Yoon Shon

Optical and magnetic measurements of p-type GaN epilayers implanted with Mn+ ions

The p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently Mn+ ions implanted. The properties of Mn+ ions-implanted GaN epilayers were investigated by optical and magnetic measurements. The results of photoluminescence measurement show that optical transitions related to Mn apparently appear at 2.5 eV and around 3.0 eV. It is confirmed that the photoluminescence peak at 2.5 eV is a donor–Mn acceptor transition. Ferromagnetic hysteresis loop was observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting up to ∼270 K.

Memory effects related to deep levels in metal–oxide–semiconductor structure with nanocrystalline Si

Nanocrystalline(nc)-Si was grown on SiO2 by rapid thermal chemical vapor deposition. The tunneling oxide layer of a thickness of 4 nm was formed on p-type Si(100) by rapid thermal oxidation at 1050 °C for 30 s. Metal–oxide–semiconductor (MOS) structures were fabricated and capacitance–voltage characterization was carried out to study the memory effects of the nc-Si embedded in the MOS structure. We found the memory effect to be dominantly related to hydrogen-related traps, in addition to being influenced by the three-dimensional quantum confinement and Coulomb charge effects. Deep level transient spectroscopy reveal that the activation energies of the hydrogen-related traps are Ev+0.29 eV (H1) and Ev+0.42 eV (H2), and the capture cross sections are 4.70×10−16 cm2 and 1.44×10−15 cm2, respectively. The presence of Si–H and Si–H2 bonds was confirmed by Fourier transform infrared spectroscopy.Nanocrystalline(nc)-Si was grown on SiO2 by rapid thermal chemical vapor deposition. The tunneling oxide layer of a thickness of 4 nm was formed on p-type Si(100) by rapid thermal oxidation at 1050 °C for 30 s. Metal–oxide–semiconductor (MOS) structures were fabricated and capacitance–voltage characterization was carried out to study the memory effects of the nc-Si embedded in the MOS structure. We found the memory effect to be dominantly related to hydrogen-related traps, in addition to being influenced by the three-dimensional quantum confinement and Coulomb charge effects. Deep level transient spectroscopy reveal that the activation energies of the hydrogen-related traps are Ev+0.29 eV (H1) and Ev+0.42 eV (H2), and the capture cross sections are 4.70×10−16 cm2 and 1.44×10−15 cm2, respectively. The presence of Si–H and Si–H2 bonds was confirmed by Fourier transform infrared spectroscopy.

Magnetic Characteristic of Mn+ Ion Implanted GaN Epilayer

Nanoscale ferromagnets (GaMn) with the implantation of Mn+ ions have been incorporated into unintentionally doped (n-type) GaN epilayers grown on sapphire substrate by molecular beam epitaxy (MBE). Energy dispersive X-ray (EDX) spectrometry, atomic force and magnetic force microscopy (AFM and MFM) are used to characterize the GaMn precipitates which form within the GaN epilayer. MFM images reveal nanoscale ferromagnets (GaMn), and a small magnetic hysteresis loop indicates that there are ferromagnetic particles in our GaN:Mn layer involving the paramagnetic property and is measured by superconducting quantum interference device (SQUID) magnetometer.

Enhanced positive magnetoresistance effect in GaAs with nanoscale magnetic clusters

The enhanced positive magnetoresistance effect has been observed in GaAs containing nanoscale magnetic clusters. The ferromagnetic metallic clusters were embedded into GaAs by Mn ion implantation and rapid thermal annealing. Positive magnetoresistance in these structures has been observed and attributed to the enhanced geometric magnetoresistance effect in inhomogeneous semiconductors with metallic inclusions. The additional enhancement of positive magnetoresistance under light illumination is due to the higher mobility of photoexcited electrons in comparison with the mobility of holes in p-type GaAs prepared by Mn ion implantation.

Mn-implanted dilute magnetic semiconductor InP:Mn

Unintentionally doped bulk InP was prepared by the liquid encapsulated Czochralski method and subsequently implanted with various doses of Mn+. The properties of Mn+-implanted InP:Mn were investigated by various measurements. The results of energy dispersive x-ray peaks displayed injected concentrations of Mn of 0.8% and 8.8%, respectively. The results of photoluminescence (PL) measurement showed that optical broad transitions related to Mn appeared near 1.089, 1.144, and 1.185 eV in samples with various doses of Mn+. It was confirmed that the photoluminescence peaks near 1.089, 1.144, and 1.185 eV were Mn-correlated PL bands by the implantation of Mn. Ferromagnetic hysteresis loops measured at 10 K were observed and the temperature-dependent magnetization showed ferromagnetic behavior around 90 K, which almost agreed with the theoretical prediction (Tc∼70 K).

Improved ferromagnetism of (Zn0.93Mn0.07)O through rapid thermal annealing

After annealing at 900°C, the ferromagnetic properties of (Zn0.93Mn0.07)O thin films were dramatically improved. The resultant remanent magnetization (Mr) and Curie temperature (TC) were 1.17μB∕Mn and 83K. The improvement of ferromagnetism was confirmed to as resulting from the enhancement of magnetic anisotropy. This result is attributed to the improvement of crystallinity and the stabilization of unstably bonded Mn2+ ions by thermal treatments. These results suggest that ferromagnetism of (Zn1−xMnx)O thin films can be improved by modifying the crystal magnetic anisotropy through postgrowth thermal treatments.

Structural, optical, and magnetic properties of As-doped (Zn0.93Mn0.07)O thin films

The As-doped (Zn0.93Mn0.07)O thin film prepared by As+ ion implantation showed a clear peak of (A0,X) having acceptor binding energy of 181meV. The sample showed high TC ferromagnetism persisting up to 285K. The contribution of magnetization from Mn ion at 280K was determined to be 0.13μB∕Mn. The improved ferromagnetism is expected to be originated from hole-induced ferromagnetism and enhanced magnetic anisotropy because crystallographically improved sample showed p-type conductivity with hole concentration of 4.8×1018cm−3 and hole mobility of 11.8cm2V−1s−1. These results suggest that high TC ferromagnetism can be realized by codoping the acceptor dopant and improving the magnetic anisotropy.

Enhanced ferromagnetism in H2O2-treated p-(Zn0.93Mn0.07)O layer

Enhanced ferromagnetism was observed from the H2O2-treated p-type (Zn0.93Mn0.07)O:As layer. Compared with the untreated sample, the H2O2-treated sample showed the enlarged ferromagnetic hysteresis loop with approximately two-times-increased spontaneous magnetization. And also, in comparison with the untreated sample (TC∼280 K), the H2O2-treated sample exhibited to have the increased TC persisting up to above 350 K. These results were confirmed to originate from the enhanced p-d hybridization due to the decrease in negatively charged residual background carriers. This is because the increased effective g-factor resulting from the decrease in oxygen-related defects acting as native deep donors was observed from the H2O2-treated sample.

Ferromagnetic behavior of p-type GaN epilayer implanted with Fe+ ions

p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently implanted with Fe+ ions. The properties of Fe+ implanted GaN epilayers were investigated by various measurements. The results of photoluminescence measurement show that optical transitions related to Fe appear at 2.5 eV and around 3.1 eV. It was confirmed that the photoluminescence peak at 2.5 eV is a donor-Fe acceptor transition and the photoluminescence peak around 3.1 eV is a conduction band-Fe acceptor transition. Apparent ferromagnetic hysteresis loops measured at 10 and 300 K were observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting above 350 K.

Enhancement of magnetic properties by nitrogen implantation to Mn-implanted p-type GaN

N and Mn ions were co-implanted into p-type GaN and subsequently annealed at 700–900 °C. Compared with Mn-implanted sample, the (Mn+N)-implanted sample revealed a larger ferromagnetic signal. This was attributed to the increase of Ga–Mn magnetic phases. Mn–N compounds, such as Mn6N2.58 and Mn3N2, decreased and the resistivity significantly increased, meaning a reduction of N vacancies. It is suggested that enhancement in ferromagnetic properties in the (Mn+N)-implanted GaN originated from the reduction of N vacancies and the increase of Ga–Mn magnetic phases.