M. V. Chukichev

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.

Cathodoluminescent contrast of direct writing patterns in the scanning electron microscope

Abstract Time dependences of local cathodoluminescence (CL) intensity for some materials and a CL contrast of direct writing patterns by means of the scanning electron microscope (SEM) have been investigated. Two types of CL contrast corresponding to decreasing or increasing of quantum yield of the investigated materials were discovered.

The effect of Fe, Cu, and Si impurities on the formation of emission spectra in bulk ZnO crystals

On the basis of the results of complex investigations (photoluminescence, x-ray fluorescence, and infrared spectroscopy), the features of emission-spectra formation are shown under the change in the type (Fe, Cu, and Si) and concentration of background impurities appearing during both growth and treatment of bulk crystals by grinding and polishing. Special attention is given to the concentration and types of bonds with hydrogen-the basic impurity preventing the formation of crystals with the p-type conductivity.

Luminescent properties of CdS crystals doped with gallium and tellurium in cadmium vapor

A technique is devised for vapor-phase doping CdS in the quaternary system Cd–Ga–Te–S. CdS crystals are doped with Ga and Te via four-zone annealing in a vapor phase containing Ga, Te, and Cd (the more volatile component of CdS). The luminescence spectra of the CdS〈Ga,Te〉[Cd] crystals are found to contain orange and red emission bands, in contrast to those of CdS[Cd] crystals, which are dominated by green emission.

Cathodoluminescence of photosensitive CdSe layers grown in a quasi-closed system

We report conditions for the growth of photosensitive CdSe epilayers on mica (muscovite) substrates in a quasi-closed system. At a substrate temperature of 600°C and source evaporation temperature of 680°C, the most perfect photosensitive wurtzite CdSe epilayers can be grown. Such layers show bright free-exciton luminescence at 78 K.

Nitrogen-Doped Chemical Vapour Deposited Diamond: a New Material for Room-Temperature Solid State Maser

Electron spin resonance (ESR) in polycrystalline diamond films grown by dc arc-jet and microwave plasma chemical vapour deposition is studied. The films with nitrogen impurity concentration up to 8×1018 cm−3 are also characterized by Raman, cathodoluminescence and optical absorption spectra. The ESR signal from P1 centre with g-factor of 2.0024 (nitrogen impurity atom occupying C site in diamond lattice) is found to exhibit an inversion with increasing the microwave power in an H102 resonator. The spin inversion effect could be of interest for further consideration of N-doped diamonds as a medium for masers operated at room temperature.

Thermal stability of zincite single crystals

The effect of temperature on the stability of synthetic ZnO crystals in neutral (N2), oxidative (O2), and reductive (95% Ar-5% H2) media and in a low vacuum has been studied. In the first and second cases, zincite does not undergo changes up to 1000°C. After an 8-h exposure in oxygen at 1100°C, a decrease in the size of hexagonal growth hillocks on the monohedron face (0001) and smoothing of its relief on the whole have been observed. In the presence of hydrogen, etching traces manifest themselves on the crystal surface even at 760°C; further heating leads to their sublimation. The effect of annealing on the luminescence properties of zincite has been demonstrated.