Mechanizmy dyfuzji Al., Ga, In w trójwymiarowych strukturach kwantowych (AlGaIn)N

Nitride semiconductors of (AlGaIn)N are the materials used in many optoelectronic and electronic devices (multibillion markets). Depite of this fact, many of their basic parameters are not known yet. This situation is related to very high densities of defects: i) dislocations present because of the lattice mismatch to foreign substrates (most frequently used are sapphire and silicon), ii) point defects present because of low growth temperatures (at higher temperatures, the nitrides get decomposed). This Project is focused on explanation how atoms of Ga, In, Al diffuse in the lattice of heterostructures of InGaN/GaN and AlGaN/GaN used for fabricating the devices. This diffusion is mediated by metal vacancies present inside the grown material and also formed during annealing. Therefore, the concentration and mobility of these vacancies are the basic parameters which should be taken into account. Unfortunately, the gallium vacancies can be only directlydetected in thick layers using Positron Annihilation Spectroscopy. Moreover, these vacancies can be passivated by impurities and dopants (hydrogen, oxygen, silicon, magnesium) what makes the research difficult and many conclusions can be drawn only from the indirect experiments and the theoretical simulations. The first part of the Project will be devoted to the explanation how gallium atoms in the annealing atmosphere block the gallium-vacancy diffusion from the surface what results in blocking diffusion of Al or In atoms. The second part will be devoted to experimental and theoretical study of Al, Ga, In diffusion in the case of 3-dimensional stripes, for which not only the upper surface is exposed to annealing atmosphere, but also the stripe walls at which the interfaces of AlGaN/GaN and InGaN/GaN terminate. The project proposed should enable us to propose the mechanisms of atomic diffusion in (AlGaIn)N heterostructures as a function of dislocation density, surface shape (stripes vs planar structures), annealing atmosphere, strains and electric field (very strong in nitrides). The experiments and theoretical calculations we are going to perform in the frame of the Project will not only enrich the basic knowledge on nitride semiconductors, but also we will supply a number of information important in the device manufacturing. In particular, we are interested in: i) Homogenization of InGaN quantum wells (QW) used in blue and green emitters (LEDs and LDs) in order to get the highest possible efficiencies, ii) Avoiding InGaN QW catastrophic decomposition at high temperature, iii) Avoiding Al out-diffusion from the AlGaN layers used in transistors and UVC emitters. All three issues are related to the metal-vacancy concentration, mobility and diffusion. However, the most interesting part of the project will be study of the effects in 3-dimensional (stripes) epi structures. These attract a big attention because they can be used for fabricating arrays of laser diodes emitting at slightly different wavelength. Such arrays would be applied in fabricating 3-dimensional projectors without goggles. However, this technology is very new and deserves optimizations partly planned in this project. The methodology of the project include a number of technologies (Metalorganic Chemical Vapour Epitaxy, lateral patterning by Reactive ion Etching) and of analytical techniques (X-ray Diffraction, Electron Microscopy, Positron Annihilation, Secondary Ion Mass Spectroscopy, Luminescence and some others). Michał Leszczyński, Instytut Wysokich Ciśnień Polskiej Akademii Nauk 576370 ZSUN