Jiro Temmyo

Single cuprous oxide films synthesized by radical oxidation at low temperature for PV application.

Cuprous oxide (Cu(2)O) films synthesis by radical oxidation with nitrogen (N(2)) plasma treatment and different RF power at low temperature (500 °C) are studied in this paper. X-ray diffraction measurements show that synthesized Cu(2)O thin films grow on c-sapphire substrate with preferred (111) orientation. With nitrogen (N(2)) plasma treatment, the optical bandgap energy is increased from 1.69 to 2.42 eV, when N(2) plasma treatment time is increased from 0 min to 40 min. Although the hole density is increased from 10(14) to 10(15) cm(-3) and the resistivity is decreased from 1879 to 780 Ω cm after N(2) plasma treatment, the performance of Cu(2)O films is poorer compared to that of Cu(2)O using RF power of 0. The fabricated ZnO/Cu(2)O solar cells based on Cu(2)O films with RF power of 0 W show a good rectifying behavior with a efficiency of 0.02%, an open-circuit voltage of 0.1 V, and a fill factor of 24%.

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.

Strong photoluminescence emission at room temperature of strained InGaAs quantum disks (200–30 nm diameter) self‐organized on GaAs (311)B substrates

We have recently found that quantum‐box‐like structures are formed during spontaneous reorganization of a sequence of AlGaAs and strained InGaAs epitaxial films grown on GaAs (311)B substrates by metalorganic vapor‐phase epitaxy into InGaAs islands (disks) buried beneath AlGaAs. The size of the disks is directly controlled by the In content in the range 200–30 nm. Strong photoluminescence (PL) efficiency at room temperature is observed in these strained quantum disks. Even for the 30 nm disk the radiative efficiency is not reduced compared to the reference (100) quantum well. The PL spectra are characterized by narrow linewidth and well resolved exciton resonances in excitation spectroscopy.

Atomic force microscopy study of strained InGaAs quantum disks self‐organizing on GaAs (n11)B substrates

Strained quantum‐box structures are naturally formed during the interrupted growth of AlGaAs and InGaAs films on GaAs (n11)B substrates. InGaAs films organize spontaneously into orderly rows of nanoscale disks buried beneath AlGaAs microcrystals. A comparative study by atomic force microscopy shows the alignment and uniformity to be optimum on (311)B surfaces. Both the uniformity and the shape of the microcrystals are not changed for base widths between 220 and 70 nm. Moreover the size and distance can be controlled independently by the In composition and the InGaAs layer thickness, respectively. In contrast, step bunching occurs on GaAs (n11)A substrates to form wirelike microstructures on GaAs (311)A substrates.

SPIN RELAXATION OF EXCITONS IN ZERO-DIMENSIONAL INGAAS QUANTUM DISKS

We report the observation of spin relaxation of excitons in zero-dimensional semiconductor nanostructures. The spin relaxation is measured in InGaAs quantum disks by using a polarization dependent time-resolved photoluminescence method. The spin relaxation time in a zero-dimensional quantum disk is as long as 0.9 ns at 4 K, which is almost twice as long as the radiative recombination lifetime and is considerably longer than that in quantum wells. The temperature dependence of the spin relaxation time suggests the importance of exciton–acoustic phonon interaction.

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.

Self‐organization of strained GaInAs microstructures on InP (311) substrates grown by metalorganic vapor‐phase epitaxy

The evolution of low‐dimensional microstructures in the growth of strained GaInAs/AlInAs and GaInAs/InP heterostructures on planar InP (311)B and (311)A substrates by metalorganic vapor‐phase epitaxy is investigated by atomic force microscopy. The surface structures are found to be similar to those previously reported for GaAs (311)B and (311)A substrates. In particular, the appearance of zero‐dimensional microstructures in the GaInAs/AlInAs system on InP (311)B substrates is analogous to the self‐organizing formation of buried InGaAs quantum disks in the case of GaAs (311)B substrates.

High responsivity and internal gain mechanisms in Au-ZnMgO Schottky photodiodes

Schottky photodiodes based on Au-ZnMgO/sapphire are demonstrated covering the spectral region from 3.35 to 3.48 eV, with UV/VIS rejection ratios up to ∼105 and responsivities as high as 185 A/W. Both the rejection ratio and the responsivity are shown to be largely enhanced by the presence of an internal gain mechanism, by which the compensated films become highly conductive as a result of illumination. This causes a large increase in the tunnel current through the Schottky barrier, yielding internal gains that are a function of the incident photon flux.

SEMICONDUCTOR NANOSTRUCTURES FORMED BY THE TURING INSTABILITY

We describe the surface topography domain in a strained InGaAs/AlGaAs system on the GaAs (311)B substrate during metalorganic-vapor-phase-epitaxial growth. The surface rearrangement resulting in the formation of nanostructures seems to belong to a Turing-type self-organization phenomenon that results from a spontaneous symmetry-breaking instability in nonlinear dynamical systems. The unique surface morphologies on the high Miller index faces suggest a novel fourth growth mode due to Turing-type self-organization.