Tetsuo Fujii

Nitrogen doped MgxZn1−xO/ZnO single heterostructure ultraviolet light-emitting diodes on ZnO substrates

We have grown nitrogen-doped MgxZn1−xO:N films on Zn-polar ZnO single crystal substrates by molecular beam epitaxy. As N-sources, we employed NO-plasma or NH3 gas itself. As x increased, optimum growth temperature window for smooth film morphology shifted to higher temperatures, while maintaining high N-concentration (∼1×1019 cm−3). The heterosructures of MgxZn1−xO:N (0.1≤x≤0.4)/ZnO were fabricated into light emitting diodes of 500-μm-diameter. We observed ultraviolet near-band-edge emission (λ∼382 nm) with an output power of 0.1 μW for a NO-plasma-doped LED and 70 μW for a NH3-doped one at a bias current of 30 mA.

Plasma-assisted Molecular Beam Epitaxy of High Optical Quality MgZnO Films on Zn-polar ZnO Substrates

The excellent structural and optical properties of pseudomorphic MgxZn1-xO films (0≤x≤0.39) are reported in this work. The MgxZn1-xO films were grown on Zn-polar ZnO substrates by plasma-assisted molecular beam epitaxy. Those MgxZn1-xO films for which x≤0.18 exhibited atomically flat surfaces, and the typical full-width-at-half-maximum (FWHM) value of the (0002) X-ray diffraction ω-rocking curves for these films was 35 arcsec. The FWHM values were less than 100 meV for the near-band-edge photoluminescence (PL) at 300 K. We observed PL lifetimes of the order of ns, and the longest fast-decay component reached 3.5 ns for the Mg0.12Zn0.88O alloy.

Halide Vapor Phase Epitaxy of MgxZn1-xO Layers on Zn-Polar ZnO Substrates

High quality MgxZn1-xO layers (0≤x≤0.16) on Zn-polar ZnO substrates were successfully grown by halide vapor phase epitaxy (HVPE) at a high temperature of 1000 °C. The MgxZn1-xO layers exhibited atomically flat surfaces, and were free from impurities. The near-band-edge emission of photoluminescence (PL) at room temperature could be varied from 3.26 to 3.56 eV with increase of the Mg concentration. PL measurements at 12 K revealed that a Mg0.16Zn0.84O layer grown by HVPE exhibited excellent optical properties.

Solid Composition Control of MgxZn1-xO in Halide Vapor Phase Epitaxy

Using thermodynamic analysis, the solid compositions of Mg in MgxZn1-xO grown by halide vapor phase epitaxy (HVPE) are calculated in terms of the various input partial pressures of the gaseous species. It is revealed that the Mg composition shows temperature stability up to 1200 °C, while there is a strong dependence on the input VI/II ratio and the input H2 partial pressure at high temperatures. Based on the thermodynamic calculations, the epitaxial growth of MgxZn1-xO layers with different Mg compositions has been demonstrated. The thermodynamic model is found to accurately describe the experimentally observed dependence of Mg compositions on the input VI/II ratio that is used in the growth of MgxZn1-xO.