J. Beringer et al., Radiation hardness and lifetime studies of LEDs and VCSELs for the opticalreadout of the ATLAS SCT, NUCL INST A, 435(3), 1999, pp. 375-392
We study the radiation hardness and the lifetime of Light Emitting Diodes (
LEDs) and Vertical Cavity Surface Emitting Laser diodes (VCSELs) in the con
text of the development of the optical readout for the ATLAS SemiConductor
Tracker (SCT) at LHC. About 170 LEDs from two different manufacturers and a
bout 130 VCSELs were irradiated with neutron and proton fluences equivalent
to (and in some cases more than twice as high as) the combined neutral and
charged particle fluence of about 5 x 10(14) n (1 MeV eq. in GaAs)/cm(2) e
xpected in the ATLAS inner detector. We report on the radiation damage and
the conditions required for its partial annealing under forward bias, we ca
lculate radiation damage constants, and we present post-irradiation failure
rates for LEDs and VCSELs. The lifetime after irradiation was investigated
by operating the diodes at an elevated temperature of 50 degrees C for sev
eral months, resulting in operating times corresponding to up to 70 years o
f operation in the ATLAS SCT. From our results we estimate the signal-to-no
ise ratio and the failure rate of optical links using LEDs developed specif
ically for application at LHC. (C) 1999 Elsevier Science B.V. All rights re
served.