Junji Ishihara

Zn1−xCdxO systems with visible band gaps

Zn1−xCdxO films in the range of the content x from x=0 to x=1 were grown by remote-plasma-enhanced metal organic chemical vapor deposition. The crystal structure of Zn1−xCdxO film changed with increase of the content x from wurtzite structure to rocksalt structure around x=0.7. The relationship between the cadmium content and axis length in the Zn1−xCdxO films was studied. Photoluminescence spectra were observed from the wurtzite Zn1−xCdxO films in the range of 3.3–1.8eV at room temperature. Stokes’s shift in the restricted composition range was compared with the previous results.

Zn1-xCdxO Film Growth Using Remote Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Zn1-xCdxO films were successfully grown by remote plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The content ratio of Zn1-xCdxO films was controlled by changing the molar ratio of diethyl zinc (DEZn) to dimethyl cadmium (DMCd). The wurtzite structure of Zn1-xCdxO films was obtained by increasing the Cd content up to x=0.697. The optical-band-gap energy of Zn1-xCdxO films was tuned between 1.85 eV and 3.28 eV at room temperature. The photoluminescence emission of hexagonal Zn1-xCdxO films up to x = 0.697 was observed at room temperature.

Full-color electroluminescence from ZnO-based heterojunction diodes

Red, green, and blue electroluminescence have been observed from ZnO-based heterojunction diodes consisting of n-ZnO∕n-MgyZn1−yO∕Zn1−xCdxO∕p-SiC layers. The heterostructures were grown by remote-plasma-enhanced metal-organic chemical vapor deposition. The rectifying I-V characteristics at room temperature reveal the red, green, and blue wavelengths near 720, 520, and 480nm, respectively, when the diodes are forward biased. It is observed that the emission color can be controlled by changing the cadmium content in the emission layer.

Characterization of Wurtzite Zn1-xCdxO Films Using Remote Plasma-Enhanced Metalorganic Chemical Vapor Deposition

The optical properties of wurtzite Zn1-xCdxO films were investigated. The films were grown on (1120) a-plane sapphire substrates by remote plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD) and a characterized by X-ray diffraction, photoluminescence (PL), ultraviolet/visible/near-infrared (UV/VIS/NIR) optical transmission spectroscopy and Hall measurement. The content ratio of the films was controlled by changing the molar ratio of diethyl zinc (DEZn) to dimethyl cadmium (DMCd). The optical band gap of the films at nearly 3.28 eV was shifted by alloying with Cd down to 1.85 eV depending on the alloy composition. The evolution of the PL lineshape was studied as a function of temperature. The activation energy of the films calculated from the variation of the PL peak intensity was as large as the binding energy of ZnO. In addition, the films showed a large Stokes shift at room temperature, which is discussed in terms of the localization of excitons in a ternary alloy.

Zn1-xCdxO/ZnO Heterostructures for Visible Light Emitting Devices

Wurtzite Zn1-xCdxO/ZnO heterostructures were successfully grown by remote plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD) and were investigated by photoluminescence (PL) spectroscopy. The flatness of Zn1-xCdxO films was investigated by an atomic force microscope (AFM), indicating the typical RMS value of 0.5 nm. The optical properties of the Zn0.96Cd0.04O film were characterized by micro-PL at 4 K, exhibiting micro-structural and positional uniformities in the films. In the double heterostructure consisting of ZnO/Zn0.92Cd0.08O/ZnO, temperature and excitation intensity dependencies of PL spectra were examined. The PL emission is characterized as localized and free exciton emission. A dependence with a slope near unity is obtained from the excitation dependence of the PL intensity. Blue-green emission (2.78 eV) was demonstrated from the double-heterostructure at room temperature.