The electrical properties and photoluminescence spectra ofLEC gallium arsenide crystals after neutron transmutation doping (NTD) have been investigated as function ofstarting material properties, irradiation dose and thermal to fast neutron fluence ratio.The residual carbon acceptors interact with radiation induced defects (RD) in neutron irradiated GaAs crystals and form nonradiative recombination centers, which are stable up to 700 °C.

No abstract

The new PL lines at 1.496 eV and 1,492 eV related to the conduction band-toacceptor (e, A?) and donor-to-acceptor (D, A?) transitions, respectively were observed in PL spectrum of bulk undoped LEC SI-GaAs and in some SI-GaAs crystals grown by VGF technique. No correlation between these PL lines and shallow residual acceptor impurity was stated. The acceptor responsible for these PL lines can be created during rapid cooling from temperature T > 1000 O C so it seems to be a native-like complex in nature. At the moment it is difficult to present a detailed model of this defect. However, one can conclude that native-like shallow acceptor can be present in as grown undoped LEC SI-GaAs crystals when the cooling of the crystal in the puller occurs enough quickly. A. IntroductionThe features of undoped semi-insulating (SI) GaAs grown by liquidencapsulated Czochralski technique (LEC) depend strongly on the post-grown annealing. During the annealing different kinds of the electrically active native-like defects are generated [l]. The improvement of the as-grown SI-GaAs is obtained by a special multistep annealing which improves homogeneity of electrical and structural parameters of the crystal [2] and by the improvement in stoichiometry [3]. We have found out that the photolumincsccnce peak related to carbon conduction band-acceptor recombination (carbon is the main residual unpurity in LEC SI-GaAs) is abnormally prolongedmoved toward higher-energy in some of undoped, arsenic-rich SI-GaAs crystals grown by LEC technique. Investigation of this problem was the main aim of this work. B. Experimental detailsMore than 30 different samples of undoped SI-GaAs grown by LEC (from As-rich melt) and vertical gradient freeze (VGF) techniques from 11 different producers were investigated. The electrical parameters obtained with van der Paw measurements at 300 K as well as etch pits density (EPD) revealed by chemical etching for selected samples are gathered in Table I. Photoluminescence measurements were performed using 488 nm line of Ar' laser for excitation. Three different annealing were carried out: at 950 OC for 4 hours (950 OU4h), at 1150 'C/4h+950 OC/4h and at 1150 OC/4h+550 ' C14h +950 OU4h. Samples of 5 mm thick were sealed in quartz ampoule in arsenic overpressure. After thermal annealing the quartz ampoule was cooled down rapidly by quick removal from the fumace to the room temperature. Around 0.8 mm thick sample were cut off from the middle of the 5 p n thick sample forHall and PL measurements. To eliminate the influence of surface damage on PL inten sity all PL measurements at 6 K were done on cleaved surface (at 2 K on polishedetched one). Content of typical chemical impurities, except of carbon, for the most of studied 0-7803-5814-7/00/$10.00 0 2000 IEEE 191

No abstract

No abstract