Influence of Be Doping on Material Properties of Low-Temperature-Grown GaAs
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Influence of Be Doping on Material Properties of Low-Temperature-Grown GaAs Saulius Marcinkevičius, Andreas Gaarder, and Jörg Siegert Department of Microelectronics and Information Technology, Royal Institute of Technology, Electrum 229, 16440 Kista, Sweden Jean-François Roux and Jean-Louis Coutaz LAHC, University of Savoie, 73 376 Le Bourget du Lac Cedex, France Agnieszka Wolos and Maria Kaminska Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw, Poland Ramūnas Adomavičius, Klemensas Bertulis, and Arūnas Krotkus Semiconductor Physics Institute, Goštauto 11, 2600 Vilnius, Lithuania ABSTRACT A number of experimental techniques were used to characterize structural quality, ultrafast carrier dynamics and deep center properties of low-temperature-grown GaAs doped with Be. GaAs layers grown at 280 oC, doped with the Be concentration from 5×1017 cm-3 to 2×1019 cm-3 and annealed at temperatures between 500 and 800 oC were studied. Electron trapping times in these samples varied from hundreds of femtoseconds to several picoseconds. A non-monotonous electron trapping time dependence on Be doping level is explained by the influence of triple-charged gallium vacancies and single-charged Be-acceptors on the number of ionized As antisite defects. INTRODUCTION Low-temperature (LT) molecular beam epitaxy (MBE) grown GaAs combines unique semi-insulating and ultrafast carrier recombination properties. This makes LT GaAs attractive material for applications in ultrafast optoelectronics [1]. Short electron lifetimes in this material have been shown to result from excess arsenic in the form of arsenic antisite AsGa and gallium vacancy VGa point defects [2]. Ionized AsGa+ defects, whose density is approximately three times larger than that of VGa [3], serve as the main electron traps. Because the VGa density is much lower than the concentration of AsGa, only a fraction of As antisites is ionized and can participate in the electron trapping, while the rest remains inactive. Therefore, attempts have been made to activate the neutral AsGa0 centers by doping LT GaAs with compensating acceptor impurities. A natural choice of the acceptor species is beryllium, which is known for its ready incorporation into GaAs during the MBE growth. Previously, the influence of Be doping on the properties of LT GaAs was studied for very large Be concentrations, of the order of 1019 cm-3 [4,5]. It has been found that Be occupies substitutional positions in the lattice and can reduce the number of nonstoichiometry-related point defects [4]. The density and size of As precipitates were found to be significantly lower for the Be-doped than for undoped or n-doped LT materials [6]. However, high doping levels used in the previous studies deteriorate semi-insulating characteristics of the LT GaAs layers by changing material conductivity to p-type. Thus, the optimal material parameters of this material should be defined by a fine adjustment of the defect compensation ratio in the lower Be concentration range. In our previous work [7] we h
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