Production of ZnO-Based Film Structures Emitting in Blue and Near-UV Spectra
Tech Area / Field
- PHY-OPL/Optics and Lasers/Physics
8 Project completed
Senior Project Manager
Ryzhova T B
Institute of the Problems of Laser and Information Technologies, Russia, Moscow reg., Shatura
- FIAN Lebedev, Russia, Moscow\nMISIS (Steel and Alloys), Russia, Moscow\nRussian Academy of Sciences / Institute of Radioengineering and Electronics, Russia, Moscow
- Technische Universität Dresden / Institut für Halbleiter- und Mikrosystemtechnik, Germany, Dresden
Project summaryProject goal. The goal of the project is the development and growing of light-emitting р-n junctions on the basis of thin-film ZnO structures. Zinc oxide is the direct gap semiconductor material with band width of 3.37 eV, high exciton binding energy (60 meV at room temperature), high electron and hole conduction. For these reasons zinc oxide is a very promising material in production of light emitting diodes and lasers oscillating in the blue and near UV wavelength regions. The light-emitting devices on the basis of ZnO could be a cheap substitute to GaN emitters.
Topicality. The problem of growing p-n junctions on the basis of epitaxial ZnO films emitting in the blue (or even ultraviolet region) is quite urgent for further development of industrial light diodes and lasers, which is proved by the activities of a number of research teams in Japan, South-East Asia, USA, and Europe in this field.
Methods and approaches. The technologies for fabricating light-emitting devices on the basis of p-n junctions must provide high repeatability and temporal stability of major electrophysical and optical characteristics of thin semiconductor materials. In the framework of the project we shall investigate in detail the new promising methods for growing p-n junctions on the basis of ZnO films. These methods are: Pulsed Laser Deposition (PLD) and Chemical Vapor Deposition using hetero-organic compositions (MOCVD). Both the methods are a great advantage because of wide possibilities to control the deposition process, lower temperature of epitaxy and exploiting the simplified technology of doping control, which permits the deposition of ZnO films possessing the specified crystallographic, electrophysical and optical characteristics.
PLD and MOCVD methods development. The method of pulsed laser deposition using excimer lasers ensures the congruence of evaporation of the targets having any composition, and offers high effective vacuum at the moment of deposition owing to high density of particles in the laser plume. In the time of next layer deposition (of the order of several microseconds) the atoms of the residual gas have no time to be adsorbed on the film.
The Project will make use of some modifications of the PLD method to improve the quality of crystalline structure of ZnO film and the stability of its characteristics.
- On irradiation of erosive plume with high-power IR CO2 laser the pulsed laser deposition method makes it possible to control the energy distribution in the plume, which is of high importance in film formation. High energy of particles (up to 100 eV) provides the possibility of stoichiometric film growth.
- The utilization of a mechanical separator in pulsed laser deposition prevents drops and clusters from falling on the film in the growth process.
- The control of variation in the composition of the buffer gas and the control of excitation and ionicity of the particles in buffer gas with high-frequency discharge provide for doping with excited atoms and ions from the gas phase in production of p-type films.
The method of gas-phase epitaxy from vapor metalloorganic compound allows using of several molecular beams containing elements, necessary for formation of a film and for doping process.
To produce epitaxial ZnO films with reproducible electrophysical and optical characteristics one needs to investigate in detail the influence of each parameter of the deposition process (temperature of the target and of the substrate, composition and features of the buffer gas, etc.) on the specific film characteristic. Special attention should be paid to considerable improvement in the accuracy of specifying and maintaining these characteristics, to flexibility of the whole process monitoring, as well as to the opportunity of its accurate reproducibility. The illumination of the laser plume with high-power CO2 laser light permits the mean energy of ions in the plume to be varied in the range from 10 to 100 eV. This provides a way of selecting the optimal conditions for film deposition to ensure the maximum structural perfection of the crystals. The monocrystalline ZnO substrates will be used in growing light-emitting р-n junctions on the basis of ZnO films. In this case the mismatch between the parameters of the substrate and the film will be eliminated, and the conditions for the ZnO film epitaxial growth will be arranged, which will permit the crystal quality of these films to be considerably improved (even if compared with the structural quality of the substrate).
The final aim of the Project provides for solving the following problems:
- To investigate the dependence of crystallographic parameters, degree of crystalline perfection of undoped homoepitaxial ZnO films and their surface morphology on the main parameters of pulsed laser deposition process (substrate temperature, buffer gas pressure, laser energy flux density). To determine the optimal conditions for growing undoped films.
- To investigate the dependence of degree of crystalline perfection of undoped heteroepitaxial ZnO films and their surface morphology on the main parameters of the process of chemical vapor deposition from hetero-organic compounds (substrate material and orientation, temperature of sedimentation, partial pressures of sources, gas flow velocity). To determine the optimal conditions for growing undoped films.
- To determine the optimal doping elements and the ways for their introduction into homoepitaxial ZnO films in order to obtain n-type conduction. To determine the dependence of optical, crystallographic and electrophysical characteristics of ZnO films on the type of doping element and its concentration.
- To determine the optimal doping elements and to develop the doping procedure for obtaining n-type conduction in heteroepitaxial ZnO films.
- To determine the optimal doping elements and the ways for their introduction into homoepitaxial ZnO films in order to obtain p-type conduction.
- To develop the procedure for growing doped homoepitaxial ZnO films of n- and p-type with reproducible optical and electrophysical characteristics by pulsed laser deposition method.
- To develop the procedure for growing doped heteroepitaxial ZnO films with reproducible optical and electrophysical characteristics by method of chemical vapor deposition from hetero-organic compositions.
- To develop the procedure for growing p-n junctions emitting in the blue and near UV spectra on the basis of doped epitaxial ZnO films and to investigate the characteristics of obtained p-n junctions.
- To develop the procedure for growing p-n junctions emitting in the blue and near UV spectra on the basis of doped heteroepitaxial ZnO films and to investigate the characteristics of obtained p-n junctions.
The work under the Project will presume the collaboration of the Institute of Laser and Information Technologies RAS (ILIT RAS), the Institute of Radioengineering and Electronics RAS (IRE RAS), Moscow State Institute of Steel and Alloys (Technological University) (MISA-TU), and P.N. Lebedev Physical Institute (FIAN).
The Project presumes the pision of the posed problems among the participants.
- The problem statement. The Project supervision.
- The investigation of the dependence of crystalline structure parameters, degree of crystalline perfection of undoped homoepitaxial ZnO films and their surface morphology on the main parameters of pulsed laser deposition process (substrate temperature, buffer gas pressure, laser energy flux density at the target).
- The determination of the optimal doping elements and the ways for their introduction into homoepitaxial ZnO films in order to obtain p- and n-type conduction.
- The determination of the dependence of optical characteristics and photoluminescence of homoepitaxial ZnO films on the type of doping element and its concentration.
- The development of the procedure for growing doped homoepitaxial ZnO films with reproducible optical and electrophysical characteristics by method of pulsed laser deposition.
- The development of the procedure for growing p-n junctions emitting in the blue and near UV spectra on the basis of homoepitaxial doped layers of ZnO films and studying their characteristics.
- Definition of dependence of crystal perfection undoped hetero-epitaxial ZnO films and morphology of their surface from the basic technological parameters of process chemical gas-phase deposition from element-organic compositionss (a material and orientation of a substrate, temperatures of deposition, partial pressure of sources, speed of a gas stream);
- Definition of optimum doping elements and ways of their infusion in structure hetero-epitaxial ZnO films for reception as n-, and p-type conductivity;
- Definition of dependences of optical properties and electroluminescence of hetero-epitaxial ZnO films from type of an entered doping element and its concentration;
- Development of a technological technique of growth of doped hetero-epitaxial ZnO films with reproducible optical and physical properties by chemical gas-phase deposition from element-organic compounds;
- Development of a technological technique of manufacturing p-n transitions on a basis of doped hetero-epitaxial ZnO films, radiating in blue and near UV range, and research of their properties.
- Carrying out the chemical and structural analysis of homoepitaxial ZnO films.
- The development of method of final chemical- mechanical polishing of substrates and single crystals of ZnO.
- The investigations of electro-physical properties of homoepitaxial ZnO films (type, concentration and mobility of carriers).
The International Science and Technology Center (ISTC) is an intergovernmental organization connecting scientists from Kazakhstan, Armenia, Tajikistan, Kyrgyzstan, and Georgia with their peers and research organizations in the EU, Japan, Republic of Korea, Norway and the United States.
ISTC facilitates international science projects and assists the global scientific and business community to source and engage with CIS and Georgian institutes that develop or possess an excellence of scientific know-how.