Blue light-emitting diode based on ZnO

A near-band-edge bluish electroluminescence (EL) band centered at around 440 nm was observed from ZnO p-i-n homojunction diodes through a semi-transparent electrode deposited on the p-type ZnO top layer. The EL peak energy coincided with the photoluminescence peak energy of an equivalent p-type ZnO layer, indicating that the electron injection from the n-type layer to the p-type layer dominates the current, giving rise to the radiative recombination in the p-type layer. The imbalance in charge injection is considered to originate from the lower majority carrier concentration in the p-type layer, which is one or two orders of magnitude lower than that in the n-type one. The current-voltage characteristics showed the presence of series resistance of several hundreds ohms, corresponding to the current spread resistance within the bottom n-type ZnO. The employment of conducting ZnO substrates may solve the latter problem.Comment: 13 pages, 4 figures. Jpn. J. Appl. Phys. in pres

Microstructural evolution in m-plane GaN growth on m-plane SiC

This letter presents a study on the nucleation and microstructural evolution of m-plane GaN epilayers on m-plane SiC substrates using high-temperature AlN buffer layers. Controlled growth interruptions were carried out to render snapshots of heteroepitaxial dynamics. It was discovered that island coalescence results in an inhomogeneous mosaic tilt along the c-axis. Mesoscopic study of nucleation evolution helps elucidate the origin of commonly observed surface undulation and striation, which is attributed to concave growth due to the coalescence of trapezoidal islands upon contact. A model correlating microstructural defects with optical properties is proposed to explain the observed pattern in spatially resolved cathodoluminescence mapping.open221

Polarity-dependence of the defect formation in c-axis oriented ZnO by the irradiation of an 8 MeV proton beam

The polarity dependence of the radiation hardness of single-crystalline ZnO bulk crystals is studied by irradiating the Zn-polar and O-polar c-planes with an 8 MeV proton beam up to the fluence of 4.2 × 1016 p/cm2. To analyze the hardness, radiation-induced defects were evaluated using positron annihilation (PA) analysis, and the recovery by post-annealing was examined using continuous-wave photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. It was suggested by the PA and PL analyses that the major defects in both polarities were VZnVO divacancies. While the PA data did not show the clear dependence on the polarity, the PL and TRPL results showed that the Zn-polar c-plane had a little higher radiation tolerance than that of the O-polar c-plane, which was consistent with the result that the increase in the electrical resistance by proton beam irradiation was smaller for the former one. Considering these results in total, the polarity dependence is considered to be not so large, but the Zn-polar c-plane has a little higher tolerance than that of the O-polar one

Cathodoluminescence spectroscopy of monolayer hexagonal boron nitride

Cathodoluminescence (CL) spectroscopy is a suitable technique for studying the luminescent properties of optoelectronic materials because CL has no limitation on the excitable bandgap energy and eliminates ambiguous signals due to simple light scattering and resonant Raman scattering potentially involved in the photoluminescence spectra. However, direct CL measurements of atomically thin two-dimensional materials have been difficult due to the small excitation volume that interacts with high-energy electron beams. Herein, distinct CL signals from a monolayer hexagonal BN (hBN), namely mBN, epitaxial film grown on a graphite substrate are shown by using a CL system capable of large-area and surface-sensitive excitation. Spatially resolved CL spectra at 13 K exhibited a predominant 5.5-eV emission band, which has been ascribed to originate from multilayered aggregates of hBN, markedly at thicker areas formed on the step edges of the substrate. Conversely, a faint peak at 6.04 ± 0.01 eV was routinely observed from atomically flat areas, which is assigned as being due to the recombination of phonon-assisted direct excitons of mBN. The CL results support the transition from indirect bandgap in bulk hBN to direct bandgap in mBN. The results also encourage one to elucidate emission properties of other low-dimensional materials by using the present CL configuration

GaN and Related Alloys - 2001: Volume 693

This book focuses on three main themes. Theme one - advances in basic science. Point defects, dislocations, doping, the properties of nitride alloys with a special emphasis on localization phenomena and GaAsN alloys (which are very promising for long-wavelength emitters), transport and optical properties are also featured. Theme two - growth and growth-related issues. Significant advances have been made in understanding/improving all major nitride growth techniques (MBE, MOCVD, HVPE). Techniques such as ELOG and the development of bulk-like substrates are receiving attention as methods to reduce the number of dislocations. Theme three - devices. Tremendous progress has been reported in device design and optimization, and also in understanding device processing issues such as p-contacts, laser lift-off, and etching. Overall, the book offers a broad exchange of scientific knowledge and technical expertise. Topics include: molecular beam epitaxy and growth kinetics; point defects and doping; light emitters; nitride alloys and lateral epitaxy; quantum wells; transport and optical properties; vapor phase epitaxy; extended defects; electronic devices and processing

GaN and Related Alloys - 2001: Volume 693

This book focuses on three main themes. Theme one - advances in basic science. Point defects, dislocations, doping, the properties of nitride alloys with a special emphasis on localization phenomena and GaAsN alloys (which are very promising for long-wavelength emitters), transport and optical properties are also featured. Theme two - growth and growth-related issues. Significant advances have been made in understanding/improving all major nitride growth techniques (MBE, MOCVD, HVPE). Techniques such as ELOG and the development of bulk-like substrates are receiving attention as methods to reduce the number of dislocations. Theme three - devices. Tremendous progress has been reported in device design and optimization, and also in understanding device processing issues such as p-contacts, laser lift-off, and etching. Overall, the book offers a broad exchange of scientific knowledge and technical expertise. Topics include: molecular beam epitaxy and growth kinetics; point defects and doping; light emitters; nitride alloys and lateral epitaxy; quantum wells; transport and optical properties; vapor phase epitaxy; extended defects; electronic devices and processing.https://corescholar.libraries.wright.edu/books/1032/thumbnail.jp