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The synthesis, structure, and optical properties of one-dimensional heteroepitaxial cored (Zn,Mg)O semiconductor nanowires grown by a catalyst-driven molecular beam epitaxy technique are discussed. The structures form spontaneously in a Zn, Mg and O2/O3 flux, consisting of a single crystal, Zn-rich Zn1-xMgxO(x<0.02) core encased by an epitaxial Zn1-yMgyO(y>0.02) sheath. High resolution Z-contrast scanning transmission electron microscopy shows core diameters as small as 4 nm. The cored structure forms spontaneously under constant flux due to a bimodal growth mechanism in which the core forms via bulk like vapor-liquid-solid growth, while the outer sheath grows as a heteroepitaxial layer. Temperature-dependent photoluminescence shows a slight blueshift in the near band edge peak, which is attributed to a few percent Mg doping in the nanoscale ZnO core. The catalyst-driven molecular beam epitaxy technique provides for site-specific nanorod growth on arbitrary substrates. [ABSTRACT FROM AUTHOR]

Electrical and optical properties of undoped n-ZnO crystals implanted with 50 keV protons with doses from 5×10[sup 13] to 5×10[sup 15] cm[sup -2] are reported. Proton implantation leads to a decrease of the carrier concentration in the near-surface region, but at the end of the proton range shallow donors are observed whose concentration tracks the implant dose and that we attribute to hydrogen donors. Three deep electron traps with apparent activation energies of 0.55, 0.75, and 0.9 eV are introduced by proton implantation. The 0.9 eV traps have been observed through the increased thermal stability of the Schottky diodes prepared on heavily implanted n-ZnO compared to unimplanted or lightly implanted samples. In addition, hole traps located 0.16 eV above the valence band edge were introduced by implantation. Proton implantation also led to the formation of persistent-photocapacitance-active defects and to considerable decrease in the intensity of the band edge luminescence and in the value of the photocurrent of the Au/n-ZnO Schottky diodes. When compared with other wide-band gap materials, such as GaN, the recombination properties of n-ZnO are shown to be more resistant to deterioration upon proton implantation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effects of hydrogen plasma treatment on high-quality bulk n-ZnO crystals were studied. It is shown that after plasma exposure at 200 °C for 0.5 h the hydrogen penetrates into the material down to about 20 µm and shows concentrations close to 10[sup 17] cm[sup -3] in that region. The incorporation of this hydrogen coincides with an increase in the shallow donor concentration to about the same level as the concentration of hydrogen. In contrast to that in most other semiconductor materials, hydrogen plasma treatment of ZnO is shown to increase the concentration of the already existing electron and hole traps and to introduce electron traps near 0.55 eV, earlier observed in proton irradiated samples. The effect is at least partially due to the surface damage caused by plasma exposure. Despite this increase in the density of deep traps, the luminescence intensity in the near band-edge region is shown to increase down to the depth corresponding to the hydrogen penetration depth in the material. [ABSTRACT FROM AUTHOR]

Deep levels introduced into n-GaN films by Fe and Cr implantation have been studied by means of optical absorption and microcathodoluminescence spectroscopy measurements and by deep level transient spectroscopy, admittance spectroscopy, and capacitance-voltage profiling. The results are compared with previous measurements on Mn and Co implanted GaN. It is shown that the acceptor levels of substitutional Mn, Co, Fe, and Cr in n-GaN are located, respectively, near E[sub v]+1.6 eV, E[sub v]+1.7 eV, E[sub v]+1.8 eV, and E[sub v]+2 eV, the trend being similar to that observed in GaAs, GaP, and InP. The Fermi level in the implanted region is pinned near deep electron traps at E[sub c]-0.5 eV that are tentatively attributed to complexes between substitutional transition metal ions and native defects such as nitrogen vacancies. It is shown that for all implanted species after 700 °C annealing a damaged region with relatively high resistivity is formed down to the depth of about 1 μm much, exceeding the projected range of implanted ions. This region is enriched with radiation-damage-related defects and is most likely formed by outdiffusion of these defects from the implanted region during annealing. The thickness of this damaged region is shown to be the lowest for Cr implantation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. The mechanism for the observed magnetic behavior is complex and appears to depend on a number of factors, including Mn-Mn spacing, and carrier density and type. For example, in a simple Ruderman-Kittel-Kasuya-Yosida carrier-mediated exchange mechanism, the free-carrier/Mn ion interaction can be either ferromagnetic or antiferromagnetic depending on the separation of the Mn ions. Potential applications for ferromagnetic semiconductors and oxides include electrically controlled magnetic sensors and actuators, high-density ultralow-power memory and logic, spin-polarized light emitters for optical encoding, advanced optical switches and modulators and devices with integrated magnetic, electronic and optical functionality. [ABSTRACT FROM AUTHOR]

Optical absorption spectra, microcathodoluminescence (MCL) spectra, and electrical properties of GaMnN films grown by molecular-beam epitaxy with Mn concentration in the range of 3 to 10 at. % were studied. Optical absorption and MCL spectra show the presence of strong bands corresponding to the transition from the Mn acceptors near E[SUBc] - 2 eV to the conduction band. The other strong band observed in MCL measurements was the blue band peaked near 2.9 eV and associated with the transition from the valence band to deep donors with a level near E[SUBc] - 0.5 eV. All GaMnN samples were shown to be lightly n-type which suggests close self-compensation of the Mn acceptors by some native defect donors. A plausible scenario is that such compensating donors could be due to nitrogen vacancies and that the E[SUBc] - 0.5 eV donor defects are complexes between the Mn acceptors and the nitrogen vacancy donors. [ABSTRACT FROM AUTHOR]

Optical transmission spectra, microcathodoluminescence spectra, capacitance-voltage and capacitance-frequency curves, temperature dependence of resistivity and deep level spectra with both electrical and optical injection were measured on n-GaN samples implanted with high doses of Mn (3 × 10[sup 16] and 4 × 10[sup 16] cm[sup -2]) and Co (4 &times ; 10[sup 16] cm[sup -2]). From optical transmission it was found that Mn forms a deep acceptor near Ev + 1.8 eV while the Co acceptor is about 0.1 eV deeper. In addition, Mn and Co form complexes with native defects and these complexes are deep electron traps with a level near Ec-0.5 eV. Such complexes are most likely responsible for a strong blue luminescence band with energy near 2.9 eV. Adjacent to the implanted region a defect region about 1 µm deep is formed, most likely by out-diffusion of point defects from the implanted zone during the 700°C annealing used to partially remove the radiation damage. This region is characterized by a high density of electron traps at Ec-0.25 eV and Ec-0.7 eV and hole traps at Ev + 0.2 eV, Ev + 0.35 eV and Ev + 0.45 eV. [ABSTRACT FROM AUTHOR]

Epitaxial layers of ZnSiN[sub 2], ZnGe[sub 0.65]Si[sub 0.35]N[sub 2], and ZnGe[sub 0.31]Si[sub 0.69]N[sub 2] grown on A1[sub 2]O[sub 3] substrates were implanted at 350°C with high doses (5 × 10[sup 16] cm[sup -2]) of Mn[sup +] ions and annealed at700 °C. The implanted region did not appear to become amorphous and showed strong selected area diffraction patterns. Hysteresis was observed in magnetization versus field curves from all of the implanted samples. Differences in field-cooled and zero field-cooled magnetization persisted to temperatures of ∼200 K for ZnSiN[sub 2], and ∼280 K for both ZnGe[sub 0.31]Si[sub 0.69]N[sub 2] and ZnGe[sub 0.69]Si[sub 0.31]N[sub 2]. The results are consistent with recent magnetic data from (Zn[sub x]Mn[sub 1-x]) GeP[sub 2], ZnSnAs[sub 2] and (Cd[sub x]Mn[sub 1-x]) GeP[sub 2] and suggest that this class of materials may be promising for dilute magnetic semiconductor applications. [ABSTRACT FROM AUTHOR]

Beryllium and magnesium were co-implanted with oxygen into GaN at precise donor-to-acceptor ratios of 0.5–2. High activation efficiency was achieved for Be+O co-implants at a donor–acceptor ratio of 2 and anneal temperatures of 1050–1100 °C. The activation process was not a simple, single-step mechanism. Hall data indicated a relatively low (<=100 meV) ionization energy for Be in the co-implanted samples. This process may have application in improving p-ohmic contact resistance by selective area Be+O implantation. By sharp contrast Mg+O co-implants produced n-type conductivity under all conditions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The synthesis, structure, and optical properties of one-dimensional heteroepitaxial cored (Zn, Mg) O semiconductor nanowires grown by a catalyst-driven molecular beam epitaxy technique are discussed. The temperature-dependent photoluminescence shows a slight blueshift in the near band edge peak, which is attributed to a few percent Mg doping in the nanoscale ZnO core.

Ion implantation of Mn or Cr at concentrations of 1-5 at. % were performed in Al[SUBx]Ga[SUB1-x]P (x=0.24,0.38) epilayers grown by gas source molecular beam epitaxy. Ferromagnetic-like ordering above 100 K for Cr and 300 K for Mn was observed in superconducting quantum interference device measurements. Structural characterization revealed no second phases that could influence the measured magnetic properties. As the AIP mole fraction in the Al[SUBx]Ga[SUB1-x]P layers increased, the magnetic ordering temperatures were generally observed to increase, while the calculated magnetic moment decreased. Mn appears to be a more promising choice than Cr for high temperature ferromagnetism in AlGaP. [ABSTRACT FROM AUTHOR]

The discovery of epitaxially grown ferromagnetic, type III-V semiconductors (Ga,Mn)As (T[sub c] = 110 K) and (In,Mn)As (T[sub c] = 35 K) holds promise for developing semiconductor electronics that utilize the electron's spin degree of freedom in addition to its charge. It has been theoretically predicted that some semiconducting systems could be ferromagnetic above room temperature, when optimally doped (p-GaN with 5% Mn). We report here on the use of ion implantation to incorporate magnetic ions into a variety of semiconducting substrates, thereby facilitating investigation of the nature of ferromagnetism in semiconducting systems that are difficult to grow with other methods. The magnetic ions, Mn, Fe, and Ni, were implanted into each of the epitaxially grown semiconductors GaN, GaP, and SiC to achieve volume concentrations between 1 and 5 at. %. The implanted samples were subsequently annealed at 700-1000°C to recrystallize the samples and remove implant damage. The implanted samples were examined with both x-ray diffraction and transmission electron microscopy to characterize their microstructure and with superconducting quantum interference device (SQUID) to determine magnetic properties. In most cases, no secondary phases were found. The magnetic measurements [hysteresis, coercive fields, and differences between field-cooled (FC) and zero field-cooled (ZFC) magnetizations] indicate ferromagnetism up to room temperature for some samples that could not be attributed to superparamagnetism or any other magnetic phase. Particularly, p-GaP:C with high hole concentration, when doped by implantation with 3 at. % Mn, showed ferromagnetic behavior very close (T[sub c] = 250 K) to room temperature. In summary, we found that ferromagnetic behavior is very dependent on the concentration of the magnetic impurities for all samples and it is even more dramatically affected by the type and the concentration of the majority carriers, in qualitative agreement with the... [ABSTRACT FROM AUTHOR]