intensities, Cr doping concentration and temperature dependences revealed the nature of donor–acceptor pair transition for the observed blue band. The participating donor and acceptor are expected to be the deep-acceptor related center, CrGa, and the shallow compensating vacancy complex, CrGa–VN respectively.

Epitaxial Growth of Ferromagnetic Cubic GaCrN on MgO Substrate

Cubic GaCrN films were synthesized on MgO(001) substrates using plasma-assisted molecular-beam epitaxy, and room-temperature ferromagnetism was observed. It is suggested that these samples show more single cubic phases than those grown on Al2O3(0001) substrates. The influences of V/III ratio and Cr cell temperature on the properties of the grown GaCrN films were characterized extensively. The V/III ratio which controls the Cr incorporation in the GaCrN thin films was one of the key parameters. The Cr incorporation was larger in the GaCrN films grown under N-rich conditions than those under Ga-rich conditions. Moreover, a Ga4Cr secondary phase was also seen in the GaCrN film when it was grown under Ga-rich conditions. High-concentration Cr doping resulted in the formation of a CrN secondary phase.

Magnetic, optical and transport properties of GaN-based ferromagnetic/nonmagnetic semiconductor heterostructures

A ferromagnetic/nonmagnetic semiconductor DyN/GaN superlattice sample showed a large coercivity Hc of about 1800 Oe at 7 K, which originates from DyN layers. Ferromagnetic order was also observed at 300 K, which may come from GaDyN alloy layers formed at GaN/DyN interfaces. For this superlattice sample, spin tunnel resistance characteristics were observed at low temperatures. GaCrN/GaN/GaCrN trilayer structures were grown by radio frequency molecular beam epitaxy. Clear hysteresis and clear saturation characteristics were observed in the magnetization versus magnetic field curves at all measuring temperatures. A hysteresis loop was observed in the magnetic field dependence of vertical electrical resistance.

Magnetoresistance in GaCrN-based ferromagnet/nonmagnet/ferromagnet trilayer structures

GaCrN-based ferromagnet/nonmagnet/ferromagnet trilayer structures were grown by radio frequency molecular beam epitaxy. During GaN and GaCrN growth, reflection high-energy electron diffraction pattern showed thin streaks and Kikuchi lines, indicating surface flatness and high crystalline quality. Clear hysteresis and clear saturation characteristics were observed in the magnetization versus magnetic field curves at all measuring temperatures. The coercivity H/sub c/ was about 130 Oe at 10 K. Hysteresis loop was observed in the magnetic field dependence of vertical electrical resistance.