ИСТИНА

The progress in semiconductors for the last fifty years basically deals with doping [1]. Dopant atoms incorporating into crystal lattice generate point defects which determine structure sensitive properties of the crystals. These properties also sufficiently influence on crystal quality such as dislocation density, twins, micro- and macro-segregations etc. But in the case of chemical compounds there is no difference what is the source of point defect generation either dopants or over stoichiometric components [2]. The advantages in technology of complex inorganic semiconductors such as AIIIBV and AIIBVI are directly associated with non-stoichiometry investigations [2,3]. To date, there is no absolutely reliable information available on non-stoichiometry of some compounds, for example AlN, GaN, InP, but investigations of pi–T diagrams, which are necessary for a successful study of nonstoichiometry, were conducted way before the nonstoichiometry of GaAs, GaSb, etc. was investigated. In the case of organic semiconductors, the situation is more uncertain. There is no available information about pi–T diagrams for organic semiconductors in the literature. The organic chemists, in general, consider chemical compounds as substances with a fixed chemical formula. But according to the thermodynamic laws at T>0 K the generation of atomic point defects is inevitable in crystalline substance [3]. This means that a crystal phase of any chemical compound exists in a range of compositions, which is customarily called the homogeneity range. The width of homogeneity range for the most compounds varies from 0.1 to 0.001 mol%, but within this range, the functional properties of the crystal phase could change in orders of values. Analysis of the relationship between non-stoichiometry, synthesis conditions and functional properties is a subject of solid state chemistry [3]. And the first step for the determination of this relationship is obtaining reliable information about the range of synthesis parameters within which one can obtain a single crystalline phase. Usually, this information is presented in the form of pi–T–x diagrams. The general approach and specific features of pi–T–x diagrams investigations for inorganic and organic compounds as well as their application for crystal growth and OLED technologies will be discussed. 1. P.Rudolph, in: Thermodynamics, Origin, and Control of Defects in Crystal Growth Technology, edited by H.J.Scheel and P.Capper (Wiley-VCH Verlag GmbH &Co. KGaA,Weinheim, 2008). 2. R.Triboulet, P.Siffert (eds.), CdTe and Related Compounds; Physics, Defects, Hetero- and Nanostructures. Part II Crystal Growth, Surfaces and Applications (Elsevier Ltd., Oxford, UK, 2010). 3. F.A.Kroger, The Chemistry of Imperfect Crystals (North-Holland Pub. Co., Amsterdam; Interscience Publishers, New York, 1964). Keywords: p-T-x diagram, nonstoichiometry, crystals Invited (25 minutes)