Experimental study of negative photoconductivity in n-PbTe(Ga) epitaxial films

We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial films prepared by the hot-wall technique on -BaF_2 substrates. Variation of the substrate temperature allowed us to change the resistivity of the films from 10^8 down to 10_{-2} Ohm x cm at 4.2 K. The resistivity reduction is associated with a slight excess of Ga concentration, disturbing the Fermi level pinning within the energy gap of n-PbTe(Ga). PC has been measured under continuous and pulse illumination in the temperature range 4.2-300 K. For films of low resistivity, the photoresponse is composed of negative and positive parts. Recombination processes for both effects are characterized by nonexponential kinetics depending on the illumination pulse duration and intensity. Analysis of the PC transient proves that the negative photoconductivity cannot be explained in terms of nonequilibrium charge carriers spatial separation of due to band modulation. Experimental results are interpreted assuming the mixed valence of Ga in lead telluride and the formation of centers with a negative correlation energy. Specifics of the PC process is determined by the energy levels attributed to donor Ga III, acceptor Ga I, and neutral Ga II states with respect to the crystal surrounding. The energy level corresponding to the metastable state Ga II is supposed to occur above the conduction band bottom, providing fast recombination rates for the negative PC. The superposition of negative and positive PC is considered to be dependent on the ratio of the densities of states corresponding to the donor and acceptor impurity centers.Comment: 7 pages, 4 figure

MAKING MARKETING DECISIONS IN AN UNSTABLE ECONOMIC ENVIRONMENT

The chapter presents an analysis of current features and difficulties in developing and making marketing decisions in the framework of enterprise management in unstable economic conditions. To a large extent, these difficulties are related to the transition of Russian socioeconomic systems from a tradi-tional development model to a transformational one. Socioeconomic trans-formations are accompanied by crisis phenomena and processes in which enterprises are developing. Their effective functioning in the interests of economic growth requires the introduction and further development of marketing systems based on the principle of mutual improvement of the economic entity, the consumer and the external market agent, that is, the creation of anti-crisis marketing. The purpose of the study is to determine the specifics of making integrated marketing decisions and their nuances in the modern economic space. The main result of the study is to identify the impact of a difficult period in the functioning and development of the national economy on the transformation of marketing activities in enterprises. It is concluded that it is necessary to create a model for making anti-crisis marketing decisions, which will be characterized by its nonstandard nature, will be aimed at taking comprehensive, necessary measures and evaluating their effectiveness, taking into account both the short-and long-term prospects for the development of the system. © 2021 by Information Age Publishing