“Radiation Induced Defects In III-V Single Crystals”

L.C.DAMONTE; M.HERNÁNDEZ FENOLLOSA; B.MARÍ

Barcelona, España

Conferencia; 20th. European Photovoltaic Solar Energy Conference; 2005

By more than twenty years, III-V semiconductors compounds have been intensively studied due to their important properties as high frequency devices and optoelectronic integrated circuits. The understanding of some of these characteristics required the complete knowledge of point defect structure. Moreover, for space based applications a high radiation resistance material is needed.             With the purpose to analyze the radiation hardness of different semiconductor systems, we have bombardment with high energy electrons InP and GaAs single crystals. We have applied two experimental techniques highly sensitive to defects and in this sense, complementary. Positron annihilation lifetime spectroscopy (PALS) is a non destructive technique and adequate for open volume defects studies. Positrons are capable to detect vacancy defects in concentration of ppm being the lifetime of trapped positron related with the size of trapping centre. Photoluminescence (PL) measurements directly probe the optically active centres which will be relevant to the response of these single-crystals and its evolution with the specific treatment applied on them.             The commercially provided single crystals were exposure to 10 MeV electrons during different time intervals, obtaining the following irradiation doses: 60, 120, 180, 240 Gy.             PALS measurements (3 x 106 counts) were collected at room temperature (RT) in a conventional fast-fast coincidence system with two scintillators detectors. The time resolution (FWHM) was 260 ps. The PL was performed on the surface using the 325 nm emission line of a He-Cd laser. The luminescence signals were acquired at RT using a grating monochromator coupled to a CCD as detector.                         The lifetime spectra for the as-grown and irradiated samples were decomposed into three exponential decays, , with a c2 close to 1.0. The evolution of lifetimes, intensities and the average lifetime (tav= , a useful annihilation parameter to analyze the creation of defects in the sample) with radiation dose were studied. The luminescence spectra for all the analysed samples consist of the near-band-edge (NBE) emission and the deep-level (DL) emission. The evolution with radiation dose of the NBE peak and the DL peak intensity ratio and the NBE peak shift in energies were analysed. The observed variation with radiation dose in the average lifetime indicates that radiation induced defects act as effective positron traps. The trends observed by both experimental techniques were discussed in terms on the origin, nature and state of charge of the radiation induced defects involved. The obtained results are compared with previous results on neutron transmutation doping in InP [1]. The radiation hardness of InP and GaAs semiconductors is also compared with the ZnO system [2]. [1] F.J.Navarro, L.C.Damonte, B.Marí, J.L.Ferrero; J.Appl.Phys.79 (1996) 9043. [2] L.C.Damonte, M.H.Fenollosa, B.Marí; Appl.Phys.Letter (2004) to be published.