Ya. I. Alivov

Fabrication and characterization of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates

We report on the fabrication of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates. Hydride vapor phase epitaxy was used to grow p-type AlGaN, while chemical vapor deposition was used to produce the n-type ZnO layers. Diode-like, rectifying I-V characteristics, with threshold voltage ~3.2V and low reverse leakage current ~10(-7)A, are observed at room temperature. Intense ultraviolet emission with a peak wavelength near 389 mn is observed when the diode is forward biased; this emission is found to be stable at temperatures up to 500K and shown to originate from recombination within the ZnO.

Observation of 430 nm Electroluminescence from ZnO/GaN Heterojunction Light-Emitting Diodes

In this work, we report on the growth, fabrication, and device characterization of wide-band-gap heterojunction light-emitting diodes based on the n-ZnO/p-GaN material system. The layer structure is achieved by first growing a Mg-doped GaN film of thickness 1 μm on Al2O3(0001) by molecular-beam epitaxy, then by growing Ga-doped ZnO film of thickness 1 μm by chemical vapor deposition on the p-GaN layer. Room-temperature electroluminescence in the blue-violet region with peak wavelength 430 nm is observed from this structure under forward bias. Light–current characteristics of these light-emitting diodes are reported, and a superlinear behavior in the low current range with a slope 1.9 and a sublinear behavior with a slope 0.85 in the high current range are observed.

Green luminescence band of zinc oxide films copper-doped by thermal diffusion

High quality ZnO single-crystal films were doped with copper by thermal diffusion, and their luminescent properties were studied by cathodoluminescence spectroscopy. Doping with copper increases the intensity of the green-emission band of the cathodoluminescence spectrum, whose peak, width, and shape at 78 and 300 K remain unchanged. At 4.2 K, a pronounced phonon structure with a phonon energy of 72 meV is detected in the cathodoluminescence green-emission band of the doped samples. In this case, the phonon peaks feature a triplet fine structure instead of the doublet one generally observed. This feature is attributed to radiative recombination of acceptor excitons that are localized at copper atoms and interact with each one of the subbands of the ZnO valence band. An analysis of the experimental data on the film cathodoluminescence and comparative studies of luminescence and electron spin resonance in single crystals allow one to conclude that the uncontrollable copper impurity typically existing in ZnO is responsible for green-emission luminescence in this material.

Cathodoluminescence of ZnO/GaN/α-Al2O3 heteroepitaxial structures grown by chemical vapor deposition

The cathodoluminescent properties of ZnO films in ZnO/GaN/α-Al2O3 and ZnO/α-Al2O3 heteroepitaxial structures grown by chemical vapor deposition in a low-pressure flowing-gas reactor were studied and compared. A superlinear dependence of the excitonic-band intensity in the cathodoluminescence spectrum of the ZnO/GaN/α-Al2O3 structures on the electron-beam current is ascertained, which indicates that the emission is stimulated for relatively low thresholds of the excitation intensity. It is shown that the ZnO films grown on the GaN substrates exhibit a much more effective cathodoluminescence compared to the cathodoluminescence in the films grown on α-Al2O3. It was observed that the luminescent properties of ZnO layers in the ZnO/GaN/α-Al2O3 structures subjected to long-term heat treatment at 750°C in an oxygen atmosphere exhibit a high thermal stability.

Fabrication and properties of an n-ZnO:Ga/p-GaN:Mg/α-Al2O3 heterojunction

The first results of growing ZnO/GaN/α-Al2O3 heteroepitaxial structures in a low-pressure flow-through reactor using chemical-vapor deposition and stimulation with a plasma of radio-frequency discharge are reported. Activation of reactants in the course of growth made it possible to significantly increase the effective pressure of atomic oxygen in the reactor, considerably reduce the temperature of epitaxy, improve the morphological and structural parameters of ZnO layers, and form a n-ZnO:Ga/p-GaN:Mg/α-Al2O3 heterojunction.

ZnO-based metal-insulator-semiconductor UV light-emitting diodes prepared by ion implantation

In this paper, we describe the N/sup +/-ion implantation of Ga doped ZnO films grown by chemical vapor deposition on a sapphire substrate. Depositing an appropriate metal onto this system can create a metal-insulator-semiconductor (MIS) type diode. Such ZnO-based MIS diodes, and their emission properties are discussed. The ohmic contact, to the lower conducting ZnO insulating layer, is made by indium. Current-voltage measurements shows good, rectifying diode-like behavior, with a threshold voltage near 3 V, and a reverse current of about 10/sup -6/ A. Under forward bias, ultraviolet emission is observed at room temperature (RT), with a wavelength maximum at /spl sim/388 m (/spl sim/3.197 eV).

ZnO/AlGaN Ultraviolet Light Emitting Diodes

We report on the optical and electrical properties of n-ZnO/p/-AlGaN heterojunctions. Ga doped n-type ZnO layers were grown using chemical vapor deposition on Mg doped p-type AlGaN epitaxial layers. AlGaN epitaxial layers with 12 at.% Al were grown on 6H-SiC by hydride vapor phase epitaxy. Rectifying diode-like behavior with a threshold voltage of 3.2 V was achieved. Intense ultraviolet electroluminescence peaking at a wavelength of 390 nm was observed at 300 and 500 K as a result of hole-injection from the n-ZnO layer into the p-AlGaN layer of the heterostructure.

A mechanism of hysteresis in brightness-voltage characteristics of ZnS: Mn-based light-emitting MISIM structures

The hysteresis phenomenon in brightness-voltage characteristics of ZnS: Mn-based thin-film metal-insulator-semiconductor-insulator-metal (MISIM) structures was investigated. The shape of the hysteresis loop depends on the frequency of an applied ac electric field. The phenomenon is explained in terms of a suggested theoretical model that postulates the presence of weakly and strongly localized charges in the semiconducting layer. Numerical model results are compared with experimental brightness-voltage characteristics.