Vacancy-Type Defects in Proton-Bombarded InP
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"VAcAY-~IYPE D9FFBMf C. Ascheron , R.
Krause",
IN PRGRN-BOMBARI~D Jn1P A.
Polity",
H.
Sobotta,
V.
Riede*
University of Leipzig, Departments of Nuclear Physics and of Semiconductor Physics, Linn~str. 5, 0-7010 Leipzig, Federal Republic of Germany Martin Luther University Halle, Department of Physics, Friedemann-Bach-Platz 6, 0-4020 Halle, Federal Republic of Germany
ABSTRACT In proton-bombarded InP single crystals the fluence-dependent production of vacancy-type radiation defects and their annealing behaviour are studied. The results are interpreted using measurements of the total defect concentration, the carrier concentration and the infrared absorption.
INTRODUCTION Ion implantation into InP is used to process optoelectronic devices in the near infrared region [1,21. A special case of ion implantation, proton bombardment, offers the opportunity to create dopant-free and selectively insulating subsurface layers suitable for interdevice isolation [3,4,51, to passivate shallow donors and deep levels [6,71 and to extend the infrared photodetection below the band edge 181. To understand the defect-induced material modifications, knowledge of the various defect types is necessary. The present work gives information on the less investigated vacancy-type radiation defects.
EXPERIMENT
The experiments were performed with (100) oriented, chemico-mechanically polished and 0.01 % Sn doped n-InP single crystals. The irradiation was carried out with 1.7 MeV protons and partially with protons of continuous energy distribution within the range 0.3 to 1.7 MeV. After the irradiation, sandwich samples were isochronally annealed for 30 min. They were analyzed at room temperature. The neutral or negatively charged vacancy-type defects were studied in identically irradiated sample pairs with the positron annihilation technique 191 detecting the lifetime spectra of the annihilating positrons. The difference in thickness of the damaged layer (t1 = 27 pm) and of the layer, where the positrons annihilate (mean depth 100 pm). has to be considered for the determination of the annihilation parameters of the damaged layer. Since the annihilation behaviour of the positrons is strongly influenced by the charge state of the vacancies, the annealing temperature-dependent changes in the carrier concentration were monitored. To relate vacancy annealing to the annealing of the mean defect density, additional measurements with the Rutherford backscattering/channeling technique were used. Information on changes in the prevailing defect type was derived from infrared spectroscopic measurements. Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
1128
RESULTS AND DISCUSSION Fluence Dependence of Defect Production In proton-bombarded InP single crystals the concentration of vacancy-t, defects increases sublinearly with rising fluence. This is expressed by the ixt creasing average lifetime - of the positrons in fig. la. 10"
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