C. S. Park

Effect of additional nonmagnetic acceptor doping on the resistivity peak and the Curie temperature of Ga1-xMnxAs epitaxial layers

We have investigated the effect of additional doping by Be on the properties of Ga1−xMnxAs (x=0.03). For this relatively low value of x, the Curie temperature is observed to increase with increasing Be concentration. We show that the temperature dependence of the resistivity at zero magnetic field, including the resistivity maximum near the Curie temperature, can be successfully described by the magnetoimpurity scattering model proposed by Nagaev [Phys. Rep. 346, 387 (2001)] in both the paramagnetic and the ferromagnetic temperature regions. Quantitative analysis of the data in terms of this model yields the value of the p–d exchange energy |N0β|≈1.6 eV for Ga0.97Mn0.03As.

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.

Ferroelectricity in Mn-implanted CdTe

CdTe:Mn was prepared by implantation of CdTe with 200 keV Mn ions with a dose of 5×1016 cm−2, which produced an insulating layer in the surface region. Ferroelectric characterization of the implanted sample revealed a clear hysteresis in its polarization–voltage curves. The remnant polarization of CdTe:Mn amounts to 0.64 μC/cm2 at 400 Hz, and it decreases with increasing temperature in a continuous and diffusive manner. Capacitance measurement demonstrated a maximum capacitance at 140 °C, and fitting of the data with Curie–Weiss law shows the occurrence of a second-order-type phase transition. The ferroelectricity is accounted for by the cation size difference in CdTe:Mn.

Hysteresis in electric polarization of InP doped with Mn

InP:Mn was grown by liquid phase epitaxy method. Ferroelectric characterization of the InMnP based capacitor revealed a clear hysteresis in its polarization-voltage curves. The remnant polarization of InP:Mn amounts to 3.84μC∕cm2 at 300Hz. Current-voltage hysteresis demonstrated a variation of built-in voltage, and capacitance versus voltage revealed a hysteresis as well. Imprint, electric conductivity, and hysteretic asymmetry of sample were enhanced after annealing at 800°C for 30s. It is considered that the hysteresis is originated from the displacement of phosphorus vacancy by Jahn-Teller distortion of [MnIn−VP] complex defect.

R&D Project Selection Methodology for Green Technology : Focused on Developing Country-Oriented Technology Commercialization

This paper proposes an R&D project selection methodology for green technology centered on developing country-oriented technology commercialization. Eight selection criteria are derived from the R&BD logic model: technology needs of developing countries, effectiveness of green technology, technological potentials, domestic technological capability, commercialization feasibility, economic benefits, business feasibility, and spillover effects of developing countries. 21 qualitative and quantitative indicators are then defined for each criterion. The analytic hierarchy process is then conducted to produce relative importance of evaluation indicators and to set final priority scores of R&D project candidates. The working of the proposed methodology is provided with the help of a case study example of Green Technology Center. The proposed methodology is expected to be effectively utilized for policy practices of R&D project selection in the field of green technology.