Identification of Radiation-Induced Defects in Si:Al
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IDENTIFICATION OF RADIATION-INDUCED DEFECTS IN Si:Al Latushko Ya.I. and Petrov V.V. Lenin Byelorussian State University, Lenin Avenue 4, 220080 Minsk, USSR ABSTRACT Radiation-induced defects (RD) in Si:Al have been investigated by means of infrared absorption (IRA) and photoluminescence (PL) methods. It has been found that the main Al containing RD in electron-irradiated Si is an interstitial Al atom (Alt). In the process of annealing at about 225 OC the production of Alt-Alt pairs takes place. The activatin energy of this RD production is 0.95 eV, which corresponds to AlI migration energy along hexagonal interstitials. AlI is shown to be a two - charge donor with the energy level E(+/++) = Ev + 0.20 eV. Besides the above mentioned defect as well as acceptor type defect with Ev + 0.21 eV level a number of other defects has been revealed in neutron-irradiated Si:Al. These centers give rise to a great number of IRA and PL lines in the spectral range from 0.1 to 1.2 eV. The classification of the observed defects has been done on the basis of the annealing results and uniaxial stress measurements. INTRLDUCTION Silicon doped with Al appeared to be a classical material while investigating RD formation in Si. The mechanism of interstitial atom formation by means of elastic collision of an electron with Al atan was suggested by Watkins [I]. However, the information concerning the properties of RD in Si:A1 is far from being exhaustive. For instance, there is no complete information on the energy levels of interstitial aluminium (AlI). Specifically, for the Ali E(+/++) level the value E& + 0.25 eV was obtained in [21. and the value E, +(O.17±0.04) eV was obtained in [31. On the basis of IRA data we obtained the value E& + 0.20 eV [4]. In this work we present more detailed data on optical measirements of the properties of interstitial aluminium as well as the other RD, which are produced in Si:Al by neutron irradiation. EXPERIMENT
Monocrystalline Si:Al with Al content from 1.3 x 1015 to 3 x 1017 cm-3 produced by means of floated-zone melting and Czochralski method was investigated. The content of oxygen and carbon impurities was 3 x 1016 - 1.0 x 1017 3 3 cm- and 1 x 1015 - 2 x 1017 re- . respectively. The irradiation by 4.5 MeV electrons was carried cut at 3OoC by fluences ($) up to 1 x 1018 ac-2. and by 2 reactor neutrons at T < 70 -C by 1 < 5 x 1018 cm- . IRA and PL spectra were recorded at temperatures 1.8 - 80 K. The resolution %as . 2 a=r1. Uniaxial stress measurements were made at 4.2 and 35 K. RESULTS AND DISC3JSSION Interstitial aluminium In Si:Al irradiated by fast electrons one could observe a characteristic helium - like series AM1 in IRA spectra when Er >, E&+ 0.20 eV. This series may be attributed to electron transitions on AlI center [4]. Taking as a basis the effective mass theory (EMT) and knowing the location of spectral lines, it is easy to determine the location of E(+/++) level of the given defect as E%- + 0.20 eV. This value is close to the values obtained by other less accurate methods [2,31 and may be
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