Richard Nickerson

Abstract:

This paper reports the radiation hardness of optical components to be used in the binary readout of one of the next generation of detectors in high energy physics. The optical components will have to sustain a total ionising dose of 500 kGy and a 1 MeV equivalent neutron fluence of 10(15)n cm(-2). Emitters of VCSEL type have been chosen and have shown a shift of 1 mA in the laser threshold current after irradiation, but are still suitable for our purpose. The epitaxial Si PIN photodiode receivers have an acceptable 30% drop in responsivity providing a higher reverse bias is applied. Speed and lifetime of both components appear to be unaffected by the radiation damage. Temperature characteristics showing differences from un-irradiated materials will be also presented.

Abstract:

We study the radiation hardness and the lifetime of Light Emitting Diodes (LEDs) and Vertical Cavity Surface Emitting Laser diodes (VCSELs) in the context of the development of the optical readout for the ATLAS SemiConductor Tracker (SCT) at LHC. About 170 LEDs from two different manufacturers and about 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 5×1014 n (1 MeV eq. in GaAs)/cm2 expected in the ATLAS inner detector. We report on the radiation damage and the conditions required for its partial annealing under forward bias, we calculate 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 °C for several months, resulting in operating times corresponding to up to 70 years of operation in the ATLAS SCT. From our results we estimate the signal-to-noise ratio and the failure rate of optical links using LEDs developed specifically for application at LHC.

Abstract:

Two kinds of photodiodes have been investigated for the ATLAS SCT readout. We present in this paper the results of irradiating bulk and epitaxial Si PIN diodes with 1 MeV-equivalent neutrons and 24 GeV protons. The devices were biased during some of the tests. They were exposed to a fluence of around 2.5×1014 n cm-2 followed by a fluence of approximately 2.5×1014 p cm-2.