0000000000273715
AUTHOR
Robert Triboulet
A new approach to the growth of ZnO by vapour transport
The crystal growth of ZnO by vapour transport is classically made in presence of additional species which enhance the growth process. Usually, additional species have been considered as chemical transport agents that promote a typical CVT (Chemical Vapour Transport) process. Recently, we have proposed a new interpretation of the chemical role of some of these species. This new interpretation considers that, in some cases, the additional species promote a partial consumption of the O2 provided by the ZnO decomposition and, consequently, a Zn excess is generated. This excess of Zn pressure activates the ZnO decomposition and the growth rate is enhanced. Among those species, carbon shows an ad…
Study of the ZnO crystal growth by vapour transport methods
Abstract The crystal growth of ZnO by vapour transport is classically made with the assistance of additional species that produce a gaseous mixture, the role of which remains often uncertain in the transport and growth process. Initially, in order to study the mass transport process, a numerical simulation is made to analyse which are the requirements to have an effective transport. As the pressure of each gaseous species is generally unknown, the numerical study has been performed for different total pressures. It is found that, if congruent and equilibrium conditions are assumed at the sublimation and crystallisation interfaces, effective growth conditions can only be attained for a narro…
Photoluminescence study of radiative transitions in ZnTe bulk crystals
Abstract This paper focuses on photoluminescence (PL) and selective photoluminescence (SPL) of ZnTe bulk crystals grown by the cold traveling heater method. The crystals exhibit a PL response with a much more intense excitonic zone than the one due to free-to-bound and donor–acceptor bands, denoting a good sample quality. In particular, we have investigated the Y 1 and Y 2 peaks which, in epitaxial layers, have usually been associated with structural defects. On bulk samples they have not been detected so far because of different masked mechanisms. SPL measurements show that the electrons are the most likely involved carriers for this emission. Additionally, the analysis of the PL variation…
Cathodoluminescence and photoluminescence study of plastically deformed ZnTe bulk single crystals
Samples of zinc telluride bulk single crystals, which were deformed in uniaxial compression, have been studied by photoluminescence (PL) and cathodoluminescence (CL). As a particular feature the deformed samples present a PL emission band peaked at 603 nm, whose intensity increases as the plastic deformation does. This band is related to the density of dislocations produced during the interaction of slip systems. This hypothesis is supported by CL images. which reveal the activation of the successive slip systems corresponding to different levels of deformation.
Some aspects of the MOCVD growth of ZnO on sapphire using tert-butanol
The growth of ZnO on (0001) sapphire substrates using metalorganic chemical vapor deposition is reported. Diethylzinc and tertiarybutanol were used, respectively, as zinc and oxygen sources. Growth conditions are detailed such as the substrate temperature and the precursors partial pressures. The influence of the cleanness state of the MOCVD silica reactor is emphasized, since it modifies both layer quality and crystalline orientation, and since it also affects growth process steps like sapphire thermal treatment and buffer layer deposition. ZnO epitaxial layers are characterised by scanning electron microscopy (SEM) to assess the surface orientation and morphology, X-ray diffraction (XRD) …
Morphology of ZnO grown by MOCVD on sapphire substrates
A quantitative roughness and microstructural analysis of ZnO grown on sapphire by atmospheric metalorganic chemical vapor deposition (MOCVD) is presented. In order to investigate the influence of the substrate on the morphology, different sapphire orientations have been employed. Scanning force microscopy data have been analyzed for a variety of thicknesses to elucidate, if possible, the growth mechanisms involved in the growth process. Our study reveals significant differences between morphologies depending on whether the substrate surface exhibits steps (misoriented a-, c- and r-planes) or not (m-plane); however, no major differences on the calculated roughness coefficients have been foun…
Heat transfer simulation in a vertical Bridgman CdTe growth configuration
Modelling and numerical simulation of crystal growth processes have been shown to be powerful tools in order to understand the physical effects of different parameters on the growth conditions. In this study a finite difference/control volume technique for the study of heat transfer has been employed. This model takes into account the whole system: furnace temperature profile, air gap between furnace walls and ampoule, ampoule geometry, crucible coating if any, solid and liquid CdTe thermal properties, conduction, convection and radiation of heat and phase change. We have used the commercial code FLUENT for the numerical resolution that can be running on a personal computer. Results show th…
Some fundamentals of the vapor and solution growth of ZnSe and ZnO
Abstract Some fundamentals of ZnSe and ZnO vapor and solution growth are investigated. Residual water present in gases or gaseous mixtures such as H 2 , Ar or H 2 +H 2 O is shown to act as a sublimation activator in the vapor-phase transport of both compounds. The processes involved in the growth by chemically activated sublimation with such gases and gas mixtures have been studied by close-spaced vapor transport (CSVT). The ZnSe growth rate is found to be constant, while in the ZnO case a high initial growth rate is followed by slower growth subsequently. Using a theoretical model, the thermodynamic constants of the transport – energies of activation, sublimation and condensation and entha…
Effect of plastic deformation on photoluminescence of ZnTe bulk monocrystals
Abstract In this work ZnTe bulk single crystals have been deformed by axial compression with the aim of analyzing the luminescence properties related to intrinsic structural defects like dislocations. Plastic deformation greatly decreases the overall PL response, near-band-edge luminescence as well as deep level-related emissions. Results indicate a close relationship between the so-called Y1 and Y2 bands and the density of generated dislocations. Plastic deformation also produces an emission band at 603 nm whose intensity is proportional to the amount of introduced deformation.
Annealing-induced Changes in the Electronic and Structural Properties of ZnTe Substrates
The aim of this study is to demonstrate that the electronic and structural properties of II–VI substrates, here ZnTe, can be dramatically affected by thermal heating at temperatures in the range of those typically used in the epitaxial metalorganic chemical vapor deposition processes. Photoluminescence response shows that annealing at these temperatures produces a reduction of the sample crystalline quality, decreasing the free exciton emission relative to the deep level related one. Some factors, like the change in the charge and stress state of dislocations, Cu diffusion, and oxygen incorporation, could be responsible for changes in the substrate properties, which can produce stresses and…
The Scope of Zinc Oxide Bulk Growth
The techniques classically used for the growth of bulk ZnO crystals, melt-growth, vapour growth, solution-growth and hydrothermal growth, are reviewed. In the case of vapor growth, numerical simulations suggest that such species as H2 + H2O, CH4, Zn, C or Fe could act as sublimation activators. The electrical and structural properties of crystals obtained by these various techniques are compared.
Study of the chemically activated sublimation of ZnSe
Abstract The reactions and processes involved in the growth of ZnSe by chemically activated sublimation in a H 2 atmosphere are studied. The rate of transport as a function of source and substrate temperatures and the difference between them are determined from close spacing vapour transport experiments. According to this process, ZnSe layers are deposited on sapphire substrates by short distance chemically assisted sublimation. The experimental results are analysed and the thermodynamic constants of the transport are determined using a theoretical model for kinetically controlled processes, assuming water to act as sublimation catalyst. A preliminary optical and structural characterisation…