Defects Introduced by Low Dose Be-Implantation Probed by a Monoenergetic Positron Beam
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DEFECTS INTRODUCED BY LOW DOSE Be-IMPLANTATION PROBED BY A MONOENERGETIC POSITRON BEAM A.
UEDONO*, Y. UJIHIRA*, L. WEI--, Y. TABUKI**, S. TANIGAWA**, K. WADA', AND H. NAKANISHI' *Department of Industrial Chemistry, Faculty of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan "**Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305, Japan tNTT LSI Laboratories, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-01, Japan ABSTRACT Vacancy-type defects in 60-key Be+-implanted GaAs and InP were studied by a monoenergetic positron beam. The depth distributions of vacancy-type defects were obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. Vacancy-type defects introduced by ion implantation were observed in n-type GaAs. For p-type GaAs, however, this was not the case. This can be attributed to the recombination of vacancy-type defects and pre-existed interstitial-type defects in p-type GaAs. The defects induced by ion implantation in InP were also studied. INTRODUCTION The positron annihilation technique is now a powerful method for the study of vacancy-type defects in materials (1,2]. When positrons implanted into a condensed matter, they rapidly slow down to thermal energies and finally they annihilate with electrons from the surrounding medium into two 511-keV y-quanta. A Doppler broadening profile of such annihilation photons can provide momentum distributions of the annihilating electrons. The shape of the Doppler broadening spectrum is characterized by a lineshape parameter S which is defined as the ratio of the central region to the total counts of the Doppler broadening energy spectrum (2] . In a material containing defects, a freely diffusing positron may be localized in vacancy-type defects by a Coulomb repulsion from surrounding ion cores. The change in the value of the S parameter due to the annihilation from the trapped state can be observed for vacancy-type defects with a concentration between -1015 cm- 3 and -1019 cm- 3 . Because of this unique character, the study of defects in compound semiconductors by positron annihilation techniques is a subject of increasing interest [3-7]. In the present paper, we report the application of the monoenergetic positron beam technique to the study of vacancy-type defects in GaAs and InP introduced by 10 13 the implantation of 60-keV Be+-ions up to doses of ixl0 -1xl0 Be/cm2 . EXPERIMENTAL The specimens used in the present experiments were GaAs and InP wafers prepared by liquid-encapsulated Czochralski method. The GaAs wafers were doped with Si (Ix10 1 6 Si/cm3 ) or Zn (3x10 1 8 Zn/cm3 ) during growth. The InP wafers were doped with S (46x10 1 8 S/cm3 ) or Zn (4x10 1 8 Zn/cm3 ) . The implantation of 60-key Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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Be+-ions was performed at room temperature up to doses of ixl01 0 Ix10 1 3 Be/cm2 . The depth distributions of vacancy-type defects were measured using the monoenergeti
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